Efficient electroreduction of carbon dioxide to formate enabled by bismuth nanosheets enriched dual V_Bi⁰ vacancy

The electrocatalytic reduction of carbon dioxide (CO₂ER) into formate presents a compelling solution for mitigating dependence on fossil energy and green utilization of CO₂. Bismuth (Bi) has been gaining recognition as a promising catalyst material for the CO₂ER to formate. The performance of Bi catalysts (named as Bi-V) can be significantly improved when they possess single metal atom vacancy. However, creating larger-sized metal atom vacancies within Bi catalysts remains a significant challenge. In this work, Bi nanosheets with dual V_Bi⁰ vacancy (Bi-DV) were synthesized utilizing in situ electrochemical transformation, using BiOBr nanosheets with triple vacancy associates (V_Bi^″'V_O^··V_Bi^″', V_Bi^″' and V_O^·· denote the Bi³⁺ and O^2- vacancy, respectively) as a template. The obtained Bi-DV achieved higher CO₂ER activity than Bi-V, showing Faradaic efficiency for formate production of >92% from -0.9 to -1.2 V_RHE in an H-type cell, and the partial current density of formate reached up to 755 mA/cm² in a flow cell. The comprehensive characterizations coupled with density functional theory calculations demonstrate that the dual V_Bi⁰ vacancy on the surface of Bi-DV expedite the reaction kinetics toward CO₂ER, by reducing the thermodynamic barrier of *OCHO intermediate formation. This research provides critical insights into the potential of large atom vacancies to enhance electrocatalysis performance.