An Electrochemical Study of Sb and Ni Doped SnO2 Electrodes for Ozone Electrolysis

Electrochemical formation of ozone as an alternative to gas phase formation via the corona discharge process (CDP) has been investigated for several decades. Most anode materials show very low current efficiency at room temperature[1] because of the competing oxygen formation reaction. Up until ten years ago, the most promising material in this respect was PbO2 coated anodes, reaching a current efficiency of ~13% at room temperature[2]. Boron doped diamond (BDD) as electrode coating has also shown promising results for the ozone formation reaction[3]. Ten years ago Wang et al.[4] discovered that antimony doped tin oxide (ATO) additionally doped with nickel (NATO) could produce ozone at high current efficiency at low overpotentials. Since then, current efficiencies as high as ~50% at room temperature have been reached, enabling the process to be as, or more energy efficient than CDP[5] while avoiding the expensive BDD and toxic PbO2. In the studies concerning ozone formation on NATO, SnCl4.5H2O has been used as the source of tin. This is a very volatile specie, making the composition of the oxide coating unpredictable and potentially very different from the precursor solution used for preparation. In this study, SnCl2.2H2O has been used as an alternative source of tin. Because of its lower volatility, the electrode coating can be made with a much higher deposition efficiency, thus yielding a cheaper and faster preparation process. As most previous studies have optimized the precursor solution composition based on tin tetrachloride, we suspect that the dopant concentrations in the final coating have been underestimated. We have here varied the concentrations of antimony and nickel in relation to tin, and compared to our previous study of SnO2 from the two different tin sources. To evaluate the kinetics and selectivity, the electrodes were examined by polarization curves and cyclic voltammetry as well as in situ ozone measurement during potential sweep and galvanostatic electrolysis. [1] Y-H Wang and Q-Y Chen. Journal of Electrochemistry, 2013:1-7, 2013. [2] P.C. Foller. Journal of The Electrochemical Society, 129(3):506, 1982. [3] P-A. Michaud. Journal of Applied Electrochemistry, 33(2):151-154, 2003. [4] Y-H Wang et al. Journal of The Electrochemical Society, 152(11):D197, 2005. [5] P.A. Christensen et al. Ozone: Science and Engineering, 31(4):287-293, Jul 2009.