In situ EPR spectroelectrochemical measurements were carried out with BRUKER A 300 using a three-electrodes spectroelectrochemical cell under applied electrochemical potential. TiO2-and VO-TiO2 modified ITO electrodes were used as working electrode with Ag/Ag + as the reference electrode and Pt as the counter electrode. TiO2 and VO-TiO2 catalysts were prepared on ITO electrode by using drop coating method.