Structures and photoelectrochemical performances of reduced TiO NTAs obtained by hydrogen thermal and electrochemical reduction methods

Reduced TiO nanotube arrays were obtained by hydrogen-thermal and electrochemical reduction methods respectively, and the photoelectrochemical performances were studied. Phase structures, elemental compositions, and surficial morphologies were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) to investigate the structural differences between as-prepared TiO NTAs and reduced TiO NTAs, including two different reducing products. The photoelectrochemical performances of TiO NTAs were found to be enhanced by both two reducing methods. The different mechanisms of hydrogen-thermal reduction and electrochemical reduction were investigated by comparing optical absorption, charge transport, separation efficiency of charge carriers, and surficial reactions during the photoelectrochemical processes. For hydrogen-thermal-reduced TiO NTAs, the improved photoelectrochemical performances are induced by high optical absorption and low recombination of charge carries, whereas for electrochemical reduced TiO NTAs, the enhanced performances are attributed to low charge transport resistance.