Hydrogen is a clean and renewable green energy source. Hydrogen is also widely considered to be the fuel of future. Over past decades, generation of hydrogen by low cost and environmental friendly ways became a popular and urgent issue for the world. As previously reported, hydrogen produced from photocatalytic or photoelectrochemical (PEC) routes have showed its strongly predominant compatibility for future developments. Titanium dioxide has been generally recognized as one of the most promising material candidate used in photocatalytic and PEC. However, this material, TiO2 was limited in the solar energy utilization due to its wide bandgap (3.2 eV). Therefore, it became great importance to loading/doping metals or other substances into TiO2 in order to enhance the hydrogen production by photocatalytic or photoelectrochemical (PEC) technologies.
In this work, CuxO/TiO2 nanotubes were prepared and used as photoanodes in PEC splitting of water for hydrogen generation. Experimentally, highly ordered nanotubular TiO2/Ti substrates were firstly synthesized by the anodization technique. The incipient wetness impregnation was then employed to load copper oxides on the surface of TiO2 nanotubes. The effects of preparation conditions including calcination temperature and concentration of impregnation solution on the properties of CuxO nanoparticles such as crystalline structure, particles size distribution and loading amount were investigated. Furthermore, the bandgap and photoactivity of the CuxO/TiO2 photoanodes were charaterized by using reflectance UV/Vis analysis and PEC reaction.
The experimental results showed that the final product was CuO with tenorite structure. The optimum preparation conditions occured at 0.01 M of initial Cu(NO3)2 concentration with impregnating for three times, and the optimized calcination temperature was 450°C in air. The Cu loading of this sample was determined as 0.6 μmole. In the PEC water spliting by using methanol as the sacrificial agent under xenon lamp illumination (1000W, 100mW/cm2), it was found that the maximum photoconversion efficiency, e.g., 0.48%, could be obtained, and the hydrogen generation rate was at 0.343 μmol/cm2.hr.
Alternatively, electrodeposition method was in advance employed to deposit CuxO on the TiO2 surface. Effects of deposition variables including copper concentration in the deposition bath, applied voltage and deposition time on the morphology and microstructure of the resulting CuxO/TiO2 nanotubes were investigated. Besides, several alcohol-water mixtures were served as electrolytes for the PEC study. From the experimental results, it revealed that the optimal deposition conditions occured at applied voltage of 1V for 15 s with a 10.45 mM CuSO4 solution. In this case, the maximum photoconversion efficiency was 0.50%, and the hydrogen generation rate was 0.384 μmol/cm2.hr.
The results concluded that maximum photoconversion efficiencies, as well as hydrogen generation rates, obtained by the two routes in this study were quite close. However, their performances were still far away from the industrial criteria. Many efforts should be paid to find more effective materials for hydrogen generation by PEC water splitting in future.

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