| In this paper, a novel electrochemical ozone generator using Nafion membrane, pure water electrolyte and an oxygen diffusion electrode was designed and manufactured. The preparation method of air electrode and anode, the electrochemical properties of the electrode and the factor affecting the properties as well were invesitigated extensively by the means of XRD, TEM and electrochemical measurements. The conditions for the generation of ozone were optimized and the various factors affecting the SPE/ Air ozone generator were studied systematically. The conclusions were as follows: (1) The electrochemical properties of the electrode without water-proof films was superior to that of the one with it. The addition of acetylene black into electrode reduced the resistance and improved the the rougbness. However, the addition of acetylene black resulted in the decrease of electrocatalytic activity due to the hetrogenously deposition of the catalyst. The optimized quantity of PTFE in the electrode 2Owt%. (2) For the loadings of catalysts, Brush-Reduction method was proved more suitable than the Impregnation-Reduction method. The electrochemical reaction occurring on the the active carbon and Mn02 was 2e reaction, the reaction occurring on the binary noble metal catalyst was approximately 4e reaction, ,however, the reaction on the noble metal catalyst was between 2e and 4e reaction. In this paper, the optimized loadings of metal catalysts was 0.4mg/cm2 , which was only 1/5?1/10 compared to the reported loadings. (3) The thin-liquid-film theory, which was suitable for this experiment was proposed, the mass-transport flux of oxygen in the diffusion film was obtained N0 (4) Compared with the ozone generator with the evolution of hydrogen, the cell voltage of SPE/air electrode ozone generator was 3.78V at the current density of IA/cm2 , which reduced by 0.86V. The current efficiency and 03 output reached 13.74% and 245.93mg/h repectively, which increased by 52.5%. And the power consumption was 92.22Wh/g03 which reduced by 46.44%. The homemade SPE membrane couldn substitute the Nafion membrane due to its limitation in the performances. The anode prepared by Pb02 that was manufactured by Tianiin YaoHua Chemical Engineering Factory had the best overall properties and lowest price, its applications was potential. (5) The electrolyte temperature and the cell voltage were kept at 300C and 3.60V over a period of 450 hoursoperation at the current density of 1 A/cm2. The constant current efficiency and the 03 output of 10% and 1 80mg/h respectively was achieved and the pH of the electrolyte kept constant stability over the long time operation.. After long time operation, the decrease of the crystal grian of f3 -Pb02 resulted in the shrinkage of surface area of the electrode. The partial loss of Pt loadings due to the decrease of the cohesion between the catalyst and the substrate will caused the deterioration of the performances of the ozone generator. (6) For air electrode using active carbon or graphite as major source of catalytic layer, an extra mass-transport feature was noticeable in the low frequency region, so the electrode performance was greatly decreased compared to carbon nanotubes. The AC impedance of carbon nanotubes consisted of two semi-cirles, of which the high frequency was ascribed to the ohmic process and the low frequency to the electrochemical kinetic process. The impedance of the diffusion process of oxygen was not occurred. |
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