Relay Catalysis of Multi-Sites Promotes Oxygen Reduction Reaction

The two-electron pathway to form hydrogen peroxide (H2O2) is undesirable for the oxygen reduction reaction (ORR) in iron and nitrogen doped carbon (Fe-N-C) material as it not only lowers the catalytic efficiency but also impairs the catalyst durability. In this study, a relay catalysis pathway is designed to minimize the two-electron selectivity of Fe-N-C catalyst. Such a design is achieved by introducing two other sites, that is, MnN4 site and a-Fe(110) face. A combination of transmission electron microscopy image and X-ray absorption spectra verify the three site formation. Electrochemical test coupled with post-treatment confirm the improvement of MnN4 site and a-Fe(110) face on catalyst performance. Theoretical calculation proposes a relay catalysis pathway of three sites, that is, H2O2 released from the FeN4 site migrates to the MnN4 site or a-Fe(110) face, on which the captive H2O2 is further reduced to H2O. The relay catalysis pathway positioned the as-prepared catalyst among the best ORR catalysts in both aqueous electrode and alkaline direct methanol fuel cell test. This study examples an interesting relay catalysis pathway of multi-sites for the ORR, which offers insights into the design of efficient electrocatalysts for fuel cells or beyond.