This paper presents a new computational framework for modeling chemically reacting flow in anode-supported solid-oxide fuel cells (SOFC). Depending on materials and operating conditions, SOFC anodes afford a possibility for internal reforming or catalytic partial oxidation of hydrocarbon fuels. An important new element of the model is the capability to represent elementary heterogeneous chemical kinetics in the form of multistep reaction mechanisms. Porous-media transport in the electrodes is represented with a dusty-gas model. Charge-transfer chemistry is represented in a modified Butler-Volmer setting that is derived from elementary reactions, but assuming a single rate-limiting step. The model is discussed in terms of systems with defined flow channels and planar membrane-electrode assemblies. However, the underlying theory is independent of the particular geometry. Examples are given to illustrate the model.

A computational model is developed to represent the coupled behavior of elementary chemistry, electrochemistry, and transport in the vicinity of solid-oxide fuel cell three-phase boundaries. The model is applied to assist the development and evaluation of <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>H2 charge-transfer reaction mechanisms for Ni–yttria-stabilized zirconia (YSZ) anodes. Elementary chemistry and surface transport for the Ni and YSZ surfaces are derived from prior literature. Previously published patterned-anode experiments [ J. Mizusaki et al. , Solid State Ionics , 70/71 , 52 (1994) ] are used to evaluate alternative electrochemical charge-transfer mechanisms. The results show that a hydrogen-spillover mechanism can explain the Mizusaki polarization measurements over wide ranges of gas-phase composition with both anodic and cathodic biases.

This paper uses previously published conductivity measurements as the basis for establishing thermodynamic and transport properties for BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_{3 − δ} (BCZYYb) proton-conducting membranes. BCZYYb is mixed ionic-electronic conducting (MIEC) doped perovskite that is dominantly a proton-conducting ceramic. In addition to protons, BCZYYb permits transport of oxygen vacancies and O-site polarons. The present analysis considers the effects of immobile polaron traps. The paper reports enthalpies ΔH° and entropies ΔS° for the defect reactions, and defect diffusion coefficients in Arrhenius form. The paper incorporates the thermodynamic and transport properties into a Nernst–Planck model to characterize BCZYYb performance as a protonic-ceramic membrane for electrolyzer and fuel-cell applications. Especially at temperatures below 600°C, BCZYYb can achieve high faradaic efficiencies (i.e., low electronic leakage) as an electrolyzer membrane.

BZY20 is a mixed ionic-electronic conducting (MIEC) heterovalently doped perovskite that under most conditions is dominantly a proton conductor. In addition to protons, mobile defects include oxygen vacancies and O-site polarons. An important aspect of the present approach is the inclusion of immobile polaron traps that are associated with the yttrium dopant. The BZY20 material can serve as an electrolyte for applications including fuel cells, electrolyzers, and membrane reactors. The principal objective of the present paper is to develop thermodynamic properties (i.e., enthalpies and entropies) for defect-incorporation reactions and transport properties (i.e., diffusion coefficients) for defect transport within the dense ceramic. Previously published conductivity measurements form the basis for fitting the needed property relationships. The paper incorporates the new thermodynamic and transport properties into Nernst–Planck models that characterize defect transport within electrolyte membranes such as in protonic-ceramic fuel cells and electrolyzers.

Syngas mixtures are excellent fuels for solid-oxide fuel cells (SOFC). Depending on the primary feedstock and the processing technology to produce the syngas, the composition (primarily mixtures of H₂ and CO, but often including CH₄, H₂O, CO₂, N₂, and other impurities) can vary considerably. Thus, it is important to understand how SOFCs perform with alternative syngas mixtures. Syngas composition can affect materials selection, system design, and operating conditions. To assist understanding and interpreting performance, the article first reviews the basic principles governing SOFC chemistry and electrochemistry. The article also discusses alternative materials and system architectures, especially in the context of syngas fuels. A detailed computational model for a particular tubular, anode-supported, cell is used to compare SOFC performance using different syngas compositions. The syngas mixtures are derived from several processes, including partial oxidation (CPOx) or steam reforming of methane and dodecane, and gasification of coal or biomass.

A model-based interpretation of measured equilibrium conductivity and conductivity relaxation is developed to establish thermodynamic, transport, and kinetics parameters for multiple charged defect conducting (MCDC) ceramic materials. The present study focuses on 10% yttrium-doped barium zirconate (BZY10). In principle, using the Nernst–Einstein relationship, equilibrium conductivity measurements are sufficient to establish thermodynamic and transport properties. However, in practice it is difficult to establish unique sets of properties using equilibrium conductivity alone. Combining equilibrium and conductivity-relaxation measurements serves to significantly improve the quantitative fidelity of the derived material properties. The models are developed using a Nernst–Planck–Poisson (NPP) formulation, which enables the quantitative representation of conductivity relaxations caused by very large changes in oxygen partial pressure.