Effects of hydrogen on the semiconductive properties of passivating $TiO_2$ films have been investigated by using AC-impedance and photocurrent measurements. The passive films were prepared on titanium in a 0.5M $H_2$ $SO_4$ solution potentiodynamically with a scanning rate of 1 mV $s^{-1}$ until the formation potential reached 3 $V_{SCE}$. Hydrogen injection was performed into the $TiO_2$ film freshly formed by applying the constant potential of -1700 $mV_{SCE}$ for various charging time. The donor densities of the uncharged film and of the hydrogen film charged for 10 s are estimated to be $1.2\times10^{19}cm^{-3}$ and $2.0\times10^{19}cm^{-3}$ respectively. Photocurrent decreases as hydrogen is charged into the uncharged films. Photocurrent responses confirm the presence of deep donor which is located at about 1 eV below the conduction band. From the results, it is suggested that most of hydrogen charged into the film act as recombination centers and that the remainder of hydrogen acts as shallow donor.
