Rozprawy doktorskie: „PEO - Polymer Electrolytes”

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Maranski, Krzysztof Jerzy. "Polymer electrolytes : synthesis and characterisation". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3411.

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Crystalline polymer/salt complexes can conduct, in contrast to the view held for 30 years. The alpha-phase of the crystalline poly(ethylene oxide)₆:LiPF₆ is composed of tunnels formed from pairs of (CH₂-CH₂-O)ₓ chains, within which the Li⁺ ions reside and along which the latter migrate.¹ When a polydispersed polymer is used, the tunnels are composed of 2 strands, each built from a string of PEO chains of varying length. It has been suggested that the number and the arrangement of the chain ends within the tunnels affects the ionic conductivity.² Using polymers with uniform chain length is important if we are to understand the conduction mechanism since monodispersity results in the chain ends occurring at regular distances along the tunnels and imposes a coincidence of the chain ends between the two strands.² Since each Li⁺ is coordinated by 6 ether oxygens (3 oxygens from each of the two polymeric strands forming a tunnel), monodispersed PEOs with the number of ether oxygen being a multiple of 3 (NO = 3n) can form either “all-ideal” or “all-broken” coordination environments at the end of each tunnel, while for both NO = 3n-1 and NO = 3n+1 complexes, both “ideal” and “broken” coordinations must occur throughout the structure. A synthetic procedure has been developed and a series of 6 consecutive (increment of EO unit) monodispersed molecular weight PEOs have been synthesised. The synthesis involves one end protection of a high purity glycol, functionalisation of the other end, ether coupling reaction (Williamson's type ether synthesis³), deprotection and reiteration of ether coupling. The parameters of the process and purification methods have been strictly controlled to ensure unprecedented level of monodispersity for all synthesised samples. Thus obtained high purity polymers have been used to study the influence of the individual chain length on the structure and conductivity of the crystalline complexes with LiPF₆. The results support the previously suggested model of the chain-ends arrangement in the crystalline complexes prepared with monodispersed PEO² over a range of consecutive chain lengths. The synthesised complexes constitute a series of test samples for establishing detailed mechanism of ionic conductivity. Such series of monodispersed crystalline complexes have been studied and characterised here (PXRD, DSC, AC impedance) for the first time. References: 1. G. S. MacGlashan, Y. G. Andreev, P. G. Bruce, Structure of the polymer electrolyte poly(ethylene oxide)₆:LiAsF₆. Nature, 1999, 398(6730): p. 792-794. 2. E. Staunton, Y. G. Andreev, P. G. Bruce, Factors influencing the conductivity of crystalline polymer electrolytes. Faraday Discussions, 2007, 134: p. 143-156. 3. A. Williamson, Theory of Aetherification. Philosophical Magazine, 1850, 37: p. 350-356.

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Ennari, Jaana. "Atomistic molecular modelling of PEO sulfonic acid anion based polymer electrolytes". Helsinki : University of Helsinki, 2000. http://ethesis.helsinki.fi/julkaisut/mat/kemia/vk/ennari/.

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Denney, Jacob Michael. "The Thermal and Mechanical Characteristics of Lithiated PEO LAGP Composite Electrolytes". Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1609971094548742.

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Eiamlamai, Priew. "Electrolytes polymères à base de liquides ioniques pour batteries au lithium". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENI016/document.

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De nouvelles familles de liquides ioniques conducteurs par ion lithium; à anions aromatiques et aliphatiques de type perfluorosulfonate perfluorosulfonylimidure attachés à des oligoéthers (méthoxy polyéthylène glycol mPEG) de longueurs différentes ont été synthétisées et caractérisées dans le but d'améliorer l'interaction entre les chaînes de POE et les sels de lithium en améliorant la mobilité segmentaire. Ainsi différentes membranes amorphes ou peu cristallines améliorent le transport cationique par rapport aux électrolytes polymères usuels. . Leurs propriétés ont été évaluées dans deux types de polymères hôtes : un polyéther linéaire (POE) et un polyéther réticulé préparé par un procédé "VERT". Leurs parties oligooxyéthylène aident à la solvatation des cations lithium et conduisent à l'augmentation des propriétés de transport; c'est à dire la conductivité cationique et le nombre de transport. Leurs stabilités thermiques et électrochimiques sont adaptées à l'application batterie lithium-polymère
The new families of lithium-conducting ionic liquids; aromatic and aliphatic lithium salts based on perfluorosulfonate and perfluorosulfonylimide anions attached to an oligoether (methoxy polyethylene glycol mPEG) with different lengths were synthesized and characterized with the aim to improve the salt interaction with the host polymer's POE chains while keeping a high segmental mobility. They allowed obtaining membranes with lower crystallization degree and higher cationic transport number as compared with benchmarked salts. Their properties as lithium salts were investigated in two types of host polymers i.e. a linear polyether (POE) and a cross-linked polyether prepared by a ‘GREEN' process. Their oligooxyethylene moieties improve the lithium cation solvation leading to an increase in cationic transference numbers. Their electrochemical and thermal stabilities are suitable for lithium battery application

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Crisanti, Samuel Nathan Crisanti. "Effect of Alumina and LAGP Fillers on the Ionic Conductivity of Printed Composite Poly(Ethylene Oxide) Electrolytes for Lithium-Ion Batteries". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1522756200308156.

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Soundiramourty, Anuradha. "Towards the low temperature reduction of carbon dioxide using a polymer electrolyte membrane electrolysis cell". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112174.

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L’objectif principal de ce travail de thèse était d’évaluer les propriétés électro catalytiques de différents composés moléculaires vis-à-vis de la réduction électrochimique basse température du dioxyde de carbone, en vue d’applications dans des cellules d’électrolyse à électrolyte polymère solide. Après avoir mesuré les performances de métaux modèles (cuivre et nickel) servant de référence, nous avons testé les performances de quelques composés moléculaires à base de nickel. Le rôle catalytique de ces différents composés a été mis en évidence en mesurant les courbes intensité-potentiel dans différents milieux. Nous avons évalué l’importance de la source en hydrogène dans le mécanisme réactionnel. Les produits de réduction du dioxyde de carbone formés dans le mélange réactionnel ont été analysés par chromatographie en phase gazeuse. Nous avons ensuite abordé la possibilité de développer des cellules d’électrolyse à électrolyte polymère solide. Nous avons testé des cellules utilisant soit des anodes à eau liquide pour le dégagement d’oxygène, soit des anodes à hydrogène gazeux. L’utilisation de complexes moléculaires à base de nickel à la cathode a permis d’abaisser le potentiel de la cathode et de réduire le CO₂ mais la réaction de dégagement d’hydrogène reste prédominante
The main objective of this research work was to put into evidence the electrocatalytic activity of various molecular compounds with regard to the electrochemical reduction of carbon dioxide, at low temperature, in view of potential application in PEM cells. First, reference values have been measured on copper and nickel metals. Then the performances of some molecular compounds have been measured. The electrochemical activity of these different compounds has been put into evidence by recording the current-potential relationships in various media. The role of a hydrogen source for the reduction processes has been evaluated. The formation of reduction products has been put into evidence and analyzed by gas phase chromatography. Then, a PEM cell has been developed and preliminary tests have been performed. PEM cells with either an oxygen-evolving anode or a hydrogen-consuming anode have been tested. Using nickel molecular complexes, it has been possible to lower the potential of the cathode and to reduce CO₂ but the parasite hydrogen evolution reaction was found to remain predominant

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Marshall, Josiah. "Synthesis of the Diazonium Zwitterionic Polymer/Monomer for Use as the Electrolyte in Polymer Electrolyte Membrane (PEM) Fuel Cells". Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3968.

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My research goals are to synthesize new zwitterionic perfluorosulfonimide (PFSI) monomer/polymers. They are expected to replace traditionally used perfluorosulfonic acid (PFSA) polymers as the electrolyte in PEM fuel cells. For the PFSI monomer preparation, we designed a nine-step synthesis route. Thus far, I have successfully completed the synthesis of 4- (2-bromotetrafluoroethoxy)-benzenesulfonyl amide, 4-acetoxybenzenesulfonic acid sodium salt, and 4-chlorosulfonyl phenyl acetate. The coupling reaction of 4-(2-bromotetrafluoroethoxy)- benzenesulfonyl amide with 4-chlorosulfonyl phenyl acetate, was troublesome due to slow reaction kinetics and byproducts. Additionally, I did a methodology study for the homopolymerziation of the perfluoro 3(oxapent-4-ene) sulfonyl fluoride monomer. We compared the weight average molecular weight (Mw) of different reaction conditions. The best Mw was achieved when the polymerization was carried out for five days at 100 °C and150 psi with 2 wt % initiator and 5 g of monomer. All the compounds were characterized by melting point, GC-MS, GPC, FT-IR, and 13C/1H/19F NMR.

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Bayrak, Pehlivan İlknur. "Functionalization of polymer electrolytes for electrochromic windows". Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-204437.

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Saving energy in buildings is of great importance because about 30 to 40 % of the energy in the world is used in buildings. An electrochromic window (ECW), which makes it possible to regulate the inflow of visible light and solar energy into buildings, is a promising technology providing a reduction in energy consumption in buildings along with indoor comfort. A polymer electrolyte is positioned at the center of multi-layer structure of an ECW and plays a significant role in the working of the ECW. In this study, polyethyleneimine: lithium (bis(trifluoromethane)sulfonimide (PEI:LiTFSI)-based polymer electrolytes were characterized by using dielectric/impedance spectroscopy, differential scanning calorimetry, viscosity recording, optical spectroscopy, and electrochromic measurements. In the first part of the study, PEI:LiTFSI electrolytes were characterized at various salt concentrations and temperatures. Temperature dependence of viscosity and ionic conductivity of the electrolytes followed Arrhenius behavior. The viscosity was modeled by the Bingham plastic equation. Molar conductivity, glass transition temperature, viscosity, Walden product, and iso-viscosity conductivity analysis showed effects of segmental flexibility, ion pairs, and mobility on the conductivity. A connection between ionic conductivity and ion-pair relaxation was seen by means of (i) the Barton-Nakajima-Namikawa relation, (ii) activation energies of the bulk relaxation, and ionic conduction and (iii) comparing two equivalent circuit models, containing different types of Havriliak-Negami elements, for the bulk response. In the second part, nanocomposite PEI:LiTFSI electrolytes with SiO2, In2O3, and In2O3:Sn (ITO) were examined. Adding SiO2 to the PEI:LiTFSI enhanced the ionic conductivity by an order of magnitude without any degradation of the optical properties. The effect of segmental flexibility and free ion concentration on the conduction in the presence of SiO2 is discussed. The PEI:LiTFSI:ITO electrolytes had high haze-free luminous transmittance and strong near-infrared absorption without diminished ionic conductivity. Ionic conductivity and optical clarity did not deteriorate for the PEI:LiTFSI:In2O3 and the PEI:LiTFSI:SiO2:ITO electrolytes. Finally, propylene carbonate (PC) and ethylene carbonate (EC) were added to PEI:LiTFSI in order to perform electrochromic measurements. ITO and SiO2 were added to the PEI:LiTFSI:PC:EC and to a proprietary electrolyte. The nanocomposite electrolytes were tested for ECWs with the configuration of the ECWs being plastic/ITO/WO3/polymer electrolyte/NiO (or IrO2)/ITO/plastic. It was seen that adding nanoparticles to polymer electrolytes can improve the coloring/bleaching dynamics of the ECWs. From this study, we show that nanocomposite polymer electrolytes can add new functionalities as well as enhancement in ECW applications.

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Pehlivan-Davis, Sebnem. "Polymer Electrolyte Membrane (PEM) fuel cell seals durability". Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21749.

