Hong Qian,Binxia Yuan,Yuhao Liu,Li Wang,Rui Zhu,Pengyu Dong
TiO 2 has low photocatalytic activity due to its easy recombination of photogenerated charges and low visible light utilization efficiency. This study utilized the keto-enol tautomerism principle of fructose in an alkaline environment to successfully obtain Cu 2 O/TiO 2 (CT), Cu 2 O/TiO 2 /Cu (CTC), and TiO 2 /Cu (TC) catalysts. As Cu(I) transformed into Cu(0), the bandgap narrowed, significantly enhancing visible light absorption. Photocatalytic tests showed that CT-0.15 exhibited the highest hydrogen production rate (279.53 μmol g −1 h −1 ), which was 25.18 times higher than that of TC-2. However, CTC-1 had the highest CO production rate (10.58 μmol g −1 h −1 ). Optoelectronic test revealed that CT-0.15 and CTC-1 had higher separation efficiency of photogenerated exciton. Density functional theory (DFT) calculations indicated that the change in the valence state of Cu influenced the reaction mechanism, with CT being favorable for the adsorption of H + in HER and CTC promoting the adsorption of CO 2 in carbon dioxide reduction reaction (CO2RR).
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.
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