Hierarchical mesoporous N-doped carbon as an efficient ORR/OER bifunctional electrocatalyst for rechargeable zinc-air battery

The construction of efficient oxygen reduction and oxygen evolution reaction (ORR/OER) bifunctional electrocatalysts is crucial for rechargeable zinc-air batteries. Hierarchical mesoporous N-doped carbon (HMNC) structures with superior catalytic activities are illustrious candidates for the ORR/OER to substitute precious metal (Pt)-based catalysts. In this study, an optimal HMNC (abbr. NDC-800) with uniform rich-defect active sites was prepared by selection of an eligible Fe complex precursor. The NDC-800 catalyst had excellent ORR activity with a high half wave potential (E1/2) of 0.88 V, and an amazing ORR/OER bifunctional performance involving a low potential gap (Delta E) of 0.76 V, which surpasses that of the benchmark Pt/C catalyst. As a rechargeable zinc-air battery catalyst, it has a large power density of 186.12 mW cm-2, a high specific capacity up to 630 mA h gZn-1, and an excellent cycling stability of 60 h (120 cycles) at 10 mA cm-2. Density functional theory (DFT) calculations indicate that the effective ORR/OER bifunctional activities can be attributed to its hierarchical mesoporous structure, which can afford sufficient exposed active sites and rich defects to synergistically promote the formation of OH- intermediates, and reduce the free energy (Delta G). Hierarchical mesoporous NDC-800 catalyst with rich N-C sites and defects exhibits ORR/OER bifunction activity and zinc-air battery properties over 20% Pt/C. DFT shows that N doping and defects have synergy, significantly improves performance.