Cu-Co bimetallic nanocluster Mott-Schottky interaction increasing oxygen reduction reaction activity in rechargeable Zn-air batteries

The rational design of bifunctional oxygen reduction and oxygen evolution electrocatalysts with high performance is crucial in developing rechargeable Zn-air batteries. In this work, a Mott-Schottky Cu_NCs-Co_NCs/NPCF catalyst with a built-in electric field was prepared by anchoring Cu/Co bimetallic ensembles on three-dimensional nitrogen-doped porous carbon nanosheet frameworks. Experiments revealed a tendency of spontaneous electron transfer between the Cu/Co bimetallic clusters and improved reaction kinetics by the built-in electric field. After the rearrangement of electrons, an electrophilic region and a nucleophilic region were formed on the Cu side and Co side, respectively. Consequently, the adsorption/desorption behaviors of O₂, OH⁻, and oxygen-containing intermediates on the catalyst surface were optimized. Meanwhile, the nitrogen-doped carbon nanosheet framework with a hierarchical porous structure and high specific surface area also accelerated the mass transport. As a result, the oxygen reduction electrocatalytic reaction on the optimal Cu_NCs-Co_NCs/NPCF catalyst sample exhibited an onset potential of 0.97 V and a low Tafel slope of 42.70 mV dec⁻¹ under alkaline conditions. An overpotential of 303 mV was observed at a current density of 10 mA cm⁻² in the electrocatalytic oxygen evolution reaction. Besides, the Zn-air battery assembled with the developed Mott-Schottky Cu_NCs-Co_NCs/NPCF bifunctional oxygen electrocatalysts displayed promising potential and long-term durability in practice.