Добірка наукової літератури з теми "Anion exchange ionomer (AEI)"

Anion exchange membrane fuel cells (AEMFCs) are known to be able to address the use of expensive platinum catalyst by employing non-PGMs (Platinum Group Metal) metal catalysts, affordable ionomers, and greater fuel flexibility. All that provides AEMFCs with advantages over PEMFCs. However, AEMFCs have not been reported to achieve high current density as desired at fault by the lack of understanding of ionomer-catalyst interaction. For stable operation of AEM-based devices, water sorption and swelling of the thin anion exchange ionomer (AEI) layer are coupled to its catalyst binding ability. Unfortunately for AEM fuel cell field there exists no commercial material as Nafion® exists for the PEM fuel cell field. The development of a high performance and durable anionic catalyst binders also referred to as anion exchange ionomers (AEIs) is the major challenge for AEMFCs. This study aims to develop an improved AEI to be tested in both in-house and commercial electrocatalysts. Electrocatalytic activity using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) will be carried out for all the electrocatalysts with the use on the developed AEI instead of the usually used nafion ionomer. Characterization techniques will include transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) for particle size, crystal structure and morphology respectively of the electrocatalysts. For the developed AEI dynamic light scattering (DLS) (with an ELS-Z Zeta-potential and particle size analyzer), nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR) for size distribution profile, material molecular structure and composition.

Anion exchange membrane water electrolysis (AEMWE) is a type of electrolysis that involves the use of an anion exchange membrane (AEM) to separate the anode and cathode compartments. During the electrolysis process, water is split into hydrogen gas (H2) at the cathode and oxygen gas (O2) at the anode. AEMWE is an emerging technology that has the potential to play a significant role in the production of green hydrogen, which is a promising energy carrier for a variety of applications, including fuel cells and transportation. One of the benefits of AEMWE is that it can be used with a variety of water sources, including seawater and wastewater. Additionally, AEMWE has the potential to be more energy-efficient and cost-effective than other types of water electrolysis because it can operate at lower voltages and use cheap Ni-based materials [1]. Recently, there has been a significant amount of interest in the development of anion exchange ionomers (AEI) that conduct hydroxide ions [2]. We recently investigated the PPO-LC-TMA ionomer (poly(2,6-dimethyl-1,4-phenylene oxide) [3] backbone with amine-functionalized by trimethyl amine) [4] as an ionomer for Ni-based catalysts in AEMWE. Commercial Aemion, Fumion, and Nafion AEI were compared to the lab-synthesized ammonium-enriched anion exchange ionomer PPO-LC-TMA as an anode catalyst layer for oxygen evolution reaction (OER). Cyclic voltammetry results showed that the NiFe catalyst layer with PPO-LC-TMA AEI showed higher Ni(OH)2/NiOOH peak current density, while current density obtained over Ni90Fe10 catalysts was 11%, 17%, and 39% for Nafion, Fumion, and Aemion AEI, respectively [5]. This resulted in increased OER activity of Ni90Fe10 with PPO-LC-TMA AEI and a lower overpotential of 151 mV at 10 mA cm-2 in 1 M KOH. Ex-situ Raman spectroscopy of as prepared and spent catalytic layer confirmed that the electrode transitioned to the Ni-OOH phase after polarization. NiFe anode catalytic layers were tested in a 5 cm2 single-cell alkaline membrane water electrolysis (AEMWE) with varying amounts of PPO-LC-TMA (7, 15, and 25 wt %). AEMWE results revealed that 25 wt% PPO-LC-TMA is the best ionomer loading, achieving a cell voltage of 1.941 V at 600 mA cm-2 in 1 M KOH at 50°C. Both three-electrode electrochemical cell and alkaline membrane water electrolysis (AEMWE) tests revealed that the PPO-LC-TMA ionomer stabilized NiFe catalyst and improved its performance compared to Fumion and Nafion ionomers. These results will be presented and discussed, along with details of electrochemical and physical characterizations. References E. Cossar, F. Murphy, E.A. Baranova, J Chem Technol Biotechnol, 97 (2022) 1611–1624. Wright, A. G.; Fan, J.; Britton, B.; Weissbach, T.; Lee, H.-F.; Kitching, E. A.; Peckham, T. J.; Holdcroft, S. Energy Environ. Sci. 9 (2016) 2130−2142. A.R. Nallayagari, E. Sgreccia, L. Pasquini, M Sette, P. Knauth and M. L. Di Vona ACS Appl. Mater. Interfaces, 14, 41 (2022) 46537–46547. R.-A. Becerra-Arciniegas, R. Narducci, G. Ercolani, E. Sgreccia, L. Pasquini, M. L. Di Vona, and P. Knauth, J. Phys. Chem. C, 124, 2 (2020) 1309–1316. E. Cossar, F. Murphy, J. Walia, A. Weck, E.A. Baranova, ACS Applied Energy Materials, 5 (2022) 9938−9951.

