Oxygen reduction reaction mechanism on a phosporus-doped pyrolyzed graphitic Fe/N/C catalyst

Abstract

The oxygen reduction reaction (ORR) mechanism on the active sites of a phosphorus-doped pyrolyzed Fe/N/C catalyst is examined by using density functional theory based calculations. The introduction of the phosphorus dopant creates three initial possible active sites for the ORR i.e., FeN₄, C–N and P-doped sites. In the presence of O₂, the P-doped sites become passivated while the rest of the catalyst sites are still functional. The ORR profile for the associative mechanism (the O₂ molecule is reduced from its molecular form) on the FeN₄ site is practically unaffected by the presence of the neighboring PO site. However, the ORR profile for the dissociative mechanism (the O₂ molecule is reduced from its dissociated form) on the FeN₄ site is significantly improved as compared to that on the undoped Fe/N/C catalyst system. This phenomenon is mainly induced by the distortion of C–C networks due to the presence of the neighboring FeN₄ and PO sites, which leads to the stabilization of the *OH adsorption state on the C atoms next to the FeN₄ site.