Structures and photoelectrochemical performances of reduced TiO2 NTAs obtained by hydrogen thermal and electrochemical reduction methods

Abstract

Reduced TiO2 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 TiO2 NTAs and reduced TiO2 NTAs, including two different reducing products. The photoelectrochemical performances of TiO2 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 TiO2 NTAs, the improved photoelectrochemical performances are induced by high optical absorption and low recombination of charge carries, whereas for electrochemical reduced TiO2 NTAs, the enhanced performances are attributed to low charge transport resistance.