Alternating current impedance and photocurrent measurements were made on anodically passivating TiO 2 films in 0.1 M NaOH solution. The experimental results suggested that hydrogen injected into the passivating TiO 2 films acts as a shallow donor, without modifying the bandgap structure of the films. Also, it is suggested that injected hydrogen increases the electric field strength and enhances the electron-hole recombination at the near-surface region of the films.