Dissertations / Theses on the topic 'Ceramic electrolytes'

Doutoramento em Nanociências e Nanotecnologia
The main objective of this dissertation is the development and processing of novel ionic conducting ceramic materials for use as electrolytes in proton or oxide-ion conducting solid oxide fuel cells. The research aims to develop new processing routes and/or materials offering superior electrochemical behavior, based on nanometric ceramic oxide powders prepared by mechanochemical processes. Protonic ceramic fuel cells (PCFCs) require electrolyte materials with high proton conductivity at intermediate temperatures, 500-700ºC, such as reported for perovskite zirconate oxides containing alkaline earth metal cations. In the current work, BaZrO3 containing 15 mol% of Y (BZY) was chosen as the base material for further study. Despite offering high bulk proton conductivity the widespread application of this material is limited by its poor sinterability and grain growth. Thus, minor additions of oxides of zinc, phosphorous and boron were studied as possible sintering additives. The introduction of ZnO can produce substantially enhanced densification, compared to the un-doped material, lowering the sintering temperature from 1600ºC to 1300ºC. Thus, the current work discusses the best solid solution mechanism to accommodate this sintering additive. Maximum proton conductivity was shown to be obtained in materials where the Zn additive is intentionally adopted into the base perovskite composition. P2O5 additions were shown to be less effective as a sintering additive. The presence of P2O5 was shown to impair grain growth, despite improving densification of BZY for intermediate concentrations in the range 4 – 8 mol%. Interreaction of BZY with P was also shown to have a highly detrimental effect on its electrical transport properties, decreasing both bulk and grain boundary conductivities. The densification behavior of H3BO3 added BaZrO3 (BZO) shows boron to be a very effective sintering aid. Nonetheless, in the yttrium containing analogue, BaZr0.85Y0.15O3- (BZY) the densification behavior with boron additives was shown to be less successful, yielding impaired levels of densification compared to the plain BZY. This phenomenon was shown to be related to the undesirable formation of barium borate compositions of high melting temperatures. In the last section of the work, the emerging oxide-ion conducting materials, (Ba,Sr)GeO3 doped with K, were studied. Work assessed if these materials could be formed by mechanochemical process and the role of the ionic radius of the alkaline earth metal cation on the crystallographic structure, compositional homogeneity and ionic transport. An abrupt jump in oxide-ion conductivity was shown on increasing operation temperature in both the Sr and Ba analogues.
O principal objetivo deste trabalho é o desenvolvimento e processamento de novos materiais cerâmicos protónicos e iónicos para utilizar como eletrólito das células de combustível de óxidos sólidos (PCFCs e SOFCs, respetivamente). Com este estudo pretende-se, então, desenvolver novas formas de processamento e/ou materiais que apresentem características eletroquímicas atrativas, à base de óxidos cerâmicos nanométricos de pós preparados por processos mecanoquímicos. Existem alguns requisitos que devem ser tidos em conta de forma a garantir a máxima eficiência das PCFCs, destacando-se a elevada condutividade protónica do eletrólito aquando da operação numa gama de temperaturas intermédias, 500-700ºC. Os materiais do tipo “perovskite” foram apresentados como potenciais candidatos a incorporar o eletrólito das PCFCs, sendo o BaZrO3 dopado com 15 mol% de ítrio (BZY) o material base escolhido neste trabalho. Apesar da sua conhecida elevada condutividade protónica, estes materiais apresentam algumas limitações, tais como a fraca sinterabilidade e crescimento de grão. De forma a ultrapassar esta dificuldade, foram adicionadas pequenas quantidades de óxidos de zinco, fósforo e boro que foram estudados como possíveis aditivos de sinterização. A adição de ZnO mostrou melhorias significativas na densificação quando comparado com o material não modificado (BZY), permitindo ainda reduzir a temperatura de sinterização de 1600ºC para 1300ºC. Neste trabalho estudou-se, também, qual o melhor mecanismo de solução sólida para a adição deste aditivo, tendo-se obtido a máxima condutividade protónica nos materiais em que o Zn é intencionalmente introduzido na composição de base de “perovskite”. O P2O5 mostrou ser menos efetivo como aditivo de sinterização. A sua presença foi bastante prejudicial no crescimento de grão, apesar dos elevados níveis de densificação obtidos quando adicionado em quantidades entre 4 e 8 mol%. Porém, a utilização de fósforo mostrou também ser dramática no transporte elétrico, diminuindo a condutividade não só no interior do grão (“bulk”) como nas suas fronteiras. Já a adição de H3BO3 ao BaZrO3 (BZO) mostrou-se muito efetiva para a sinterização deste componente. Contudo, quando adicionado ao sistema dopado com ítria (BaZr0.85Y0.15O3-, BZY), o comportamento é diferente, produzindo níveis deficientes de densificação quando comparado com o BZY puro. Este fenómeno ocorre devido à formação de fases secundárias de borato de bário, cujas temperaturas de fusão são bastante elevadas. Na última parte deste trabalho foi estudado um novo material com condutividade iónica de iões óxido, o (Ba,Sr)GeO3 dopado com K. Neste estudo pretendia-se, não só avaliar a possibilidade de preparar estes pós com recurso a processos mecanoquímicos, como também estudar o papel da variação do raio iónico do catião metálico alcalino-terroso no transporte iónico, homogeneidade composicional e estrutura cristalina. Verificou-se que este material apresenta uma alteração significativa na condutividade iónica com o aumento da temperatura de operação em ambas as composições (Ba e Sr).

All-solid-state lithium batteries are of great interest scientifically as a next-generation of electrochemical energy storage devices, owing to their superior safety features and their potential to enable new chemistries to improve performance. The properties of the solid state electrolyte are integral to the overall cell capability – to date the most promising group of materials are the garnet-structured oxides, based on Li7La3Zr2O12 (LLZO), with high room temperature ionic conductivity and a wide electrochemical stability window. There are several aspects in the development of this relatively new material which are yet to be fully understood – these are the focus of this thesis. In this work, processing cubic doped LLZO as a bulk ceramic was investigated and served as a basis for understanding its stability and electrochemical performance; it was optimised to obtain highly dense microstructures under atmosphere-controlled conditions to prevent reaction with moisture. Chemical inhomogeneities in the pellets, especially at the grain boundaries, as investigated by secondary ion mass spectrometry (SIMS) and low energy ion scattering, were shown to be important in determining the transport properties of the electrolyte - in particular the propensity for dendrite formation during cell cycling. It was shown that aluminium-rich grain boundaries in aluminium-doped LLZO favour the formation of inter-granular lithium dendrites (with a 60 % lower critical current density for cell failure) over gallium-doped LLZO. The use of germanium (Ge4+) as a dopant was studied, and shown to stabilise the cubic LLZO phase through substitution of 0.10 moles of Ge at the lithium sub-lattice (at the tetrahedral 24d sites), giving conductivities of the order 10-4 S cm-1 and redox stability over a 4.5 V range with lithium electrodes. Chemical and electrochemical characterisation of the moisture reactivity of gallium-doped LLZO was also carried out, showing a chemically-altered proton-rich region extending to 1.35 micrometres following 30 minutes immersion in H2O at 100 °C and highly reactive grain boundaries. These chemical changes led to a threefold increase in the resistance of both the electrolyte and the interface with lithium electrodes. Chemical and tracer diffusivity of protons were estimated from the diffusion profiles of H+ and D+ obtained by SIMS depth-profiling. A new methodology for measuring macroscopic lithium tracer diffusion in LLZO was introduced, using SIMS depth-profiling and isotopic labelling, in which a number of experimental parameters were varied to optimise the technique. The preliminary results for lithium diffusivity in doped LLZO obtained from this method were compared with values from other methods (impedance and nuclear magnetic resonance) and used to comment on the mechanism for lithium diffusion in the materials.

The research work presented in this thesis comprises a detailed investigation of conductivity mechanism in crystalline polymer electrolytes and development of a new class of ceramic-polymer composite electrolytes for Li-ion batteries. Firstly, a robust methodology for the synthesis of monodispersed poly(ethylene oxides) has been established and a series of dimethyl-protected homologues with 13, 15, 17, 28, 29, 30 ethylene oxide repeat units was prepared. The approach is based on reiterative cycles of chain extension and deprotection, followed by end-capping of the oligomeric chain ends with methyl groups. The poly(ethylene oxide) homologues show a superior level of monodispersity to previous work and were subsequently used to prepare crystalline PEO6:LiPF6 polymer electrolytes. A correlation between the number of ether oxygens in the polymer chain and the ionic conductivity of crystalline polymer electrolytes has been established. The structure and dynamics of the monodispersed complexes were studied using solid-state NMR spectroscopy for the first time. The results are in agreement with the proposed mechanism of ionic conductivity in crystalline polymer electrolytes. A new class of composite solid electrolytes for all-solid-state batteries with a lithium metal anode is reported. The composite material consists of a 3D interpenetrating network of a ceramic electrolyte, Li₁.₄Al₀.₄Ge₁.₆(PO₄)₃, and an inert polymer (polypropylene), providing continuous pathways for the ionic transport and excellent mechanical properties. 3D connectivity of this novel composite was confirmed using X-ray microtomography and AC impedance spectroscopy.

