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 SnCl45H2O, SnCl22H2O, SbCl3 and NiCl26H2O. It was shown that the use of SnCl45H20 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 SnCl22H20 instead of SnCl45H2O can reduce the tin loss to less than 50 %. This tin loss occurs at higher temperatures than when using SnCl45H2O 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.

The oxide formation process (i.e heating of salts and solution) was characterized using coupled TG-DSC (Thermogravimetry-Dierential Scanning Calorimetry). The TG-DSC instrument was calibrated both for temperature and heat ow prior to use by heating pure metals of Zn, Al, Sn, and In at the same heating rate (5 K/min) and in the same temperature range 25-600 • C as the experiments were performed. The calibration was made in both nitrogen and air atmosphere to make sure that none of the calibration standards were oxidized during calibration in air. All Stem solutions of concentrations 2, 0.1 and 0.1 M was prepared for the tin, antimony and nickel salts, respectively.
All salts were dissolved in ethanol and no HCl was added as no precipitation was seen after stirring for about 3 hours.
These stem solutions were then mixed to the molar ratio 1000:16:2 with a Sn concentration of 1 M. Upon mixing the antimony solution with the SnCl 2 · 2 H 2 O solution a white, gel-like, precipitate was formed. The precursor solution was stirrer for approximately 3 hours after which the precipitate was gone.
Titanium substrates 0.5 mm in thickness and 59 mm in diameter were prepared as follows: Cleaned with detergent and rinsed with MilliQ water 3 S4 Pickled in a room temperature bath of hydrogen uoride (diluted to 1 %) for 2 minutes

Rinsed thoroughly in MilliQ water
Ultrasonic bath with detergent for approximately 10 minutes

Rinsed thoroughly in EtOH and MilliQ water
Dried at 80 • C for 40 -60 minutes The clean titanium substrates were coated with the precursor solutions by spin-coating at 500 rpm for 20 seconds followed by 1500 rpm for 30 seconds. After application of precursor solution, the electrodes were rst dried at 80 • C for 10 minutes and then calcinated at 500 • C for 10 minutes. The coating was repeated 5 times. After the nal layer, the electrodes were calcined at 500 • C for 60 minutes. Three electrode samples was prepared using each type of precursor solution. The loading increase per layer can be seen in Figure 8 in the manuscript. As this did not dissolve by mixing, 37 % HCl was added until the solutions cleared (3 mL to a total volume of 50 mL). The titanium substrates (0.5 mm in thickness and 59 mm in diameter) were prepared in the same way as described for Batch 1. The clean titanium substrates were coated by spin-coating with the precursor solutions using SnCl 2 · 2 H 2 O and by drip coating for the SnCl 4 · 5 H 2 O solution. The spin coating was made at 500 rpm for 20 seconds followed by 1500 rpm for 30 seconds and the drip coating was made by dripping solution on the substrates followed by manually tilting them to spread the solution as equally as possible. After application of precursor solution, the electrodes were rst dried at 80 • C for 10 minutes and then calcinated at 500 • C for 10 minutes. The coating was repeated 7 times. After the nal layer, the electrodes were calcined at 500 • C for 60 minutes. Two electrode samples was prepared using each type of precursor solution. The loading increase per layer can be seen in Figure 4.