It is established that a cathodic pretreatment of thermic titanium dioxide increases considerably the photoresponse to TiO2 under uv radiation in chloride solution. The effects of the duration of the pretreatment and of the nature of the acidic media used to perform the cathodic pretreatment are investigated. The variation law of the increase of the photocurrent with the pretreatment duration, which is the sum of two exponential laws at least, reveals the presence of various phenomena in the improvement of the energetic efficiency. The various mechanism involved there are discussed according to different hypotheses.