Le premier objectif de cette thèse est l’étude de l’influence de charges inorganiques (additifs) sur les propriétés des électrolytes polymères composites, à base de poly(oxyde d’éthylène) de basses et hautes masses moléculaires. Pour étudier tout les facteurs, nous avons choisi trois oxydes d’aluminium et deux oxydes de titane, distincts de par la taille des grains. Il apparaît exclusivement que les échantillons d’oxyde d’aluminium aux grains de taille micrométrique sont clairement modifiés ; les particules d’oxyde d’aluminium sont plus sensibles au traitement que les oxyde de titane et l’effet est plus marqué pour les particules de taille micrométriques par rapport aux particules nanométriques d’oxyde d’aluminium. Ensuite les poudres (au total 26) étaient utilisées comme charge pour les électrolytes polymères à base de dimétoxy-poly(oxyde d’éthylène) de masse moléculaire moyenne 500 g•mol-1 (liquide à température ambiante) et le poly(oxyde d'éthylène de masse moléculaire moyenne 5•102g•mol-1(solide à température ambiante). Le perchlorate de lithium (LiClO4) a été à chaque fois utilisé comme sel et sa concentration fixée à de 1 mol•kg-1. En résumé – des électrolytes contenant un large panel de poudres ont été étudiés, et il a été montré que les conditions de préparation des électrolytes avec les mêmes matériaux de départ peuvent conduire à l’obtention de matériaux finaux différents. Cela peut expliquer les divergences entre les résultats rapportés dans la littérature ces dernières années. Enfin, l’influence des poudres sur la conductivité et les conditions de son augmentation ont été déterminées
The primary goal of this work was to study the influence of surface-modified inorganic fillers on the properties of composite polymeric electrolytes based on poly(oxyethylene) of both low and high molecular weight. To study all interesting factors we chose three different aluminas and two titanias characterised by different grain sizes. It appeared that only microsized aluminas are readily modified. Less sensitive to the treatment is nano alumina and the least are titanias. Then obtained powders (26 in total) were applied as fillers for polymeric electrolytes based on poly(oxyethylene) of molecular weight aqual to 500 g•mol-1 (liquid at room temperature) and 5•106 g•mol-1 (liquid at room temperature) and 5•106 g•mol-1(solid at room temperature). Lithium perchlorate was used as a salt, its concentration was fixed to be 1 mol•kg-1. In general, a vast population of samples was prepared and it was shown that starting with the same material, one can obtain totally different products. That can explain many of the discrepancies found in the literature published on this subject over the last 20 years. Apart from that a universal procedure of samples preparation was established and conditions of conductivity improvement determined

Thin ceramic substrates are widely used in engineering applications in modern industry. For example, they are used as molecular filters in fuel cells and solid oxide electrolyzers for oxygen generation. Development of high-reliability substrate materials inevitably requires the accurate characterization of their mechanical properties. The loading conditions in service on the ceramic substrates, such as the solid oxide electrolytes with a thickness of much less than 2 mm, often involve multiaxial bending instead of simple tension or bending. In this dissertation, the ASTM standard piston-on-3-ball experimental technique at ambient temperature is employed to investigate the quasi-static biaxial flexural strength of pure 8YSZ and Al₂O₃ or 3YSZ doped 8YSZ ceramic substrates. Furthermore, this piston-on-3-ball experimental technique is developed into a dynamic piston-on-3-ball technique at ambient temperature and a quasi-static piston-on-3-ball technique at elevated temperatures. Stress distribution functions in the tensile surface of a specimen under piston-on-3-ball loading condition are formulated and used to develop statistical models, which are proven to be in the form of a Weibull distribution function, to describe the biaxial flexural strength behavior of ceramic substrates under piston-on-3-ball loading condition. Analytical modeling was conducted on the dynamic piston-on-3-ball loading configuration. This analytical model can be used to guide the experimental design and judge the validity of experimental results. A new material constitutive model is developed to give a good description of the dynamic strength behavior of ceramic materials under constant stress-rate loading. Quasi-static experiments under piston-on-3-ball loading are conducted at both ambient temperature and elevated temperatures, while dynamic experiments are conducted at ambient temperature. Experimental results, as well as observations from SEM microstructure images and values of fracture toughness measured using a newly developed Vickers micro-indentation toughness technique, lead to a conclusion that no obvious overall improvement to the SYSZ ceramic substrates in the biaxial flexural strength can be observed by adding Al₂O₃ additive with amount up to 3 mol% or 3YSZ additive with amount up to 30 wt%.

La technologie Lithium-air développée par EDF utilise une électrode à air qui fonctionne avec un électrolyte aqueux ce qui empêche l’utilisation de lithium métal non protégé comme électrode négative. Une membrane céramique (LATP:Li1+xAlxTi2-x(PO4)3) conductrice d’ion Li+ est utilisée pour séparer le milieu aqueux de l’électrode négative. Cependant, cette céramique n'est pas stable au contact du lithium, il est donc nécessaire d'intercaler entre le lithium et la céramique un matériau conducteur des ions Li+. Celui-ci devant être stable au contact du lithium et empêcher ou fortement limiter la croissance dendritique. Ainsi, ce projet s'est intéressé à l'étude d'électrolytes copolymères à blocs (BCE).Tout d'abord, l'étude des propriétés physico-chimiques spécifiques de ces BCEs en cellule lithium-lithium symétrique a été réalisée notamment les propriétés de transport (conductivités, nombre de transport), et la résistance à la croissance dendritique du lithium. Puis dans un second temps, l'étude des composites BCE-céramique a été mise en place. Nous nous sommes en particulier focalisés sur l'analyse du transfert ionique polymère-céramique.Plusieurs techniques de caractérisation ont été utilisées telles que la spectroscopie d'impédance électrochimique (transport et interface), le SAXS (morphologies des BCEs), la micro-tomographie par rayons X (morphologies des interfaces et des dendrites).Pour des électrolytes possédant un nombre de transport unitaire (single-ion), nous avons obtenus des résultats remarquables concernant la limitation à la croissance dendritique. La micro-tomographie des rayons X a permis de montrer que le mécanisme de croissance hétérogène dans le cas des single-ion est très différent de celui des BCEs neutres (t+ < 0.2)
The lithium-air (Li-air) technology developed by EDF uses an air electrode which works with an aqueous electrolyte, which prevents the use of unprotected lithium metal electrode as a negative electrode. A Li+ ionic conductor glass ceramic (LATP:Li1+xAlxTi2-x(PO4)3) has been used to separate the aqueous electrolyte compartment from the negative electrode. However, this glass-ceramic is not stable in contact with lithium, it is thus necessary to add between the lithium and the ceramic a buffer layer. In another hand, this protection should ideally resist to lithium dendritic growth. Thus, this project has been focused on the study of block copolymer electrolytes (BCE).In a first part, the study of the physical and chemical properties of these BCEs in lithium symmetric cells has been realized especially transport properties (ionic conductivities, transference number), and resistance to dendritic growth. Then, in a second part, the composites BCE-ceramic have been studied.Several characterization techniques have been employed and especially the electrochemical impedance spectroscopy (for the transport and the interface properties), the small angle X-ray scattering (for the BCE morphologies) and the hard X-ray micro-tomography (for the interfaces and the dendrites morphologies). For single-ion BCE, we have obtained interesting results concerning the mitigation of the dendritic growth. The hard X-ray micro-tomography has permitted to show that the mechanism involved in the heterogeneous lithium growth in the case of the single-ion is very different from the one involved for the neutral BCEs (t+ < 0.2)

High temperature co-electrolysis of carbon dioxide and steam may provide an efficient, cost effective, and environmentally friendly production of syngas from curtailed wind energy. To achieve cost competitive high performance (e.g. with minimum internal resistance) electrolysis cells, it is critical to develop materials and cell configuration optimal for coelectrolysis. In addition, a cost-effective fabrication procedure is important in allowing broader commercialisation of Solid Oxide Electrolysis Cells (SOECs). The initial part of this work emphasises on the feasibility of SOECs plant for converting curtailed wind energy to syngas to enhance the grid flexibility. We first obtained operating parameters for the conversion plant based on the most recent literature data on the performance of high temperature co-electrolysis for syngas production. In addition, an evaluation of the interaction between variable generation and typical electricity demand patterns was presented; and, limitations in the flexibility of traditional electric generators were considered. Furthermore, in a projection of wind generation made for 2020, we estimated the maximum power value of the curtailment wind profile to be 23.9 GW. It was remarked that the cost increase for constraining wind in future could make SOEC conversion technology more commercially attractive. An estimation of the total investment costs for grid connected electrolysis system was made by considering the share of operating cost. The share of electricity price in the total cost of syngas production was estimated to be 61%. It was shown that using cost effective electricity could significantly reduce the syngas production price. The total investment costs for grid connected electrolysers were projected to be 0.38 M£/MW in 2020. It was highlighted that the scope of electrochemical conversion of CO2 to fuel offers flexible demand that is not yet sufficiently understood. There are still technical barriers that need to be addressed in the field of manufacturing processes, grid integration and system operation. A key factor in operating solid oxide electrolysis cells (SOECs) is the ability to provide a sufficiently high level of oxide ion conduction through the electrolyte in the cell. Commonly, high performance cells use Y-stabilised ZrO2 (YSZ) or Gd-doped CeO2 (GDC10). Whilst GDC10 has higher oxide ion conductivity than YSZ, it suffers from electronic conduction due to the partial reduction of Ce4+ to Ce3+ during operation at high temperature and low oxygen partial pressure environment. Here we describe the fabrication of a bilayer GDC10/8YSZ electrolyte support using tape casting and single step co-sintering. A cost effective fabrication procedure is important in allowing broader commercialisation of Solid Oxide Cells for fuel cell/electrolysis applications. A bi-layer 8YSZ/GDC electrolyte is suggested as an effective solution to avoid ceria reduction in a fuel (reducing) environment, thereby preventing current leakage across the electrolyte, while maintaining high oxide ion conduction. Bilayer zirconia/ceria processing has proven problematic due to thermochemical instability at high sintering temperatures. We first prepared and optimised the slip formulations for tape casting process, this was necessary to achieve high green density and uniform tapes. Furthermore, the shrinkage profile of the two bulk materials in bilayer electrolyte were matched using a Fe2O3 sintering additive. Additions of 5 mol% of Fe2O3 in the GDC layer and 2 mol% of Fe2O3 in the YSZ layer prevents delamination during co-sintering. The addition of Fe2O3 promotes densification behaviour, enabling achievement of a dense bilayer (~90%) at a reduced sintering temperature of 1300 °C; ~ 150 °C below conventional sintering temperatures. Bilayer 8YSZ/GDC10 electrolytes with relative thickness of 73/154 μm was successfully fabricated by tape casting and low-temperature co-sintering at 1300 °C. No significant microstructural defects or delamination were observed after co-firing The effect of the Fe2O3 sintering aid on the crystal structure of two bulk materials used in bilayer electrolyte were investigated by X-ray diffraction. Results showed that, both materials with Fe2O3 additions maintain their fluorite structure. The analysis revealed a reduction in unit cell volume for both Fe2O3-doped samples. While using Fe2O3 sintering aid was found to improve the sinterability of the two bulk materials, increasing the dopant concentration above the solubility limit leads to the formation of an iron rich phase, which was subsequently analysed by energy-dispersive X-ray spectroscopy. Elemental analysis at YSZ/GDC interface revealed asymmetric elemental diffusion behaviour when using Fe2O3 to co-sinter YSZ/GDC bilayers, with lower diffusivity of Zr and Y ions in the GDC layer compared to that of Ce and Gd ions detected in the YSZ layer, showing the positive effect of Fe2O3 on limiting the interdiffusion behaviour. Electrochemical impedance measurements in air revealed the total conductivity of the Fe2O3 containing bilayer electrolytes increased by an order of magnitude compared to Fe2O3-free bilayers. This was attributed to two factors; first, by limiting the overall elemental interdiffusion length from ~15 to ~5μm and, second, by achieving better contact between the YSZ and GDC layers and higher sintered density when using a Fe2O3 additive as a sintering aid. The cost-effective low-temperature processing technique presented in this study is expected to help widen the material selection and resolve the thermochemical issues associated with high-temperature co-sintering allowing a broader commercialisation of SOECs.

