Effect of Surface Plasmon Resonance and the Heterojunction on Photoelectrochemical Activity of Metal-Loaded TiO2 Electrodes under Visible Light Irradiation

This study examines the influence of surface plasmon resonance (SPR) and the semiconducting heterojunction on the photoelectrochemical (PEC) activity of metal-loaded TiO2 electrodes under visible light irradiation. Different metal nanoparticles (including Au, Ag, Rh, and Cu) have been selected deliberately and deposited on the TiO2 electrode layers via photodeposition and subsequent annealing at 300 °C. UV–vis spectra show an increased absorbance in the visible light region with the metal loading. X-ray photon spectroscopy reveals the formation of CuO, Ag2O, and Ru2O3 after annealing, while only Au remains in its metallic state. The PEC activity increases in the ascending order of Cu < Au < Rh < Ag. This is consistent with the electrochemical impedance measurement where the Ag-loaded TiO2 electrode shows the lowest charge transfer resistance together with the highest ion diffusion rate. Our findings suggest that the presence of semiconducting p–n heterojunctions with associated oxygen-vacancy defects facilitates the enhanced PEC activity by reducing the electron–hole recombination in addition to the SPR effect.