Fe3C cluster-promoted single-atom Fe, N doped carbon for oxygen-reduction reaction

A key challenge to carry out efficient oxygen reduction reaction (ORR) is the design of highly efficient electrocatalyst that must have fast kinetics, low cost and high stability used in an energy-conversion device (e.g. metal-air batteries). Herein, we developed a platinum-free ORR electrocatalyst with high surface area and pore volume via a molten salt method along with subsequent KOH activation. The activation treatment not only increases the surface area to 940.8 m2 g-1 by generating lots of pores, but also promotes the formation of uniform Fe3C nanoclusters within the atomic dispersed Fe-NX carbon matrix in the final material (A-FeNC). The A-FeNC displays excellent activity and long-term stability for ORR in alkaline media, which show a greater half-wave potential (0.85 V) and faster kinetics toward ORR as compared to those for 20 wt% Pt/C (0.83 V). It also improves a highly efficient four-electron reaction mechanism for A-FeNC, avoiding the formation of peroxides poisoning the devices. As a cathode catalyst for Zn-air battery, A-FeNC presents a peak power density of 102.2 mW cm-2, higher than that of Pt/C constructed Zn-air battery (57.2 mW cm-2). The superior ORR catalytic performance of A-FeNC is ascribed to increased exposure of active sites, active single-atom Fe-N-C centers, and enhancement by Fe3C nanoclusters.