The ongoing, rapid increase in atmospheric CO2 concentration has led to a growing interest in the electrochemical reduction of CO2 to value-added products like CO. To attain high current densities, the latter reaction is often performed using an anion exchange membrane(AEM) electrolyte that is well known to operate through the transport of (bi)carbonate ions from cathode to anode. This can in turn result in a CO2 pumping effect that decreases the device’s net CO2-consumption, and that can be prevented by using a bipolar membrane in a so-called forward-bias configuration (i.e., with the anion vs. cation exchange layers (AEL, CEL) contacting the cathode vs. anode electrodes, respectively). However, the recombination of protons and (bi)carbonate and concomitant production of H2O and CO2 at the AEL-CEL interface in this operative mode can also lead to the delamination of the membrane and cell failure. In order to prevent such a delamination, this study proposes the introduction of a three-dimensional (3D) AEL-CEL junction, utilizing Nafion® as the cation exchange layer and PiperION as the anion exchange one. Two different methods were applied to fabricate the 3D junction bipolar membrane. The first method involves the fabrication of a 3D interlocking layer using polystyrene (PS) beads that are sprayed (along with Nafion ionomer) onto a Nafion membrane, and removed using toluene. This results in an inverse-opal structure atop the Nafion membrane whose pores can be filled with anion exchange ionomer (AEI). Complementarily, the second method involves the introduction of a layer, consisting of a mixture of AEI and cation exchange ionomer (CEI) between the AEM and CEM. Additionally, a non-conductive oxide material is added to this ionomer layer to increase the contact area of AEI and CEI. Finally, the electrochemical CO2 reduction performance and durability of the resulting, 3D junction bipolar membranes are evaluated and compared to those of an equivalent, 2D junction bipolar membrane, in all cases in a forward bias configuration.

Anion exchange membrane fuel cells (AEMFCs) have been intensively studied in recent years to replace proton exchange membrane fuel cells (PEMFCs). The acid-to-alkali transitions have the potential to lower overall system costs because it allows the non-precious metal catalysts and inexpensive metal stack hardware. Significant strides have been made in materials science in the last few decades, particularly the development of high IEC-containing anion exchange membrane (AEM) and ionomer (AEI) possessing high OH- conductivity, enabling comparable cell performance to that of PEMFC. In addition, the discovery of high HOR activity of PtRu by oxophilic and/or electronic effects, and reducing ionomer poisoning, provided an opportunity to further advance the cell performance of AEMFC. However, despite the remarkable development of materials, modest AEMFCs still have inadequate power performance (< 0.5 W cm-2) even using the precious catalysts, which stems from a lack of understanding of the catalyst layer (CL) design. CL consists of a catalyst and an ionomer, where the chemical energy of the fuel is converted into electrical energy in triple-phase-boundaries (TPBs). TPB is an electrochemically active site where catalyst (electrons), ionomer (H+ or OH-), and reactant gases were concurrent. In order to realize a high-performance fuel cell, the TPB should be high enough to utilize the capabilities of the catalyst, and the ideal state would be to maximize the contact area between the ionomer and the catalyst while minimizing the loss of CL porosity. Accordingly, the structure of the CL is one of the key factors that directly affect the performance of the fuel cell and is in great account. CL is fabricated from a slurry containing a catalyst, ionomer, and dispersing solvent, whose structure is determined by the complex interactions between slurry components. Therefore, fine-tuning of comprehensive interaction (catalyst/ionomer, catalyst/solvent, and ionomer/solvent) is the core technology in CL design, and an in-depth understanding of each interaction is also essential. In this regard, we recently presented the rational design of the CL by controlling AEI size, distribution via a solvent selection of the catalyst slurry. Specifically, the larger the solubility parameter (excluding the hydrogen bonding term) of the organic solvent mixed with water, the smaller the dispersed AEI size, leading to an even distribution of the AEI in the CL. This induces a high electrochemical surface area of the CL, making it possible to achieve high performance AEMFC from the low current region. However, nevertheless, we found that the distribution