Elucidation of oxygen reduction reaction and nanostructure of platinum-loaded graphene mesosponge for polymer electrolyte fuel cell electrocatalyst

Abstract A graphene mesosponge (GMS), which has a sponge-like mesoporous framework, was applied to a catalyst support for polymer electrolyte fuel cell. Platinum loaded GMS (Pt/GMS) was prepared as electrocatalyst for oxygen reduction reaction (ORR) measurement and compared with platinum loaded Ketjen black (Pt/KB). ORR activity was evaluated by rotating ring disk electrode (RRDE) method to analyze hydrogen peroxide (H2O2) evolution behavior as an indicator of ionomer coverage on Pt. It was found that the ORR area specific activity of Pt/GMS was 1.2 times higher than that of Pt/KB with less H2O2 yield, mainly attributed to the lower ionomer coverage at Pt/GMS. It was also observed by transmission electron microtomography (3D-TEM) that Pt/GMS has a lot of pores between the sponge-like mesoporous framework with Pt nanoparticles therein. On the other hand, Pt/KB showed smoother agglomerate shapes with Pt nanoparticles inside the KB agglomerates mainly. Considering the frame-like mesoporous carbon network having hydrophobic basal nanosurface of the graphene of GMS and the aqueous electrolyte in this system, it is concluded that the ionomer can form self-aggregation with its hydrophobic domain inside, resulting in ineffective coverage of the ionomer on the nanostructure of GMS and the Pt nanoparticles in the GMS agglomerates.