Kinetics of the volmer reaction on platinum-gold alloys in sulphuric acid solution

Abstract

Impedance measurements were carried out on heterogeneous platinum-gold alloys at anodic potentials in the region of hydrogen adsorption by voltammetry with superimposed a.c. voltage between 10,000 and 100 c/sec in N H₂SO₄ at 30°C. The capacitative and ohmic component of the impedance resulting from the Volmer reaction depend upon the potential in a similar way on the platinum-rich alloys as on smooth platinum. The impedance of a gold-rich alloy is determined by the small amount of the platinum-rich phase on the surface. The discharge resistance of the Volmer reaction was obtained as a function of hydrogen coverage for the different alloys whose surface composition was characterized by the charge equivalent of a monolayer of H-atoms adsorbed on the platinum-rich phase. The discharge resistance was correlated to the surface composition at constant coverages. This correlation is discussed under consideration of the heterogeneity of the surface of the alloys.