The electrodeless preparation of M (M = Pt, Pd, Ru, Cu) NiCo oxide/graphite electrodes for the electrochemical inactivation of Escherichia coli

Graphite electrodes incorporated with multi-metal oxides (Pt, Pd, Ru, Cu, Ni and Co) were prepared by electrodeless deposition technique using NaBH4 as the reductant. The electrodes so prepared were characterized with SEM, EDS, XRD, and XPS. Electrochlorination was carried out using Escherichia coli (E. coli) as the model microorganism. Results showed that the metal oxides significantly improved the efficiency of chlorine generation. The rate constant of chlorine generation increased in the order: PtNiCo/G > RuNiCo/G > NiCo/G > PdNiCo/G > CuNiCo/G > graphite (G). Pt-, Ni-, and Co-oxides were formed on the PtNiCo/G electrode surface, which contributed to the generation of high chlorine concentration at high current efficiency and low energy consumption. Cyclic votammetry (CV) analysis of the PtNiCo/G electrode showed that the chlorine evolution potential was lower than the oxygen evolution potential. The PtNiCo/G electrode had a high chlorine evolution potential due to the presence of Co(II) and Co(III) on the electrode surface and the unique morphology that brought about active surface sites. An E. coli killing efficiency of 5.2-log could be achieved over a contact time of around 10 min on the PtNiCo/G electrode in the presence of NaCl at a dilute concentration of 0.01 M NaCl and a constant current density of 10 mA cm−2.