Platinum crystallite size effects on the electrocatalytic oxidation and deposition of adsorbed hydrogen—III

Abstract

Kinetic parameters for the oxidation and deposition of the two adsorbed hydrogen species on platinum in acid were examined using rapid linear potentiodynamic scans with good agreement between the theory and experimental data. Specific rate constants obtained from the magnitudes of the current peak potential shifts from quasi-equilibrium with potential scan rates were shown to be dependent upon the surface areas of the platinum electrocatalysts. It is postulated that the decrease in the specific rate constant with decreasing platinum crystallite size is caused by an increasing preponderance of surface platinum atoms as a fraction of the total atom content in the crystallites. Changes in the electronic, “metallic” or ionic—co-valent character of the surface platinum atoms are reflected in the changes of this specific rate constant and is an indication of the importance of the electronic structure due to the electrocatalyst sites in determining the electrocatalytic activity.