Electrochemical characterisation of Pd modified ceramic | carbon electrodes:: partially flooded versus wetted channel hydrophobic gas electrodes

Inert metal modified composite ceramic \ carbon electrodes (CCE) were recently introduced and found potential applications as biosensors and gas electrodes. The electrodes comprise graphite powder dispersed in hydrophobically modified silicate xerogels. The interconnected graphite network provides percolative conductivity. The silicate backbone provides rigidity and porosity. The hydrophobic moieties reject water and thus limit the thickness of the electrochemically active portion of the electrodes. Inert metal dispersion is introduced for catalysis. The characterisation of the geometric configuration of the wetted section of the gas electrodes and the inert metal dispersion in porous electrodes poses an interesting challenge since these cannot be resolved by spectroscopic or microscopic techniques or by gas adsorption isotherms. It is demonstrated that electrochemical techniques provide a means to characterise the morphology of the wetted section of Pd-modified gas electrodes. The surface area of the palladium dispersion in CCEs was characterised by cathodic stripping of adsorbed oxygen and underpotential copper deposition (upd), and the active volume of the palladium in the CCE was estimated by electrochemical formation of beta-phase palladium hydride. Finally, the parameters that were obtained by the electrochemical characterisation were used in order to fit the potential-current polarisation curves of oxygen reduction on CCEs of different compositions and preparation protocols. (C) 1999 Elsevier Science S.A. All rights reserved.