Role of Hydrogen in the Electronic Transport through Passivating TiO2 Films

Abstract

The role of hydrogen in determining electronic transport in passivating TiO2 films is investigated by using a.c. impedance spectroscopy in a 0.1 M NaOH solution. The passive film was prepared on titanium galvanostatically with 10 mA cm-2 at a formation potential of 50 V (SCE) in a 0.5 M H2SO4 solution. Hydrogen was injected into the fresh passivating TiO2 film by scanning the applied potential range from -1.7 to -1.5 V(SCE) and back at a rate of 2 mV s-1 in a 0.1 M NaOH solution. Hydrogen injection into the TiO2 film increases a.c. conductivity as well as donor concentration. The experimental results suggest that hydrogen donates an electron to the conduction band inside the passive film. The frequency dependence of a.c. conductivity is discussed in terms of electronic hopping between deep donor levels.