Nonprecious Bimetallic Sites Coordinated on N-Doped Carbons with Efficient and Durable Catalytic Activity for Oxygen Reduction.

Developing efficient, inexpensive, and durable electrocatalysts for the oxygen reduction reaction (ORR) is important for the large-scale commercialization of fuel cells and metal-air batteries. Herein, a hierarchically porous bimetallic Fe/Co single-atom-coordinated N-doped carbon (Fe/Co-Nx -C) electrocatalyst for ORR is synthesized from Fe/Co-coordinated polyporphyrin using silica template-assisted and silica-protection synthetic strategies. In the synthesis, first silica nanoparticles-embedded, silica-protected Fe/Co-polyporphyrin is prepared. It is then pyrolyzed and treated with acidic solution. The resulting Fe/Co-Nx -C material has a large specific surface area, large electrochemically active surface area, good conductivity, and catalytically active Fe/Co-Nx sites. The material exhibits a very good electrocatalytic activity for the ORR in alkaline media, with a half-wave potential of 0.86 V versus reversible hydrogen electrode, which is better than that of Pt/C (20 wt%). Furthermore, it shows an outstanding operational stability and durability during the reaction. A zinc-air battery (ZAB) assembled using Fe/Co-Nx -C as an air-cathode electrocatalyst gives a high peak power density (152.0 mW cm-2 ) and shows a good recovery property. Furthermore, the performance of the battery is better than a corresponding ZAB containing Pt/C as an electrocatalyst. The work also demonstrates a synthetic route to a highly active, stable, and scalable single-atom electrocatalyst for ORR in ZABs.