Enhanced visible-NIR absorption and oxygen vacancy generation of Pt/HxMoWOy by H-spillover to facilitate photothermal catalytic CO2 hydrogenation

Abstract

Photothermal catalytic hydrogenation of CO₂ is an intriguing approach to reduce CO₂ under mild conditions, which is possible because of photoinduced electron–hole pair generation and an overall increase in the localized temperature under light irradiation. However, the lack of a catalyst with an adequate photothermal conversion efficiency and the ability to generate a sufficient number of photoinduced electrons are the main factors limiting the applicability of this method. H-doped WO_y demonstrates surface plasmon resonance (SPR) capabilities, and can be adjusted by changing the dopant (H⁺) concentration. To improve the potential of the WO_y plasmonic effect based on H-doping, we herein report that the Mo-doped Pt/WO_y (Pt/MoWO_y) substantially increases the dopant (H⁺) and oxygen vacancy concentration in Pt/H_xMoWO_y during the H₂ reduction process, facilitating photothermal hydrogenation of CO₂ to CO. The developed Pt/H_xMoWO_y exhibits excellent catalytic performance (3.1 mmol h⁻¹ g⁻¹) in the photothermal reverse water-gas shift (RWGS) reaction at 140 °C, outperforming undoped Pt/H_xWO_y (1.02 mmol h⁻¹ g⁻¹). Experimental and comprehensive analyses, including photoelectrochemical measurements, UV-Vis-NIR diffuse-reflectance spectroscopy, and a model reaction, showed that abundant surface free electrons and oxygen vacancies (V_O) in Pt/H_xMoWO_y are responsible for the efficient CO₂ adsorption and transfer of photoinduced electrons to carry out the reduction of CO₂ to CO. X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption fine structure (XAFS) measurements revealed a reversible redox event for the Mo and W atoms during the RWGS reaction, confirming that the oxygen vacancies between Mo and W atoms in Pt/H_xMoWO_y act as active sites and that Pt nanoparticles activate H₂ to enable the regeneration of the oxygen vacancies. Moreover, density functional theory (DFT) calculations demonstrated that Mo-doping substantially decreases the energy barrier for oxygen vacancy formation in WO_y in the H₂ reduction process. We expect that this study will provide an innovative strategy for designing a highly efficient catalyst for photothermal CO₂ conversion.