Photoelectrochemical approach for metal corrosion prevention using a semiconductor photoanode

Metal corrosion was successfully prevented using a TiO2-based photoelectrochemical system. Under UV illumination, a TiO2 electrode in a hole scavenging medium supplied photogenerated conduction band electrons to an electrically connected steel electrode with the generation of photocurrent and shifted the coupled potential to much more negative values. In this galvanic pair, the steel and the TiO2 electrode acted as a cathode and a photoanode, respectively, which is essentially a variation of cathodic protection, The performance of the photocathodic protection depended little on the light intensity as long as there were enough photons to compensate for the dark corrosion current of the steel. The shiny surface of the steel electrode remained intact in a corrosive electrolyte solution as long as it was connected to the UV-illuminated TiO2 photoanode, but it quickly corroded and was covered by red-brown rust in the absence of light. An outdoor test under solar light also showed a similar effect of corrosion prevention, which verified the possibility of using solar light for corrosion prevention. Although formate was useful as a hole scavenger. pure water without any added hole scavenger was also successful in protecting metal. The performance of the ZnO photoanode was similar to that of TiO2. Various experimental parameters affecting the new photocathodic protection system were investigated and are discussed.