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Polymer electrolyte membrane fuel cell (PEMFC) stacks require sealing around the perimeter of the cells to prevent the gases inside the cell from leaking. Elastomeric materials are commonly used for this purpose. The overall performance and durability of the fuel cell is heavily dependent on the long-term stability of the gasket. In this study, the degradation of three elastomeric gasket materials (silicone rubber, commercial EPDM and a developed EPDM 2 compound) in an accelerated ageing environment was investigated. The change in properties and structure of a silicone rubber gasket caused by use in a real fuel cell was studied and compared to the changes in the same silicone rubber gasket material brought about by accelerated aging. The accelerated aging conditions were chosen to relate to the PEM fuel cell environment, but with more extreme conditions of elevated temperature (140°C) and greater acidity. Three accelerated ageing media were used. The first one was dilute sulphuric acid solution with the pH values of 1, 2 and 4. Secondly, Nafion® membrane suspended in water was used for accelerated ageing at a pH 3 to 4. Finally, diluted trifluoroacetic acid (TFA) solution of pH 3.3 was chosen. Weight change and the tensile properties of the aged gasket samples were measured. In addition, compression set behaviour of the elastomeric seal materials was investigated in order to evaluate their potential sealing performance in PEM fuel cells. The results showed that acid hydrolysis was the most likely mechanism of silicone rubber degradation and that similar degradation occurred under both real fuel cell and accelerated aging conditions. The effect of TFA solution on silicone rubber was more aggressive than sulphuric acid and Nafion® solutions with the same acidity (pH value) suggesting that TFA accelerated the acid hydrolysis of silicone rubber. In addition, acid ageing in all three acidic solutions caused visible surface damage and a significant decrease in tensile strength of the silicone rubber material, but did not significantly affect the EPDM materials. EPDM 2 compound had a desirable (low) compression set value which was similar to silicone rubber and much better than the commercial EPDM. It also showed a very good performance in the fuel cell test rig conforming that it a potential replacement for silicone rubber in PEMFCs.

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Verma, Atul. "Transients in Polymer Electrolyte Membrane (PEM) Fuel Cells". Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64247.

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The need for energy efficient, clean and quiet, energy conversion devices for mobile and stationary applications has presented proton exchange membrane (PEM) fuel cells as a potential energy source. The use of PEM fuel cells for automotive and other transient applications, where there are rapid changes in load, presents a need for better understanding of transient behavior. In particular at low humidity operations; one of the factors critical to the performance and durability of fuel cell systems is water transport in various fuel cell layers, including water absorption in membrane. An essential aspect to optimization of transient behavior of fuel cells is a fundamental understanding of response of fuel cell system to dynamic changes in load and operating parameters. This forms the first objective of the dissertation. An insight in to the time scales associated with various transport phenomena will be discussed in detail. In the second component on the study, the effects of membrane properties on the dynamic behavior of the fuel cells are analyzed with focus on membrane dry-out for low humidity operations. The mechanical behavior of the membrane is directly related to the changes in humidity levels in membrane and is explored as a part third objective of the dissertation. Numerical studies addressing this objective will be presented. Finally, porous media undergoing physical deposition (or erosion) are common in many applications, including electrochemical systems such as fuel cells (for example, electrodes, catalyst layer s, etc.) and batteries. The transport properties of these porous media are a function of the deposition and the change in the porous structures with time. A dynamic fractal model is introduced to describe such structures undergoing deposition and, in turn, to evaluate the changes in their physical properties as a function of the deposition.
Ph. D.

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Yin, Yijing. "An Experimental Study on PEO Polymer Electrolyte Based All-Solid-State Supercapacitor". Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/440.

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Supercapacitors are one of the most important electrochemical energy storage and conversion devices, however low ionic conductivity of solid state polymer electrolytes and the poor accessibility of the ions to the active sites in the porous electrode will cause low performance for all-solid-state supercapacitors and will limit their application. The objective of the dissertation is to improve the performance of all-solid-state supercapactor by improving electrolyte conductivity and solving accessibility problem of the ions to the active sites. The low ionic conductivity (10-8 S/cm) of poly(ethylene oxide) (PEO) limits its application as an electrolyte. Since PEO is a semicrystal polymer and the ion conduction take place mainly in the amorphous regions of the PEO/Lithium salt complex, improvements in the percentage of amorphous phase in PEO or increasing the charge carrier concentration and mobility could increase the ionic conductivity of PEO electrolyte. Hot pressing along with the additions of different lithium salts, inorganic fillers and plasticizers were applied to improve the ionic conductivity of PEO polymer electrolytes. Four electrode methods were used to evaluate the conductivity of PEO based polymer electrolytes. Results show that adding certain lithium salts, inorganic fillers, and plasticizers could improve the ionic conductivity of PEO electrolytes up 10-4 S/cm. Further hot pressing treatment could improve the ionic conductivity of PEO electrolytes up to 10-3 S/cm. The conductivity improvement after hot pressing treatment is elucidated as that the spherulite crystal phase is convert into the fringed micelle crystal phase or the amorphous phase of PEO electrolytes. PEO electrolytes were added into active carbon as a binder and an ion conductor, so as to provide electrodes with not only ion conduction, but also the accessibility of ion to the active sites of electrodes. The NaI/I2 mediator was added to improve the conductivity of PEO electrolyte and provide pseudocapacitance for all-solid-state supercapacitors. Impedance, cyclic voltammetry, and gavalnostatic charge/discharge measurements were conducted to evaluate the electrochemical performance of PEO polymer electrolytes based all-solid-state supercapacitors. Results demonstrate that the conductivity of PEO electrolyte could be improved to 0.1 S/cm with a mediator concentration of 50wt%. A high conductivity in the PEO electrolyte with mediator is an indication of a high electron exchange rate between the mediator and mediator. The high electron exchange rates at mediator carbon interface and between mediator and mediator are essential in order to obtain a high response rate and high power. This automatically solves the accessibility problem. With the addition of NaI/I2 mediator, the specific capacitance increased more than 30 folds, specific power increased almost 20 folds, and specific energy increased around 10 folds. Further addition of filler to the electrodes along with the mediator could double the specific capacitor and specific power of the all-solid-state supercapacitor. The stability of the corresponded supercapacitor is good within 2000 cycles.

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Balogun, Emmanuel O. "Comparative analysis of Polymer Electrolyte Membrane (PEM) fuel cells". Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29764.

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Per-Fluoro-Sulphonic-Acid (PFSA) ionomers have been singled out as the preferable ionomers for making the Polymer Electrolyte Membrane Fuel Cells (PEMFC) membranes owing to their extensive intrinsic chemical stability and super sulfonic acid strength which is core to the PEMFC proton conductivity. This thesis presents a deeper analysis into these PFSA ionomer membrane electrode assemblies (MEA), presenting an electrochemical-analytical comparative analysis of the two basic types, which are the Long-Side-Chain (LSC) Nafion® and the ShortSide-Chain (SSC) Aquivion® ionomer MEA with emphasis on performance and durability which are currently not well understood. In particular, electrochemical circuit models and semiempirical models were employed to enable distinguishable comparative analysis. Also, in this thesis, we present a further probe into the effect of ionomer ink making processes, critically investigating the effect of the High Share Dispersion (HSD) process on both the Nafion® and Aquivion® ionomer membrane electrode assembly (MEA). The findings in this research provides a valuable insight into the performance and durability of PFSA ionomer membrane under various application criteria. The effect of operating parameters and accelerated stress testing (AST) on the PFSA ionomers was determined using electrochemical impedance spectroscopy (EIS) and electronic circuit model (ECM) analysis. The result of this study, shows that the ionomer ink making process for Nafion® and Aquivion® MEAs are not transferrable. Analysis of the PEMFC performance upon application of the high shear dispersion (HSD) process showed that Nafion® MEA had a 10.47% increase in voltage while the Aquivion® MEA had a 2.53% decrease in voltage at current density of 1.14A/cm2 . Also, upon accelerated stress testing, the Nafion® showed a 10.49% increase in its voltage while the Aquivion® on the other hand had a 7.16% decrease in voltage at 0.66A/cm2 . Thus indicating the HSD process enhances the performance of the Nafion® MEA and inhibits the performance of the Aquivion® MEA.

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Santi, Vasile Nicolò. "3D multi-physics modelling and validation of the model of a Polymer Electrolyte Membrane Fuel". Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2690105.

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This Ph.D. thesis focuses on testing and modelling PEMFC single cell systems, to better understand internal phenomena and to find out operative solutions able to increase the overall cell performance. Thus, the first step is based on the creation and validation of a wide spectrum of multi-physics models of PEMFC fed with hydrogen or methanol, by using Comsol® Multi-physics platform coupled with Matlab®. All models are able to work under different operating conditions and with materials of different characteristics (membranes and catalysts). Moreover, the efforts were also focused on the creation of models of systems similar to fuel cell, as the gas diffusion electrode (GDE). The GDE is usually employed to analyze the electrochemical properties of the catalytic layer. Each single model was validated against a huge set of experimental data (partly obtained at POLITO, partly provided by the partners of two research projects: DURAMET and NAMEDPEM). After the model validation, these models were used to investigate the internal phenomena, and how materials, geometry and operative conditions affect the cell performance. Furthermore, particular problems affecting the entire FC system such as water flooding, methanol crossover, flow patterns design and current density distribution were deeply investigated to provide reasonable solutions. In general, the 3D multi-physics, multi-component, multi-phase and not-isothermal models developed in this Ph.D. include Maxwell-Stefan, Navier-Stokes-Brinckman, and extended two-phase Darcy-law to solve velocity, pressure, and mass transfer equations, and modified Butler-Volmer and Tafel equations to describe the electrochemical kinetics. All the equations are coupled to each other to simulate the performance of a single cell PEMFC (or GDE), reproducing the electrochemical, fluid-dynamics, and thermal phenomena. Each model was validated by comparing the simulated results, in terms of electric performance (polarization curves and power density curves), with experimental data obtained by changing several parameters: -Type of membranes: Nafion® (N112, N115, N117), Fumapem® (F1850) for the DMFC, Nafion® (N-HP and NR-212) for the hydrogen-fed PEMFC. -Dimensions of active area of the single cell: 5cm2 and 25cm2. -Catalyst: eight different catalysts for the DMFC, four for the hydrogen-fed PEMFC, three for the GDE (commercial Pt/C, PtRu/C and lab-made FeNC-based catalysts). -Operative conditions: pressure, methanol inlet concentration, air or oxygen at the cathode, cell and flow temperatures, anode and cathode flow rates, humidification and stoichiometric ratio (for the hydrogen-fed PEMFC). -Flow field designs: unique serpentine, four parallel serpentines and four inlet serpentine. After the validation, the models were used to reproduce and study the multi-dimensional trends of particular phenomena which produce system losses and/or affect the performance. In first istance, the multi-physics analysis was used to improve the way to deposit the catalyst, thus the catalytic layer distribution was investigated in order to have a better uniformity in the current density distribution at the membrane/anodic catalyst interface. The proposed solutions, the 3-Layers MEA, was modelled in Comsol® and tested in the lab. It should avoid hot-spots on the membrane as a consequence of the better uniformity in the current density distribution, with a consequent increase in the life-time of the MEA (chapter I) The second step was the analysis of the influence of water flooding and catalyst materials. The extended two-phase Darcy-law was used into the model to describe the mass transport inside the micro-porous structure of the noble/non-noble metal cathode catalyst, produced in our labs. The multi-physics analysis displays a direct relationship between the water saturation, the oxygen diffusion flow, and the oxygen consumption. Thus, water condensation inside the micro-pores may produce the flooding of micro and meso-porous, showing a consequent link between condensation and decreasing of cell performance (chapter II). The third step of the multi-physics analysis was the study of the influence of FF design (unique serpentine, four parallel serpentines, four inlet serpentines.) and types of membrane on system performance. A large amount of lab tests and simulation were performed for each FF, by changing the temperatures, the inlet flow rates, the inlet methanol concentrations and the type of cathode flow. Pulse Field Gradient (PFG) NMR spectroscopy was used to get a direct measurement of the diffusion coefficients of water and methanol through the membranes. Thus, the model was used as a tool to investigate anodic overpotentials, water and methanol crossover flow rates, current density distribution along the membrane, understanding the relationship between the shape of the FF and cell performance (i.e. pressure and methanol consumption).(chapter III) To improve the research on the area of catalyst properties, the study focused on the cathode using the gas diffusion electrode (GDE), trying to find out key parameters which influence the performance of catalysts for the oxygen reduction reaction. A commercial Pt-based catalysts and the non-noble metal Fe–N–C catalyst prepared in-house were tested and modelled, to carry out a sensitive analysis by varying the inlet oxygen flow rate, showing the influence of oxygen diffusive flow on the catalyst performance. The multi-physics analysis provides the way to increase the performance of the non-noble metal catalyst by changing some system properties as tortuosity, porosity and hydrophobicity (chapter IV) After the large analysis developed for DMFC, the PhD work continued with the modelling of hydrogen-fed PEMFC, to complete, in such way, the general sensitivity analysis on PEMFC systems. Obviously, some innovations and changings were introduced to adapt the model with the new inlet fuel, as new equations and parameters for the electrochemical behaviours, initial and boundary conditions, H2 crossover and controlled parameters, i.e., relative humidity. The multi-physics analysis and the lab tests show how the relative humidity influence the performance, in relation to the variation of pressure and temperature (chapter V) After the experimental and modelling studies, the PhD work was focused on several aspects, in order to improve the performance of the single cell with Fe-N-C catalyst on the cathode, related to material improvement and the single cell system: the active surface area, the percentage of micro-pores present in the catalytic layer, the membrane type, the procedure of catalyst deposition, the back pressure and the closing force. Thus, the modelling and lab work performed outcome in an excellent result: the system performance increases four times than the initial computed value, from about 10 mW cm–2 to 40.6 mW cm–2.

