Zinc-iron bimetallic-nitrogen doped porous carbon microspheres as efficient oxygen reduction electrocatalyst for zinc-air batteries

Highlights: • Fe-Zn-N doped carbon could be derived from MF@PVA-FeCl₃-ZnCl₂ gel. • ZnCl₂ benefits the formation of spherical morphology and larger surface area. • Zinc doping could produce more bimetallic-nitrogen and pyridone-N sites. • FeZnNC achieves high limiting current density and onset/half-wave potentials. • FeZnNC presents higher electrocatalytic stability than FeNC. Bimetallic-nitrogen doped carbons (bi-MNC) have attracted great attention as oxygen reduction reaction (ORR) catalysts due to their favorable activation of the O-O bond on the dual metal sites. However, zinc based bi-MNC were seldom investigated because the zinc tended to be neglected at elevated temperature owing to its volatile nature. In this work, a zinc-iron–nitrogen doped porous carbon (FeZnNC) was facilely prepared by pyrolysis of PVA-FeCl₃-ZnCl₂ gel coated commercial melamine foam. It is found that the zinc not only acted as porogen and dopant but also as structural regulator, leading to spherical morphology with more porous defects, larger surface area and more pyridone-N sites. The electrochemical measurements showed that the FeZnNC not only could achieve higher limiting current density of 5.97 mA/cm², positive onset potential (0.965 V) and half-wave potential (0.873 V), but also display superior electrocatalytic stability than monometallic-nitrogen doped carbons (mono-MNC). Furthermore, the FeZnNC + RuO₂ powered rechargeable zinc-air battery could also present longer cycling life than that powered by mono-MNC.