O óxido de cério (CeO2), quando dopado com óxidos de terras raras, tem sua condutividade iônica aumentada, possibilitando seu uso como eletrólito de Células a Combustível de Óxido Sólido de Temperatura Intermediária (IT-SOFC), que são operadas entre 500 e 700°C. Os aditivos ou dopantes mais eficientes para o aumento da condutividade iônica são a samária (óxido de samário Sm2O3) e a gadolínia (óxido de gadolínio Gd2O3), com concentrações molares entre 10 e 20%. Neste contexto foram sintetizados, neste trabalho, pós de composição Ce0,8(SmGd)0,2O1,9 pelas rotas de síntese por coprecipitação de hidróxidos, carbonatos e oxalatos. O efeito do tratamento hidrotérmico foi avaliado para pós precipitados com hidróxido de amônio. Utilizou-se, como matériasprimas, concentrados de terras raras contendo 90% em massa de CeO2 e outro contendo 51% de Sm2O3 e 30% de Gd2O3, ambos provenientes do processamento da monazita. Estes concentrados foram utilizados devido ao menor custo em relação às matérias-primas puras adquiridas comercialmente e a semelhança química dos demais elementos de terras raras contidos. Inicialmente, foram definidas as condições das etapas de coprecipitação e a influência da temperatura de calcinação nas características dos pós e produtos sinterizados. Os resultados obtidos mostraram que os pós calcinados na faixa de temperatura entre 450 e 800ºC apresentam elevada área de superfície específica (90-150 m2.g-1) e estrutura cristalina cúbica tipo fluorita da céria, indicando a formação da solução sólida. Observou-se, por microscopia eletrônica de varredura, que a forma das partículas e dos aglomerados é função do tipo de agente precipitante. As análises dilatométricas indicaram maior taxa de retração em temperatura próxima a 1300-1350ºC. Entretanto, valores elevados de densificação (>95% DT) são obtidos em temperaturas superiores a 1400ºC. A síntese por coprecipitação de hidróxidos seguida pelo tratamento hidrotérmico demonstrou ser uma rota promissora para cristalização, em baixas temperaturas (200oC), de nanopós à base de céria, mantendo-se elevados os valores de área de superfície específica (cerca de 100 m2.g-1). Cerâmicas com densificação superior a 95%DT foram obtidas em menores temperaturas de sinterização (1400oC), quando comparadas às provenientes de pós cristalizados por calcinação.
Cerium oxide (CeO2) when doped with rare earth oxides has its ionic conductivity enhanced, enabling its use as electrolyte for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC), which is operated in temperatures between 500 e 700°C. The most effective aditives or dopants for ionic condutivity improvement are (samarium oxide Sm2O3) and gadolinia (gadolinium oxide Gd2O3), fixing the concentration between 10 and 20 molar%. In this work, Ce0,8(SmGd)0,2O1,9 powders have been synthesized by hydroxide, carbonate and oxalate coprecipitation routes. The hydrothermal treatment has been studied for powders precipitated with ammonium hydroxide. A concentrate of rare earths containing 90wt% of CeO2 and other containing 51% of Sm2O3 and 30% of Gd2O3, both prepared from monazite processing, were used as starting materials. These concentrates were used due the lower cost compared to pure commercial materials and the chemical similarity of others rare earth elements. Initially, the coprecipitation and calcination conditions were defined. The process efficiency was verified by ceramic sinterability evaluation. The results showed that powders calcined in the range of 450 and 800°C presented high specific surface area (90 - 150 m2.g-1) and fluorite cubic structure, indicating the solid solution formation. It was observed, by scanning electron microscopy, that morphology of particles and agglomerates is a function of precipitant agent. The dilatometric analysis indicated the higher rate of shrinkage at temperatures around 1300-1350°C. High densification values (>95% TD) was obtained at temperatures above 1400ºC. Synthesis by hydroxides coprecipitation followed by hydrothermal treatment demonstrated to be a promising route for crystallization of ceria nanopowders at low temperatures (200oC). High values of specific surface area were reached with the employment of hydrothermal treatment (about 100 m2.g-1). High density ceramics were obtained at lower temperatures (1400oC), compared to those employed for calcined powders.

Flammable solvents contained in liquid electrolytes pose a serious safety risk when used in lithium batteries. Oxide ceramic electrolytes are a safer alternative, but suffer from inadequate mechanical properties and ionic conductivity. Thin electrolyte layers resolve the issue of conductance, but accentuate the detrimental mechanical properties of oxide ceramics. The presented work has investigated oxide ceramic electrolyte reinforcement in composite electrolytes for all-solid-state batteries. Fabricating oxide ceramic electrolytes with engineered microstructure enabled development of a reinforced composite. This approach is based on the formation of 3D- porous ceramics via stereolithography printing of polymer templates from designed cubic, gyroid, diamond and bijel architectures. The microstructural parameters of templates were analysed and modified using computational techniques. Infiltration of the prepared 3D-porous electrolyte with polymeric-fibre reinforcement created the reinforced composite electrolyte. The prepared ceramic composite showed excellent reproduction of the template microstructure, good retention of ionic conductivity and enhanced mechanical properties. The final composite was composed of NASICON-type Li_1.6Al_0.6Ge_1.4(PO₄)₃ oxide ceramic electrolyte and epoxy and aramid fibre reinforcement. The gyroid architecture was computationally determined as having the optimal stress transfer efficiency between two phases. The printed gyroid polymer template gave excellent pore microstructure reproduction in ceramic that had 3D-interconnected porosity, high relative density and the most uniform thickness distribution. The ceramic matrix porosity allowed for complete infiltration of reinforcement by aramid and epoxy forming the fibre-reinforced ceramic matrix composite. The interpenetrating composite microstructure with ceramic and epoxy gave a flexural strength increase of 45.65 MPa compared to the ceramic. Unfortunately, the infiltration procedure of aramid-epoxy reinforcement did not realise the full tensile strength potential of aramid fibres.

Dissertation (Ph.D.)--University of Toledo, 2004.
Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Engineering." Bibliography: leaves 317-322.

La mobilité est un enjeu clé, et le véhicule électrique (VE) progresse face aux défis environnementaux. Actuellement basé sur des batteries Li-Ion, le VE rencontre cependant certaines limites, telles que l'utilisation de solvants inflammables et une faible densité d'énergie, réduisant son autonomie. Une avancée technologique est donc nécessaire, et la batterie tout solide s'impose comme une solution prometteuse. En remplaçant l'électrolyte liquide par un électrolyte solide, il devient possible d'utiliser du lithium métallique, augmentant ainsi la densité d'énergie de 372 à 3862 mAh.g-1. Toutefois, des défis demeurent, notamment les variations volumiques des électrodes qui provoquent des dégradations mécaniques aux interfaces. Notre étude explore les relations entre les propriétés électrochimiques et mécaniques des batteries tout solide. Nous avons choisi l'argyrodite Li6PS5Cl pour ses avantages, notamment sa capacité de compactage à froid et sa conductivité ionique élevée (10⁻³ S.cm⁻¹). Des simulations DFT montrent que son module de Young est relativement faible (22 GPa), le rendant plus souple que d'autres matériaux solides. Notre stratégie pour ajuster ses propriétés mécaniques repose sur trois axes : 1) modifier la taille des particules afin d'influencer les défauts, 2) ajuster la stœchiométrie avec des variantes Li6PS5X (X = Cl, Br, I, F) pour modifier les liaisons chimiques, et 3) incorporer des polymères pour former un composite, ajustant ainsi les propriétés mécaniques globales. Nous avons étudié l'impact de deux voies de synthèse, en solution liquide et sèche. Cependant, ces deux méthodes ne permettent pas de contrôler efficacement la taille des particules. Grâce à un procédé innovant, le cryobroyage, la taille des particules a pu être réduite post-synthèse jusqu'à 2 µm. Pour éviter les problèmes de réactivité à l'air et à l'humidité, nous avons développé un dispositif permettant de mesurer le module de Young de l'argyrodite. La méthode consiste à fabriquer une pastille d'argyrodite dans un moule en acier, sous atmosphère inerte, à déposer une huile minérale pour assurer l'étanchéité, permettant ainsi une analyse par nano-indentation en atmosphère ambiante. Cette méthode permet de mesurer plusieurs propriétés du matériau, telles que le module de Young (E), la dureté (H) et la viscoélasticité. Les valeurs moyennes de E, basées sur 400 indents, sont autour de 20 GPa. Les résultats révèlent un domaine élastique limité et un comportement visqueux. Concernant Li6PS5X (X = Cl, Br, I, F), nos expériences n'ont pas mis en évidence de changements significatifs dans les propriétés mécaniques. En revanche, l'ajout de polymère PVDF, à des ratios massiques de 20 % et 50 %, diminue le module de Young. Nous avons également étudié l'impact de la taille des particules de l'électrolyte solide (2 µm vs 20 µm) sur les performances en cyclage dans une batterie complète, ainsi que l'effet de l'ajout de PVDF dans l'électrode positive composite. Plusieurs cellules ont montré une bonne cyclabilité sur plus de 200 cycles, avec une rétention de capacité supérieure à 85 %. Il apparaît que les procédés de mise en forme des cellules influencent davantage les performances que la taille des particules. À un taux de 20 % de PVDF, les cellules présentent des performances similaires à celles sans ajout de polymère. Cependant, à des taux plus élevés, le PVDF gêne la conductivité ionique, augmentant ainsi la polarisation de la cellule. L'apport bénéfique ou non du PVDF en fonction du ratio massique est discuté en détail dans le manuscrit
Mobility is a key issue, and the electric vehicle (EV) is advancing in response to environmental challenges. Currently relying on Li-Ion batteries, the EV faces certain limitations, such as the use of flammable solvents and low energy density, which reduces its range. A technological breakthrough is therefore necessary, and the all-solid-state battery is emerging as a promising solution. By replacing the liquid electrolyte with a solid electrolyte, it becomes possible to use metallic lithium, thereby increasing the energy density from 372 to 3862 mAh.g⁻¹. However, challenges remain, notably the volumetric changes in the electrodes, which cause mechanical degradation at the interfaces. Our study explores the relationships between the electrochemical and mechanical properties of all-solid-state batteries. We selected Li6PS5Cl argyrodite for its advantages, including its cold-pressing capability and high ionic conductivity (10⁻³ S.cm⁻¹). DFT simulations show that its Young's modulus is relatively low (22 GPa), making it more flexible than other solid materials. Our strategy to adjust its mechanical properties is based on three approaches: 1) modifying the particle size to influence defects, 2) adjusting the stoichiometry with Li6PS5X variants (X = Cl, Br, I, F) to modify chemical bonds, and 3) incorporating polymers to form a composite, thereby fine-tuning the overall mechanical properties. We investigated the impact of two synthesis routes, solution-based and dry, but neither method allowed effective control of particle size. Thanks to an innovative cryo-milling process, the particle size was reduced post-synthesis to as small as 2 µm. To address issues of air and moisture reactivity, we developed a setup to measure the Young's modulus of argyrodite. The method involves creating an argyrodite pellet in a steel mold under an inert atmosphere, applying mineral oil to ensure sealing, thus enabling nano-indentation analysis in ambient conditions. This method allows us to measure several material properties, such as Young's modulus (E), hardness (H), and viscoelasticity. The average E values, based on 400 indents, are around 20 GPa. The results reveal a limited elastic domain and a viscous behavior. Regarding Li6PS5X (X = Cl, Br, I, F), our experiments did not show significant changes in mechanical properties. However, the addition of PVDF polymer, at mass ratios of 20% and 50%, reduces the Young's modulus. We also studied the impact of solid electrolyte particle size (2 µm vs. 20 µm) on cycling performance in a full battery, as well as the effect of adding PVDF in the composite positive electrode. Several cells showed good cyclability over more than 200 cycles, with capacity retention above 85%. It appears that cell-forming processes influence performance more than particle size. At a 20% PVDF ratio, the cells exhibit similar performance to those without polymer addition. However, at higher ratios, PVDF hinders ionic conductivity, thus increasing cell polarization. The beneficial or detrimental effect of PVDF depending on the mass ratio is discussed in detail in the manuscript

