Guiding effective nanostructure design for photo-thermochemical CO2 conversion: From DFT calculations to experimental verifications

The solar photo-thermochemical cycle (PTC) for the conversion of CO2 into fuels over metal oxides is a novel and promising method to alleviate the increasing energy crisis and worsening global climate change. Density functional theory (DFT) calculations of the anatase (101) surface of TiO2 and M-doped TiO2 (M = Zn, Ni, and Cu) were performed to provide guidance for enhancing the PTC. Additionally, M-doped TiO2 films were produced using a sol-gel method and applied to the PTC for CO2 conversion to provide experimental verifications. A maximum, stable production of CO of 10.80 mu mol/g was achieved using Cu-doped TiO2, which was nearly 6.39-fold higher than the amount of CO produced by clean TiO2. The CO yield was in good agreement with the calculation results. High-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD) and electron spin resonance (ESR) were used to evaluate the crystal structures and morphologies. UV-visible diffuse reflectance spectra (UV-visible DRS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) analyses were also conducted to investigate the surface charge-transfer and reaction mechanisms. As a result, a complete cycle reaction mechanism for Cu-doped TiO2 was proposed. Several key factors of the mechanism were clarified, and an effective guide for nanostructure design was proposed.