of AEI in the AEMFC catalyst layer was still not completely uniform through various types of electron microscopy analysis. In particular, when the morphology of the AEMFC CL was compared with the Nafion ionomer (commonly used in PEMFC field) as a reference, AEI caused lower porosity by clogging the pores of Pt/C nanoparticles. For this reason, we found that AEMFCs had lower performance than Nafion-based PEMFCs, despite their high ORR activity under alkaline conditions. Molecular dynamics (MD) and density functional theory (DFT) simulation analyzes show that AEI has a particularly low interaction with carbon compared to Nafion, and for this reason, we found that AEI aggregates with each other rather than evenly distributed on the Pt/C surface. We used QPC-TMA as AEI in this study and confirmed that commercialized AEI (FAA-3 and XA-9) also form low CL porosity and pore-closing characteristics. This result suggests that low interaction between AEI/carbon is a universal property of current levels of AEI. Therefore, when designing an ionomer to improve the performance of AEMFC, high interaction with carbon should be considered as another important variable.

Anion exchange membrane fuel cells (AEMFCs) are seen as a possible successor to proton exchange membrane fuel cell technologies. A major motivation behind AEMFC development is the potential to use less costly materials, such as non-platinum group metal catalysts, thus reducing the stack cost. Anion exchange ionomers (AEIs) are polymers that facilitate ion transport in the catalyst layer play and a critical role in the performance of fuel cells. In fact, cell performance is profoundly affected by fundamental interactions between the catalyst surface and the AEI. Two such interactions are of particular importance: phenyl adsorption on hydrogen oxidation catalysts and electrochemical oxidation of phenyl moieties on oxygen evolution catalysts. Both are detrimental to an alkaline device’s performance and durability. We compared the adsorption energy of phenyl-containing ionomers for implementing phenyl-free ionomers. Density functional theory calculations indicated that the norbornane fragment has minimal adsorption energy on Pt(111) due to the absence of aromatic electrons. A soluble quaternized polynorbornene ionomer was prepared by vinyl addition polymerization. This ionomer enables high performance in fuel cells, (peak power density > 2 W cm-2), proving the advantage of the phenyl-free structure. This study establishes the phenyl adsorption energy-electrode performance relationship, highlighting the importance of material interactions between the catalysts and ionomers.

Anion exchange membrane fuel cells (AEMFCs) have recently attracted significant attention as low-cost alternative fuel cells to traditional proton exchange membrane fuel cells due to the possible use of platinum-group metal-free electrocatalysts [1]. Over the past decade, new materials dedicated to the alkaline medium, such as anion exchange membranes (AEMs) and anion exchange ionomers (AEIs), have been developed and studied in AEMFCs [2, 3]. However, only a few AEMs and AEIs are commercially available, and there are not ready to use catalyst coated membranes (CCMs) and/or gas diffusion electrodes (GDEs) with the wished AEMs or AEIs. In order to manufacture CCMs and/or GDEs on the basis of commercial materials, catalyst inks need to be prepared before testing them in AEMFC. It is well known that the composition of catalytic ink and the way to deposit it can influence the interaction between solvent, ionomer and catalyst particles during solvent evaporation and thus on the final structure and morphology of the catalyst layer. However, there are only a few papers dealing with catalyst layer compositions and structures for AEMFCs [4, 5], probably due to the recent development of alkaline fuel cells and new dedicated materials such as AEM and AEI. Since the ionomer/catalyst particle interface plays a crucial role in electrochemical reactions, it is essential to understand the impact of ionomer content on AEMFC performance as well as on water management. For this purpose, catalytic inks were prepared with different amounts of ionomer, ranging from 13 to 33 % in ratio. During this work, Pt / C (40 % in wt) catalyst as well as Aemion® membranes and ionomers were used. Different CCMs and GDEs were manufactured at 60 °C using a commercial ultrasonic spray coating bench. The morphology of the catalyst layers was characterized by scanning electron microscopy, and the thickness of the deposition was measured by a profilometer. Before testing in AEMFC, all prepared samples and membranes were converted to OH- form for 48 h in KOH 