Anomalous electrochemical behaviour of palladium in aqueous solution

Palladium electrode surfaces in aqueous sulphuric acid solution were activated or disrupted by repeated growth and reduction of multilayer hydrous oxide films. A very low percentage (<1.0%) of the metal deposited on reduction of such films existed initially in an unusually active state. This active palladium exhibited a reversible redox transition at ca. 0.24 V (RHE) at 25 degrees C and the charge involved in the latter process was directly proportional to the much larger charge value associated with the reduction of the HO2 component in the multilayer hydrous oxide deposit. The charge associated with the active state of the metal decreased gradually, in a first-order maimer, subsequent to the generation of the active state. The nature of the active state of metal surfaces, which is assumed to be of considerable importance in heterogeneous catalysis and electrocatalysis, is discussed briefly. (C) 1999 Elsevier Science S.A. All rights reserved.