Structure regulated CuSn alloy catalyst for selective electrochemical CO₂-to-formate conversion at higher current densities

CuSn alloy electrocatalysts have shown a promising CO₂ electroreduction performance towards formate production. However, it is still a big challenge for the electrode to achieve superior selectivity towards formate at a current density over hundreds of mA cm⁻². Herein, a CuSn alloy catalyst with predominant electrochemical CO₂-to-formate conversion was designed. With a unique dendritic-like structure, CuSn₄ (prepared at current density of 4 A cm⁻²) exhibited a maximum faradaic efficiency (FE_formate) of 82.1 %, and the FE_formate could be maintained over 80 % with the partial current density close to −200 mA cm⁻². Mechanism analysis unveiled that the dendritic structure of CuSn₄ induced higher CO₂ concentration around the reaction sites. Meanwhile, the higher electric density due to the unique structure and the generated Sn (II) species lowered the binding energy of CO₂^[rad]− intermediate. Such a structure and Sn (II)-enriched interfaces could be stably maintained and sustainably generated as a result of “natural oxidation-CO₂ reduction”. This study presents a straightforward approach to develop an efficient electrode for CO₂-to-formate conversion at higher current densities.