3M (the solution was changed every 12h). The performance of the prepared CCMs and GDEs was studied in a home-made AEMFC bench after an activation step. The results shown in Fig.1 highlight that: (i) the ionomer content in the catalyst layers affects the performance of the fuel cell, regardless of the coated support (membrane or GDL), (ii) concerning CCMs-based MEAs, the lower the ionomer content, the better the performance via the polarization curve, (iii) CCMs and GDEs-based MEAs do not behave similarly, (iv) GDEs-based MEAs show high OCV and high voltage for a given current density in comparison with CCMs-based MEAs, (v) concerning GDEs-based MEAs, the variation of the ionomer content in catalyst layer affects less the OCV value than the water management, and (vi) the water management of GDEs-based MEAs seems depend on the relative humidity of both gases and ionomer content in catalyst layers. This work is still under investigation. We will attempt to understand the relationship between the membrane/ionomer under different relative humidity and gas flow rates. [1] H. A. Firouzjaie and W. E. Mustain, “Catalytic Advantages, Challenges, and Priorities in Alkaline Membrane Fuel Cells,” ACS Catal., pp. 225–234, 2019, doi: 10.1021/acscatal.9b03892. [2] J. R. Varcoe et al., “Anion-exchange membranes in electrochemical energy systems †,” 2014, doi: 10.1039/c4ee01303d. [3] N. Chen and Y. M. Lee, “Anion exchange polyelectrolytes for membranes and ionomers,” Prog. Polym. Sci., vol. 113, p. 101345, Feb. 2021, doi: 10.1016/j.progpolymsci.2020.101345. [4] J. Hyun et al., “Tailoring catalyst layer structures for anion exchange membrane fuel cells by controlling the size of ionomer aggreates in dispersion,” Chem. Eng. J., vol. 427, no. August 2021, 2022, doi: 10.1016/j.cej.2021.131737. [5] P. Santori, A. Mondal, D. Dekel, and F. Jaouen, “The critical importance of ionomers on the electrochemical activity of platinum and platinum-free catalysts for anion-exchange membrane fuel cells,” R. Soc. Chem., vol. 2020, no. 7, pp. 3300–3307, doi: 10.1039/d0se00483aï. Figure 1

The oxygen reduction reaction (ORR) is one of the bottlenecks in many electrochemical applications and plays an important role in commercial fuel cell systems. Platinum is highly used as a catalyzer especially in proton exchange membrane fuel cells. Given its rarity and cost, platinum, is not a viable choice as a catalyst, so there is a need to shift to alternative materials such as a metal-free catalyst possible in anion exchange membrane fuel cells. There were several theoretical and experimental studies to address this issue and a direction toward metal-free catalysts is of great interest. In this study, we focus on the oxygen reduction reaction in alkaline medium using a novel metal-free catalyst composite with carbon quantum dots and anion exchange ionomer (AEI). Doped carbon quantum dots were synthesized by a hydrothermal method and an AEI was integrated to improve the hydroxide ion transport and have a composite of desired functionality. These composites showed significant electrochemical activity with a good current response and four-electron ORR. The characterization comprised various microscopic, spectroscopic and electrochemical techniques. Figure 1

The performance of anion exchange membrane fuel cells (AEMFC) has dramatically progressed in the past few years, with initial power performance matching, if not exceeding, those of proton exchange membrane fuel cells (PEMFC). The remaining challenges are i) the replacement of platinum-group-metal catalysts by catalysts based on Earth-abundant elements, ii) improved durability, and iii) the carbonatation issue when the cathode is fed with natural air. Compared to PEMFCs, the water management of AEMFC is more challenging, due to higher flux of water transported from one electrode to the other for a given current density, but also due to the high swelling of anion exchange ionomer (AEI) [1]. An optimized water management was shown to be not only critical for AEMFC power performance [2], but also for the cell stability. The chemical stability of AEM and AEI was recently shown to decrease dramatically with decreasing relative humidity [3]. During AEMFC operation, low humidity is expected on the cathode due to water consumption by the oxygen reduction reaction and due to electroosmotic drag from cathode to anode. While the water management of AEMFC is a recognized challenge, only few works have hitherto investigated it with operando techniques [4-5]. In this presentation, we will discuss the application of humidity sensors to measure on-line the relative humidity of the gas outlets of a single-cell AEMFC, allowing us to derive the water