Theoretical Investigation on the Reaction Pathways of the Oxygen Reduction Reaction on Graphene Codoped with Manganese and Phosphorus as a Potential Nonprecious Metal Catalyst

The non-precious metal doped graphene catalysts are recently proposed as promising candidates in substituting Pt catalyst for oxygen reduction reaction (ORR) in the fuel cells. By codoping of Mn and P in the divacancy graphene (MnPx, x = 1-4), we studied the stability and the catalytic activity for the ORR. The calculated formation energy indicates that MnP2 doped divacancy graphene is energetically the most stable. The MnP2 moiety and its adjacent six carbon atoms are the catalytic active sites for the ORR. The kinetically most favorable pathway is the hydrogenation of OOH to form O+H2O, which is a four-electron pathway. The rate determining step is the second H2O formation with an energy barrier of 0.91 eV. The free energy diagrams show that for OOH hydrogenation into O+H2O, all of the elementary steps are downhill except for the second H2O formation at potentials 0.0 ~ 0.67 V.