Indiscrete metal/metal-N-C synergic active sites for efficient and durable oxygen electrocatalysis toward advanced Zn-air batteries

Carbon has been deemed promising electrocatalyst for oxygen reduction/evolution reaction (ORR/OER). However, most carbon materials are not stable in highly oxidative OER environments. Herein, nitrogen (N) and transition metal (TM) co-doped carbon nanosheets hybridizing with transition metal (TM/TM-N-C, TM= Fe, Co, Ni) are developed from biomass lysine by employing a NaCl template and molten-salt-promoted graphitization process. Among the as-synthesized TM/TM-N-C, the Ni/Ni-N-C with Ni nanocubes embedded in carbon demonstrates an excellent ORR-OER stability during the potential of 0.06-1.96 V. The rechargeable Zn-air battery with the fabricated Ni/Ni-N-C as the cathode catalyst produces a low voltage gap of 0.773 V, which is only slightly increased by 5 % after 150 cycles testing. Combined experimental and theoretical studies reveal that the exceptional activity and ORR-OER wide potential durability of Ni/Ni-N-C can be ascribed to highly active Ni-N-4-C configuration, synergistic effect between Ni and Ni-N-4-C, carbon nanosheets structure and formation of stable Ni3+-N for protecting carbon from oxidation.