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Leahy, Scott B. "Active Flow Control of Lab-Scale Solid Polymer Electrolyte Fuel Cells". Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5188.

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The effects of actively pulsing reactant flow rates into solid polymer electrolyte fuel cells were investigated in this thesis. First, work was conducted to determine the magnitude of voltage response to pulsed reactant flow on a direct hydrogen proton exchange membrane (PEM) cell. The effects of pulsed reactant flow into a direct methanol fuel cell (DMFC) were then considered. The PEM work showed substantially greater response to pulsed air flow than to pulsed fuel flow. It was found that several parameters affect the magnitude of cell response to active flow control (AFC). Increasing current load, increasing the magnitude of flow oscillation, decreasing the frequency of oscillation, and decreasing the average level of excess reactant supplied were found to maximize both the level of voltage oscillations and the decrease in cell power from steady state performance. Greater response to pulsed oxidant flow is believed to have been observed due to effects brought about by changes in membrane humidity. In contrast, pulsed fuel flow showed the greatest response in the study of DMFC technology. In this case, time averaged cell voltage was found to increase as the time averaged fuel flow rate was reduced. The increase in average cell power is the result of a reduction in methanol crossover; sustainable increases of up to 6% in power output were measured. The parameters found to effect the increase in cell power observed include the frequency of oscillation and the time-averaged NOSfuel. Pulsed air flow on the DMFC did not show any such rise in voltage, supporting the hypothesis that a reduction in methanol crossover is the phenomenon which brings about enhanced performance.

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Jalani, Nikhil H. "Development of nanocomposite polymer electrolyte membranes for higher temperature PEM fuel cells". Link to electronic dissertation, 2006. https://www.wpi.edu/ETD-db/ETD-catalog/view%5Fetd?URN=etd-032706-165027.

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Park, Yong Hun. "Investigation of the performance and water transport of a polymer electrolyte membrane (pem) fuel cell". [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2549.

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STASSI, ALESSANDRO. "Preparation and characterization of electrocatalysts for high temperature polymer electrolyte fuel cells". Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1338.

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E’ noto che per una effettiva immissione nel settore automotive delle celle a combustibile ad elettrolita polimerico (PEFCs) alimentate a idrogeno, una delle principali barriere da superare è legata durata dei materiali adoperati. Il fenomeno di sintering del platino e la corrosione che quest’ultimo assieme al supporto, subiscono operando alle alte temperature richieste dal settore automotive (120 ÷ 130 °C), si traduce in una riduzione del tempo di vita del catalizzatore nel suo complesso. Gli effetti del sintering e della corrosione del catalizzatore si traducono in una perdita di area superficiale attiva del platino e di conseguenza una diminuzione della potenza erogata dal sistema. Un’altra problematica da superare, per una diffusione concorrenziale nel settore automotive delle PEFCs rispetto ai classici motori a combustione interna, è il carico totale di platino. Ad oggi, le potenze erogate da questi apparati (ca. 100 kW) richiedono, soprattutto nel comparto catodico, una quantità notevole di metallo prezioso che, di riflesso, causa un aumento del costo complessivo del prodotto finito. Risulta ovvio che l’abbassamento del tenore di platino nel catalizzatore catodico gioca un ruolo determinante per una effettiva ed efficace immissione delle celle a combustibile all’interno di questo vasto mercato. Scopo di questo dottorato di ricerca è stato lo sviluppo di nuovi elettrocatalizzatori supportati in grado resistere al sintering ed alla corrosione. Per ridurre il carico di platino questi materiali devono anche essere caratterizzati da una maggiore efficienza. Si è deciso, quindi, di sviluppare catalizzatori a base di platino e di leghe platino-cobalto con caratteristiche chimico-fisiche ben definite. La scelta del cobalto deriva dalle numerose indagini effettuate su questi catalizzatori; queste hanno mostrato che alcuni catalizzatori di leghe binarie di Pt-M (dove M = Co, Fe, Ni, Cu, ecc) presentano una maggiore attività elettrocatalitica per la reazione di riduzione dell’ossigeno rispetto ai catalizzatori di solo Pt. Tra queste la lega PtCo sembra risultare quella più promettente. Ancora, vari studi hanno indicato che per i catalizzatori supportati Pt/C si ha un’attività massima a circa 3 nm come compromesso adatto tra il numero di siti e la fase cristallografica con basso indice di Miller caratterizzata da alta attività intrinseca. Obiettivo di questa attività è stato, quindi, quello di sintetizzare catalizzatori supportati a base di Pt e leghe PtCo con dimensione di particelle minore di 3 nm e contraddistinti da un adeguato grado di lega. I catalizzatori sviluppati sono stati infine caratterizzati dal punto di vista chimico-fisico ed elettrochimico (in semicella ed in cella singola) ad elevate temperature (75 °C ÷ 130 °C) con lo scopo di analizzarne il comportamento e approfondire le cause della loro degradazione.
Large scale application of polymer electrolyte fuel cell (PEFC) system technology requires a reduction of its high cost as well as improvement of performance and stability. The catalysts employed for operation in the present PEMFC are nanosized platinum particles supported on carbon. The reduction of the noble metal content and enhancement of catalytic stability are significant challenges for this fuel cell technology on the way to become cost competitive. High temperature PEFC operation (130°C) requires the development of catalyst with proper resistance to sintering and corrosion under working conditions. In order to reach these goals, the aim of this research was the development of practical carbon supported Pt anode and cathode catalysts with high metal surface area capable of operation at high temperature (130°C) with suitable resistance to corrosion, Pt dissolution, thermal and electrochemical sintering. Another aspect was the development of new alloyed electrocatalysts. Several papers in the current literature address to the development of binary and ternary Pt-alloys. In fact, results show more active and less expensive Pt-alloy for oxygen reduction reaction (ORR) catalysts with better stability than pure Pt based catalysts. Accordingly, the work was focused on the development of practical carbon supported Pt-Co alloyed catalysts. The choice of cobalt as a transition metal in alloy with platinum was derived from literature, as many of investigations shown that it is the most promising catalyst for high temperature PEFC operation. The purpose of this work was addressed on the achievement of a proper crystalline structure with face-centered-cubic phase and a high degree of alloying for the catalysts with small mean particle size (< 3 nm). The synthesis method was optimized to obtain a suitable dispersion of the metal particles on the support for high metal concentration catalysts (50 wt.%) with a mean particle size smaller than 3 nm for both Pt and Pt-Co alloyed electrocatalysts. Moreover, further studied were addressed to different pre-leaching methods on the performance and stability of synthesized Pt-Co alloy catalysts supported on carbon. These treatments were adopted to reduce the dissolution of cobalt from the particle surface in PEFCs. To understand catalysts behaviour in terms of resistance to corrosion and electrochemical sintering, different analyses (XRD, cycling voltammetry and polarization) were carried out before and after various accelerated degradation tests (ADTs) performed in a gas-fed sulphuric acid electrolyte half cell at 75°C and in a PEM single cell in a temperature range of 80 – 130°C. In conclusion, an appropriate synthesis method was developed to obtain Pt and PtCo electrocatalysts with a small particle size (< 3 nm) and suitable degree of alloying in the bimetallic electrocatalysts. Pre-leaching treatments were adopted to improve the catalytic activity and the resistance towards sintering and degradation. Accelerated degradation tests in sulphuric acid gas-fed half cell were carried out in order to investigate the influence of different pre-leaching treatments on the electrochemical behaviour. These analyses showed that the particle size of all catalysts increased after the tests. It was observed that after the Pt degradation test, the HClO4 pre-leached catalyst showed the best performance in terms of electrochemical activity and resistance to sintering.

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Gle, David. "Synthèse de copolymères à architectures complexes à base de POE utilisés en tant qu'électrolytes polymères solides pour une application dans les batteries lithium métal-polymère". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4761/document.

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Dans le contexte d'un développement durable, les véhicules électriques apparaissent comme une solution incontournable dans le futur. Parmi les dernières évolutions sur les batteries, les systèmes constitués d'une électrode au lithium (technologie lithium métal) présente des performances remarquables en termes de densité d'énergie. L'inconvénient majeur de cette méthodologie est lié à la formation de dendrites lors de la recharge susceptibles d'occasionner des courts-circuits conduisant à l'explosion de la batterie. C'est dans cet axe que s'inscrit mon sujet de thèse dont l'objectif est de développer un électrolyte polymère solide présentant une conductivité ionique élevée (2.10-4 S.cm-1 à40°C) et une tenue mécanique suffisante (30 MPa) pour limiter les phénomènes de croissance dendritique. Pour cela, la polymérisation contrôlée par les nitroxydes (NMP) a été utilisée pour synthétiser des copolymères à blocs avec un bloc possédant des groupes d'oxyde d'éthylène –CH2-CH2-O- permettant la conduction des ions lithium et un bloc de polystyrène assurant la tenue mécanique de l'électrolyte final. Le bloc assurant la conduction ionique des architectures ainsi synthétisées sont constituées soit de POE sous forme linéaire soit de POE sous forme de peigne
In the context of sustainable development, electric vehicles appear to be a major solution for the future. Among the lastest technologies, the Lithium Metal Polymer battery has presented very interesting performances in terms of energy density. The main drawback of this system is the formation of lithium dendrites during the refill of the battery that could cause short circuits leading to the explosion of the battery. The aim of my PhD is to develop a Solid Polymer Electrolyte showing a high ionic conductivity (2.10-4 S.cm-1 at 40°C) and a high mechanical strength (30 MPa) to prevent dendritic growth. For that purpose, Nitroxide Mediated Polymerization is used to synthesize block copolymers with a PEO moiety for ionic conduction –CH2-CH2-O- and polystyrene for mechanical strength. Different kind of architectures have been synthesized : block copolymer with linear PEO moiety or with grafted PEO moiety

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Shevock, Bryan Wesley. "System Level Modeling of Thermal Transients in PEMFC Systems". Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31079.

