Boosting electrochemical CO2 reduction via valence state and oxygen vacancy controllable Bi–Sn/CeO2 nanorod

Electrocatalytic CO2 reduction reaction (CO2RR) to produce formate has been recognized as one of the most efficient strategies to convert CO2 to energy-rich products and store renewable energy compared with other methods such as biological reduction, thermal catalytic reduction, and photocatalytic reduction. Developing an efficient catalyst is crucial to enhance the formate Faradaic efficiency (FEformate) and retard the competing H2 evolution reaction. The combination of Sn and Bi has been demonstrated to be effective in inhibiting the evolution of H2 and the generation of CO, promoting the formation of formate. Herein, we design Bi- and Sn-anchored CeO2 nanorods catalysts with the valence state and oxygen vacancy (Vo) concentration controllable for CO2RR by reduction treatment at different environments. The m-Bi1Sn2Ox/CeO2 with moderate H2 composition reduction and suitable Sn/Bi molar ratio achieves a remarkable FEformate of 87.7% at -1.18 V vs. RHE compared with other catalysts. Additionally, the selectivity of formate was maintained over 20 h with an outstanding FEformate of above 80% in 0.5 M KHCO3 electrolyte. The outstanding CO2RR performance was attributed to the highest surface Sn2+ concentration which improves the formate selectivity. Further, the electron delocalization effect between Bi, Sn, and CeO2 tunes electronic structure and Vo concentration, promoting the CO2 adsorption and activation as well as facilitating the formation of key intermediates HCOO* as evidenced by the in-situ Attenuated Total Reflectance-Fourier Transform Infrared measurements and Density Functional Theory calculations. This work provides an interesting measure for the rational design of efficient CO2RR catalysts via valence state and Vo concentration control.