Influence of the subsurface layer on the measurements of the diffusion coefficient of hydrogen in polycrystalline palladium

Abstract

Effects of the roughness factor ƒ w of the permeation surface and of the thickness l on the galvanostatic desorption of hydrogen from a finite polycrystalline palladium electrode in 0.1 N H 2SO 4 are reported. The I aπ functions (where I a is the anodic current and π is the transition time) were measured under different conditions and further used to establish the influence of the subsurface layer on the measurements of the diffusion coefficient of hydrogen in polycrystalline palladium electrodes. The relative weight of the equilibrium processes involving the subsurface hydrogen in the overall desorption process depends on the ratio of the permeation surface area to the geometrical volume of the finite palladium electrode. The diffusion coefficient of hydrogen in palladium estimated by the galvanostatic desorption method was D = (3.98±0.09) × 10 -7 cm 2 s -1 at25 °C for a thickness l much greater than 10 -2 cm.