Interfacial Engineering of NiO/NiCo2O4 Porous Nanofibers as Efficient Bifunctional Catalysts for Rechargeable Zinc-Air Batteries.

To meet the crucial demand of regenerative Zn-air (ZA) batteries, low cost, highly efficient, and durable electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are needed to replace the noble metal. Herein, porous NiO/NiCo2O4 nanofibers with superior electrocatalytic performance are synthesized by a facile electrospinning strategy with precursor transition metal salts in nonstoichiometric ratio, which confers the heterostructured NiO/NiCo2O4 with abundant interface-related active sites and electronic transmission channels. Density functional calculation results reveal the chemical bonds easily form between NiO and NiCo2O4 to facilitate the charge transfer, while X-ray absorption fine spectroscopy and X-ray photoelectron spectroscopy results demonstrate there are abundant Ni3+ and Co3+ species in NiO/NiCo2O4 due to the interfacial engineering. As a result, the NiO/NiCo2O4 porous nanofibers exhibit highly efficient and durable performances of OER and ORR in KOH solution, including a lower overpotential of 357 mV at 10 mA cm-2 (OER) and half-wave potential of 0.73 V (ORR) than that of the individual. What's more, the NiO/NiCo2O4-based ZA battery displays excellent specific capacities of 814.4 mA h g-1, and good cycling stability of 175 h. Additionally, the flexible ZA battery displays a long cycling life of 14 h and decent flexibility. This work shows that construction of the heterostructure could provide a feasible method to optimize their electrocatalytic performance and make them widely used in power source devices.