Triple-Phase Interface Engineered Hierarchical Porous Electrode for CO₂ Electroreduction to Formate

The aqueous electrochemical CO₂ reduction to valuable products is seen as one of the most promising candidates to achieve carbon neutrality yet still suffers from poor selectivity and lower current density. Highly efficient CO₂ reduction significantly relies on well-constructed electrode to realize efficient and stable triple-phase contact of CO₂ , electrolyte, and active sites. Herein, a triple-phase interface engineering approach featuring the combination of hierarchical porous morphology design and surface modification is presented. A hierarchical porous electrode is constructed by depositing bismuth nanosheet array on copper foam followed by trimethoxy (1H,1H,2H,2H-heptadecafluorodecyl) silane modification on the nanosheet surface. This electrode not only achieves highly selective and efficient CO₂ reduction performance with formate selectivity above 90% over wide potentials and a partial current density over -90 mA cm^-2 in H-cell but also maintains a superior stability during the long-term operation. It is demonstrated that this remarkable performance is attributed to the construction of efficient and stable triple-phase interface. Theoretical calculations also show that the modified surface optimizes the activation path by lowering thermodynamic barriers of the key intermediates *OCHO for the formation of formate during electrochemical CO₂ reduction.