On governing equations and closure relations for the multiscale modeling of concentration polarization in solid-oxide fuel cells: mass transfer and concentration-induced voltage losses.

• Ano de defesa: 2017
• Autor(a) principal: Teixeira Junior, Roberto Janny
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Células a combustível; Diffusion; Electrochemistry; Eletroquímica; Heterogeneous catalysis; Mass transfer; Mathematical modeling; Polarização; Polarization; Porous media; SOFC; Solid-oxide fuel cell
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/3/3137/tde-07112017-075939/

The aim of this dissertation is to appraise and critically reflect on the physical pertinence of governing equations and closure relations often used for the modeling of gas-phase transport phenomena in high-temperature solid-oxide fuel cells (SOFCs). More precisely, this work conducts a critical literature review on the concentration-induced voltage losses (i.e., concentration polarization) resulting from mass transfer limitations. Thus, the overall object of this work was to stress awareness of the limits of mathematical models studied and developed in the SOFC literature to date, and which are specifically related to concentration polarization processes. To a great extent, the design of SOFC porous layers is likened to that of optimizing the transport of multicomponent gas mixtures in structured porous catalysts, for which diffusional and flow limitations are of cardinal importance. In both cases, severe inconsistencies in mass transport models cannot be simply ignored and the main uncertainties in utilizing such models should be clarified. It is hoped that the information herein will serve usefully to support future developments of more consistent theoretical frameworks, thereby improving the confidence on the results of numerical simulations. The critical literature review has been carried out so to identify a number of physical inconsistences, ill-defined approximations, and misleading mathematical derivations. Along the review, it is argued that the choice (or, more properly, the lack of conceptual refinement) of a particular mathematical model can significantly impair the \"prediction\" of transport processes relevant to concentration-induced power losses in SOFCs. One of the keystones of this work was therefore to re-interpret and thus to reassess the frequently contradictory literature related to certain classes of gas-phase transport models pertinent to the evaluation of concentration polarization. With this revisionary approach, it is expected that one could reduce confusion, clear up apparent contradictions, and improve the possibility of gaining new insights.