Enhanced photocatalytic H2 generation via in-situ grown CuO-decorated TiO2 nanotubes on Ti-Cu alloys: A synergistic thermo-electrochemical approach

Abstract

In the present study, we developed a thermo-electrochemical strategy to grow CuO self-decorated TiO2 nanotubes (TiNTs) on Ti-xCu alloys (x = 0, 2, 4, 6, and 8 wt%). The Ti-xCu metastable solid solution alloys were prepared by rapid quenching after solid solution heat treatment. Based on microstructural analyses, unlike all other samples, which consist of the α-Ti phase, the microstructure of the Ti-8Cu sample is biphasic, consisting of α-Ti and the Ti2Cu intermetallic compound. Electrochemical anodization of the Ti-xCu samples results in the in-situ formation of CuO nanoparticles decorating the TiO2 nanotubes on substrates containing Cu. As the Cu concentration increases, the order and integrity of the nanotube arrays gradually decrease while the Cu concentration within the nanotubes increases; however, the Ti-6Cu sample presents a satisfactory structural order and a uniform distribution of Cu. Based on XPS analysis, it has been determined that CuO is the main species decorating the TiNTs. This results in a maximum reduction of the band gap by approximately 0.5 eV for the Ti-6Cu sample compared to the pure Ti sample (3.35 eV), leading to improved absorption of visible light. Furthermore, the CuO species extended the lifetime of charge carriers, as demonstrated by electrochemical impedance spectroscopy. This combination of band gap reduction and enhanced charge carrier separation in Ti-6Cu resulted in a photocatalytic H2 production rate of 35.8 µL/cm2·h, more than ten times higher than the pure Ti sample. These findings hold significant promise for developing efficient and sustainable energy production systems.