CO ₂ Photoreduction with CuO NPs Supported by TiO ₂ and BaTiO ₃ Photoactive Materials: An <i>Operando</i> AP-NEXAFS Study

Using light and water vapor to reduce CO2 into various carbon-based products, such as methane, is a promising strategy to achieve the conversion of CO2 into useful products. Copper (Cu) is a well-studied photocatalyst due to its high affinity for carbon intermediates, favoring the CO2 evolution reaction (CER) over the hydrogen evolution reaction (HER). Recently, we have shown that adding CuO nanoparticles to light-sensitive materials such as BaTiO3 (BTO) and TiO2 enhances the photocatalytic performance of the materials. Therefore, to elucidate the interaction between CuO nanoparticles and support materials, we combined the results of standard (scanning electron microscopy, X-ray photoemission spectroscopy) and advanced characterization techniques, namely, operando ambient-pressure near-edge X-ray absorption fine structure (NEXAFS) and in situ Fourier transform infrared (FTIR) spectroscopies, for investigating the photocatalytic reaction mechanism of CuO–BTO and CuO–TiO2 photocatalysts in operando CO2 photoreduction conditions. Our results confirmed enhanced methanation on the CuO–BTO system over a TiO2-based catalyst: NEXAFS analysis allowed to establish that the activity of both catalysts is linked to the formation of a reversible redox couple Cu+/Cu2+ and that the CuO–BTO interface can promote a more efficient charge separation; the electron trapping on Ti centers was directly observed on Ti NEXAFS spectra, evidencing a strong charge recombination suppression, which can favor CO2 reduction. IR revealed that CO2 is strongly activated on the CuO–BTO surface, forming carbonates that are converted to CH4 through the formation of formates as intermediates.