Esistono attualmente varie ragioni per cui ampio interesse scientifico e tecnologico è rivolto verso sistemi di generazione di energia alternativi rispetto ai metodi convenzionali (quali i sistemi a turbine o i motori a combustione interna). Dal punto di vista ecologico, cresce il bisogno di ridurre la produzione di sostanze inquinanti per far fronte a uno sviluppo sostenibile. Da un punto di vista socio-economico, invece, aumenta il bisogno di far fronte a un continuo aumento della richiesta di energia, mentre nello stesso tempo le principali fonti di energia, quali i combustibili fossili, si stanno esaurendo. E infine, da un punto di vista socio-politico, la scarsità delle attuali fonti di energia sta creando drammatiche tensioni tra le varie aree economiche del mondo. La diminuzione della dipendenza mondiale dai combustibili fossili e l’introduzione di forme di generazione di energia alternative potrebbero sanare tale situazione. Il concetto di energia alternativa è stato introdotto già da vari anni. Ci sono diverse fonti d energia alternativa, come l’energia solare, l’energia eolica o la fusione nucleare. Un diverso approccio consiste nello sviluppo di sistemi di generazione di energia alternativi, che siano in grado di lavorare con alti rendimenti e di limitare al massimo la produzione di inquinanti. Allo stato attuale i motori a combustione interna presentano un’efficienza totale del 20-30%. Questo significa che solo il 20-30% dell’energia termica contenuta nel gasolio viene utilizzata come lavoro meccanico. Alti rendimenti si traducono, invece, in costi ridotti per unità di lavoro prodotto. Le celle a combustibile sono sistemi di conversione di energia alternativi i quali permettono la conversione diretta dell’energia chimica dei reagenti in energia elettrica, producendo al contempo basse emissioni inquinanti. Tra i diversi tipi di celle a combustibile, le celle a ossidi solidi (SOFCs) presentano vari vantaggi; tra i primi, lavorando ad alta temperatura (800-100°C) queste celle raggiungono valori di rendimento molto alti, permettono l’uso di diversi combustibili e l’unica emissione inquinante rilevante è quella di CO2, la quale rimane comunque un terzo di quella emessa da un motore a combustione interna a parità di kW/h prodotti. Tuttavia le alte temperature di lavoro comportano anche degli svantaggi: materiali costosi, elevati stress termici, difficoltà nel sigillare la cella, lunghi tempi di accensione e spegnimento del sistema. Per risolvere questi problemi la ricerca è orientata nell’abbassare la temperatura di funzionamento delle SOFCs nel cosiddetto range di temperature intermedie (400-700°C). Abbassare la temperatura di funzionamento si traduce in un peggioramento delle performance dei vari componenti della cella, e per questo lo studio di nuovi materiali risulta essenziale nella prospettiva di rendere le SOFC commercializzabili. Lo scopo di tale lavoro di tesi è appunto lo studio di materiali elettrolitici ed elettrodici che presentino buone proprietà conduttive a temperature di funzionamento intermedie e che allo stesso tempo siano chimicamente stabili. Nel capitolo 1A della tesi si presentano i principi basilari di funzionamento di una SOFC e una breve illustrazione dei materiali più studiati in letteratura sia per le alte e intermedie temperature di funzionamento. In particolare, tra i materiali ceramici con buone proprietà conduttive a basse temperature si trovano i conduttori protonici. Nel Capitolo 2A vengono illustrate le principali proprietà chimico-fisiche ed elettrochimiche di tali materiali ceramici. Molti ossidi perovskitici presentano conduzione protonica a temperature intermedie quando esposti ad atmosfera di idrogeno e/o vapore acqueo. Tuttavia nessuno di questi ossidi presenta contemporaneamente le due proprietà essenziali richieste ad un buon elettrolita: alta conducibilità ionica e buona stabilità chimica. La seconda parte della tesi presenta i risultati del lavoro sperimentale svolto, il quale è stato rivolto alla preparazione e caratterizzazione di conduttori protonici ceramici elettrolitici con alta conducibilità e buona stabilità chimica e allo sviluppo di elettrodi a - hoc per tali elettroliti. Il Capitolo 1B riporta l’ottimizzazione di una tecnica di sintesi sol gel per produrre i seguenti conduttori protonici: BaZr0.8Y0.2O3-δ (BZY) e BaCe0.8Y0.2O3-δ (BCY). Attraverso il metodo di sintesi ottimizzato si sono sintetizzate fasi singole dei suddetti composti. Le basse temperature di calcinazione richieste dal processo hanno portato a polveri di particelle nanometriche. I due composti sono stati sinterizzati in forma di pasticche circolari e caratterizzati elettricamente mediante spettroscopia di impedenza. Inoltre sono stati svolti test termici in flusso di anidride carbonica per valutare la stabilità chimica dei due composti, osservando una buona stabilità solo nel caso del BZY. Tuttavia le performance in cella di tale elettrolita si sono rilevate insufficienti rispetto ai target richiesti per la commercializzazione. Nel Capitolo 2B si è cercato di implementare le prestazioni del BZY sostituendo nel sito B della struttura perovskitica diverse quantità di Ce. Gli elettroliti cosi prodotti sono stati analizzati ai raggi X, sotto il punto di vista della stabilità chimica e della conducibilità elettrica. Il miglior compromesso tra stabilità chimica e conducibilità elettrica è risultato il composto con stechiometria BaZr0.5Ce0.3Y0.2O3-δ. Un ulteriore miglioramento della conduzione elettrica rispetto al BaZr0.5Ce0.3Y0.2O3-δ, pur mantenendo un’ottima stabilità chimica, è stato ottenuto realizzando un elettrolita “a doppio strato”, il quale è descritto nel Capitolo 3B. Una pasticca spessa 1 mm di BCY è stata protetta con uno strato sottile (circa un micron) di BZY cresciuto tramite la tecnica di deposizione a laser pulsato. Questo nuovo elettrolita ha presentato elevata conducibilità e buone prestazioni in cella in termini di stabilità chimica e densità potenza fornita. Nel Capitolo 4B si sono invece investigati elettrodi funzionali per tali elettroliti a conduzione protonica. Un catodo composito e stato realizzato unendo un conduttore misto ionico/elettronico, La1-xSrxCo1-yFeyO3-δ (LSCF), e un conduttore misto protonico/elettronico BaCe0.9Yb0.1O3-δ (10YbBC). L’uso di catodi compositi aumenta i siti di reazione al catodo, diminuendo quindi le cadute di potenziale dovute alle reazioni catodiche.
There are increasing reasons to explore alternatives to conventional energy generation methods (that is to say coal-fired steam turbine and gasoline internal combustion engine). From an ecological point of view, there is the need to reduce the polluting by-products of conventional energy generation. From a socio-economical standpoint, the worldwide demand for energy continues to rise as more and more nations join the group of the industrialized countries, while hydrocarbon fuels go to exhaustion. Finally, from a socio-political perspective, the situation described above has created several and often dramatic tensions between different world economic areas, as evidenced by frequent wars. Lowering the global dependence on oil might reduce such tensions. However, despite all of this, changes in the energy generation methods are extremely slow, as evidenced by the wide (if we cannot say total) use of the internal combustion engine. The concept of alternative energy has been introduced a long time ago. Several different sources of energy are proposed, which can have the potential to replace conventional generation methods. Popular examples include solar radiation, wind motion, and nuclear fusion. Each of these technologies has its own set of problems that have slowed down its commercialization, but much research is being conducted to overcome these problems. In fact, the research towards the development of alternative, highly efficient, eco-friendly energy production technologies is expanding. There is a general push towards higher efficiencies. At present, automobiles based on internal combustion engines have an overall efficiency of about 20-30%. That is, only 20-30% of the thermal energy content of the gasoline is converted into useful mechanical work and the rest is wasted. Higher efficiencies translate into reduced energy costs per unit of work done. Fuel cells, an alternative energy technology, have received growing interest in recent years since they represent one of the most promising energy production systems to reduce pollutant emissions. They are electrochemical devices that allow the direct conversion of chemical energy into electrical energy. Among the different type of fuel cells, solid oxide fuel cells (SOFCs) offer great promise as a clean and efficient technology for energy generation and provide significant environmental benefits. They produce negligible hydrocarbons, CO or NOx emissions, and, as a result of their high efficiency, about one-third less CO2 per kW/h than internal combustion engines. Unfortunately, the current SOFC technology based on a stabilized zirconia electrolyte requires the cell to operate from 700 to 1000°C to avoid unacceptable ohmic losses. These high operating temperatures demand specialized (expensive) materials for fuel cell interconnectors, long start-up time, and large energy input to heat the cell up to the operating temperature. Therefore, if fuel cells could be designed to give a reasonable power output at intermediate temperatures (IT, 400-700°C), tremendous benefits may result. In particular, in the IT range ferrite steel interconnects can be used instead of expensive and brittle ceramic materials. In addition, sealing becomes easier and more reliable; rapid start-up is possible; thermal stresses (namely, those caused by thermal expansion mismatches) are reduced; electrode sintering becomes negligible. Combined together, all these improvements result in reduced initial and operating costs. Therefore, the major trend in the present research activities on SOFCs is the reduction of the operating temperature. The problem is that lowering the operating temperatures lowers the electrolyte conductivity, whereas the electrode polarization greatly increases, reducing the overall fuel cell performance. Considering the described scenario, it is clear how the study of materials assumes a considerable role in lowering SOFC operating temperature. Making SOFCs commercially competitive with conventional energy generation methods means developing a highly efficient and environmental friendly energy production device to provide for a global sustainable energy system. IT-SOFCs represent not only a laboratory research activity, but a great challenge for the entire society. The purpose of the present dissertation is the development of a stable highly-conductive electrolyte and performing electrodes for lower temperature SOFCs. Chapter 1A presents the physico-chemical principles of SOFCs functioning, the demands imposed on the components materials, together with a literature survey on the state of-the art technology. Starting from more “conventional” oxygen ion conducting electrolytes, the need for reducing the operation temperature leads to a discussion on the properties of proton conducting materials as a feasible alternative to reach the goal of fabricating an IT-SOFCs. Chapter 2A describes the main properties of ceramic proton conductors. Several perovskite-type oxides, such as doped BaCeO3, SrCeO3, BaZrO3, and SrZrO3, show proton conductivity in the IT range when exposed to hydrogen and/or water vapour containing atmospheres. They are generally known as high temperature proton conductors (HTPCs). The main challenge in the field of HTPC is to find a compound that concurrently satisfies two of the essential requirements for fuel cell application, namely high proton conductivity and good chemical stability under fuel cell operating conditions. The second part of this dissertation describes the experimental results achieved during the research carried out. In view of the considerations given in Chapter 2a, Chapter 1B describes the optimization of the sol-gel procedure to prepare BaZr0.8Y0.2O3-δ (BZY) proton conductor electrolyte. Producing BZY powders with controlled compositional homogeneity and microstructure using a proper synthesis method could improve the electrochemical performance of this electrolyte. The optimized sol–gel procedure allowed the reduction of the diffusion path up to a nanometric scale, and thus required lower calcination temperatures. Nanocrystalline single-phase powders of BZY were produced at temperatures as low as 1100 °C. The same sol-gel procedure was also used to synthesize BaCe0.8Y0.2O3-δ (BCY) proton conductor electrolyte achieving also in this case nanometric particles powder at the calcination temperature of 100°C. The performance of the synthesized BZY and BCY proton conductors were examined in terms of chemical stability. After exposure to CO2 at high temperatures, the synthesized BZY powders presented good chemical and microstructural stability, differently from BCY which strongly decomposed after the CO2 treatment. Electrical conductivity and fuel cell performance were investigated only for the stable BZY electrolyte, however without achieving the required performance for practical application. Chapter 2 presents the application of the optimized synthetic procedure to the preparation of different proton conductor electrolytes. To further improve the electrochemical performance of barium zirconate electrolyte, the B-site of the BZY perovskite structure was doped with Ce producing several BaZr0.8-xCexY0.2O3-δ compounds (0.0≤x≤0.8). The prepared samples were analyzed in terms of chemical stability in CO2 environment, electrical conductivity, microstructural characteristics, and finally under fuel cell tests. Among the tested electrolytes, the BaZr0.5Ce0.3Y0.2O3-δ composition represented the best compromise between electrical performance and chemical stability. In fact it was able to maintain almost the same chemical stability of BZY, but with improved, more than twice, fuel cell performance. Chapter 3 describes a further improvement of the HTPC electrolyte performance. To obtain a highly conductive and chemically stable proton conductor electrolyte, a sintered Y-doped barium cerate (BCY) pellet was protected with a thin BZY layer, grown by pulsed laser deposition. The overall performance of the bilayer electrolyte turned out to be of great interest for practical use in IT-SOFCs application. The promising performance of this bilayer electrolyte rose from the very good crystallographic matching at the interface between the two materials, as well as the microstructure properties of the protecting layer in terms of uniformity, density and filling factor. However, while the bilayer conductivity was only slightly smaller than the conductivity of the BCY pellet, the measured fuel cell performances were negatively affected by the interface of the Pt electrodes with the BZY layer. For this reason the development of a superior cathode is crucial to make IT-SOFCs based on proton conductors competitive with the more established SOFCs using oxygen-ion conductor electrolytes. Chapter 4 focuses on the optimization of composite cathodes for application in IT-SOFC based on HTCP electrolytes. To explore different cathode materials with respect to the most commonly used for proton conductor electrolytes, such as platinum or cobalto-ferrites, the area specific resistance (ASR) of composite cathodes was investigated. Firstly, BaCe0.9Yb0.1O3-δ (10YbBC) and SrCe0.9Yb0.1O3-δ (10YbSC) were tested as cathode materials since they show mixed protonic-electronic conductivity. However, the ASR of the interface of these cathode materials with Y-doped barium cerate proton conductor electrolyte was extremely large, probably because of their too low partial electronic conductivity. For this reason, La1-xSrxCo1-yFeyO3-δ (LSCF), which presents high electronic conductivity, was combined with 10YbSC or 10YbBC to form composite cathodes. LSCF was chosen also because it allows faster oxygen surface exchange being a mixed O2-/e- conductor. The lowest ASR values were achieved with the composite cathode made of LSCF and 10YbBC in a1:1 ratio. Single phase Pt and LSCF cathodes were tested and it was found that they showed higher interfacial resistance than LSCF/10YbBC(1:1) composite cathode. This finding clearly suggests the importance of the proton conductor phase within the electrode, which actually should increase the triple phase boundary (TPB) density and so improve the cathode performance. The good performance observed for LSCF/10YbBC(1:1) composite cathode make it a cheaper and more efficient alternative to the Pt cathode that can actually improve the performance of IT-SOFCs based on proton conductor electrolytes.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The influence of the structure and elemental composition of lithium ions’ and oxygen vacancies’ (Vo) solid electrolytes (SE) on their electrical properties are investigated in the dissertation. The technological conditions of SE ceramics’ and films’ fabrication, which influence their microstructure, are described. The results of the investigation of the surfaces, temperature stability, and electrical properties are presented. Li+ SE belong to monoclinic, orthorhombic, or rhombohedral symmetries. The microstructure of the ceramics is mainly influenced by the temperature of their sintering. It has been shown by XPS that LiCe2/3PO4 ceramic is Li+-ion conductor. Complex impedance spectroscopy investigation showed that the increase of x in the systems Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3, and Li1+xGe2-2xAlxTix(PO4)3 (where x = 0.1, 0.2, 0.3) leads to the increase of bulk ionic conductivity of the ceramics and to the decrease of its activation energy. Phase transition temperature in Li3Sc2–xBx(PO4)3 compounds depends on x. The anomalies of temperature dependencies of bulk conductivity of Li3-xSc2-x-yYyZrx(PO4)3 system were observed when x = 0.1, y = 0, 0.1. The anomalies are related to superionic phase transitions in the materials, but no phase transitions have been detected for x = 0.2 compound in the studied temperature range. Ionic conductivity and its activation energy of YSZ thick films prepared by magnetron sputtering depend on their preparation’s technological... [to full text]
Disertacijoje yra nagrinėjama, kokią įtaką ličio katijonų ir deguonies vakansijų (Vo) kietųjų elektrolitų elektrinėms savybėms daro jų struktūra ir elementinė sudėtis. Darbe yra aprašomos technologinės superjoninių junginių (SJ) keramikų ir sluoksnių gamybos sąlygos, lemiančios jų mikrostruktūrą, bei pateikiami SJ paviršių, temperatūrinio stabilumo ir elektrinių savybių tyrimo rezultatai. Li+ SJ priklauso monoklininei, ortorombinei arba romboedrinei singonijoms. Keramikų mikrostruktūra labiausiai priklauso nuo jų kepinimo temperatūros. LiCe2/3PO4 keramiką paveikus elektriniu lauku, XPS buvo parodyta, kad šioje medžiagoje vyksta Li+ jonų pernaša. Kompleksinės varžos spektroskopijos tyrimai parodė, kad sistemose Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3 ir Li1+xGe2-2xAlxTix(PO4)3 (čia x = 0,1, 0,2, 0,3), didinant x, didėja kristalitiniai keramikų laidžiai, o jų aktyvacijos energijos mažėja. Li3Sc2–xBx(PO4)3 junginiuose vykstančio superjoninio fazinio virsmo temperatūra priklauso nuo x. Li3-xSc2-x-yYyZrx(PO4)3 sistemoje kai x = 0,1, y = 0, 0,1 temperatūrinėse kristalitinio laidžio prieklausose yra stebimos anomalijos, susijusios su superjoniniais faziniais virsmais šiose medžiagose, o kai x = 0,2 tirtame temperatūrų intervale faziniai virsmai nevyksta. Magnetroninio dulkinimo metodu suformuotų YSZ storųjų sluoksnių joninis laidis ir šio laidžio aktyvacijos energija priklauso nuo jų paruošimo technologinių sąlygų. Didinant NiO-CGO sluoksnių, suformuotų purškimo pirolizės... [toliau žr. visą tekstą]

