Ozone is recognized as a safe and
powerful disinfectant in water that leaves no harmful residuals because it rapidly
decays into oxygen. The current method of ozone generation is cold corona
discharge, which is unfavorable because it creates harmful nitrogen oxides in
air and yields low concentrations of ozone when dissolved in water, lowering
operational efficiency. A possible solution to this problem is generating ozone
electrochemically, which can be done by choosing electrode materials that are
much more selective in oxidizing water into ozone than oxygen. Nickel- and
antimony-doped tin dioxide (NATO) has proven to be an electrode material active
for ozone generation; however, its current efficiency (i.e. selectivity of
ozone instead of oxygen) has not exceeded 50% in literature [1] and the
material has poor stability.
Typically, NATO electrodes are synthesized as a sol-gel from a coating of metal precursors decomposed thermally in air. In this study, we electrodeposit thin films of NATO to control catalyst loading and compare the effects of synthetic routes on the ozone generation reaction. From baths containing either chloride or nitrate ions, we deposit either metallic or oxide films. With chloride ions, Sn(II) is reduced directly to Sn(0) on the substrate, and then is thermally oxidized to SnO2. With nitrate ions, reduction of nitrate ions increases local pH and causes SnO to precipitate onto the substrate. The films are characterized by X-ray diffraction and Scanning Electron Microscopy/Energy Dispersive X-ray analysis, and ozone selectivity is measured with spectroelectrochemistry. We observe that thermal oxidation yields higher current efficiencies than electrochemical oxidation. Annealing time does not affect ozone current efficiency, but high annealing temperatures increase both SnO2 crystallinity and ozone current efficiency. Increasing the concentration of Sb and Ni in the electrodeposition bath increases both the amount of dopant present and the ozone current efficiency. This electrodeposited NATO synthesis method has yet to be optimized, but achieves ozone current efficiencies of 35-45%, comparable to the sol-gel method. Efforts to relate the structural and material properties of NATO to ozone selectivity and activity are ongoing.
Sources: [1]. Christensen, P. A. “Room Temperature, Electrochemical Generation of Ozone with 50% Current Efficiency in 0.5M Sulfuric Acid at Cell Voltages < 3V.” Ozone: Science and Engineering, no. 31, 2009, pp. 287–293., doi:10.1080/01919510903039309.
Typically, NATO electrodes are synthesized as a sol-gel from a coating of metal precursors decomposed thermally in air. In this study, we electrodeposit thin films of NATO to control catalyst loading and compare the effects of synthetic routes on the ozone generation reaction. From baths containing either chloride or nitrate ions, we deposit either metallic or oxide films. With chloride ions, Sn(II) is reduced directly to Sn(0) on the substrate, and then is thermally oxidized to SnO2. With nitrate ions, reduction of nitrate ions increases local pH and causes SnO to precipitate onto the substrate. The films are characterized by X-ray diffraction and Scanning Electron Microscopy/Energy Dispersive X-ray analysis, and ozone selectivity is measured with spectroelectrochemistry. We observe that thermal oxidation yields higher current efficiencies than electrochemical oxidation. Annealing time does not affect ozone current efficiency, but high annealing temperatures increase both SnO2 crystallinity and ozone current efficiency. Increasing the concentration of Sb and Ni in the electrodeposition bath increases both the amount of dopant present and the ozone current efficiency. This electrodeposited NATO synthesis method has yet to be optimized, but achieves ozone current efficiencies of 35-45%, comparable to the sol-gel method. Efforts to relate the structural and material properties of NATO to ozone selectivity and activity are ongoing.
Sources: [1]. Christensen, P. A. “Room Temperature, Electrochemical Generation of Ozone with 50% Current Efficiency in 0.5M Sulfuric Acid at Cell Voltages < 3V.” Ozone: Science and Engineering, no. 31, 2009, pp. 287–293., doi:10.1080/01919510903039309.