In this study, we developed a novel photo-electrochemical catalytic oxidation wastewater treatment system by interacting the cathodic in-situ generated H2O2 with TiO2 suspension to form interfacial equivalent to Ti-IV-OOH species, which endowed the PEC system with superior efficiency for degrading sodium pentachlorophenate (PCP-Na) under visible light irradiation at neutral pH. The apparent PCP-Na degradation rate constant of the PEC system was more than 10 times that of the electrochemical oxidation counterpart. In the PEC system, the interfacial equivalent to Ti-IV-OOH species injected electrons to the conduction band of TiO2 to initiate the activation of O-2 and the in-situ generated H2O2 adsorbed on the surface of TiO2, lead to producing reactive oxygen species of superoxide anions and hydroxyl radicals, which were responsible for the dechlorination and mineralization of PCP-Na during the PEC process, respectively. The dosage of TiO2 catalyst and the current intensity applied on PCP-Na degradation were optimized. This study develops a high efficient PEC oxidation system for wastewater treatment and provides new insight into the role of cathodic in-situ generated H2O2 on PEC oxidation of PCP-Na with TiO2 under visible light irradiation. (C) 2015 Elsevier B.V. All rights reserved.