Lawrence Berkeley National Laboratory

Proton-exchange membrane fuel cells (PEMFCs) are promising energy-conversion systems, offering an appealing blend of high energy efficiency and low environmental impact. However, carbon corrosion of PEMFCs is known to significantly degrade their performance, remaining a critical challenge to overcome. In this study, we applied a Nb-doped SnO2 (Nb-SnO2) nanoparticle coating on Pt/C catalysts as a protective layer, with the Sn/C ratio in the precursors varying from 0.25:1 to 2.0:1. Contradictory behaviors of the coated Pt/C catalysts were observed at different Sn/C ratios. The Sn/C = 1.0 sample exhibited improved electrochemically active surface area retention after 500 cycles of accelerated stress testing (AST) but with more significant polarization and resistance increase observed in the polarization curves. In addition, agglomeration of Nb-SnO2 particles was observed at a higher Sn/C ratio in the AST of a membrane electrode assembly, with less shrinkage of the total thickness of the Nb-SnO2-coated Pt/C electrode. We speculate that formation of Nb-SnO2 agglomerates occurs once the protective layer is broken down or the unprotected carbon surface is corroded and that these Nb-SnO2 agglomerates increase the tortuosity of the electron pathways and significantly increase the cell polarization.