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.