Synergistic effect of surface oxygen vacancies and hydroxyl groups on Cu-doped TiO2 photocatalyst for hydrogen evolution

Abstract

The intricate nature of the titanium dioxide (TiO2) photocatalytic system, influenced by Cu doping, often yields conflicting outcomes. This study addresses this complexity by examining the impact of Cu ion doping in nanostructured TiO2 to augment its photocatalytic efficacy in hydrogen generation from ethanol-water mixtures. The improved performance is primarily attributed to the generation of oxygen vacancies (Ovac) within the TiO2 lattice. By adjusting the thermal processing parameters, the chemical state of Cu is modulated to optimize photocatalytic performance. Solid-state nuclear magnetic resonance (SSNMR) and density functional theory (DFT) calculations confirm that the presence of Ovac and hydroxyl groups (OH-) surface species not only facilitates local spatial charge separation but also enhances light absorption, thereby improving photocatalytic hydrogen evolution reaction (HER) rate up to 20.2 mmol h-1 g- 1 under UV light. Furthermore, a proposed mechanism involves the participation of Ovac and OH- species, supported by Mott-Schottky (M - S) plots and ultraviolet photoelectron spectroscopy (UPS), revealing that Cu-TiO2 exhibits a lower flat band potential (Efb) and smaller work function compared to TiO2. This research underscores the pivotal role of Cu ions and Ovac:OHin advancing the photocatalytic activity of TiO2-based crystals, imparting noteworthy implications for sustainable hydrogen generation.