Functionally hydrogenated surfaces and interfaces of TiO₂ nanotubes formed by electrochemically hydrogenation and decoration of ZnIn₂S₄ nanosheets for efficient photocatalytic CO₂ conversion

In this study, we report electrochemically hydrogenated TiO₂ (HTNT) with a partially amorphized surface due to the abundant oxygen vacancies. This reconstructed surface of TiO₂ helps in forming an optimal heterostructure with ZnIn₂S₄ (ZIS) nanoflakes with functionally regulated heterointerface by further introducing oxygen vacancy contents for photocatalytic CO₂ conversion, as experimentally confirmed by electron paramagnetic resonance (EPR) spectroscopy. Accordingly, the optimum heterostructured catalyst (i.e., ZIS-5/HTNT) exhibited improved CO₂ conversion performance with a superior production rate of 0.886 μmol∙h⁻¹ cm⁻² for CO and 0.853 μmol∙h⁻¹ cm⁻² for CH₄ compared to pristine TiO₂ (0.288 μmol∙h⁻¹ cm⁻² for CH₄). This performance is the highest among TiO₂-based thin film photocatalysts. The significantly boosted CO₂ conversion efficiency is attributed to the enhanced visible light harvesting ability resulted from the induced mid-gap states and the improved charge carriert generation/separation by hydrogenated surfaces. In addition, facile interfacial charge carrier transportation of the heterostructured catalyst through the Z-scheme mechanism and strong reduction/oxidation efficiency by rationally separating the oxidation and reduction active sites, as experimentally proved by nanoparticles photodeposition and radical trapping experiments. This work provides a sophisticated study on the critical role of hydrogenated surfaces and heterointerfaces in designing efficient heterostructured-based photocatalysts for CO₂ conversion.