Efficient CO2 reduction over a Ru-pincer complex/TiO2 hybrid photocatalyst via direct Z-scheme mechanism

Abstract

Solar-driven CO₂ conversion to hydrocarbon fuels is a feasible way to solve the increasingly serious energy problem and greenhouse effect. Herein, we fabricate a novel hybrid photocatalyst for CO₂ reduction reaction (CO₂RR) by immobilizing the Ru-pincer complex [Ru(N₃)(ONO)] on TiO₂ nanoparticles. The resultant Ru(N₃)(ONO)/TiO₂ hybrid photocatalyst achieves maximum CO/CH₄ yields of 122.9/12.4 μmol g⁻¹ h⁻¹, corresponding to an overall photoactivity of 344.8 μmol g⁻¹ h⁻¹, which is ∼20.0 times higher than that of pristine TiO₂ nanoparticles. The characterization results of quasi in situ X-ray photoelectron spectroscopy, reactive oxygen species quantification experiment, and femtosecond transient absorption spectroscopy demonstrate that a direct Z-scheme charge transfer mechanism proceeds in the hybrid material, in which the two components can be excited, and the photoexcited electrons of TiO₂ nanoparticles combine with the holes of the Ru(N₃)(ONO) complex at their interface. In this Z-scheme hybrid photocatalyst, the Ru-pincer complex is a rare example of both the photoabsorber and active unit for catalyzing CO₂RR, and the high oxidation capacity of the holes in the TiO₂ nanoparticles and the high reduction ability of the electrons in the Ru(N₃)(ONO) complex can be maintained, thus significantly boosting the CO₂RR activity. These results demonstrate that the hybridization of the semiconductor with the Ru-based complex would be an effective strategy for artificial photosynthesis with high-performance solar-driven CO₂ conversion.