Disertacijoje yra nagrinėjama, kokią įtaką ličio katijonų ir deguonies vakansijų (Vo) kietųjų elektrolitų elektrinėms savybėms daro jų struktūra ir elementinė sudėtis. Darbe yra aprašomos technologinės superjoninių junginių (SJ) keramikų ir sluoksnių gamybos sąlygos, lemiančios jų mikrostruktūrą, bei pateikiami SJ paviršių, temperatūrinio stabilumo ir elektrinių savybių tyrimo rezultatai. Li+ SJ priklauso monoklininei, ortorombinei arba romboedrinei singonijoms. Keramikų mikrostruktūra labiausiai priklauso nuo jų kepinimo temperatūros. LiCe2/3PO4 keramiką paveikus elektriniu lauku, XPS buvo parodyta, kad šioje medžiagoje vyksta Li+ jonų pernaša. Kompleksinės varžos spektroskopijos tyrimai parodė, kad sistemose Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3 ir Li1+xGe2-2xAlxTix(PO4)3 (čia x = 0,1, 0,2, 0,3), didinant x, didėja kristalitiniai keramikų laidžiai, o jų aktyvacijos energijos mažėja. Li3Sc2–xBx(PO4)3 junginiuose vykstančio superjoninio fazinio virsmo temperatūra priklauso nuo x. Li3-xSc2-x-yYyZrx(PO4)3 sistemoje kai x = 0,1, y = 0, 0,1 temperatūrinėse kristalitinio laidžio prieklausose yra stebimos anomalijos, susijusios su superjoniniais faziniais virsmais šiose medžiagose, o kai x = 0,2 tirtame temperatūrų intervale faziniai virsmai nevyksta. Magnetroninio dulkinimo metodu suformuotų YSZ storųjų sluoksnių joninis laidis ir šio laidžio aktyvacijos energija priklauso nuo jų paruošimo technologinių sąlygų. Didinant NiO-CGO sluoksnių, suformuotų purškimo pirolizės... [toliau žr. visą tekstą]
The influence of the structure and elemental composition of lithium ions’ and oxygen vacancies’ (Vo) solid electrolytes (SE) on their electrical properties are investigated in the dissertation. The technological conditions of SE ceramics’ and films’ fabrication, which influence their microstructure, are described. The results of the investigation of the surfaces, temperature stability, and electrical properties are presented. Li+ SE belong to monoclinic, orthorhombic, or rhombohedral symmetries. The microstructure of the ceramics is mainly influenced by the temperature of their sintering. It has been shown by XPS that LiCe2/3PO4 ceramic is Li+-ion conductor. Complex impedance spectroscopy investigation showed that the increase of x in the systems Li1+xScxZr2-x(PO4)3, Li1+xZr2-2xAlxTix(PO4)3, and Li1+xGe2-2xAlxTix(PO4)3 (where x = 0.1, 0.2, 0.3) leads to the increase of bulk ionic conductivity of the ceramics and to the decrease of its activation energy. Phase transition temperature in Li3Sc2–xBx(PO4)3 compounds depends on x. The anomalies of temperature dependencies of bulk conductivity of Li3-xSc2-x-yYyZrx(PO4)3 system were observed when x = 0.1, y = 0, 0.1. The anomalies are related to superionic phase transitions in the materials, but no phase transitions have been detected for x = 0.2 compound in the studied temperature range. Ionic conductivity and its activation energy of YSZ thick films prepared by magnetron sputtering depend on their preparation’s technological... [to full text]

