Electrochemical oxidation of a carbon black loaded polymer electrode in aqueous electrolytes

The suitability of a polymeric composite material for use as part of an ano de structure in a cathodic protection system has been examined. The composi te material was a conductive blend (volume resistivity typically 1.5 Omega cm) of carbon black in a polyethylene binder. A long operational lifetime f or the material demands that the rate of carbon loss must be low. In the wo rk reported here, electrochemical and in situ analytical techniques were em ployed to characterise the performance of the material over a wide range of anodic current densities in a variety of aqueous electrolytes. The predomi nant anodic electrochemical reaction on the polymeric material is CO2 forma tion in acid and neutral solutions, which causes loss of carbon from the su rface and the development of a non-conducting layer of polyethylene. The ch aracteristics of the reaction suggest that it occurs via the discharge of H 2O. In alkaline pH, however, the anodic reactions are more complex. A high OH- concentration (pH 12 or higher) favours the formation of oxygen rather than CO2, particularly at low anodic potentials. The presence of CO32- in t he electrolyte catalyses the evolution of oxygen at pH values as low as 9. The electrochemical formation of oxygen always occurs in parallel with the generation of some humic acid in the solution.