Effect of fine structure and pore volume in the Marimo-like carbon cathode material on the oxygen reduction reaction for the polymer electrolyte fuel cell

We measured the rotating ring-disk electrode (RRDE) voltammetry curves of a Pt catalyst supported on Marimo-like carbon (MC) to clarify the effect of carbon nanofilaments (CNFs) morphology and fine structures consisting of MC cathode material on the oxygen reduction reaction (ORR) activity for Polymer electrolyte fuel cells. The specific surface area and pore volume of MCs are influenced by their morphology and fine structures. MCs grown with Ni–Cu bimetal catalyst (represented as Ni80Cu20MC), having an octopus-like morphology, yielded four times larger total pore volume than that measured from the MC grown with Ni catalyst (Ni100MC). In the case of Ni80Cu20MC, coin-stacked graphenes perpendicular to the filament axis formed CNFs. Ni100MC consists of cup-stacked CNFs. The difference in the graphene stacked fine structure resulted in a different number of graphene edges covering the CNF surface; however, both supported Pt particle sizes and their distributions were similar. Linear sweep voltammetry with a RRDE revealed that the Pt/Ni80Cu20MC ORR onset potential was higher than that observed from the Pt/Ni100MC. This value is suggested to be correlates with the ORR activity. The origin of the ORR difference was discussed on the basis of the structural difference in the MCs.