Boosted C-C coupling with Cu-Ag alloy sub-nanoclusters for CO₂-to-C₂H₄ photosynthesis

The selective photocatalytic conversion of CO₂ and H₂O to high value-added C₂H₄ remains a great challenge, mainly attributed to the difficulties in C-C coupling of reaction intermediates and desorption of C₂H₄* intermediates from the catalyst surface. These two key issues can be simultaneously overcome by alloying Ag with Cu which gives enhanced activity to both reactions. Herein, we developed a facile stepwise photodeposition strategy to load Cu-Ag alloy sub-nanoclusters (ASNCs) on TiO₂ for CO₂ photoreduction to produce C₂H₄. The optimized catalyst exhibits a record-high C₂H₄ formation rate (1110.6 ± 82.5 μmol g^-1 h^-1) with selectivity of 49.1 ± 1.9%, which is an order-of-magnitude enhancement relative to current work for C₂H₄ photosynthesis. The in situ FT-IR spectra combined with DFT calculations reveal the synergistic effect of Cu and Ag in Cu-Ag ASNCs, which enable an excellent C-C coupling capability like Ag and promoted C₂H₄* desorption property like Cu, thus advancing the selective and efficient production of C₂H₄. The present work provides a deeper understanding on cluster chemistry and C-C coupling mechanism for CO₂ reduction on ASNCs and develops a feasible strategy for photoreduction CO₂ to C₂ fuels or industrial feedstocks.