Deposition efficiency in the preparation of ozone-producing nickel and antimony doped tin oxide anodes

The influence of precursor salts in the synthesis of nickel and antimony doped tin oxide (NATO) electrodes using thermal decomposition from dissolved chloride salts was investigated. The salts investigated were SnCl45H2O, SnCl22H2O, SbCl3 and NiCl26H2O. It was shown that the use of SnCl45H20 in the preparation process leads to a tin loss of more than 85 %. The loss of Sb can be as high as 90 % while no indications of Ni loss was observed. As a consequence, the concentration of Ni in the NATO coating will be much higher than in the precursor solution. This high and uncontrolled loss of precursors during the preparation process will lead to an unpredictable composition in the NATO coating and will have negative economic and environmental effects. It was found that using SnCl22H20 instead of SnCl45H2O can reduce the tin loss to less than 50 %. This tin loss occurs at higher temperatures than when using SnCl45H2O where the tin loss occurs from 56 – 147 °C causing the composition to change both during the drying (80 – 110 °C) and calcination (460 -550 °C) steps of the preparation process. Electrodes coated with NATO based on the two different tin salts were investigated for morphology, composition, structure, and ozone electrocatalytic properties

In-situ activated hydrogen evolution by molybdate addition to neutral and alkaline electrolytes

Activation of the hydrogen evolution reaction (HER) by in-situ addition of Mo(VI) to the electrolyte has been studied in alkaline and pH neutral electrolytes, the latter with the chlorate process in focus. Catalytic molybdenum containing films formed on the cathodes during polarization were investigated using scanning electron microscopy (SEM), energy-dispersive X ray analysis (EDS), X-ray photoelectron spectroscopy (XPS), and X ray fluorescence (XRF). In-situ addition of Mo(VI) activates the HER on titanium in both alkaline and neutral electrolytes and makes the reaction kinetics independent of the substrate material. Films formed in neutral electrolyte consisted of molybdenum oxides and contained more molybdenum than those formed in alkaline solution. Films formed in neutral electrolyte in the presence of phosphate buffer activated the HER, but were too thin to be detected by EDS. Since molybdenum oxides are generally not stable in strongly alkaline electrolyte, films formed in alkaline electrolyte were thinner and probably co-deposited with iron. A cast iron molybdenum alloy was also investigated with respect to activity for HER. When polished in the same way as iron, the alloy displayed a similar activity for HER as pure iron

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

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 surfac