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Fuel cell system models are key tools for automotive fuel cell system engineers to properly size components to meet design parameters without compromising efficiency by over-sizing parasitic components. A transient fuel cell system level model is being developed that includes a simplified transient thermal and parasitics model. Model validation is achieved using a small 1.2 kW fuel cell system, due to its availability. While this is a relatively small stack compared to a full size automotive stack, the power, general thermal behavior, and compressor parasitics portions of the model can be scaled to any number of cells with any size membrane area. With flexibility in membrane size and cell numbers, this model can be easily scaled to match full automotive stacks of any size. The electrical model employs a generalized polarization curve to approximate system performance and efficiency parameters needed for the other components of the model. General parameters of a stackâ s individual cells must be known to scale the stack model. These parameters are usually known by the time system level design begins. The thermal model relies on a lumped capacity approximation of an individual cell system with convective cooling. From the thermal parameters calculated by the model, a designer can effectively size thermal components to remove stack thermal loads. The transient thermal model was found to match experimental data well. The steady state and transient sections of the curve have good agreement during warm up and cool down cycles. In all, the model provides a useful tool for system level engineers in the early stages of stack system development. The flexibility of this model will be critical for providing engineers with the ability to look at possible solutions for their fuel cell power requirements.
Master of Science

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Bhamidipati, Kanthi Latha. "Detection and elimination of defects during manufacture of high-temperature polymer electrolyte membranes". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43616.

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Defect generation and propagation in thin films, such as separation membranes, can lead to premature or catastrophic failure of devices such as polymer electrolyte membrane fuel cells (PEMFC). It is hypothesized that defects (e.g., air bubbles, pin-holes, and holes) originate during the manufacturing stage, if precise control is not maintained over the coating process, and they propagate during system operation. Experimental and numerical studies were performed to detect and eliminate defects that were induced during slot die coating of high-viscosity (1 to 40 Pa-s), shear-thinning solutions. The effects of fluid properties, geometric parameters and processing conditions on air entrainment and coating windows (limited set of processing conditions for which defect-free coating exists) were studied. When smaller slot gaps and coating gaps were used, relatively small bubbles were entrained in the coated film. The air bubble sizes increased as the viscosity of the coating solution decreased. A semi-empirical model correlating the maximum coating speed to a solution's material properties, geometric parameters and processing conditions was developed. Such a predictive model will enable engineers to determine the maximum coating boundary for shear-thinning and Newtonian solutions within certain constraints. Smaller coating gaps and low-viscosity solutions produced higher coating speeds. The surface tension property of the coating solution provided stability to the coating bead. Therefore, solutions with higher surface tension could be processed at higher coating speeds.

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Hays, Daniel George. "Testing of an Axial Flow Moisture Separator in a Turbocharger System for Polymer Electrolyte Membrane Fuel Cells". Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7134.

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Proton exchange membrane (PEM) fuel cells, with low operating temperatures and high power density, are a reasonable candidate for use in mobile power generation. One large drawback to their use is that their fuel reformer requires not only fuel but also water, thereby requiring two separate reservoirs to be available. PEM fuel cells exhaust enough water in their oxidant stream to potentially meet the needs of the fuel reformer. If this water could be recovered and routed to the fuel reformer it would markedly increase the portability of PEM fuel cells. The goal of this research was to test a previously designed axial flow moisture separator. The separator was employed in a test bed which utilized compressed, heated air mixed with steam to simulate the oxidant exhaust conditions of a 25 kW PEM fuel cell. The simulated exhaust was saturated with water. The mixture was expanded through the turbine side of an automotive turbocharger, which dropped the temperature and pressure of the mixture, causing water to condense, making it available for separation. The humid air mixture was passed over an axial flow centrifugal separator and water was removed from the flow. The separator was tested in a variety of conditions with and without passing chilled water through the separator. The axial separator was tested independently, with a flow straightener preceding it, and with a commercially available centrifugal moisture separator in series following it. It was shown that cooling makes a significant impact on the separation rate while adding a flow straightener does not. Separation efficiencies of 19% on average were experienced without cooling, while efficiencies of 50% were experienced with 3.1 kW of cooling. The separation efficiency of the two moisture separators combined was found to be 31.7% which is 165% that of the axial separator alone under uncooled conditions.

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Mrozewski, Kamil Janusz. "Diagnosis of mechanical tightening of a single polymer electrolyte membrane fuel cell (LT-PEM and HT-PEM) in aeronautical applications". Thesis, Toulouse, INPT, 2019. http://www.theses.fr/2019INPT0034/document.

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Les activités R&D dans le domaine d’aéronautique sont actuellement orientées par l’évolution naturelle vers des technologies plus efficaces et durables. La motivation principale de cette tendance est le besoin de résoudre les problèmes liés à la nature de l’industrie très polluante. À cet égard, le développement d’avions plus électriques contribuerait à la réduction de la consommation de combustibles fossiles en intégrant des sources et des convertisseurs d’énergie alternatifs, tels que les piles à combustibles (PàC). Cependant, un système PàC devrait se conformer à des contraintes de fiabilité et de sécurité particulières, d’autant plus que l’environnement aéronautique n’est guère clément : cyclages en pression et en température, ainsi que des forces mécaniques, agissants dans les trois dimensions. Les vibrations et les chocs peuvent notamment entraîner un desserrage brusque ou graduel de la PàC, dégradant ainsi ses performances et pouvant aller jusqu’à une fuite de gaz. Il semble donc important de pouvoir surveiller l’état de serrage mécanique d’une PàC au cours du temps, idéalement de manière non intrusive. Les résultats présentés dans la littérature indiquent que la qualité du serrage mécanique d’une PàC peut être évaluée à travers sa résistance ohmique (Rohm), plus précisément par sa partie électronique (Re-, formée par les résistances des couches de la PàC et les résistances de contact). Dans les conditions nominales de fonctionnement, l’autre partie plus importante de la Rohm – la résistance protonique (RH+, formée par la résistance de la membrane et de l’ionomère) – ne dépend pas de la force de serrage. Cette amalgamation de résistances de natures différentes empêche une extraction de la Re- sans l’utilisation de capteurs invasifs. Par conséquent, l’estimation de la qualité du serrage mécanique d’une PàC n’est pas aisée. Au cours de cette thèse, une méthode de diagnostic préventif in situ capable de détecter la dégradation des conditions de serrage d’une PàC par la modélisation de sa résistance ohmique est proposée. Une étude théorique est d’abord réalisée afin de démontrer que les résistances RH+ et Re- peuvent être séparées de la Rohm totale, à partir de leur dépendance à la température. La méthode de diagnostic est ensuite validée à l’aide de données expérimentales générées lors de la caractérisation de deux PàC à membrane échangeuse de protons : basse et haute température. Quelques divergences entre les valeurs identifiées par l’algorithme et celles rapportées dans la littérature sont observées, néanmoins, elles représentent correctement l’état du serrage mécanique de la PàC. Dans l’ensemble, les résultats sont encourageants dans le but d’estimer la qualité du serrage mécanique d’une PàC à travers l’évolution de RH+ et Re-
The aeronautical R&D activities are currently shaped by the issues associated with the pollutantrich nature of the industry and the natural evolution towards more effective and sustainable technologies. In this regard, the development of more electric aircraft would contribute to reducing fossil fuel consumption by incorporating alternative sources and converters of energy, such as FCs. However, a FC system would have to comply with particular reliability and safety constraints, especially as the aeronautical environment is not very indulgent: abundant pressure and temperature cycling as well as mechanical loads, varying both in frequency and amplitude, in all three dimensions. Vibrations and shocks can in particular lead to a sudden or gradual loosening of the FC, thus degrading its performance, and possibly provoking a gas leak. It therefore seems important to be able to monitor the tightening state of a FC over time, ideally in a non-intrusive manner. Results reported in the literature indicate that the quality of the mechanical tightening of a FC assembly might be assessed through its ohmic resistance (Rohm), more precisely through its electronic part (Re-, formed by the bulk resistances of FC layers and the interfacial contact resistances). In nominal operating conditions, the second and more dominant part of Rohm – the protonic resistance (RH+, formed by the membrane and ionomer resistances) – does not depend on clamping pressure. This amalgamation of resistances of different natures prevents an easy extraction of Re- without the use of invasive sensors and thus an estimation of the quality of the mechanical tightening of a FC assembly. This thesis proposes an in situ preventive diagnosis method that is capable of detecting the degradation of clamping conditions of a FC through the modelling of its ohmic resistance. A theoretical study is performed and demonstrates that the RH+ and Re- resistances can be separated from the total Rohm, based on their temperature dependence. The proposed method is verified with experimental data generated during the characterization of low and high temperature Polymer Electrolyte Membrane (PEM) single cells. Although some differences between the values identified by the algorithm and those reported in the literature are observed, they correctly depict the behavior of the mechanical tightening of the tested FCs. Overall, the results are encouraging in the aim of monitoring the quality of mechanical tightening of a FC through the evolution of RH+ and Re-

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Al-Smail, Jamal Hussain. "Optimal Shape Design for Polymer Electrolyte Membrane Fuel Cell Cathode Air Channel: Modelling, Computational and Mathematical Analysis". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22660.

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Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right. The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.

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Santos, Júnior Garbas Anacleto 1988. "Desenvolvimento de um novo eletrólito polimérico baseado num derivado de PEO e metais de transição para aplicação em dispositivos fotoeletroquímicos". [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/248375.

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Orientador: Ana Flávia Nogueira
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química
Made available in DSpace on 2018-08-24T11:57:50Z (GMT). No. of bitstreams: 1 SantosJunior_GarbasAnacleto_M.pdf: 5163839 bytes, checksum: 6d357533b5e3fc16413a4febf8f9d075 (MD5) Previous issue date: 2014
Resumo: Neste trabalho são apresentados os resultados da preparação e caracterização de eletrólitos poliméricos usando matriz polimérica de um copolímero derivado de PEO - poli (óxido de etileno-co-2-(2-metoxietoxi) etil glicidil éter) - P(EO-EM) - visando à substituição do par redox, I/I3 , usualmente mais comum em células solares do tipo DSSC, por pares de íons de metais de transição, como Fe e Co . Os eletrólitos foram preparados utilizando razões mássicas fixas de P(EO-EM):GBL de 30-70%. Para os eletrólitos de ferro foram utilizados os sais de FeCl2 + FeCl3·6H2O e para os eletrólitos de cobalto CoCl2 · 6H2O + CoF3. Em ambos os casos foram estudados razões molares entre os cátions de valência II:III de 1:1 e 10:1. Diferentes razões mássicas foram estudadas, sendo estas de 2, 5, 8 e 16% para os eletrólitos de ferro e de 1, 2, 3 e 5% para os eletrólitos de cobalto. Valores máximos de condutividade para os eletrólitos contendo sais de ferro foram de 1,88 x 10 e 1,40 x 10 S cm-1, para concentrações de 16% de sal e razões de 1:1 e 10:1 (Fe:Fe), respectivamente. Enquanto que no caso dos eletrólitos contendo cátions de cobalto foram de 1,41 x 10 e 1,16 x 10 S cm, para concentrações de 5% de sal e razões de 1:1 e 10:1 (Co:Co), respectivamente. Testes de PIA- Photoinduced Absorption Spectroscopy mostraram a eficiência do par redox Fe para regeneração dos corantes L0, N719, D35 e Z907. Entretanto, os mesmos testes mostraram a eficiência do par redox Co para regeneração somente do corante L0. A confecção de dispositivos do tipo DSSC com eletrólitos contendo sais de Fe e Co apresentaram resultados insatisfatórios, possivelmente relacionado com a alta taxa de recombinação do elétron ejetado no TiO2 com os mediadores redox
Abstract: This work presents the results of the preparation and characterization of polymer electrolytes using polymeric matrix of a PEO copolymer-poly (ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether) - P (EO-EM) - in order to substitute the redox couple , I-/I3-, usually most common mediators in DSSC solar cells, by transition metal ions pairs, such as Fe and Co . The electrolytes were prepared using fixed P(EO-EM) : GBL weight ratios of 30-70 % . The iron electrolytes were prepared using FeCl2 + FeCl3 o 6H2O salts and CoCl2 o 6H2O + CoF3 were used for the cobalt electrolytes. In both cases, it was studied the molar ratios between cations with valence of II: III of 1:1 to 10:1. Different weight ratios were studied, 2 , 5, 8 and 16% for iron electrolytes and 1 , 2, 3 and 5% for the cobalt electrolytes . Maximum conductivity values for the electrolyte containing iron salts were 1.88 x 10 and 1.40 x 10 S cm at salts concentrations of 16 % and ratios from 1:1 to 10:1 (Fe:Fe), respectively. While in the case of electrolyte containing cobalt cations the conductivity values were 1.41 x 10 and 1.16 x 10 S cm -1 at salts concentrations of 5 % and ratios from 1:1 to 10:1 ( Co:Co), respectively . PIA tests - Photoinduced Absorption Spectroscopy- showed the efficiency of the FeII/III redox couple for the regeneration of L0 , N719 , Z907 and D35 dyes. However, the same tests have shown that the CoI redox couple were only able to regenerate the L0 dye. The DSSC devices with electrolytes containing Fe and Co salts showed unsatisfactory results, possibly related to the high rate of recombination of the electron ejected in TiO2 with the redox mediators
Mestrado
Quimica Inorganica
Mestre em Química

