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

Abstract

Here we report a facile low-temperature solvothermal method by using Li-dissolved ethanediamine to prepare uniform hydrogenated blue H-TiO 2– x with wide spectrum response. H-TiO 2– x possesses a distinct crystalline core–amorphous shell structure (TiO 2 @TiO 2– x ) with numerous oxygen vacancies and doped H in the amorphous shell. Efficient solar to chemical energy conversions, likely photocatalytic reduction of CO 2, degradation of contaminants, and H 2 generation from water splitting can be achieved over this blue titania. Notably, the optimized H-TiO 2– x (200) shows high activity of CH 4 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 CO 2 rather than the O–H bond from H 2 O is the rate-determining step in CH 4 formation. Meanwhile, in situ diffuse reflectance infrared Fourier transform spectroscopy shows the existence of the key intermediate CO 2 – species. The formation of intermediate CO 2 – indicates that the defective surface of H-TiO 2– x can efficiently accelerate the adsorption and chemical activation of the extremely stable CO 2 molecule, which makes the single-electron reduction of CO 2 to CO 2 – easier.