Size-induced H-adsorption self-optimization of Au cocatalysts for robust photocatalytic H₂ production

Achieving a near balance between hydrogen adsorption and desorption behaviors at active sites is essential for efficient photocatalytic hydrogen production. However, precise regulation over the kinetics of hydrogen adsorption and desorption remains a major challenge. In this study, we propose a cocatalyst size-tuning strategy to finely modulate the hydrogen adsorption/desorption kinetics on Au-decorated TiO₂ photocatalysts (TiO₂/Au). Using a straightforward two-step photodeposition method, we successfully deposited Au nanoparticles with controlled sizes ranging from 3 to 13 nm onto the TiO₂ surface. Among the prepared photocatalysts, the TiO₂ modified with 8-nm Au nanoparticles exhibited the highest performance, achieving a hydrogen evolution rate of 6.6 mmol g^-1 h^-1 and an apparent quantum efficiency of 21 %, which is 220 times higher than that of pure TiO₂. Both experimental and theoretical analyses reveal that as the size of the Au nanoparticles increases in the TiO₂/Au system, the electron density of surface Au atoms gradually rises, resulting in a continuous downshift of the d-band center at the active Au sites. This tunable d-band modulation facilitates a near-optimal equilibrium between hydrogen adsorption and desorption on Au, thereby significantly enhancing the catalytic activity. Furthermore, femtosecond transient absorption spectroscopy confirmed the occurrence of ultrafast electron transfer within the TiO₂/Au system, which promotes efficient separation of photogenerated charge carriers and accelerates the catalytic reaction kinetics. This study provides valuable insights for the rational design and optimization of highly efficient cocatalysts for hydrogen evolution.