N-doped TiO2 nanotube arrays with mixed phase for enhanced photocathodic protection of 304 stainless steel under visible light

Abstract

Effective N-doped TiO2 nanotube arrays with rutile–anatase mixed phase were fabricated by two-step anodization method and annealing in a NH3 atmosphere. Compared with pure anatase TiO2 nanotube arrays, the photocurrent density of N-doped TiO2 nanotube arrays with mixed phase increased by about three times under visible light. Moreover, the open circuit potential of 304 stainless steel obviously negatively shifted when coupled with N-doped TiO2 nanotube arrays with mixed phase under visible light. The enhancement was mainly because N-doping extends light absorbance and the mixed phase is beneficial for the separation of photoexcited electrons–holes. Therefore, N-doped TiO2 nanotube arrays with mixed phase showed highly effective photogenerated cathodic protection of 304 stainless steel under visible light. Interestingly, the photoelectrode also displayed a cathodic protection effect after removing irradiation, which is meaningful for practical applications.