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Turan, Cabir. "Investigations on the Effect of Manufacturing on the Contact Resistance Behavior of Metallic Bipolar Plates for Polymer Electrolyte Membrane Fuel Cells". VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2629.

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Polymer electrolyte membrane fuel cells (PEMFCs) have emerged as a strong and promising candidate to replace internal combustion engines (ICE) due their high efficiency, high power density and near-zero hazardous emissions. However, their commercialization waits for solutions to bring about significant cost-reductions and significant durability for given power densities. Bipolar plate (BPP) with its multi-faceted functions is one of the essential components of the PEMFC stacks. Stainless steel alloys are considered promising materials of choice for bipolar plate (BPP) applications in polymer electrolyte membrane fuel cells (PEMFC) due to their relatively low cost and commercial availability in thin sheets. Stainless steel materials build a protective passive metal oxide layer on their surface against corrosion attack. This passive layer does not demonstrate good electrical conductivity and increases interfacial electric contact resistance (ICR) between BPP and gas diffusion layer GDL in PEMFC. Lower ICR values are desired to reduce parasitic power losses and increase current density in order to improve efficiency and power density of PEMFC. This study aimed to bring about a broader understanding of manufacturing effects on the BPP contact resistance. In first stage, BPP samples manufactured with stamping and hydroforming under different process conditions were tested for their electrical contact resistance characteristics to reveal the effect of manufacturing type and conditions. As a general conclusion, stamped BPPs showed higher contact conductivity than the hydroformed BPPs. Moreover, pressure in hydroforming and geometry had significant effects on the contact resistance behavior of BPPs. Short term corrosion exposure was found to decrease the contact resistance of bipolar plates. Results also indicated that contact resistance values of uncoated stainless steel BPPs are significantly higher than the respective target set by U.S. Department of Energy. Proper coating or surface treatments were found to be necessary to satisfy the requirements. In the second stage, physical vapor deposition technique was used to coat bipolar plates with CrN, TiN and ZrN coatings at 0.1, 0.5 and 1 μm coating thicknesses. Effects of different coatings and coating thickness parameters were studied as manufactured BPPs. Interfacial contact resistance tests indicated that CrN coating increased the contact resistance of the samples. 1 µm TiN coated samples showed the best performance in terms of low ICR; however, ICR increased dramatically after short term exposure to corrosion under PEMFC working conditions. ZrN coating also improved conductivity of the SS316L BPP samples. It was found that the effect of coating material and coating thickness was significant whereas the manufacturing method and BPP channel size slightly affected the ICR of the metallic BPP samples. Finally, effect of process sequence on coated BPPs was investigated. In terms of ICR, BPP samples which were coated prior to forming exhibited similar or even better performance than coated after forming samples. Thus, continuous coating of unformed stripes, then, applying forming process seemed to be favorable and worth further investigation in the quest of making cost effective BPPs for mass production of PEMFC.

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Bhatti, Wasim. "Mechanical integration of a PEM fuel cell for a multifunctional aerospace structure". Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21513.

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A multifunctional structural polymer electrolyte membrane (PEM) fuel cell was designed, developed and manufactured. The structural fuel cell was designed to represent the rear rib section of an aircraft wing. Custom membrane electrode assemblies (MEA s) were manufactured in house. Each MEA had an active area of 25cm2.The platinum loading on each electrode (anode and cathode) was 0.5mg/cm2. Sandwiched between the electrodes was a Nafion 212 electrolyte membrane. Additional components of the structural fuel included metallic bipolar plates and end plates. Initially all the components were manufactured from aluminium in order for the structural fuel cell to closely represent an aircraft wing rib. However due to corrosion problems the bipolar plate had to be manufactured from marine grade 361L stainless steel with a protective coating system. A number of different protective coating systems were tried with wood nickel strike, followed by a 5μm intermediate coat of silver and a 2μm gold top coat being the most successful. Full fuel cell experimental setup was developed which included balance of plant, data acquisition and control unit, and a mechanical loading assembly. Loads were applied to the structural fuel cells tip to achieve a static deflection of ±7mm and dynamic deflections of ±3mm, ±5mm, and ±7mm. Static and dynamic torsion induced 1° to 5° of twist to the structural fuel cell tip. Polarisation curves were produced for each load case. Finite element analysis was used to determine the structural fuel cell displacement, and stress/strain over the range of mechanical loads. The structural fuel cells peak power performance dropped 3.9% from 5.5 watts to 5.3 watts during static bending and 2% from 6.2 watts to 6.1 watts during static torsion. During dynamic bending (2000 cycles) the structural fuel cell peak power performance dropped 11% from 6.7 watts to 6 watts (3mm deflection at 190N), 23% from 6.3 watts to 4.8 watts (5mm deflection at 270N), and 41% from 7.2 watts to 5 watts (7mm deflection at 350N). During dynamic torsion (2000 cycles) the structural fuel cell peak power performance dropped 16% from 6 watts to 5.1 watt (3° of torsional loading), and 30% from 6.4 watts to 4.3 watts (5° of torsional loading). The simulated (finite element modelling) displacement of -6.6mm (At maximum bending load of 364.95N) was within 9% of the actual measured displacement of -7.2mm at 364.95N. Furthermore the majority of the simulated strain values were within 10% of the actual measured strain for the structural fuel cell.

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Subbaraman, Ramachandran. "A MULTI-SCALE HIERARCHICAL APPROACH FOR UNDERSTANDING THE STRUCTURE OF THE POLYMER ELECTROLYTE MEMBRANE FUEL CELL (PEMFC) ELECTRODES - FROM NANOPARTICLES TO COMPOSITES". Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1205852564.

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SALOMOV, UKTAM. "3D pore-scale simulation of the fluid flow through the electrodes of High Temperature Polymeric Electrolyte Fuel Cell". Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2546336.

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Fuel cells and hydrogen are two key components for building a competitive, secure, and sustainable clean energy economy, due to possibility to convert diverse fuels directly into electrical power without combustion and a carbon-free fuel that can be produced from renewable resources. However, to become competitive in a market, fuel cells should overcome the issues by improvements in durability and performance as well as reductions in manufacturing cost. Recent advances in fuel cell technology has been made by development of the high temperature (HT) polymeric electrolyte membrane (PEM) fuel cells (FC). Owing to combination of the advantages of two types of fuel cells, namely polymeric electrolyte membrane and phosphoric acid, it is considered as one of the best technological solutions. Further improvements cannot be done without deep understanding of the major causes and underlying physico-chemical phenomena for specific degradation mechanisms of different compartments of HT-PEMFC, especially porous electrodes, which are the most vulnerable part prone to degradation processes, and predicting the impact of these degradation effects. Modeling can provide insight into the mechanisms that lead to irreversible or reversible performance loss and the relation between these mechanisms and the operating conditions, based on the changes in materials properties that can be observed. Moreover, another important issue of modeling is understanding the interaction between different specific membrane degradation mechanisms and their complex and mixed effects due to their simultaneously occurrence in real fuel cell operation, which requires multi-scale analysis of undergoing phenomena. This work represents a step towards reliable algorithms for reconstructing micro-morphology of electrode materials of high-temperature proton-exchange membrane fuel cells and for performing pore-scale simulations of fluid flow (including rarefaction effects). In particular, we developed a deterministic model for a woven gas diffusion layer (GDL) and the stochastic model for a non-woven GDL and a carbon- supported catalyst layer (CL) based on clusterization of carbon particles. We verified that both developed models accurately recover the experimental values of permeability, without any special ad-hoc tuning. Moreover, we investigated the effect of catalyst particle distributions inside the CL on the degree of clusterization and on the microscopic fluid flow, which is relevant for degradation modeling (e.g. loss of phosphoric acid). The three-dimensional pore-scale simulations of fluid flow for the direct numerical calculation of macroscopic transport parameters, like permeability, were performed by the Lattice Boltzmann Method (LBM). Within framework of this thesis, we investigate how distribution of catalyst (Pt) particles can affect gas dynamics, electro-chemistry and consequently performance in high temperature proton exchange membrane fuel cells. Optimal distribution of catalyst can be used as a mitigation strategy for phosphoric acid loss and crossover of reagents through membrane. The main idea is that one of the reasons of degradation is the gas dynamic pulling stress at the interface between the catalyst and the membrane. This stress can be highly reduced by tuning the main morphological parameters of the catalyst layer, like distribution of catalyst particles and clusterization. We have performed direct numerical pore-scale simulations of the gas flow through catalyst layer for different distributions of catalyst particles, in order to minimize this stress and hence to improve durability. The results of pore-scale simulation for exponential decay distribution show more than one order of magnitude reduction of the pulling stress, compared to the homogeneous (conventional) distribution. Moreover, a simplified three-dimensional macroscopic model of the membrane electrode assembly (MEA) with catalyst layer comprised of three sublayers with different catalyst loadings, has been developed to analyze how the proposed mitigation strategy affects the polarization curve and hence the performance. This macroscopic model presents 67% reduction in pulling stress for feasible mitigation strategy, at the price of only 9.3% reduction in efficiency at high current densities.

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Pearman, Benjamin. "The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests". Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5368.

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Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components. Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications. Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work. Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states. In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests. The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 – 5 nm and 20 – 150 nm size, respectively, that did not change size or shape when incorporated into the membranes. At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.
Ph.D.
Doctorate
Chemistry
Sciences
Chemistry

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GADDUCCI, ELEONORA. "Polymer Electrolyte Membrane Fuel Cells for maritime applications: state of art of the technology, experimental assessment of a 240-kW system, and Response Surface Methodology application to data analysis". Doctoral thesis, Università degli studi di Genova, 2022. http://hdl.handle.net/11567/1082870.

