Electrochemical Deposition of Pt and Pd on TiO₂ Nanotubes for Application in the Photoelectrocatalytic Conversion of Biomethane and Biogas for Hydrogen Generation

The photoelectrocatalytic conversion of biomethane/biogas using semiconductor materials is a promising method for production of green H-2, the fuel of the future. In this work, TiO2 nanotubes (TiO2NTs) prepared by electrochemical anodization were modified with Pt and Pd nanoparticles by electrochemical deposition using cyclic voltammetry, producing TiO2NTs/Pt and TiO2NTs/Pd catalysts, respectively. Evaluation of the morphology, composition, and crystallinity of the materials employed scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The photoactivities of the electrodes were studied using linear scanning voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The introduction of Pt and Pd on the TiO2NTs resulted in electrodes that presented excellent photogenerated charge separation and transfer properties. In the presence of methane, the current densities obtained increased further, by around 2.23- and 2.95-fold for the TiO2NTs/Pt and TiO2NTs/Pd electrodes, respectively, compared to the pure TiO2NTs, confirming the capacity of CH4 to act as a hole scavenger. The maximum amounts of H-2 obtained from the photoelectrocatalytic conversion of methane were 120.7, 304.7, and 393 mmol.cm(-2) for the TiO2NTs, TiO2NTs/Pt, and TiO2NTs/Pd electrodes, respectively, clearly showing the positive contribution of the metallic nanoparticles electrodeposited on the TiO2NTs surface. A lower amount of H-2 was produced in the photoelectrocatalytic conversion of biogas, with the possible occurrence of additional reactions, such as the reduction of CO2.