The electrochemical oxidation of chloride on Pt-Ni-Co-G electrodes and its application in in-situ disinfection of water

Abstract

In-situ chlorine generation has high disinfection potential for small to medium scale water treatment systems. Electrodes were prepared by coating Pt-, Ni-, Co-oxides on graphite substrate using electrodeless deposition method and characterized with SEM, EDS, XRD, XPS and cyclic voltammetry. Results showed that the molar ratio of Ni- and Co-oxides on graphite surface influenced surface structure and in-situ chlorine generation capacity. Pt0.01Ni0.24Co0.75 electrode exhibited a unique surface structure and the highest in-situ chlorine generation capability. The Pt0.01Ni0.24Co0.75-G electrode exhibited highly porous 3D structure and high oxygen deficit, which significantly promoted the formation of M-Cl− binding on electrode surface and enhanced chlorine generation. The onset of chlorine evolution potential was lower than that of oxygen on Pt0.01Ni0.24Co0.75-G electrode. Moreover, the transfer coefficient of chloride oxidation was smaller than that of water oxidation, which would enhance chloride oxidation current efficiency. The in-situ chlorine generation capability increased with NaCl concentration. The kinetics of chlorine generation was well described by the Langmuir-Hinsheldwood mechanism. The in-situ disinfection rate decreased with the increase in initial E. coli density. A 7.5-log disinfection was achieved in 15 min in the presence of 0.01 M NaCl under 5 mA/cm2 current density at room temperature. The lipid peroxide, morphology changes and destruction of E. coli cell membrane were observed in the in-situ disinfection process, indicating that reactive species such as chlorine radical in addition to free chlorine played the main role of in-situ disinfection.