Unravelling the photoactivity of metal-loaded TiO₂ for hydrogen production: Insights from a combined experimental and computational analysis

Despite being the most employed material for photocatalytic hydrogen generation, TiO₂ suffers limitations such as a high rate of electron-hole recombination and poor light absorption in the visible spectrum. Among the various strategies developed to overcome these drawbacks, combining TiO₂ with a metal co-catalyst emerged as one of the most promising. In this study, we integrated experimental findings, advanced characterization techniques, and computational methods to shed light on how different noble metals influence the enhancement of the photocatalytic activity of TiO₂. Among the tested noble metal co-catalysts, the hydrogen production rate under UV and visible light irradiation followed the trend Pt > Au ≈ Pd > Ag > bare TiO₂, with Pt-decorated TiO₂ exhibiting a hydrogen production rate of 28 mmol/h g. The noble metals were found to significantly suppress the electron-hole recombination rate compared to bare TiO₂. Upon photodeposition, Pd and Pt formed the smallest nanoparticles with average sizes of 13.4 nm and 4.1 nm, respectively. Computational analyses were conducted to rationalize the difference in nanoparticle sizes by analyzing the binding and cohesive energies of the metal clusters on the TiO₂ surface. Additionally, calculations demonstrated the strong interaction of Pt, Au, and Pd nanoclusters with adsorbed hydrogen, with Pt achieving the closest-to-zero Gibbs free energy of hydrogen adsorption and displaying the most polar interaction with hydrogen. These findings align closely with the observed hydrogen production rates, where UV/Vis-driven hydrogen production is governed by the coupling of hydrogen radicals on the co-catalyst surface, while visible-light-driven production is limited by charge carrier lifetimes.