Steering the reaction pathway of CO2 electroreduction and stabilizing Cu+ species by constructing the Cu2+/Cu+ valence state fluctuation buffer zone

Ag@Cu 2 O tandem catalysts is effective to improve the selectivity of hydrocarbons in CO 2 RR, where Ag core generates *CO intermediates, which migrate to Cu 2+ /Cu + interface, promoting proton transfer and C-C coupling forming *OCCHO. However, Cu + crucial for C-C coupling exhibits instability under reductive conditions. Herein, we used Ag@Cu 2 O tandem catalysts as a sacrificial template to synthesize Ag@Cu 2 O@Cu-BDC (BDC = 1,4-benzenedicarboxylic acid) tandem catalysts through an in-situ conversion strategy, which can not only introduce Cu 2+ , but also stabilize Cu + by forming a Cu-BDC MOF shell. In addition, by adjusting the amount of sacrificial template, the controllable regulation of Cu 2+ and Cu + content was successfully achieved, forming a Cu 2+ /Cu + valence state fluctuation buffer zone. It is found that this modulation not only significantly improve the selectivity towards hydrocarbons (CH 4 +C 2 H 4 ), but also enables the regulation of the reaction pathway, thereby allowing for fine-tuning of product selectivity. Notably, the Ag@Cu 2 O@Cu-BDC-5 tandem catalyst with a lower Cu 2+ /Cu + ratio demonstrated superior CH 4 selectivity (59.3 %), while the Ag@Cu 2 O@Cu-BDC-10 tandem catalyst with a higher Cu 2 ⁺/Cu + ratio achieved dominant C 2 H 4 production (43.0 %) under applied potential of −1.4 V vs. RHE for 20 h. This is attributed to Cu 2+ sites facilitated *CHO generation, while Cu + sites promoted C-C coupling as evidenced by the in-situ infrared and DFT calculations. Additionally, this study demonstrated the existence of a tandem catalysts that could increase the CO coverage on Cu sites, ensuring the full utilization of Cu + and Cu 2+ sites to further enhance product selectivity and reduce the overpotential for optimal product generation.