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

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. , FeN 4 , C-N and P-doped sites. In the presence of O 2 , the P-doped sites become passivated while the rest of the catalyst sites are still functional. The ORR profile for the associative mechanism (the O 2 molecule is reduced from its molecular form) on the FeN 4 site is practically unaffected by the presence of the neighboring P&z.dbd;O site. However, the ORR profile for the dissociative mechanism (the O 2 molecule is reduced from its dissociated form) on the FeN 4 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 FeN 4 and P&z.dbd;O sites, which leads to the stabilization of the *OH adsorption state on the C atoms next to the FeN 4 site. The interaction between neighbouring FeN 4 and P subs sites of a P-doped pyrolyzed Fe/N/C catalyst promotes four-electron reduction through associative and dissociative mechanisms.