Water-splitting Performance of TiO_2 Nanotube Arrays Annealed in NH_3 Ambient

Abstract

Increase of surface area and decrease of band gap in TiO_2 semiconductors are significant to improve the efficiency of water splitting by photoelectrolysis. In this study TiO_2 nanotube arrays with ~7 um length and ~100 nm diameter were fabricated by an anodizing technique of titanium foils using DMSO (dimethyl sulfoxide)-based electrolytes. Then to control the band gap of the TiO_2 arrays, they were annealed at 550℃ for up to 180 min in NH_3 gas ambient. The samples annealed in NH_3 gas for 30 min and 60 min showed superior photo-conversion efficiency for water splitting under white and visible light. A TiO_2 nanotube annealed in NH_3 gas ambient for a period longer than 120 min showed 1 order higher leakage current. It is believed that the decrease of band gap and increase of conductivity in TiO_2 nanotube arrays due to NH_3 gas treatments result in the superior water-splitting performance.