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The performance of highly doped SnO2 anodes for the oxidative treatment of biologically refi'actory waste water was compared with PbO2 and Pt. The oxidation of a wide range of organic compounds proceeds with an efficiency which is about 5 times higher than with platinum anodes. The oxidation efficiency was found to be independent of the pH of the wa_ter. In chloride containing media, SnO2 anodes produce less chlorine gas than platinum anodes and hence show less potential to form hazardous chlorinated organic by-products. The design of a simple plate-and-frame reactor with undivided cells for waste water treatment using SnO2 anodes was based on two experimental findings: (a) no interference of the cathode with the oxidation has been found: (b) the rate of oxidation is not limited by mass transfer, indicating the participation of homogeneous reactions in the overatl oxidation. The new anode material reduces the specific energy requirement of electrochemical oxidation of organics in waste water to 30 to 50kWhkg-~ of COD removed. This makes the process an interesting alternative to chemical oxidation using oxidants such as ozone and hydrogen peroxide, or wet oxidation using oxygen at elevated temperature and pressure.

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The anodic oxidation of iridium and O2 evolution on iridium oxide films in 1N H2SO4 has been investigated using x‐ray photoelectron spectroscopy. The binding energy of the O 1s level decreases with anodic polarization of the electrode while the relative amount of oxygen compared to iridium remains constant. The XPS results are consistent with a model of subsequent deprotonation of the anodic iridium oxide upon anodic polarization. A reaction path for O2 evolution and corrosion on iridium oxide is proposed. Valence band spectra of the oxide surfaces confirm the proposed model.

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