In Situ Growth of Metal-Organic Layer on Polyoxometalate-etching Cu₂O to Boost CO₂ Reduction with High Stability

Low-cost Cu₂O with a suitable band gap holds great potential for solar utilization. However severe photocorrosion and weak CO₂ capture capability have significantly hindered their application in artificial photosynthesis. Herein, polyoxometalate (POM)-etching and in situ growth of metal-organic framework (MOF) can simultaneously incorporate electron-sponge and HKUST protective layer into Cu₂O. The resulting ternary composites Cu₂O@POM@HKUST-n (POM=PMo₁₂O₄₀ and PW₁₂O₄₀) with dual hetero-interfaces can efficiently convert CO₂ to HCOOH with 5226 μmol g^-1 yield, over 5 and 55 times higher than that of Cu₂O (1010 μmol g^-1) and Cu₂O@HKUST (95.02 μmol g^-1). In situ XPS and DFT studies reveal that Cu mainly existed in the form of Cu₂O and Cu-MOF, while a unique Cu^x+ (12O matrix surrounding POMs for CO₂ absorption and activation. Systematic investigations demonstrate that the electron-sponge can efficiently capture electrons from excited Cu₂O to promote the generation of a Cu^x+ surface layer, while the closely surface-coating metal-organic layer can act as protective layer and CO₂ adsorbent. This dual function concurrently contributes to promote photocatalysis and prevent Cu₂O degradation. Remarkably, the composites exhibit much enhanced photochemical stability and can be used for over 60 h without noticeable activity loss.