On the suppression of cathodic hypochlorite reduction by electrolyte additions of molybdate and chromate ions

  • John Gustavsson Applied Electrochemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE 100 44 Stockholm
  • Gongzhuo Li Applied Electrochemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE 100 44 Stockholm
  • Christine Hummelgård Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, SE 851 70 Sundsvall
  • Joakim Bäckström Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, SE 851 70 Sundsvall
  • Ann Cornell Applied Electrochemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE 100 44 Stockholm

Abstract

The goal of this study was to gain a better understanding of the feasibility of replacing Cr(VI) in the chlorate process by Mo(VI), focusing on the cathode reaction selectivity for hydrogen evolution on steel and titanium in a hypochlorite containing electrolyte. To evaluate the ability of Cr(VI) and Mo(VI) additions to hinder hypochlorite reduction, potential sweep experiments on rotating disc electrodes and cathodic current efficiency (CE) measurements on stationary electrodes were performed. Formed electrode films were investigated with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cathodic hypochlorite reduction is hindered by the Mo-containing films formed on the cathode surface after Mo(VI) addition to the electrolyte, but much less efficient compared to Cr(VI) addition. Very low levels of Cr(VI), in the mM range, can efficiently suppress hypochlorite reduction on polished titanium and steel. Phosphate does not negatively influence the CE in the presence of Cr(VI) or Mo(VI) but the Mo-containing cathode films become thinner if the electrolyte during the film build-up also contains phosphate. For a RuO2-TiO2 anode polarized in electrolyte with 40 mM Mo(VI), the anode potential increased and increased molybdenum levels were detected on the electrode surface.

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Published
10-11-2012
Section
Electrochemical Engineering