STUDY OF THE POWDER MEMBRANE INTERFACE BY USING THE POWDER MICROELECTRODE TECHNIQUE I - THE PT-BLACK/NAFION(R) INTERFACES/

The polarization behavior of a Pt microdisk electrode, a platinized Pt microdisk electrode and a Pt-black powder microelectrode immersed in sulfuric acid solution, in contact with a moist Nafion(R) membrane wer e studied by cyclic voltammetry. The experimental results reveal that the surface diffusion of the adsorbed species plays an important role in determining the kinetics of interfacial reactions taking place at t he powder/Nafion(R) membrane interface. The weakly adsorbed hydrogen a toms diffuse significantly faster than the strongly adsorbed hydrogen and the oxygen-containing surface species. Surface active sites in the range of tens of microns from the powder/Nafion(R) interface can be i nvolved in interfacial reactions. The apparent coefficients of diffusi on of various surface species were estimated from the variation of pea k current with scan rate of potential. The apparently higher irreversi bility of electrode reaction observed at the powder/membrane composite electrode is explained by considering mechanism of current generation of this type of electrode. (C) 1998 Elsevier Science Ltd. All rights reserved.