Defect-Driven Dynamics in Gas-Phase Photocatalytic CO₂ Conversion to Solar Fuels Using Ti³⁺/Ti⁴⁺ Containing TiO₂ and Nonstoichiometric Ag₂S Nanowires

Abstract

We studied CO 2 photoreduction on nonstoichiometric surface photocatalysts using a comprehensive approach combining materials design, advanced spectroscopy, and Quantum Mechanics (QM) calculations. We developed a direct Z-scheme heterostructure, A-TiO 2 /Ag 2 S NWs, composed of amorphous TiO 2 and nonstoichiometric Ag 2 S nanowires. This structure promotes defect-rich characteristics and a strong internal electric field (IEF), enhancing charge separation and minimizing electron–hole recombination. Employing in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and QM-simulated IR spectra revealed the CO 2 -to-CH 4 conversion mechanism which involves H 2 COH* intermediate. Ti 3+ /Ti 4+ and Ag + defect environments were precisely characterized through X-ray photoelectron spectroscopy (XPS) and in situ extended X-ray absorption fine structure (EXAFS). Under concentrated solar illumination, this heterostructure achieved a CH 4 production rate of 30.31 μmol/g, a 5-fold enhancement over conventional 1-sun conditions. These findings provide valuable insights into solar-driven fuel synthesis through targeted defect engineering and strategic heterostructure design.