balance at each electrode (Figure 1a). The setup was applied to study the water balance and understand how it affects the AEMC power performance, focusing on one type of membrane-electrode assembly, comprising of a state-of-art anode (PtRu/C), cathode (Fe-N-C) and AEM/AEI (low density polyethylene/ethylenetetrafluoroethylene). The effect of dew point, backpressure and flow rates on cell performance and water transport were investigated. As an example of the type of results that can be obtained, Figure 1b shows the water balance at the anode and cathode as a function of time (blue and red curves, respectively), for different galvanostatic holds of 5 min each, from 0.2 to 1.2 A cm-2, at otherwise fixed conditions. As expected, the water balance is positive at the anode, and increases fairly linearly with the current density. Importantly, the water balance at the anode is always lower than the anode water balance expected if all the produced water (through the hydrogen oxidation reaction) would stay in the anode. This implies that the electroosmotic drag effect of water transport from cathode to anode is minor, and that the transport of water from anode to cathode (via back-diffusion, or other mechanism) is significant. As a result, the water balance is also positive at the cathode. Figure 1b shows also the total water balance (green curve), and that it matches with the theoretical total simply derived from the cell current density (black curve). In fact, for all operating conditions tested, the water balance was positive at the cathode, implying that the so-called cathode dry-out seldom occurs in AEMFC. The results also generally show that anode flooding is strongly connected with the maximum current density at which an AEMFC can stably operate. In conclusion, the use of humidity sensors can provide quantified insights on water dynamics in operating AEMFC, providing a tool for understanding optimized operating conditions, or for optimizing materials and components when they are designed to improve water management. References [1] J. R. Varcoe et al, Anion-exchange membrane in electrochemical energy systems, Energy & Environ. Science 7 (2014) 3135-3191 [2] N. Ul Hassan, M. Mandal, G. Huang, H. A. Firouzjaie, P. A. Kohl, W. E. Mustain, Achieving high performance and 200 h stability in anion exchange membrane fuel cells by manipulating ionomer properties and electrode optimization, Adv. Energy Materials 10 (2020) 2001986. [3] D. R. Dekel, M. Amar, S. Willdorf, M. Kosa, S. Dhara, C. E. Diesendruck, Effect of water on the stability of quaternary ammonium groups for anion exchange membrane fuel cell applications, Chem. Mater. 29 (2017) 4425-4431. [4] X. Peng et al, Using operando techniques to understand and design high performance and stable alkaline membrane fuel cells, Nature Commun. 11 (2020) 3561. [5] B. Eriksson, H. Grimler, A. Carlson, H. Ekström, R. Wreland Lindström, G. Lindbergh, C. Lagergren, Quantifying water transport in anion exchange membrane fuel cells, Int. J. Hydrogen Energy 44 (2019) 4930-4939. Acknowledgments This study was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement CREATE [721065]. We are grateful to Prof. John R. Varcoe (Univ. Surrey, UK) for providing the ionomer and membrane Figure 1

Anion-exchange membranes (AEM) are being developed for use in electrochemical technologies including fuel cells (AEMFC),water electrolysis (AEMWE for green hydrogen), electrolysers for CO2 reduction (CO2RR), and reverse electrodialysis (RED). Radiation-grafted AEMs (RG-AEM) represent a promising class of AEM that can exhibit high conductivities (OH- conductivities of > 200 mS cm-1 at temperatures above 60 °C) and favourable in situ water transport characteristics). Hence, RG-AEMs have shown significant promise when tested in AEMFCs alongside powdered radiation-grafted anion-exchange ionomers (RG-AEI), producing high performances and promising durabilities [Energy Environ. Sci., 12, 1575 (2019) and Nature Commun., 11, 3561 (2020)], even at temperatures above 100 °C [Dekel et al., J. Power Sources Adv., 5, 100023 (2020)]. An Achilles heel with RG-AEM types is that they can swell excessively in water and have large dimensional changes between the dehydrated and hydrated states. This limits the ion-exchange capacities (IEC) that can be used: excessive IECs in RG-AEM will cause excessive swelling and poorer robustness. This clearly indicates that additional crosslinking is needed. As Kohl et al. have highlighted, optimised crosslinking can lead to production of high-IEC AEMs that are both robust enough to be < 20 µm in thickness and also low swelling [e.g. J. Electrochem. Soc., 166, F637 (2019)], allowing truly world-leading