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Hydrogen energy technology allows the production of electricity from hydrogen and backward to store large amounts of energy by converting electricity into hydrogen, using a fuel cell, an electrolyzer, and a hydrogen storage system. The fuel cell market is increasing, offering components with improved converting performances; the expansion of this market and the spread of hydrogen system applications are bringing down the industrial costs of such technology offering new opportunities for commercial applications. This work concerns the Polymer Electrolyte Membrane technology, giving a complete overview of opportunities and problems that may arise from the employment of this type of system for maritime applications. The starting point of the analysis follows a more theoretical approach. Performance and degradation issues have been deeply investigated through thorough literature analysis, to issue the main problematics that can appear in the real operation of the PEM fuel cell system. In this context, a degradation map has been drawn, which can help the prediction of voltage degradation linked to the poisoning of the cell components. Therefore, since the external parameters that can influence the FC performance are highlighted, a statistical approach is investigated to understand how the reactants' flow rates and the thermal control can affect the performance. This has been possible thanks to the employment of the software Design Expert. In the second part of the Thesis, a more experimental approach to the thematic of PEM fuel cell systems for maritime applications is faced. This has been possible thanks to the test campaign carried out on the HI-SEA system, a 240-kW system located in the IES Laboratory of the University of Genoa (Savona Campus), made up of eight Polymer Membrane Fuel Cell modules supplied by Nuvera. This is one of the few complete and existing real-size laboratories for the assessment of PEMFC technology for maritime applications. The laboratory activities are part of the collaboration between the University and Fincantieri, the main Italian shipbuilder. The system has undergone a commissioning phase, which is accurately described, where previous issues are analyzed, understood, and solved to optimize the control system. Therefore, despite a prolonged inactivity time, the PEM fuel cell stacks have been reactivated thanks to a dedicated and innovative procedure. Finally, the system is fully operative: the results of the whole system operation confirm its suitability for operation in a ship-likely environment.

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Skoglund, Emil. "A NUMERICAL MODEL OF HEAT- AND MASS TRANSFER IN POLYMER ELECTROLYTE FUEL CELLS : A two-dimensional 1+1D approach to solve the steady-state temperature- and mass- distributions". Thesis, Mälardalens högskola, Framtidens energi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-55223.

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Methods of solving the steady state characteristics of a node matrix equation system over a polymer electrolyte fuel cell (PEFC) were evaluated. The most suitable method, referred to as the semi-implicit method, was set up in a MATLAB program. The model covers heat transfer due to thermal diffusion throughout the layers and due to thermal advection+diffusion in the gas channels. Included mass transport processes cover only transport of water vapor and consist of the same diffusion/advection schematics as the heat transfer processes. The mass transport processes are hence Fickian diffusion throughout all the layers and diffusion+advection in the gas channels. Data regarding all the relevant properties of the layer materials were gathered to simulate these heat- and mass transfer processes.Comparing the simulated temperature profiles obtained with the model to the temperature profiles of a previous work’s model, showed that the characteristics and behavior of the temperature profile are realistic. There were however differences between the results, but due to the number of unknown parameters in the previous work’s model it was not possible to draw conclusions regarding the accuracy of the model by comparing the results.Comparing the simulated water concentration profiles of the model and measured values, showed that the model produced concentration characteristics that for the most part alignedwell with the measurement data. The part of the fuel cell where the concentration profile did not match the measured data was the cathode side gas diffusion layer (GDL). This comparison was however performed with the assumption that relative humidity corresponds to liquid water concentration, and that this liquid water concentration is in the same range as the measured data. Because of this assumption it was not possible to determine the accuracy of the model.

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Morizur, Vincent. "Fonctionnalisation de polymères et applications dans les domaines de l’énergie, de la catalyse, de la cosmétique et de la santé". Thesis, Nice, 2014. http://www.theses.fr/2014NICE4102.

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Les polymères sont à l’heure actuelle étudiés dans de nombreux domaines comme la chimie, la biochimie, les nanotechnologies, l'électronique, la médecine ou encore les sciences des matériaux et trouvent des applications dans des domaines comme l’industrie automobile, la chimie fine. L’objectif de cette thèse est de réaliser la fonctionnalisation de polymères et de modifier les propriétés de ces matériaux afin d’envisager des nouvelles applications. Nous nous sommes intéressés à des polymères de la famille des poly(aryle éther) et plus particulièrement au poly(éther éther cétone) (PEEK). Ce polymère est connu pour ses propriétés mécaniques, thermiques, électriques ou encore pour sa résistance aux produits chimiques. Dans le premier chapitre, il est question de la fonctionnalisation des différents polymères de départ par des fonctions chlorures de sulfonyle, acides sulfoniques et sulfonamides. Le second chapitre est consacré à la synthèse et à l’étude électrochimique de nouveaux électrolytes polymériques et à de nouvelles membranes pour d’éventuelles applications dans le domaine des batteries au lithium et au sodium, ainsi que dans le domaine des piles à combustible. Dans un troisième chapitre, la préparation de nouveaux catalyseurs métalliques dérivés d’acides sulfoniques polymériques est discutée. Une étude de l’activité catalytique de ces différents catalyseurs a été réalisée sur la réaction d’acylation de Friedel-Crafts. Le quatrième chapitre est consacré à la préparation de nouveaux matériaux ayant des propriétés optiques intéressantes. Enfin dans un cinquième chapitre, la préparation et l’étude de nouveaux matériaux ayant des propriétés antibactériennes sont exposées
Polymers are now being studied in many fields such as chemistry, biochemistry, nanotechnology, electronics, medicine or material science and have applications in areas such as automotive industry, food industry, fine chemistry. The objective of this thesis is to achieve the functionalization of polymers and modify the properties of these materials in order to consider new applications. We were interested in polymers with the poly(aryl ether) motif, more particularly poly(ether ether ketone) (PEEK). This polymer is known for its mechanical, thermal, electrical properties and for its resistance to chemicals. In the first chapter, we present the functionalization of different polymers by sulfonyl chloride, sulfonic acid and sulfonamide functions. The second chapter is devoted to the synthesis and electrochemical study of novel polymeric electrolytes and new membranes for potential applications in the field of lithium and sodium batteries, as well as in the field of fuel cells. In the third chapter, the preparation of new metal catalysts derived from polymeric sulfonic acids is discussed. A study of the catalytic activity of these different polymeric catalysts was carried out on the Friedel-Crafts acylation reaction. The fourth chapter is devoted to the preparation of new materials with interesting optical properties. Finally, in the fifth chapter, the preparation and the study of new materials with antibacterial properties are reported

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Ressam, Ibitissam. "Élaboration et caractérisation de nouvelles membranes composites à conduction protonique pour les piles à combustible". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066732.

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Le Nafion a été considéré comme électrolyte modèle pour les piles à combustible (PAC), grâce à sa stabilité thermique et chimique ainsi que sa bonne conductivité protonique. Cependant, la conductivité protonique du Nafion se détériore à des taux d’humidité < 50% et à des températures >80°C. Pour cette raison de nouvelles membranes hybrides ont été élaborées afin d’en améliorer les performances. Plusieurs pistes ont été envisagées comme par exemple i) Membranes à base de chitosane, considéré comme le second polysaccharide le plus abondant après la cellulose. Ce polymère naturel permet d’assurer la stabilité physique et chimique de la membrane en présence d’eau, sans oublier son coût de revient qui reste moins cher en comparaison avec celui du Nafion et ii) Membranes à base de Nafion et d'argiles fibreuses (HNT), ces dernières confèrent à la membrane une conductivité protonique élevée en construisant des voies de transfert larges et continues. Cela permet aussi d'améliorer les propriétés thermiques et mécaniques des PEM. Notre étude est basée sur l'élaboration de membranes composites, nafion, chitosane et HNT. Des mesures de conductivité ont été entreprises et les valeurs obtenues comparées à celles du nafion. Des mesures d'ac-électrogravimétrie ont aussi été entreprises afin de mieux aborder les mécanismes de conduction
The perfluoro-sulfonated ionomer membranes are employed as separators in many industrialapplications such as fuel cells, chloro-alkali industry, electrodialysis and gaining inclininginterest in aqueous rechargeable or redox-flow batteries where the knowledge of their ionictransport and transfer properties is fundamental.Particularly, Nafion is adopted as a referencemembrane for polymer electrolyte membrane (PEM) fuel cells due to its thermal stability andgood proton conductivity. However, Nafion membranes have several disadvantages such as a decrease in the proton conductivity at low relative humidity (<50%) and high temperatures(>80°C), and excessive dimensional changes due to the swelling/deswelling, leading tomechanical instabilities.To circumvent these problems, novel proton conducting membraneshave been developed, either by completely replacing or by using organic and/or inorganiccomponents to Nafion.3 In this regard, a large spectrum of membranes have been elaboratedconsidering many attributes such as high proton conductivity, physical separation between theanode and the cathode and fuel barrier characteristics, good chemical and physical stability andlow elaboration cost of the membrane. Two types of additives were examined to improve the performances, particularly : Membranes based on Nafion with Chitosan biopolymer. This naturel polymer is consideredas the second most abundant polysaccharide after cellulose.6 Chitosan improves the physical andchemical stability of the membrane in the presence of water, and it is considered as a less costlyadditive to Nafion7.The improvement of the proton conductivity with pristine chitosan isessentially challenging. Previous studies demonstrated that vehicularandGrotthuss mechanismjointly govern the proton transfer in chitosan membranes.In the vehicular mechanism, the protons diffuse together with solvent molecules in the form of hydronium ions byforming acomplex such as H5O2+ and H9O4+. In the Grotthuss mechanism, however, the protons jump fromone solvent molecule or functional group to the next by the continuous formation and breakingof hydrogen bonds. Membranes based on Nafion with Halloysite nanotubes (HNT). These clays confer to themembrane high proton conductivity by constructing large and continuous conductionpathways.These inorganic additives also improve the thermal and mechanical properties of PEM. Composite membranes of Nafion/Chitosan- SO3H and Nafion/HNT-SO3H are prepared. Theresulting composite membranes were studied by various conventional structural characterizationtechniques. H+ conductivity measurements were performed and the values obtained are higherthan those of pristine Nafion at various relative humidity (RH%) levels and temperatures (30°C-80°C). Our results highlight the beneficial character of functionalized chitosan biopolymer andHalloysite nanotube clays as additives to improve PEM performances

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McGee, Seán. "Thermal energy management and chemical reaction investigation of micro-proton exchange membrane fuel cell and fuel cell system using finite element modelling". Thesis, KTH, Kraft- och värmeteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173001.

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Fuel cell systems are becoming more commonplace as a power generation method and are being researched, developed, and explored for commercial use, including portable fuel cells that appear in laptops, phones, and of course, chargers. This thesis examines a model constructed on inspiration from the myFC PowerTrekk, a portable fuel cell charger, using COMSOL Multiphysics, a finite element analysis software. As an educational tool and in the form of zero-dimensional, two-dimensional, and three-dimensional models, an investigation was completed into the geometric construction, air conditions and compositions, and product materials with a best case scenario completed that summarizes the results identified. On the basis of the results of this research, it can be concluded that polyoximetylen and high-density polyethylene were considered as possible materials for the majority of the product, though a more thorough investigation is needed. Air flow of above 10 m/s, air water vapour mass fraction below 50% and initial temperature between 308K and 298K was considered in this best scenario. Suggestions on future expansions to this project are also given in the conclusion.

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Lo, Cheng Hsing, i 羅正欣. "Experimental investigations on PVA/PEO hybrid polymer electrolytes". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/11099861979646423606.

