TiO2 treated in hydrogen atmosphere showed enhanced photocatalytic activity in degrading the sul-fosalicylic acid (SSal). The results of the electrochemical impedance spectroscopy (EIS) investigation showed that the diameters of the capacitive arcs for the H-TiO2 were much smaller than those of bare TiO2 and thermally treated TiO2 in air, indicating that the charge transfer of the H-TiO2 occurs more rapidly, thus inviting a higher photocatalytic activity. When an external bias was applied on the H-TiO2, the arc of the EIS Nyquist plot decreased obviously than without the bias, suggesting more efficient separation of the photo-generated carriers.