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.