Valence state effect of Cu on photocatalytic CO2 reduction

Copper (Cu) is extensively employed in photocatalytic CO2 reduction reactions for the production of high-value products. The valence state of transition metals plays a pivotal role in influencing the catalytic process. However, due to the complex valence state changes of Cu in the CO2 reduction reaction, research on its valence state effect is lacking. The current work is to prepare a series of TiO2/CuX with stable Cu valence composition using different copper halides (CuX and CuX2, X = Br or Cl) as precursors. The results show that the CuBr2 loading leads to Cu+/Cu2+ mixed cocatalyst and exhibits the highest activity for CO2 photoreduction. The CH4 evolution rate of the TiO2/CuBr2 catalyst is as high as 100.59 μmol h−1 g−1, which is 6.6 times that of pristine TiO2. The CH4 selectivity reaches 77%. The enhanced catalytic activity and selectivity can be ascribed to the efficient surface adsorption, activation, excellent carrier separation, and transfer of Cu+/Cu2+ mixed cocatalyst. Our findings provide a reference for designing highly active Cu-based photocatalysts.