This thesis summarizes the work carried out during the three-year Ph.D in Industrial Engineering and involve the study and characterization of coatings obtained on light alloys with the technique known as Plasma Electrolytic Oxidation (PEO). PEO process is, from the practice point of view, similar to the traditional anodic oxidation process as it's based on the electrochemical growth of a protective oxide layer on a metal surface. Compared with the traditional anodizing, PEO process works at higher currents and higher voltages, thus modifying the characteristics of the obtained layer. In recent years the importance of PEO process is increasing both in the research and in the industrial world. In fact the potentiality of the coatings obtained with this type of process are higher than those of the coatings obtained with the traditional techniques of chemical conversion or anodizing. However, the relatively high cost and some problems related to the process (in particular the need of a post treatment to ensure galvanic corrosion) have now slowed to the widespread use on an industrial scale. So the scientific research on one hand is looking for new solutions to further improve the properties of the coatings, in order to justify the higher costs, on the other is trying to modify the existing process to reduce the above-mentioned costs. The obtained results explained in this thesis have allowed an expansion in the knowledge regarding the PEO coatings and in particular to move towards greater industrial development of the technique. In fact new process parameters that permit to reduce the total time for the obtainment of good PEO coatings maintaining good corrosion resistance were found, especially working with higher current densities if compared with the ones reported in literature. Moreover the addiction of molybdenum and lanthanum salts as additives in the electrolyte used in the PEO process, has permitted to improve the performances of the coating in terms of corrosion resistance. The addiction of graphite nanoparticles and silver particles has permitted to obtain respectively coatings with improved corrosion and wear resistance and coatings with an intrinsic antimicrobial effect. PEO process was also successfully applied on steels.
Questo lavoro di tesi riassume il lavoro svolto durante i tre anni di dottorato in Ingegneria Industriale e riguarda lo studio e la caratterizzazione di rivestimenti ottenuti mediante la tecnica denominata Plasma Electrolytic Oxidation (PEO) su leghe leggere. Il processo PEO è, dal punto di vista operativo, molto simile ai tradizionali processi di ossidazione anodica in quanto si basa sulla crescita per via elettrochimica di uno strato di ossido protettivo sulla superficie del metallo. Rispetto al tradizionale processo di anodizzazione il processo PEO lavora però a correnti e voltaggi più elevati, modificando così le caratteristiche dello strato ottenuto. Il processo PEO sta assumendo negli ultimi anni sempre maggiore rilevanza sia nell'ambito della ricerca che in quello industriale. Le potenzialità, infatti, dei rivestimenti ottenuti con questo tipo di processo sono molto più elevate rispetto a quelle dei rivestimenti ottenibili con le tradizionali tecniche di conversione chimica o di anodizzazione. Tuttavia il costo abbastanza elevato ed alcune problematiche relative al processo ne hanno per ora frenato la diffusione su larga scala a livello industriale. Dal punto di vista della ricerca scientifica quindi, da un lato si stanno cercando nuove soluzioni che consentano di migliorare ulteriormente le proprietà dei rivestimenti, in modo da giustificare i costi più elevati, dall'altro si stanno cercando delle variazioni al processo che consentano di ridurre i costi sopracitati. I risultati ottenuti durante il dottorato di ricerca e descritti in questo lavoro di tesi hanno permesso di ampliare le conoscenze inerenti i rivestimenti PEO e in particolare di procedere verso un maggiore sviluppo industriale della tecnica. Infatti è stata sviluppata una nuova sequenza di parametri di processo, basata sul lavorare ad elevate densità di corrente, che permette di ottenere rivestimenti di ottima qualità con tempi inferiori rispetto a ciò che viene attualmente realizzato. Inoltre l'aggiunta di sali di molibdeno e lantanio, come additivi dell'elettrolita usato nel processo PEO, ha permesso di incrementare notevolmente la resistenza a corrosione dei rivestimenti in modo tale da consentire la realizzazione di componenti a più alto valore aggiunto. L'aggiunta di nanoparticelle di grafite ha permesso di ottenere rivestimenti con buona resistenza a corrosione e ad usura. L'inserimento di altre tipologie di additivi (particelle d'argento) ha poi permesso di conferire proprietà battericide al rivestimento. Infine la tecnica PEO è stata anche con successo applicata agli acciai basso legati aprendo un importante filone di sviluppo a livello tecnologico.

The goal of this thesis is to generate fundamental understandings of charge transport behaviors of composites consisting of garnet structured Al substituted Li7La3Zr2O12 (LLZO) electrolyte and LiCoO2 electrode. In order to take full advantage of all-solid-state batteries, bulk type composite electrodes should be introduced to increase energy and power density. However, the charge utilization of bulk type composite electrodes is quite low. Understanding ionic conduction behavior is, therefore, important for improving the performance of all-solid-state batteries, because ion conduction within solids depends on effective pathways. Electronic conductivity can be easily compensated by adding carbon black, but ionic conductivity can only depend on composites electrode itself. Here, we show that electronic and ionic conductivities of composites consisting of LiCoO2 and Al doped LLZO can be achieved separately. 3D reconstructed image obtained from focused ion beam-scanning electron microscope (FIB-SEM) demonstrates that porosity, percolation, and grain boundaries often play antagonistic roles in controlling the charge transport behaviors in the composite electrodes, resulting in an overall conductivity dominated by electrons. This work suggests an approach to optimize electronic and ionic conductivities for bulk type composite electrodes, which may eventually be utilized in all-solid-state batteries.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis (M.S.)--University of Toledo, 2009.
Typescript. "Submitted as partial fulfillments of the requirements for The Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 104-110.

The transition from fossil fuels to renewable resources has created more demand for energy storage devices. Lithium-oxygen (Li-O2) batteries have attracted much attention due to their high theoretical energy densities. They, however, are still in their infancy and several fundamental challenges remain to be addressed. Advanced analytical techniques have revealed that all components of a Li-O2 battery undergo undesirable degradation during discharge/charge cycling, contributing to reduced cyclability. Despite many attempts to minimize the anode and cathode degradation, the electrolyte remains as the leading cause for rapid capacity fading and poor cyclability in Li-O2 batteries. In this dissertation, composite gel polymer electrolytes (cGPEs) consisting of a UV-curable polymer, tetragylme based electrolyte, and glass microfibers with a diameter of ~1 µm and an aspect ratio of >100 have been developed for their use in Li-O2 battery application. The Li-O2 batteries containing cGPEs showed superior charge/discharge cycling for 500 mAh.g-1 cycle capacity with as high as 400% increase in cycles for cGPE over gel polymer electrolytes (GPEs). Results using in-situ electrochemical impedance spectroscopy (EIS), Raman spectroscopy, and scanning electron microscopy revealed that the source of the improvement was the reduction of the rate of lithium carbonates formation on the surface of the cathode. This decrease in formation rate afforded by cGPE-containing batteries was possible due to the decrease of the rate of electrolyte decomposition. The increase in solvated to the paired Li+ ratio at the cathode, afforded by increased lithium transference number, helped lessen the probability of superoxide radicals reacting with the tetraglyme solvent. This stabilization during cycling helped prolong the cycling life of the batteries. The effect of ion complexes on the stability of liquid glyme based electrolytes with various lithium salt concentrations has also been investigated for Li-O2 batteries. Charge/discharge cycling with a cycle capacity of 500 mAh·g-1 showed an improvement as high as 300% for electrolytes containing higher lithium salt concentrations. Analysis of the Raman spectroscopy data of the electrolytes suggested that the increase in lithium salt concentration afforded the formation of cation-solvent complexes, which in turn, mitigated the tetragylme degradation.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:01/08029-0

