Sulfate-Decorated Nitrogen Doped CoO Porous Ultrathin Nanosheets as High-Efficiency Bifunctional Oxygen Electrocatalysts for Rechargeable Zn-Air Batteries.

Spinel oxides have emerged as promising electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) owing to their flexible structure and intrinsic catalytic activity. However, developing high-performance bifunctional spinel oxide electrocatalysts and elucidating the underlying mechanisms for enhanced activity remain significant challenges. Herein, a highly efficient electrocatalyst, N-CoO-SO, featuring N doping and in situ surface sulfate (SO ) modification on a spinel oxide structure is developed. The synthesized N-CoO-SO exhibits an ultrathin nanosheet morphology with abundant micropores and mesopores, offering ample active sites and efficient mass transport. Theoretical simulations reveal that SO can form a moderate hydrogen bond interaction between sulfate and oxygen-containing intermediates, thereby combing with N doping for synergistically enhancing the electronic conductivity and reducing the energy barriers for protonation/deprotonation of intermediates. As a result, N-CoO-SO demonstrates a remarkably low potential difference (ΔE  =  0.66 V) between the OER potential at 10 mA cm⁻ and the ORR half-wave potential, outperforming the benchmark RuO + Pt/C (0.71 V). Furthermore, rechargeable liquid and flexible solid-state Zn-air batteries employing N-CoO-SO as the air electrode catalyst achieve higher peak power density and superior stability compared to RuO + Pt/C catalyst.