Atomically Defined Undercoordinated Active Sites for Highly Efficient CO2 Electroreduction

Electrocatalytic reduction of carbon dioxide (CO2ER) in rechargeable Zn-CO2 battery still remains a great challenge. Herein, a highly efficient CO2ER electrocatalyst composed of coordinatively unsaturated single-atom copper coordinated with nitrogen sites anchored into graphene matrix (Cu-N-2/GN) is reported. Benefitting from the unsaturated coordination environment and atomic dispersion, the ultrathin Cu-N-2/GN nanosheets exhibit a high CO2ER activity and selectivity for CO production with an onset potential of -0.33 V and the maximum Faradaic efficiency of 81% at a low potential of -0.50 V, superior to the previously reported atomically dispersed Cu-N anchored on carbon materials. Experimental results manifest the highly exposed and atomically dispersed Cu-N-2 active sites in graphene framework where the Cu species are coordinated by two N atoms. Theoretical calculations demonstrate that the optimized reaction free energy for Cu-N-2 sites to capture CO2 promote the adsorption of CO2 molecules on Cu-N-2 sites; meanwhile, the short bond lengths of Cu-N-2 sites accelerate the electron transfer from Cu-N-2 sites to *CO2, thus efficiently boosting the *COOH generation and CO2ER performance. A designed rechargeable Zn-CO2 battery with Cu-N-2/GN nanosheets deliver a peak power density of 0.6 mW cm(-2), and the charge process of battery can be driven by natural solar energy.