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碩士
長庚大學
化工與材料工程研究所
91
The alkaline polymer electrolyte membranes containing polyethylene oxide (PEO), polyvinyl alcohol (PVA) and using water as the solvent and potassium hydroxide (KOH) as the salt have been investigated in the present study. These polymer electrolyte membranes were characterized by A.C. impedance spectroscopic techniques. The ionic conductivity of the polymer electrolyte membranes increased with increasing PEO/PVA ratio. Ionic conductivity of these polymer membranes increases from 6.8×10-6 S/cm to 1.12×10-2 S/cm at room temperature when the ratio of PEO:PVA varied from 10:0 to 2:8. Temperature dependence of the conductivity was found to be in agreement with Arrhenius type with activation energy in the range of 2-9 kJ mole-1, depending on the electrolyte compositions. The characterizations of electrolyte properties were carried out on the PEO/PVA hybrid polymer membranes using DSC, SEM, POM, a.c impedance spectroscopic techniques and electrochemical spectroscopic techniques. It was found that the polymer electrolyte membranes exhibited high ionic conductivity, good mechanical property and excellent electrochemical stability.

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Lee, Hsin-Ying, i 李心穎. "Synthesis and characterization of styrene-based PEO polymer electrolytes". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/tdzt62.

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碩士
國立臺北科技大學
有機高分子研究所
94
It is the current tendency to be “ light, thin, short, little” for modern electronic products. The important factor for the application in reality is the design of power supply. For the portable personal electronics, lithium batteries are the most common used power supply due to their potential advantages, such as the high-energy density, very small-scale, slim, high security and low cost. Currently, the liquid electrolytes are used though it has the potential danger of liquid linkage. In this research, the styrene-based PEO polymer electrolyte is synthesized. Polystyrene as the backbone structure can offer mechanical strength, and glycol repeat units provide lone pair electrons forming a continuous ion-conducting pathway. PEO side chain is attached into acrylate monomer via Williamson Ether Synthesis. The polymer electrolyte films are fabricated with LiN(CF3SO2)2 salt under UV-illumination. The UV polymerization condition is analyzed by FTIR and DPA (Double Bean Photocalorimetric Accessory). Ionic conductivity, thermal stability of films are examined by AC impedence technique, differential scanning calorimetry and X-ray diffraction analysis, respectively. Finally, the coin-type lithium polymer batteries are assembled to test charge and discharge.

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Wang, Yao-Lin, i 王耀琳. "Preparation and characterization of PEO/LiClO4/mesoporous silica composite polymer electrolytes". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/07141186150120600586.

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碩士
中原大學
化學研究所
94
In this study, a series of totally amorphous PEO/LiClO4/mesoporous silica nanocomposite polymer electrolytes were prepared with high molecule weight polyethylene oxide, high concentration lithium perchlorate and low content of a homemade mesoporous silica. The SEM/EDS images of the nanocomposite polymer electrolytes indicated that 2wt.% of the mesoporous silica was well dispersed in the PEO polymer electrolyte matrix. The interactions in the system and possible conduction mechanism were studied by DSC, XRD, FT-IR, and 7Li-NMR analysis. It was found that conductivity was significantly improved by the addition of the as-prepared mesoporous silica. A maximum ambient conductivity value of 7.09×10-5 S/cm was obtained for the nanocomposite polymer electrolyte O6A2. The AC-DC polarization results showed that the lithium ion transference number(t+) of O6A2 was about 0.67, which is the highest value reported in PEO/LiClO4/SiO2 system up to now. The high ionic conductivity and lithium ion transference number suggested that it can be used as a potential candidate of the electrolyte material for lithium polymer batteries.

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Liu, Chien-lin, i 劉建麟. "Study on the Novel Synthesis of PEO Derivatives and Properties of Self-assembly Solid Polymer Electrolytes". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/x864g3.

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碩士
國立臺灣科技大學
高分子系
94
A poly(ethylene glycol) methyl ether (M.w.＝750) containing self-assembly compound, poly(ethylene glycol) methyl ether-3,5-bis (11-methacryloylundecyl-1-oxybenzyloxy) benzoate (PEO-MBA), was synthesized by the polyesterification of 3,5-bis(11-methacryloylundecyl -1-oxybenzyloxy) benzoic acid (MBA) with poly(ethylene glycol) methyl ether. The structures of PEO-MBA and the intermediates were identified by FTIR and NMR. Solid polymer electrolyte film (SPEF) was prepared by photopolymerization of the solution composed of 50wt% of PEO-MBA, mixture of EMA(ethyl methacrylate)/HMA(hexyl methacryl ate)/TEGDMA(tri(ethylene glycol) methyl methacrylate) (mole ratio(%) : 30/20/50), and various amount of LiClO4. The structure, morphology, and properties of the SPEF was characterized by FT-IR, SEM, SAXS, DSC, and TGA. It was found that the lithium ion in the SPEF formed complex with poly(ethylene oxide) (EO)n segments in PEO-MBA that caused PEO segments in the films became amorphous. The Tg of PEO segments in the SPEF increased with the concentration of lithium ion. The ionic conductivity of the SPEF was measured by AC Impedance. The value at room temperature could reach as high as 1.6×10-5 Scm-1 at the mole ratio of [Li+]/[EO]=30mole%, which was higher than that of the conventional PEO film(10-6~10-7 Scm-1). It seemed to us that the phase separation between PEO-MBA and the matrix in SPEF was of great advantages to the ionic conductivity.

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FAN, YU-WEN, i 范玉玟. "A study on the characteristics and morphology of PEO/Li-salt polymer electrolytes and their blends with PVDF". Thesis, 1992. http://ndltd.ncl.edu.tw/handle/81276773761004959217.

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(8083202), Andres Villa Pulido. "DESIGN AND CHARACTERIZATION OF A PEO-BASED POLYMER COMPOSITE ELECTROLYTE EMBEDDED WITH DOPED-LLZO: ROLE OF DOPANT IN BULK IONIC CONDUCTIVITY". Thesis, 2019.

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Ionic conductivity of solid polymer electrolytes (SPEs) can be enhanced by the addition of fillers, while maintaining good chemical stability, and compatibility with popular cathode and anode materials. Additionally, polymer composite electrolytes can replace the flammable organic liquid in a lithium-ion battery design and are compatible with lithium metal. Compatibility with Li-metal is a key development towards a next-generation rechargeable Li-ion battery, as a Li-metal anode has a specific capacity an order of magnitude higher than LiC6 anodes used today in everyday devices. The addition of fillers is understood to suppress the crystalline fraction in the polymer phase, increasing the ionic conductivity, as Li-ion conduction is most mobile through the amorphous phase. A full model for a conduction mechanism has not yet constructed, as there is evidence that a semi-crystalline PEO-based electrolyte performs better than a fully amorphous electrolyte. Furthermore, it is not yet fully understood why the weight load of fillers in PCEs can range from 2.5%wt to 52.5%wt, in order to achieve high ionic conductivity (~10-4S/cm). This work seeks to investigate the conduction mechanism in the PCE through the use of doped-Li7La3Zr2O12 as a filler and analysis of the PCE microstructure. In this work, a solid-state electrolyte, doped-Li7La3Zr2O12 (LLZO) was synthesized via a sol-gel method, and characterized. The effect of doping and co-doping the Li, La and Zr sites in the LLZO garnet was investigated. A PEO-based polymer composite electrolyte (PCE) was prepared by adding bismuth doped LLZO (Li7-xLa3Zr2-xBixO12) as a filler. The bismuth molar ratio was changed in value to study the dopant role on the bulk PCE ionic conductivity, polymer phase crystallinity and microstructure. Results suggest that small variations in dopant can determine the optimal weight load of filler at which the maximum ionic conductivity is reached. By understanding the relationship between filler properties and electrochemical properties, higher performance can be achieved with minimal filler content, lowering manufacturing costs a solid-state rechargeable Li-ion battery.

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Chiou, Bor-Ning, i 邱伯寧. "In Situ Synthesis Of PEO-Based Composite Solid Polymer Electrolyte". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/00307978419789010611.

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碩士
國立中央大學
化學研究所
92
The major challenge of Solid Polymer Electrolytes (SPE) is to achieve fair ionic conductivities at ambient temperature, while maintaining film-forming property. Present study disclosed a unique network structured polymer electrolyte by in-situ polymerize phenolic in PEO solution which is subsequently cross-linked by HMTA to form a mechanical stable freestanding and homogenous film.The structure and PEO crystalline before and after cross-linking、thermal stability、surface morphology、molecular motion ability and state、structure and ion transport are characterized. by DSC、TGA、XRD、SEM、FT-IR、NMR、AC-impedance experiments, respectively. These results show the present in situ composite Solid Polymer electrolytes (in situ CSPE) establish a fair interpenetrating network (IPN) structure with good mechanical properties suitable for general electrolyte applications. The CSPE exhibits lower Tm and Tc than that obtained from blending, which implies the PEO crystallite is well-dispersed and large crystallite is hindered in the confined polymer matrix which results in lowering crystalline of polymer. Due to the unique microstructure, re-crystallization of PEO polymer is not occurring after cross-linking phenolic.

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Kuo, Lung-Che, i 郭榮哲. "Study on the polymer electrolyte material using PO random modified PEO". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/50929863742611150338.

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碩士
義守大學
材料科學與工程學系
92
In this study, the polymers of PEG (polyethylene glycol) and PEO (polyethylene oxide) were modified by adding PO (propylene oxide) at random and employed as polymer electrolytes with various molecular weights and PO ratios. It was observed that the thermo behavior of PEO was affected by the steric effect of methyl of propylene oxide. The changes of structure and thermo property of this polymer with various ratios of PO were analyzed and characterized by GPC, DSC, viscosity meter, and FT-IR. The Tg, Tm and crystallinity of PEO were reduced by the PO random modification. The relations between PO ratios and Tg, Tm, crystallization temperature and crystallinity of the modified polymer were investigated. The 3% PO random modification of PEO would cause a decrease of Tg from -52℃ to -58℃, Tm from 66℃ to 52℃, and crystallinity from 95% to 64% of the original PEO polymer.

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Wu, Chiung-Hui, i 吳炯輝. "New Polymer Electrolyte for Lithium battery Based on PEO-PAN-LiClO4 System". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/85015927562567652565.

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碩士
國立中央大學
化學研究所
91
Abstract Since 1975 Wright et al. discovered the ionic conductivity (1x10-7 S/cm) of PEO-Lithium salt, PEO-Lthium salt based solid electrolytes have under extensively studied. However, the room temperature conductivities of PEO-Li salts are usually too low (due to the semi-crystalline nature of PEO) to be applied practically in lithium batteries. Therefore, increasing the conductivity via various physical or chemical methods has become the major research efforts. To enhance the conductivity of PEO-LiClO4 system, one of the good strategies was forming polymer blend. In this thesis, we blended the precursor of conjugated polymer PAN (polyacrylonitrile) (with PAN/PEO ratios equal to 0wt%, 1wt%, 3wty%, 5wt%) into the PEO-LiClO4 system (and/or heat the blend polymer to crosslink the PAN) to increase the conductivity and film dimension stability. It was found that by adding 1wt% PAN into PEO-LiClO4(15wt%) the hybrid polymer electrolyte has the highest ionic conductivity (up to 6.8x10-4 S/cm at 50oC) and exhibit good mechanical properties. Heating the polymer blends up to 200oC can further increase their conductivity. XRD data showed that the domain size of PEO-LiClO4-PAN is smaller than that of PEO-LiClO4. DSC results also indicated that both the melting point and crystalinility of PEO-LiClO4(15wt%) decreased after adding PAN. The crystallinity of PAN- PEO-LiClO4(15wt%) decreased further after rapidly heating and cooling of the electrolyte films. SEM micrographs showed that when small amount of PAN (PAN/PEO <5wt%) was added, the electrolyte films have a smoother surface compared to pure PEO-LiClO4. The function of PAN can be regarded as a polymer support for dispersing PEO matrix and increase the dimension stability when the crystallinity of PEO decreased.

