Four-Dimensional Identical-Location X-ray Imaging of Fuel Cell Degradation during Start-Up/Shut-Down Cycling

Abstract

In this work, local electrode degradation effects from start-up/shut-down cycling of polymer electrolyte fuel cells are visualized using X-ray tomographic imaging of specialized, miniature fuel cell hardware. This combination enables non-invasive in situ tracking of the same cathode catalyst layer domain throughout various degradation stages in four dimensions. Critical, localized regions are identified within the cathode catalyst layer where progressive structural deterioration occurs from carbon support corrosion leading to thinning and collapse of the material. A greater structural change is observed under the landing area than under the channels due to delayed resident gas purge. This finding differs from the results of voltage cycling accelerated stress test, where more structural change was observed under the channel area than the landing area. However, overall similarities in degradation and performance loss supports the use of voltage cycling for accelerated degradation studies. A direct correlation between the structural deterioration and the electrochemical performance reduction of the fuel cell is found. In addition, reduced reactant gas flow in a restricted anode flow channel enhances the local cathode degradation due to delayed gas purge. However, no influence on the degradation is observed in a cell with intentional anode/cathode channel misalignment, compared to generic test cells.