Hydrogenated Blue Titania for Efficient Solar to Chemical Conversions: Preparation, Characterization, and Reaction Mechanism of CO2 Reduction

Here we report a facile low-temperature solvothermal method by using Li-dissolved ethanediamine to prepare uniform hydrogenated blue H-TiO2–x with wide spectrum response. H-TiO2–x possesses a distinct crystalline core–amorphous shell structure (TiO2@TiO2–x) with numerous oxygen vacancies and doped H in the amorphous shell. Efficient solar to chemical energy conversions, likely photocatalytic reduction of CO2, degradation of contaminants, and H2 generation from water splitting can be achieved over this blue titania. Notably, the optimized H-TiO2–x(200) shows high activity of CH4 formation at a rate of 16.2 μmol g–1 h–1 and a selectivity of 79% under full solar irradiation. The kinetic isotope effects measurements reveal that the cleavage of the C═O bond from CO2 rather than the O–H bond from H2O is the rate-determining step in CH4 formation. Meanwhile, in situ diffuse reflectance infrared Fourier transform spectroscopy shows the existence of the key intermediate CO2– species. The formation of intermediate CO2– indicates that the defective surface of H-TiO2–x can efficiently accelerate the adsorption and chemical activation of the extremely stable CO2 molecule, which makes the single-electron reduction of CO2 to CO2– easier.