AEMFC performances. RG-AEMs are also being used as a screening platform for down-selecting different (cationic) head-group chemistries for use in RED cells (a salinity gradient power technology), where different head-groups may lead to different AEM characteristics such as: in-cell resistance (when in contact with aqueous electrolytes), permselectivity, and fouling characteristics (when real world waters such as industrial brines, seawater and freshwater are used). It was evident very early on in these studies that RG-AEMs (desirably) exhibit extremely low resistances but also (undesirably) very low permselectivities when un-crosslinked (less than the required 90%+ permselectivity). Our work on RG-type cation-exchange membranes [Sustainable Energy Fuels, 3, 1682 (2019)] clearly shows that introduction of crosslinking can improve permselectivity. Crosslinking always involves a compromise, where its introduction can improve a membrane characteristic (e.g. reduced swelling or improved permselectivity) but also leads to lower conductivities or poorer transport of chemical species through the membranes. Hence, crosslinking types and levels need to be carefully controlled. With RG-AEMs (made by electron-beam activation (peroxidation) of inert polymer films, followed by grafting of monomers and post-graft amination), we have a choice of introducing crosslinking at various stages. The figure below summarises the two different approaches to crosslinking that will be discussed in the presentation: adding a divinyl-type crosslinker into the grafting mixture or adding a diamine-type crosslinker into the amination step. This presentation will present a selection of recent RG-AEM and RG-AEI developments from a number of projects: (1) REDAEM: AEMs for RED cells [EPSRC Grant EP/R044163/1]; (2) CARAEM: Novel RG-AEMs for AEMFCs and AEMWE [EPSRC Grant EP/T009233/1]; (3) SELECTCO2: RG-AEMs being tested in CO2RR cells [EU Horizon 2020 grant agreement 851441]. This presentation will show: (a) RG-AEMs made from thin high density polyethylene (HDPE) precursors appear better for application in AEMFCs, while RG-AEMs from made from thicker ETFE precursors appear to be better for CO2RR cells and RED; (b) RG-AEMs can be made using a variety of crosslinking strategies; (c) RG-AEIs can be made using ETFE powders and give optimal performance after cryogrinding down to micrometer sizes; Figure 1

Anion exchange membrane water electrolyzers (AEMWEs) represent an attractive technology for producing “green” hydrogen that enables operation on pure water using platinum group metal (PGM)-free electrocatalysts at both anode and cathode. Also, AEMWEs do not require the use of highly concentrated and corrosive alkaline electrolytes and PGM-based catalysts, which are the major drawbacks of the incumbent low-temperature liquid-alkaline and proton exchange membrane electrolyzers, respectively.1,2 In this context, the development of PGM-free electrocatalysts for oxygen evolution reaction (OER) in alkaline media has attracted considerable research interest. Among different types of transition metal-based oxides, Ni oxides doped with Fe have shown the highest OER activity in alkaline media.3,4 Recently, we have developed at Los Alamos National Laboratory (LANL) a series of Ni oxide-based aerogel materials that, primarily in combination with Fe in different proportions, have shown respectable OER performance in the electrochemical cell and at the AEMWE anode operating on either neat deionized water or with a supporting electrolyte, 0.1 M KOH or K2CO3.5 For application at the AEMWE anode, the catalyst integration into the electrode catalyst layer, i.e., combining the catalyst with anion exchange ionomer (AEI) and binding agents, is crucial to prevent catalyst layer delamination and to create a good catalyst/electrolyte interface, which in turn enables high OH- conductivity within the catalyst layer.6 This latter aspect is especially important for achieving high AEMWE performance in pure water operation. In this work, we investigate the impact of combining our Ni-Fe oxide aerogel catalysts with different AEIs (various backbone chemistries, OH- functional groups) and different binding agents (e.g., Nafion ionomer) on the AEMWE performance. We will show that full activation of the catalyst by phase transformation from the original Ni oxide-like structure to the active layered (oxy)hydroxide is essential for achieving high OER activity, and it can be influenced by the catalyst layer composition. By advanced characterization techniques such as high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and Mössbauer spectroscopy, we will shed light onto the phase transformation process that