MOFs-derived hierarchical porous carbon supported Co@NC nanocapsules for pH universal oxygen reduction reaction and Zn-air batteries

The rational design and construction of the hierarchical porous structure of carbon framework to support transition metal-based catalysts is critical to increase their active sites density and facilitate mass/electron transport. Herein, we report a novel nanocapsules with cobalt core and nitrogen-doped carbon shells (Co@NC) supported on MOFs-derived hierarchical porous carbon framework. The rational hierarchical porous carbon framework with controllable size and micropore/mesoporous ratio was achieved by one-step pyrolysis of Zn (acac)2.phen ligand and ZIF-67 precursor, which is beneficial for the mass transport in the oxygen reduction reaction (ORR). The 0.4Co@NC-900 electrocatalyst display a distinguished ORR activity in the pH-universal range, with a half-wave potential of 0.91 V in alkaline and 0.76 V in acid electrolytes. The excellent ORR per-formance of our electrocatalyst can be attributed to its optimized micropore/mesoporous ratio of carbon framework with efficient mass transport, together with the graphitized carbon shell on Co nanoparticles which not only enhances the electron/proton transport, but also suppresses the chemical corrosion of the Co nano-particles. Impressively, the Zinc-air battery as air electrode offers peak power density of 203 mW cm(-2) and long-term stability of 130 h, showing an excellent battery performance. This study offers a fresh method of con-structing ORR catalysts with increased activity and durability over a universal pH range.