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Solid Oxide Fuel Cells (SOFCs) are emerging as a potential breakthrough energy conversion technology for clean and efficient production of electricity and heat from hydrogen and hydro-carbon fuels. Sc₀.₁Ce₀.₀₁ZrO₂ electrolytes for Solid Oxide Fuel Cells are very promising materials because their high ionic conductivity in the intermediate temperature range 700°C-800°C. The vibration response of cubic and rhombohedral ([beta]) 10 mol%Sc₂O₃ - 1 mol%CeO₂ - ZrO₂ (Sc₀.₁Ce₀.₀₁ZrO₂) both at room and high-temperatures is reported. The in-situ heating experiments and ex-situ indentation experiments were performed to characterize the vibrational behavior of these important materials. A temperature and stress-assisted phase transition from cubic to rhombohedral phase was detected during in-situ Raman spectroscopy experiments. While heating and indentation experiments performed separately did not cause the transition of the cubic phase into the rhombohedral structure under the performed experimental conditions and only broadened or strained peaks of the cubic phase could be detected, the heating of the indented (strained) surface leaded to the formation of the rhombohedral Sc₀.₁Ce₀.₀₁ZrO₂. Both temperature range and strained zone were estimated by in situ heating and 2D mapping, where a formation of rhombohedral or retention of cubic phase has been promoted. The mechanical properties, such as Young’s modulus, Vickers hardness, indentation fracture resistance, room and high temperature four point bending strength and SEVNB fracture toughness along with the stress--strain deformation behavior in compression, of 10 mol% Sc₂O₃--1 mol % CeO₂ - ZrO₂ (ScCeZrO₂) ceramics have been studied. The chosen composition of the ScCeZrO₂ has very high ionic conductivity and, therefore, is very promising oxygen ion conducting electrolyte for the intermediate temperature Solid Oxide Fuel Cells. Therefore, its mechanical behavior is of importance and is presented in this study.
M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE

The solid oxide fuel cell (SOFC) is a potential high efficient electrochemical device for vehicles, auxiliary power units and large-scale stationary power plants combined heat and power application. The main challenges of this technology for market acceptance are associated with cost and lifetime due to the high temperature (700-1000 oC) operation and complex cell structure, i.e. the conventional membrane electrode assemblies. Therefore, it has become a top R&D goal to develop SOFCs for lower temperatures, preferably below 600 oC. To address those above problems, within the framework of this thesis, two kinds of innovative approaches are adopted. One is developing functional composite materials with desirable electrical properties at the reduced temperature, which results of the research on ceria-based composite based low temperature ceramic fuel cell (LTCFC). The other one is discovering novel energy conversion technology - Single-component/ electrolyte-free fuel cell (EFFC), in which the electrolyte layer of conventional SOFC is physically removed while this device still exhibits the fuel cell function. Thus, the focus of this thesis is then put on the characterization of materials physical and electrochemical properties for those advanced energy conversion applications. The major scientific content and contribution to this challenging field are divided into four aspects except the Introduction, Experiments and Conclusions parts. They are: Continuous developments and optimizations of advanced electrolyte materials, ceria-carbonate composite, for LTCFC. An electrolysis study has been carried out on ceria-carbonate composite based LTCFC with cheap Ni-based electrodes. Both oxygen ion and proton conductance in electrolysis mode are observed. High current outputs have been achieved at the given electrolysis voltage below 600 oC. This study also provides alternative manner for high efficient hydrogen production.  Compatible and high active electrode development for ceria-carbonate composite electrolyte based LTCFC. A symmetrical fuel cell configuration is intentionally employed. The electro-catalytic activities of novel symmetrical transition metal oxide composite electrode toward hydrogen oxidation reaction and oxygen reduction reaction have been experimentally investigated. In addition, the origin of high activity of transition metal oxide composite electrode is studied, which is believed to relate to the hydration effect of the composite oxide. A novel all-nanocomposite fuel cell (ANFC) concept proposal and feasibility demonstration. The ANFC is successfully constructed by Ni/Fe-SDC anode, SDC-carbonate electrolyte and lithiated NiO/ZnO cathode at an extremely low in-situ sintering temperature, 600 oC. The ANFC manifests excellent fuel cell performance (over 550 mWcm-2 at 600 oC) and a good short-term operation as well as thermo-cycling stability. All results demonstrated its feasibility and potential for energy conversion. Fundamental study results on breakthrough research Single-Component/Electrolyte-Free Fuel Cell (EFFC) based on above nanocomposite materials (ion and semi-conductive composite) research activities. This is also the key innovation point of this thesis. Compared with classic three-layer fuel cells, EFFC with an electrolyte layer shows a much simpler but more efficient way for energy conversion. The physical-electrical properties of composite, the effects of cell configuration and parameters on cell performance, materials composition and cell fabrication process optimization, micro electrochemical reaction process and possible working principle were systematically investigated and discussed. Besides, the EFFC, joining solar cell and fuel cell working principle, is suggested to provide a research platform for integrating multi-energy-related device and technology application, such as fuel cell, electrolysis, solar cell and micro-reactor etc. This thesis provides a new methodology for materials and system innovation for the fuel cell community, which is expected to accelerate the wide implementation of this high efficient and green fuel cell technology and open new horizons for other related research fields.

QC 20131122

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.
Bachelors
Engineering and Computer Science
Engineering

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:97/00727-3

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:99/12494-9

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The last decades have been characterized by a constant increase in the need of energy coupled with an increase in the greenhouse gases emissions, since a large amount of the energy is provided by combustion plants burning fossil fuels. The level of CO2 has reached a negative record and this tendency has to be reversed in favor of a more environmentally sustainable approach. In this scenario different solutions for energy conversion and storage need to be found: the use of fossil fuels has to be reduced and replace with other and more sustainable forms of energy conversion. At the same time the change has to be guided by an improvement in the current technology for energy conversion to facilitate the transition process. For this purpose, the traditional combustion process can be improved using oxy-fuel conditions, where a stream of pure O2 provided by an oxygen transport membrane is used instead of air and the resulting high concentrated CO2 flue gas is easier to capture. A cleaner form of energy can be obtained using Solid Oxide Reversible Cells (SORCs), highly efficient electrochemical devices able convert chemicals directly into electrical current without production of pollutants. When operated in electrolysis mode, SORCs allow to store electrical energy in the form of fuels, obtained from CO2 reduction. Despite being extremely appealing, both these possibilities are not integrated in large scale energy plants yet, due mainly to their cost and long-term stability issues. These aspects can be improved with materials having a better performance and this can be achieved by an appropriate tailoring of their properties. This thesis presents the attempt to address these issues by developing novel advanced ceramic materials with high performances in order to fulfill a lower temperature application. In particular, this has been pursued aiming at improving the ionic conductivity of the materials. A GDC/YSZ nanocomposite has been prepared by inkjet printing and characterized as electrolyte, with attention to the interaction between the two phases. Complex perovskites have been designed and optimized to stabilize a high oxygen defective crystal phase displaying mixed ionic and electronic conductivity. These materials have been characterized in their structure, oxygen mobility and conductivity, before being tested as oxygen transport membranes and cathodes for solid oxide fuel cells.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Deutsche Forschungsgemeinschaft (DFG)
A fundição é o processo de produção de peças metálicas que consiste em despejar metal líquido em um molde com formato e medidas correspondentes aos da peça a ser fabricada. Durante a confecção dos moldes de areia é gerado pó de exaustão como resíduo desse processo. O descarte desse resíduo traz diversos danos ambientais e visando a utilização do resíduo, este trabalho propõe o seu uso para a produção de revestimentos, como filme de proteção em uma superfície de liga de alumínio, através da técnica de oxidação eletrolítica assistida por plasma (do inglês: Plasma Electrolytic Oxidation (PEO)). O PEO é um processo em que o plasma atmosférico e a eletrólise convencional são combinados para a alteração de superfícies metálicas em óxidos cerâmicos. Neste trabalho, foram obtidos recobrimentos em ligas de alumínio 5052, através da oxidação em plasma eletrolítico, utilizando solução eletrolítica preparada com pó de exaustão e água destilada nas concentrações de 5 g/L e 10 g/L. O plasma eletrolítico foi obtido aplicando-se uma diferença de potencial de 650 V, frequência de 200 Hz e utilizando tempo de deposição de 300 s, 600 s e 900 s. Foi feita a caracterização do resíduo pó de exaustão por Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Energia Dispersiva (EDS), Difração de Raios X (DRX) e Espectroscopia de Infravermelho (FTIR). Os revestimentos foram analisados por MEV/EDS, DRX, FTIR, ângulo de contato e energia de superfície, rugosidade, espessura e ensaio de desgaste por pino-sobre-disco. O pó de exaustão de areia de fundição apresentou ser composto por O, Si, Al, Fe, Mg, Ti, Na, K, Ca, nas fases quartzo (SiO2), hematita (Fe2O3), óxido de potássio (K2O), óxido de alumínio (Al2O3), óxido de sódio (Na2O2) e periclase (MgO). Os revestimentos apresentaram C, O, Mg, Al, Si, P, Ca, Fe, K, Zn, Ti, Na, Mn. Ao final das 20 semanas, foi constatado que os revestimentos se apresentaram hidrofílicos, com o ângulo de contato entre 70º a 90º. Os revestimentos tiveram maior rugosidade que o alumínio. O aumento da concentração acarretou na diminuição da rugosidade para as deposições. A concentração e o tempo influenciaram positivamente no aumento da espessura dos revestimentos. Independente da concentração da solução eletrolítica, a taxa de deposição diminui com o aumento do tempo de deposição. O ensaio de pino sobre disco mostrou que a placa de alumínio sem tratamento perde muita massa em relação ao pino que é de aço. Os revestimentos obtidos têm ganho de massa indicando serem abrasivos, retirando massa do pino.
Casting is the production process for metal parts that consists in pouring molten metal in a mold with corresponding shape and measurement of the part to be manufactured. During the manufacturing of sand molds exhaustion powder is generated as this process residue. The disposal of this waste causes lots of environmental damage . This work aims to propose the usage of this waste in the production of coating, as a protective film on an aluminum alloy surface through the use of electrolytic oxidation technique assisted by plasma (the English: Plasma Electrolytic Oxidation (PEO)). The PEO is a process in which the atmospheric plasma and conventional electrolysis are combined for the modification of metal surfaces on ceramic oxides. In this work, coatings in 5052 aluminum alloys were obtained through electrolytic oxidation in plasma using the electrolytic solution prepared with fume powder and distilled water at concentrations of 5 g / L and 10 g / L. The electrolytic plasma was obtained by applying a potential difference of 650 V, frequency 200 Hz and using a deposition time of 300 s, 600 s and 900 s. The characterization of the exhaustion dust residue was carried out through Scanning Electron Microscopy (MEV), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (DRX) and Infrared Spectroscopy (FTIR). The coatings were analyzed by MEV / EDS, DRX, FTIR, contact angle and surface energy, roughness, thickness and wear test in pin-on-disc. The exhaust powder from sand casting was composed of O, Si, Al, Fe, Mg, Ti, Na, K, Ca in the quartz layers (SiO2), hematite (Fe2O3), potassium oxide (K2O) oxide aluminum oxide (Al2O3), sodium oxide (Na2O2) and periclase (MgO). The coatings showed C, O, Mg, Al, Si, P, Ca, Fe, K, Zn, Ti, In, Mn. After of 20 weeks, it was verified that the coatings presented hydrophilic, with contact angle between 70º to 90º. The coatings surface presented higher roughness than aluminum. The increase in the concentration resulted in a decrease in the roughness for deposition. The concentration and the time had affected positively the increase in thickness of the coatings. Regardless the concentration of the electrolyte solution, the deposition rate decreases with the increase of deposition time. The pin on disk test showed that the untreated aluminum plate loses much mass in relation to the steel pin. The coatings obtained have weight gain which indicates that they are abrasive and able to remove the mass of the pin.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:03/07331-0

