Synergetic effects of edge formation and sulfur doping on the catalytic activity of a graphene-based catalyst for the oxygen reduction reaction

Abstract

An edge activated S doped Fe-N-graphene (EA-SFeNG) was successfully synthesized via facile ball milling followed by a pyrolysis process. The oxygen reduction reaction (ORR) performance of EA-SFeNG was dramatically improved by doping S and forming edge sites in Fe-N-graphene; the onset potential was shifted from 0.91 V_RHE to 1.0 V_RHE with the half-wave potential increased from 0.77 V_RHE to 0.848 V_RHE. The EA-SFeNG exhibited catalytic performances that are comparable to those of commercial 20 wt% Pt/C (V_onset: 1.05 V, V_1/2: 0.865 V); however, its durability was better than that of the Pt catalyst in alkaline media. The excellent ORR activity can be attributed to the increase in defect density and SO_x bonding in the EA-SFeNG. Furthermore, we experimentally demonstrate that the work function of the Fe-N-graphene is significantly reduced from 4.06 eV to 4.01 eV by the increase in edge density and doping S, thereby improving the ORR kinetics of EA-SFeNG.