Carbonate shell regulates CuO surface reconstruction for enhanced CO₂ electroreduction

The surface structure of catalysts greatly impacts the performance of the electrochemical CO₂ reduction reaction. However, the reconstruction caused by applied potential can affect the surface structure and is difficult to control. Here, inspired by drug capsules with extended-release structures, we construct a water-soluble carbonate shell on metal oxide catalysts. The shell acts as a protective coating, effectively slowing down the surface evolution process of the catalyst from high to low valence state under the applied electric field. Therefore, by tuning the shell thickness and dissolution rates, the surface reconstruction can be regulated, steering it towards the formation of an abundant low-coordinated structure. This strategy could promote the generation of Cu(0) with rich grain boundaries and small particles. The C₂₊ Faradaic efficiency was 82.8 ± 2.2% with a current density of 2.0 A cm⁻², exceeding the performance of conventional CuO catalysts. Ex situ and in situ characterizations indicate that these generated surface structures enhance *CO intermediate stabilization and C–C coupling. Our approach for regulating surface reconstruction can be applied to other catalysts, such as ZnO, In₂O₃, SnO₂ and Bi₂O₃, elevating their selectivity towards CO and formate.