Dans ce travail, nous avons établi un protocole de fabrication industrielle pour réaliser des cellules de piles à combustible avec interfaces électrode/électrolyte architecturées, ou planes. Nous avons démontré que pour deux types d'échantillons, différents par les matériaux, la microstructure, le nombre de couches et l'emplacement de l'architecture, l'architecture de l'interface électrode/électrolyte entraîne une augmentation très significative des performances. Les mesures de polarisation et l'EIS sont utilisées pour étudier les performances électrochimiques des cellules, ainsi que pour comparer les cellules architecturées et les cellules planes. Nous isolons l'influence de l'architecture sur les spectres d'impédance globaux en utilisant une méthode de comparaison innovante basée sur l'étude des écarts relatifs des parties de résistance dépendantes de la fréquence. Ainsi, l'architecture a une influence favorable sur les performances électrochimiques en améliorant les capacités catalytiques des électrodes ainsi que le transfert de charges (et en particulier le transfert d'ions) dans la cellule. L'architecture induit une augmentation de 60 % de la densité de puissance maximale pour les cellules de Type I et de 75 % pour les cellules de Type II
In this work, we have established an industrial fabrication protocol for single fuel cells with either architectured or planar electrode/electrolyte interfaces. We have demonstrated that in two types of samples, differing in materials, microstructure, number of layers, and architecture location, the architecturation of the electrode/electrolyte interface results in a highly significant performance increase. Polarization measurements and EIS are used to study the electrochemical performances of the cells, to compare the architectured and planar ones. We isolate the influence of the architecturation on global impedance spectra by using an innovative comparison method based on the study of the relative gaps of the frequency-dependent resistance parts. Thus, the architecturation has a strongly favorable influence on the electrochemical performances by enhancing the catalytic capabilities of the electrodes as well as the charge transfer (and in particular the ion transfer) within the cell. The architecturation induces a 60 % increase of the maximum power density for the Type I cells and 75% for the Type II cells

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Face au réchauffement climatique dû aux activités humaines et à l’utilisation de ressources fossiles, le besoin de trouver de nouvelles sources d’énergies décarbonées devient urgent. Le dihydrogène (H2) communément appelé « hydrogène » s’impose comme un vecteur énergétique d’intérêt de par sa capacité à produire une énergie de combustion supérieure à celle des énergies fossiles et à ne produire que de l’eau comme déchet lors de son utilisation dans une pile à combustible. De plus, son utilisation ne génère aucune nuisance sonore à la différence des moteurs thermiques couramment employés. Néanmoins, elle requiert un très haut degré de pureté afin d’éviter la pollution des matériaux catalytiques contenus dans ces piles à combustible. De nos jours, près de 95% de l’hydrogène produit se fait par reformage catalytique du méthane et nécessite donc des procédés de purification souvent complexes et couteux. Une façon de s’affranchir de ces procédés serait de produire l’hydrogène directement par électrolyse de l’eau. Cette méthode consiste à séparer une molécule d’eau sous l’action d’un courant électrique (produit de façon renouvelable) pour produire de l’hydrogène et du dioxygène (O2) aux bornes d’électrodes d’un électrolyseur. Malheureusement, cette réaction se heurte à des limitations cinétiques en raison d’un mécanisme de réaction de dégagement de dioxygène (RDO) très complexe, incluant plusieurs électrons et plusieurs intermédiaires réactionnel. L’émergence de nouvelles technologies de membranes échangeuses d’anion a ouvert la voie à l’utilisation de l’électrolyse en milieu alcalin, permettant donc l’utilisation de métaux de transition non nobles comme catalyseurs, moins couteux que les métaux traditionnellement employés (Ir et Ru). Ce manuscrit de thèse a donc exploré la synthèse de matériaux à visée catalytique pour réduire les barrières énergétiques et cinétiques de la RDO. Afin de proposer des matériaux performants, stables dans le temps et résistant aux milieux agressifs imposés par l’électrolyse de l’eau en milieu alcalin, la voie des céramiques dérivées de polymères précéramiques (PDC pour Polymer-Derived Ceramics) s’est avéré être une méthode d’élaboration de choix pour y parvenir. L’intérêt de cette méthode est de mettre en œuvre des polymères organosiliciés (ici un polysilazane) servant de plateforme moléculaire pour la croissance de métaux non nobles via l’utilisation de complexes métalliques tels que des chlorures et des acétylacétonates de nickel (Ni), de fer (Fe) ou encore de cobalt (Co). Ce polymère modifié par ces métaux sert de précurseur à la formation in situ de nanoparticules métalliques dans une matrice poreuse à base des éléments silicium (Si), carbone (C), oxygène (O) et azote (N) et garantissant leur accessibilité et stabilité après traitement thermique à 500°C sous argon. Ce manuscrit illustré à travers cinq chapitres décrit des travaux sur la synthèse et la caractérisation de nanoparticules de Ni (chapitre 3), Ni-Fe (chapitre 4) et d’alliages à moyenne et haute entropie (chapitre 5) qui complètent un état de l’art (chapitre 1) et une description des matériaux et méthodes mises en œuvre au cours de cette thèse (chapitre 2). Les matériaux formés ont été étudiés à chaque étape de leur synthèse à travers la mise en œuvre d’outils de caractérisation complémentaires avant d’en évaluer les performances électrochimiques ; notamment par mesure de la surtension anodique lors de la RDO afin d’identifier la meilleure combinaison métallique. Des tests post mortem ont été réalisés pour évaluer le potentiel des matériaux préparés. Compte tenu de la simplicité de la voie de synthèse et du faible coût des réactifs utilisés, ces travaux conduisent à une nouvelle famille de matériaux et à plusieurs perspectives prometteuses, non seulement pour le développement de catalyseurs efficaces et stables pour l'OER mais plus généralement pour de nombreuses applications en électrochimie. Ces opportunités sont désormais exploitées
Global warming caused by human activity and the use of fossil fuels, urges the need to find new sources of carbon free energy. Dihydrogen (H2) more known as “hydrogen” is rapidly emerging as a technically viable and benign energy vector according to its ability to produce a higher density of combustion than fossil fuels and to produce only water as a waste product when used in a fuel cell. Moreover, its use generates no noise pollution, unlike the combustion engines currently in use. Nevertheless, it requires a very high degree of purity in order to avoid pollution of the catalytic materials contained in the cells. Nowadays, nearly 95% of the hydrogen produced is obtained by catalytic reforming of methane, and therefore requires purification processes that are often complex and costly. One way of avoiding these purification steps would be to produce hydrogen directly by electrolysis of water more known as water splitting. This process consists of separating a molecule of water under the action of an electric current (produced in a renewable way) to produce hydrogen and dioxygen (O2) at the electrodes of an electrolyser. Unfortunately, this reaction has kinetic limitations due to a very complex Oxygen Evolution Reaction (OER) mechanism, including several electrons and several reaction intermediates. The emergence of new anion exchange membrane technologies has paved the way for the use of electrolysis in alkaline media, thus allowing the use of non-noble transition metals as catalysts, which are less expensive than the metals traditionally used (Ir and Ru). Within this context, this PhD thesis has explored the synthesis of catalytic materials to reduce the energy and kinetic barriers of OER. In order to propose materials that are performant, stable over time and resistant to the aggressive environments imposed by the electrolysis of water in an alkaline medium, the polymer-derived ceramics (PDC) route has been selected as a synthesis method of choice. The interest of this method is to implement organosilicon polymers (here a polysilazane) serving as a molecular platform for the growth of non-noble metals via the use of metal complexes such as chlorides and acetylacetonates of nickel (Ni), iron (Fe) or cobalt (Co). This polymer modified by these metals serves as a precursor for the in situ formation of metal nanoparticles in a porous matrix based on the elements silicon (Si), carbon (C), oxygen (O) and nitrogen (N) allowing their accessibility and stability after heat treatment at 500 ° C under argon. This manuscript illustrated through five chapters describes works dedicated to the synthesis and characterization of Ni (chapter 3), Ni-Fe (chapter 4) and medium and high entropy alloys (chapter 5) nanoparticles which complete a state of the art (chapter 1) and a description of the materials and methods implemented during this thesis (chapter 2). The materials which have been prepared were studied at each stage of their synthesis through the implementation of complementary characterization tools before assessing their electrochemical performances; in particular by measuring the anodic overpotential during OER, in order to determine the best metal combinations. Post mortem tests were carried out to evaluate the potential of the prepared materials. Considering the simplicity of the synthesis route, and the low cost of reactants used, this work leads to a new family of materials and to several promising perspectives, not only for the development of efficient and stable catalysts for the OER but more generally for numerous applications in electrochemistry. These opportunities are now being addressed