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Herein, we highlight redox-inert Zn2+ in spinel-type oxide (ZnX Ni1-X Co2 O4 ) to synergistically optimize physical pore structure and increase the formation of active species on the catalyst surface. The presence of Zn2+ segregation has been identified experimentally and theoretically under oxygen-evolving condition, the newly formed VZn -O-Co allows more suitable binding interaction between the active center Co and the oxygenated species, resulting in superior ORR performance. Moreover, a liquid flow Zn-air battery is constituted employing the structurally optimized Zn0.4 Ni0.6 Co2 O4 nanoparticles supported on N-doped carbon nanotube (ZNCO/NCNTs) as an efficient air cathode, which presents remarkable power density (109.1 mW cm-2 ), high open circuit potential (1.48 V vs. Zn), excellent durability, and high-rate performance. This finding could elucidate the experimentally observed enhancement in the ORR activity of ZnX Ni1-X Co2 O4 oxides after the OER test.
Wang et al. (Mon,) studied this question.