PNNL

Abstract

A common assumption in solid oxide fuel cell models is that the anodic hydrogen-oxygen reaction that produces the electrical current is strictly localized at the triple phase boundary between the metal catalyst particle, the supporting zirconia electrolyte, and the gas atmosphere. This assumption is tested in the present work, and found to lead to the erroneous conclusion that surface diffusion on the catalyst particle is responsible for the anodic concentration polarization that limits the maximum current output of the device. A more detailed analysis that permits oxygen spillover onto the catalyst particle surface indicates that the reactive area simply spreads over the surface as needed to support the current. Hydrogen is readily available for reaction by adsorption over the entire surface. There were no indications in this work that surface diffusion mechanisms can be responsible for anodic concentration polarization.