Synthesis and Evaluation of High Durable Electrocatalysts Using Oxide Supports for Polymer Electrolyte Fuel Cells

Abstract

The practical application of polymer electrolyte fuel cells (PEFCs) to the electric vehicles (FCVs) can lead to the reduction of carbon dioxide emissions and environmental friendly. Platinum-based catalyst supported on carbon is one of the important cathode catalysts for PEFCs, but the degradation of the carbon support at the high potential region should be resolved to improve the performance of PEFCs. We invented the high durable SnO₂ nanoparticles with “fused aggregate network structure” as new candidate supports to replace the carbon one. The fused aggregate network structure has some abilities to construct the electrical conducting pathways and gas diffusion pathways in the catalyst layers. The Pt supported on SnO₂ (Pt/SnO₂) showed higher oxygen reduction reaction (ORR) activity than that of commercialized Pt supported on carbon black (c-Pt/CB), especially, the Pt₇₅Co₂₅ catalysts supported on the SnO₂ showed 3 times higher ORR activity compared to c-Pt/CB. The current-voltage performance and resistivity of the cell using Pt/SnO₂ catalyst layer (I/S = 0.24) were equal to those using Pt/GCB catalyst layer (I/S = 0.67, optimized I/S ratio). The durability of Pt/SnO₂ under the load cycle and startup/shut down cycles was also confirmed to be superior to that of Pt/GCB by use of membrane electrode assembly (80oC, 80%RH). The evaluation by a low acceleration transmission electron microscopy proved that the Nafion® ionomer covered uniformly on the hydrophilic surface of the SnO₂support, though the ionomer did not on the hydrophobic surface of the Pt/GCB. The thin and uniform coverage of the Nafion® ionomer on Pt/SnO₂surface would decrease the ionomer content, mitigate the overpotential originated from the oxygen diffusion resistance in the Nafion® ionomer, and improve the cell performance.