Preparation and evaluation of electrocatalytic oxide coatings on conductive carbon-polymer composite substrates for use as dimensionally stable anodes

Abstract

This work investigates the feasibility of developing a lower cost dimensionally stable anode based on a polymer substrate by examining possible methods of applying coatings, such as MnO₂, to catalyse the oxygen evolution reaction. The conductive polymer is based on a blend of polypropylene and a rubber, to provide the mechanical strength and acid resistance of the electrode, with graphite fibre and carbon black dispersed through the composite to ensure a reasonable conductivity. Of the different compositions analysed, the best incorporated Degussa XE-2 carbon black. This material not only displays an overpotential at its bare surface which was comparable to the lead electrode, but also it provides excellent contact with the catalyst coatings. Two methods of applying a catalytic coating, thermal decomposition and pressed oxide coating, are evaluated. Coatings prepared by thermal decomposition displays an overpotential greater than the standard lead electrode, although the poor performance of the catalysts is found to be due to poor contact with the conductive sites of the substrate and to incomplete thermal decomposition of the metal chlorides to the oxide. The pressed oxide coating method is the technique developed during this work to take advantage of the properties of the polymer composites. Polymer substrates are heated until soft and the MnO₂ catalyst (in its active form) is pushed into the surface. Electrodes coated in this manner with MnO₂ all display excellent overpotentials which, on average, are 0.2 V less than the lead electrodes. Extension of this technique to the coating of polymeric substrates with other catalytic oxides shows great potential.