Jointly Engineering Surface Area and Oxygen Vacancies on ZnO for Efficient Electrochemical CO₂ Reduction to CO

Zinc oxide (ZnO) is an outstanding functional material with high selectivity and features low cost and nontoxicity for the electroreduction of CO₂ to CO. To ensure the industrialization of the prepared materials, besides catalytic performance, the synthetic method is also crucial. In this work, porous ZnO nanosheets (ZnO NSs) with moderate concentrations of oxygen vacancies were successfully synthesized through a facile method by annealing treatment under an inert atmosphere. The effects of different temperatures on the morphology and catalytic properties of the porous ZnO NSs were systematically studied. The catalyst, ZnO NS-500, exhibits outstanding selectivity and catalytic activity for CO in the electrocatalytic CO₂ reduction reaction, achieving a Faradaic efficiency as high as 86% at -1.3 V vs RHE. Furthermore, when ZnO NS-500 was constructed as the cathode of a Zn-CO₂ battery (ZCB) with a Zn plate as the anode, the battery reached a power density as high as 1.58 mW cm^-2 at 1.8 mA cm^-2 during discharge, showing its outstanding capability for power supply. Besides its large Brunauer-Emmett-Teller (BET) surface area, the excellent catalytic performance of ZnO NS-500 is mainly attributed to the adsorption and activation of CO₂ molecules at oxygen vacancy sites. This work offers an experimental strategy for the synthesis of high-performance undoped ZnO-based electrocatalysts.