Highly selective electrochemical CO2 reduction to CO using a redox-active couple on low-crystallinity mesoporous ZnGa2O4 catalyst

The substantial overpotential of CO2 activation, the complex CO2 reduction pathway, and the competitive H2 evolution reaction (HER) limit the practical applications of CO2-based electrochemical energy conversion and storage technologies due to their low energy efficiency and product selectivity. Here, we proposed a strategy that combines mesopores and redox-active couple to effectively capture CO2 and selectively generate CO product. As an example, we construct a redox-active couple, Zn2+/Zn+, on the low-crystallinity mesoporous ZnGa2O4 electrocatalyst. The mesopores not only help to capture CO2 effectively but also inhibit the H2 evolution. The weak lattice constraint of low crystallinity benefits the formation of a Zn2+/Zn+ redox couple to strongly interact with CO2 molecule for subsequent activation and catalytic conversion, thus effectively decreasing the activation energy of CO2 to the active species CO2− and accelerating the proton transfer to form the crucial COOH* intermediate. Consequently, this catalyst exhibited a high faradaic efficiency of 96% among Zn-based electrodes for CO generation at the relatively low applied potential of −1.4 V vs. Ag/AgCl (−0.8 V vs. RHE), and excellent stability during 10 h operation in a 0.1 M KHCO3 solution.