results in superior OER activity of these materials in alkaline media. Following our prior machine learning studies aimed at optimizing for the synthesis of oxygen reduction electrocatalysts,7,8 we will also show how to improve the synthesis of Ni oxide aerogel-based OER catalysts to maximize activity and stability. This work is further supported by density functional theory (DFT) modeling studies to better understand reaction mechanisms, active sites, and ultimately what role transition metal dopants (Fe and Co) play in modifying OER activity. Studies of in situ dissolution of these dopants using DFT-generated, phase-constrained Pourbaix diagrams9 will guide synthesis through understanding this likely materials degradation pathway. References H. A. Miller et al., Sustain. Energy Fuels, 4, 2114–2133 (2020). C. Santoro et al., ChemSusChem, 202200027 (2022). S. Fu et al., Nano Energy, 44, 319–326 (2018) D. Xu et al., ACS Catal., 9, 7–15 (2019). P. Zelenay and D. Myers, "ElectroCat (Electrocatalysis Consortium);” U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Program, 2022 Annual Merit Review and Peer Evaluation Meeting, June 6-8, 2022. https://www.hydrogen.energy.gov/pdfs/review22/fc160_myers_zelenay_2022_o.pdf L. Osmieri et al., J. Power Sources, 556, 232484 (2023). M. R. Karim et al., ACS Appl. Energy Mater., 3, 9083–9088 (2020). W. J. M. Kort-Kamp et al., J. Power Sources, 559 (2023). E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020).

Les piles à combustible à membrane échangeuse d'anions (AEMFC) ont récemment attiré l'attention en tant que piles à combustible alternatives à faible coût aux piles à combustible à membrane échangeuse de protons traditionnelles en raison de l'utilisation possible d'électrocatalyseurs non-nobles. Bien que l'AEMFC ressemble à la PEMFC, les problèmes de gestion de l'eau sont plus prégnants dans une AEMFC car l'ORR en milieu alcalin nécessite de l'eau, tandis qu'en même temps, de l'eau est produite en grande quantité du côté de l'anode. Pour mieux comprendre la gestion de l'eau dans ce type de pile à combustible, il faut d'abord développer et acquérir de l'expérience avec ce type de pile à combustible à l'échelle du laboratoire. Puisque les matériaux prêts à l'emploi n'existaient pas au commencement de la thèse, nous avons dû fabriquer nos propres assemblages électrode-membranes (AMEs) à partir des matériaux disponibles dans le commerce. Etant donné que la thématique de fabrication des AMEs est nouvelle pour les chercheurs du LEMTA, cette thèse est articulée en deux parties, une dédiée à la formulation, la préparation et l'optimisation des AMEs pour PEMFC ; et une autre dédiée au développement d'AEMFC. Les résultats ont indiqué que la composition et préparation de l'encre, ainsi que la manière de déposer l'encre modifient systématiquement la structure de l'électrode, de même que ses performances en piles à combustible. En outre, l'étude fournit des informations sur les procédures et les méthodes pour les tests en AEMFC. Ici, nous souhaiterions partager notre savoir-faire avec les nouveaux venus dans le domaine de la préparation des AMEs pour piles à combustibles à membranes échangeuses d'ions
Anion exchange membrane fuel cells (AEMFCs) have recently attracted significant attention as low-cost alternative fuel cells to traditional proton exchange membrane fuel cells as a result of the possible use of platinum-group metal-free electrocatalysts. Although AEMFC is a mimic of PEMFC but working in an alkaline medium, water management issues are more severe in AEMFC because ORR in alkaline media requires water, while at the same time water is produced at the anode side. To better understand water management in this type of fuel cell, it is necessary first to develop and gain experience with this kind of fuel cell on the laboratory scale. Since no ready-to-use materials are available at the beginning of the project, the necessity of fabricating homemade MEAs from commercially available materials becomes a reality that we must face. As MEA fabrication is a new topic to LEMTA's researchers, this is why this thesis was divided into two parts: one part dedicated to the formulation, preparation, and optimization of MEAs for PEMFC through physico-chemical and electrochemical characterizations; another part dedicated to the development of AEMFC. The results indicated that ink deposition, composition, and preparation systematically change the electrode structure and thus affect fuel cells performance. Furthermore, the study provides information on the AEMFC procedures and methods. Here, we would like to share our know-how with newcomers in the field of preparation of MEA in ion exchange membrane fuel cells