Chemically coupling SnO 2 quantum dots and MXene for efficient CO 2 electroreduction to formate and Zn-CO 2 battery.

Electrochemical conversion of CO 2 into formate is a promising strategy for mitigating the energy and environmental crisis, but simultaneously achieving high selectivity and activity of electrocatalysts remains challenging. Here, we report low-dimensional SnO 2 quantum dots chemically coupled with ultrathin Ti 3 C 2 T x MXene nanosheets (SnO 2 /MXene) that boost the CO 2 conversion. The coupling structure is well visualized and verified by high-resolution electron tomography together with nanoscale scanning transmission X-ray microscopy and ptychography imaging. The catalyst achieves a large partial current density of -57.8 mA cm -2 and high Faradaic efficiency of 94% for formate formation. Additionally, the SnO 2 /MXene cathode shows excellent Zn-CO 2 battery performance, with a maximum power density of 4.28 mW cm -2 , an open-circuit voltage of 0.83 V, and superior rechargeability of 60 h. In situ X-ray absorption spectroscopy analysis and first-principles calculations reveal that this remarkable performance is attributed to the unique and stable structure of the SnO 2 /MXene, which can significantly reduce the reaction energy of CO 2 hydrogenation to formate by increasing the surface coverage of adsorbed hydrogen.