Genuine four-electron oxygen reduction over precious-metal-free catalyst in alkaline media

Understanding the kinetics of oxygen reduction reactions (ORRs) over non-precious-metal (NPM) catalysts in alkaline media is quite important for commercializing anion exchange membrane fuel cells. Rotating ring-disk electrode (RRDE) voltammetry has been useful for studying the selectivity of ORR, but typical analytical models might overestimate the four-electron pathway. The present study investigated ORR in alkaline media over Fe/N/C and N/C catalysts, which were prepared by pyrolyzing polyimide nano-particles. The obtained data were analyzed using the novel RRDE theory, which involves the Nabae model to distinguish a genuine four-electron reduction from a quasi-four-electron reduction (two plus two-electron reduction). The results demonstrated that the reduction with the Fe/N/C catalyst proceeded via an inherent four-electron pathway while that with the N/C catalyst prepared by a similar method proceeded majorly via a two-electron pathway.