Photocatalytic Hydrogen Evolution Using Ni-Pd/TiO₂: Correlation of Light Absorption, Charge-Carrier Dynamics, and Quantum Efficiency

TiO₂ surface modification with bimetallic nanoparticles (NPs) has demonstrated to be a strategy to enhance the hydrogen generation via photocatalysis and to minimize the use of expensive noble metals. A better understanding of the role of bimetallic NPs is of crucial importance to design efficient photocatalysts. Here, we show a systematic study of surface modification of commercial TiO₂ (P25) with mono- and bimetallic (Ni, Pd, and Ni-Pd) NPs synthesized by radiolysis. The photocatalysts were characterized by High Resolution Transmission Microscopy (HRTEM), Scanning Transmission Electron Microscope (STEM), X-ray Diffraction (XRD), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and UV-vis Diffuse Reflectance Spectroscopy (DRS). The charge-carrier dynamics was studied by Time Resolved Microwave Conductivity (TRMC). The photocatalytic activity was evaluated for hydrogen generation under UV-vis irradiation using polychromatic and monochromatic lights (action spectra analysis of apparent quantum efficiency). TiO₂ modified with Pd-Ni bimetallic NPs exhibits a high activity for H₂ generation, and a synergetic effect of the two metals was obtained. The study of light absorption, charge-carrier dynamics, and photocatalytic activity revealed that the main role of the metal NPs is to act as catalytic sites for recombination of atomic hydrogen. (Chemical Equation Presented).