Gas transport in porous electrodes of solid oxide fuel cells: A review on diffusion and diffusivity measurement

A reduction in Ohmic, activation and concentration-polarization losses is of paramount importance in improving the efficiency of solid oxide fuel cells, proton-exchange-membrane fuel cells, and molten-carbonate fuel cells. Efficient measurements of gas diffusivities at the operating conditions of fuel cells allow concentration polarization losses of these fuel cells to be reliably evaluated. To enhance the applicability of solid oxide fuel cells, tremendous work on the development of gas diffusion models and gas diffusivity measurement techniques have been done to pre-evaluate the concentration polarization losses of fuel cells. This review focuses on the recent advancement of gas diffusion models and diffusivity measurement techniques of solid oxide fuel cells. The review seeks to provide an insightful guidance for designing high-performance solid oxide fuel cell electrodes with efficient thickness, porosity, among other parameters.

Graphical abstractA review on the mathematical models for gas transport in micro/nano-porous electrodes of solid oxide fuels is presented. Based on the Knudsen number and complexity of fuel gas systems, the different gas diffusion models show different advantages/disadvantages. The review then focuses on the different techniques of gas diffusivity measurements in solid oxide fuel cells. Such direct gas diffusivity measurement techniques largely facilitate the efficient pre-evaluation of energy loss in solid oxide fuel cells. Such pre-evaluation improves our understanding on the parameters associated with the electrode microstructure of solid oxide fuel cells, such as porosity, thickness, and tortuosity.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Reviews models for gas transport in electrodes of solid oxide fuel cells (SOFCs). ► Discusses recently-developed devices for direct diffusivity measurement in SOFCs. ► Shows that diffusivity measurement facilitates the research on SOFC electrodes.