NiCo₂ O₄ -Based Nanosheets with Uniform 4 nm Mesopores for Excellent Zn-Air Battery Performance

Herein, a strategy is reported for the fabrication of NiCo₂ O₄ -based mesoporous nanosheets (PNSs) with tunable cobalt valence states and oxygen vacancies. The optimized NiCo_2.148 O₄ 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_2.148 O₄ 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_2.148 O₄ 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.