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44

Angjeli, Kristina, Carlo Versace, Isabella Nicotera i Roberto Bartolino. "Hybrid nanostructured fillers for polymer electrolytes in the PEM Fuel Cells". Thesis, 2012. http://hdl.handle.net/10955/1150.

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Dottorato di Ricerca in Scienze e Tecnologie delle Mesofasi e dei Materiali Molecolari, XXV Ciclo, a.a. 2011-2012
The present thesis is focused on the development of novel nancomposite membranes, prepared by the incorporation of two-dimensional inorganic layered structures such as (i) smectite clays (synthetic and natural), (ii) graphene oxide (GO), and (iii) layered double hydroxides (LDHs) with different compositions into the polymer matrix of Nafion, for use as electrolytes in Proton Exchange Membrane fuel cells. The characteristics of the membranes were studied mainly, in terms of transport properties by NMR spectroscopy, in order to study the water dynamics inside the electrolyte membranes. For this purpose the Pulse-Field-Gradient Spin-Echo NMR (PFGSENMR) method was employed to obtain a direct measurement of water self-diffusion coefficients on the water-swelled membranes in a wide temperature range (25-140 °C). This technique together with the 1H-NMR spectral analysis and NMR spin-lattice relaxation times (T1) conducted under variable temperature. Furthermore, both pristine materials (fillers and Nafion) as well as the resulted nanocomposite membranes were characterized by a combination of X-ray diffraction, FTIR spectroscopy, thermal analysis (DTA/TGA), Raman spectroscopies and scanning electronic microscopy (SEM).
Università della Calabria

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45

Sauder, Rebecca. "Effect of Anode Purge on Polymer Electrolyte Membrane Fuel Cell Performance". Thesis, 2009. http://hdl.handle.net/10012/4914.

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Polymer Electrolyte Membrane Fuel Cells (PEMFC) are promising power generating devices that use an electrochemical reaction to convert the energy from hydrogen fuel into usable electricity. One cell produces a small voltage so many cells are combined in series in order to produce a useful voltage, this configuration is referred to as a stack. Hydrogen is supplied to the anode of the stack in amounts greater than the electrochemical reaction requires to guarantee that enough hydrogen is available for every cell in the stack and to provide enough pressure throughout the cell flow channels for good mass transfer. For reasonable fuel efficiency, the anode outlet gas containing unconverted hydrogen is recycled (or recirculated) back to the anode inlet. PEMFC performance is highest when pure hydrogen fuel is supplied, however, nitrogen at the cathode will permeate through the membrane and accumulate in the anode gas with recirculation. Nitrogen buildup dilutes the hydrogen gas which adversely affects fuel cell performance at the anode. Also, in practical applications hydrogen-rich gas produced from reformed methane, called reformate, is used as the fuel. Reformate contains impurities such as, nitrogen, carbon dioxide, carbon monoxide, and sulfur compounds. This thesis will focus on trace levels of carbon monoxide entering in the hydrogen fuel stream, and the impact of contaminant build-up due to anode recirculation. Carbon monoxide adsorbs readily onto the platinum catalyst sites, called poisoning, thus decreasing PEMFC performance. In efforts to minimize the buildup of impurities and crossed over nitrogen, a portion of the anode outlet gas is periodically and continuously purged to the exhaust. How often the outlet gas is purged depends on a variable called the purge fraction. The purpose of this research is to study the effect of purge fraction on PEMFC performance, measured by the average cell voltage, for a Hydrogenics 10 cell stack. The operating parameters used for testing and the experimental apparatus were designed to mimic a Hydrogenics 8kW Hydrogen Fuel Cell Power Module. A pump connected between the anode outlet and anode inlet form the anode recirculation loop. In Phase 1 of the test program the effect of purge in the absence of carbon monoxide was studied to see if hydrogen dilution from nitrogen crossover and accumulation would cause significant cell voltage degradation. In Phase 2 the effect down to 0.2 ppm carbon monoxide was evaluated. The results showed that nitrogen buildup, in the absence of carbon monoxide, did not significantly penalize the cell performance in the range of purge fractions tested. However, for the same purge fraction but with as little as 0.2 ppm carbon monoxide present, the voltage loss was significant. A discussion of the effect of purge on the impurity concentration and the associated cell voltage degradation is detailed with particular emphasis on carbon monoxide poisoning.

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46

Headley, Alexander John. "Dynamic subdivided relative humidity model of a polymer electrolyte membrane fuel cell". 2013. http://hdl.handle.net/2152/22264.

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The development of a control-oriented dynamic relative humidity model for a polymer electrolyte membrane (PEM) fuel cell stack is presented. This model is integrated with a first law based thermal model, which tracks energy flow within four defined control volumes in the fuel cell; the cathode channel, anode channel, coolant channel, and fuel cell stack body. Energy and mass conservation equations are developed for each control volume. On top of mass conservation, electro-drag and osmosis models were also implemented within the model to account for the major modes of vapor transfer through the membrane between the anode and cathode. Requisite alterations to the thermal model as well as mass flow rate calculations are also discussed. Initially, the model utilized a single lumped control volume for the calculation of all values each channel (anode and cathode). This lumped value method is computationally inexpensive, and makes the model optimal for control design. However, investigation of the mass-based Biot number showed the need for greater granularity along the length of the channels to properly capture the relative humidity dynamics. In order to improve the resolution of the model, while still minimizing the computation expense, the model was subdivided into a series of lumped value models. The cathode channel was the point of focus as it is the major concern from a controls perspective. This method captures the proper trends found in far more complex CFD models, while still maintaining a quick calculation time. Different levels are subdivision (3 and 6 submodels) are investigated, and the differences discussed. Particularly, temperature range, relative humidity range, the effect on the modeled voltage, and calculation time are compared. This control-oriented model is low order and based on lumped parameters, which makes the computational expense low. Formulation of this model enables the development of control algorithms to achieve optimal thermal and water management.
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47

Guvelioglu, Galip Hakan. "Transport limitations and water management in polymer electrolyte membrane (PEM) fuel cells /". Diss., 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3167055.

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48

Hsu, Chia-Hao, i 許家豪. "Stress Analysis and Simulation of Polymer Electrolyte Membrane (PEM) in the Fuel Cell". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/95735104224244352677.

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碩士
元智大學
機械工程學系
94
Due to progress of human society and growing of population, the needs of energy resources were increased day by day. It is necessary to exploit new energy resources and energy technology. There were some deficiencies in traditional methods for generating electric power. Polymer electrolyte membrane of full cell (PEMFC) is a new material with non-pollution, few noise, high efficiency and could be generally applied. It has become an alteration in developing energy technology. The studies on PEMFC have been developed for several years. Because PEMFC will be deteriorated by cycling between wet and dry. The purposes of this study was to investigate the mechanical properties of cycling between wet and dry of PEMFC, to analyze swelling and shrinkage and stress by using finite element analysis based on Viscoelasticity ,to analyze creep and relaxation of PEMFC, and to compare the differences between PTFE-Nafion composite membranes and Nafion 211. The results showed under the same experimental condition, The stress generated from swelling of wet and dry of PTFE-Nafion composite membranes was smaller than that from Nafion 211.According to finite element analysis, stress was concentrated on the four corners of the material, these could be inferred to the destructive area of membrane.

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49

Chen, Weihuang, i 陳偉皇. "Preparation of composite PVA/PEO-PPO-PEO triblock(F127) polymer electrolyte membranes and its application to a direct methanol fuel cell (DMFC)". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/32097205702808927306.

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碩士
明志科技大學
化學工程研究所
99
英文摘要 The composite proton electrolyte membrane based on poly(vinyl alcohol) (PVA), PEO100-PPO70-PEO100 triblock copolymer(F127), and sulfosuccinic acid (SSA) was prepared by a solution casting method. The PVA/F127 blend composite polymer membrane was further sulfonated by chlorosulfuric acid in DMSO at 60oC for 4 h. The sulfosuccinic acid (SSA) was used as a proton source and crosslinker. The sulfonation for the PVA/F127/SSA composite polymer membrane greatly enhanced the ionic conductivity. The characteristic properties were examined by by thermal gravimetric analysis (TGA), micro-Raman and FTIR spectroscopies, scanning electron microscopy (SEM), and AC impedance method. The contents of F127 varied from 0 to 50 wt.%, but the SSA was maintained at 20 wt.%. It was found that the maximum ionic conductivity of PVA/20wt.%F127/20wt.%SSA polymer electrolyte membrane is about 7.10×10-3 S cm-1. It was observed that the highest peak power density of DMFC with a 4M CH3OH fuel was around 11.2 and 14.1 mW cm-2 at 25 and 60oC, respectively. The methanol permeability is of the order of 10-6~10-7 cm2 s-1. It was shown that the sulfonated PVA/F127/SSA composite polymer membrane exhibited a good candidate for application to a DMFC. Keywords: Direct methanol fuel cell (DMFC), Poly(vinyl alcohol), PEO100- PPO70-PEO100 triblock copolymer(F127) , Chlororulfuric Acid, Methanol permeability, Sulfosuccinic acid (SSA)

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50

Rea, Christopher. "Degradation of a Polymer Electrolyte Membrane Fuel Cell Under Freeze Start-up Operation". Thesis, 2011. http://hdl.handle.net/10012/6232.

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The polymer electrolyte membrane fuel cell (PEMFC) is an electrochemical device used for the production of power, which is a key for the transition towards green and renewable power delivery devices for mobile, stationary and back-up power applications. PEMFCs consume hydrogen and oxygen to produce power, water and heat. The transient start-up from sub-zero freezing temperature conditions is a problem for the successful, undamaged and unhindered operation. The generation and presence of water in the PEMFC stack in such an environment leads to the formation of ice that hinders the flow of gases, causes morphological changes in the membrane electrode assembly (MEA) leading to reversible and irreversible degradation of stack performance. Start-up performance is highly dependent on start-up operational conditions and procedures. The previous state of the stack will influence the ability to perform upon the next start-up and operation. Water generated during normal operation is vital and improves performance when properly managed. Liquid water present at shut-down can form ice and cause unwanted start-up effects. This phase change may cause damage to the MEA and gas diffusion media due to volume expansion. Removal of high water content at shutdown decreases proton conductivity which can delay start-up times. The United States Department of Energy (DOE) has established a set of criteria that will make fuel cell technology viable when attained. As specified by DOE, an 80 kWe fuel cell will be required by 2015 to reach 50% power in 30 seconds from start-up at an ambient temperature of -20°C. This work investigates freeze start-up in a multi-kilowatt stack approaching both shut-down conditioning and start-up operations to improve performance, moderate fuel cell damage and determine the limits of current stack technology. The investigation involved a Hydrogenics Corporation 5 kW 506 series fuel cell stack. The investigation is completed through conditioning the fuel cell start-up performance at various temperatures ranging from -5°C to below -20°C. The control of system start-up temperature is achieved with an environmental chamber that maintains the desired set point during dwell time and start-up. The supply gases for the experiment are conditioned at ambient stack temperature to create a realistic environment that could be experienced in colder weather climates. Temperature controls aim to maintain steady ambient temperatures during progressive start-up in order to best simulate ambient conditions. The control and operation of the fuel cell is maintained by the use of a fuel cell automated test station (FCATS™). FCATS supplies gas feeds, coolant medium and can control temperature and reactant humidity in reactants according to a prescribed procedure for continuous operation. The iv collection of data occurs by the same system recording cell voltage, temperatures, pressures, flow rates and current densities. A procedural start-up and characterization are conducted in order improve start-of performance and examine reactant flows, coolant activation time, stack conditioning and the effects by freezing temperatures. The resulting degradation is investigated by polarization curves and various ex-situ measurements. In this work, it was found that freeze start-up of a fuel cell stack can be aided and managed by conditioning the stack at shut-down and applying a procedure to successfully start-up and mitigate the damage that freezing can cause.

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