Oxygen Reduction Reaction Mechanisms on Al-Doped X-Graphene (X = N, P, and S) Catalysts in Acidic Medium: A Comparative DFT Study

Abstract

Density functional theory (DFT) is applied to study the oxygen reduction reaction (ORR) mechanisms on Al-doped X-graphene (X = N, P, and S) electrocatalyst in acidic medium in a fuel cell cathode comparatively. In order to study the catalytic properties of Al-doped X-graphene (X = N, P, and S), we calculate the adsorption properties of the ORR intermediates O2, O, OOH, OH, H2O, and H2O2. We also examine 2e and 4e pathways during the ORR process in terms of adsorption energy of each ORR step. Our calculated results reveal that each Al-doped X-graphene (X = N, P, and S) catalyst follows a 4e transfer pathway with favorable (exothermic) reaction energies. We observe that both Al-doped N-graphene and Al-doped P-graphene are energetically more favorable than Al-doped S-graphene catalysts for enhanced and stable ORR via 4e pathways in an acidic environment. Such analysis is quite useful in choosing the appropriate catalyst in applications of a polymer electrolyte fuel cell cathode.