BDD, PbO2,Sb-doped SnO2, RuO2 and IrO2 Anode for Electrochemical Oxidation of Organic Pollutants

Electrochemical oxidation processes have been used for treating various wastewater since it produces highly active hydroxyl radicals (•OH) that are promising in the removal of anions, toxic metals, pharmaceuticals, chromium, arsenic, organic pollutants, and bio-refractory wastewater.

Various electrode materials include BDD, PbO2, Pt, Ti/IrO2, glassy carbon, SnO2-Sb and graphite have been investigated for the electrochemical oxidation of organic pollutants. Some anodes favor the selective oxidation or conversion of the organics to various metabolites, while others can achieve complete degradation of organics to CO2 and H2O.

Boron Doped Diamond (BDD) electrode has a large electro-activity window with a high overpotential for O2 evolution. It enables the large production of hydroxyl radicals by water discharge on the BDD surface. BDD electrode is found to be promising electrocatalytic materials with enhanced mineralization of refractory organics. The main impediment to the large-scale application of BDD electrodes is the high cost of the substrate onto which the BDD the film is deposited (Nb, W, Ta) and its poor mechanical strength in the case of Si substrate.

Lead dioxide (PbO2), with its high oxygen overpotential, is one of the most commonly used DSA anodes for the removal of organic contamination. However, the application of PbO2 may lead to secondary water pollution due to electrochemical corrosion.

Sb-doped SnO2 anode has been demonstrated to have relatively high OEP and be superior for the oxidation of organic compounds. It is cost-effective compared with other MMO anodes, making it more attractive for the electrochemical oxidation process. Pollutants such as phenol and phenolic compounds can be readily oxidized at SnO2-Sb anode, favoring complete oxidation of pollutants to CO2 and H2O. However, the short service life of the SnO2-Sb electrode resulting from the weak adhesion between Ti substrate and SnO2.

RuO2 and IrO2 are known to be active electro-catalysts for chlorine evolution, being RuO2 more active than IrO2. IrO 2 is one of the cheapest dimensionally stable anodes and shows low chlorine and oxygen evolution overpotential. The addition of NaCl as a supporting electrolyte improves the removal efficiency, indicating that electrochemical treatment using Ti/IrO 2 and Ti/RuO 2 involves both direct and indirect oxidation. Enhancement in the COD removal efficiency was observed due to oxidation mediated by the electrochemically generated oxidants in the presence of chloride ions using Ti/RuO 2 anode in wastewater treatment. The degradation process involved the formation of intermediates followed by further oxidation to CO 2 and water.