NiCo₂O₄-Based Nanosheets with Uniform 4 nm Mesopores for Excellent Zn–Air Battery Performance

Herein, a strategy is reported for the fabrication of NiCo₂O₄-based mesoporous nanosheets (PNSs) with tunable cobalt valence states and oxygen vacancies. The optimized NiCo_2.148O₄ PNSs with an average Co valence state of 2.3 and uniform 4 nm nanopores present excellent catalytic performance with an ultralow overpotential of 190 mV at a current density of 10 mA cm⁻² and long-term stability (700 h) for the oxygen evolution reaction (OER) in alkaline media. Furthermore, Zn–air batteries built using the NiCo_2.148O₄ PNSs present a high power and energy density of 83 mW cm⁻² and 910 Wh kg⁻¹, respectively. Moreover, a portable battery box with NiCo_2.148O₄ PNSs as the air cathode presents long-term stability for 120 h under low temperatures in the range of 0 to −35 °C. Density functional theory calculations reveal that the prominent electron exchange and transfer activity of the electrocatalyst is attributed to the surface lower-coordinated Co-sites in the porous region presenting a merging 3d–e_g–t_2g band, which overlaps with the Fermi level of the Zn–air battery system. This favors the adsorption of the *OH, and stabilized *O radicals are reached, toward competitively lower overpotential, demonstrating a generalized key for optimally boosting overall OER performance. © 2020 Wiley-VCH GmbH.