Palladium electrodeposits: Dependence of structure and sorption properties on the deposition potential

Abstract

A series of Pd electrodeposits (edPd) on Pt substrates is prepared at deposition potentials of -0.05 to 0.55 V with respect to a reversible hydrogen electrode in 0.5 M H2SO4. Their nanostructure is characterized by scanning tunneling microscopy. The size distribution of particles is estimated, and dependences of its maximum and half width on the deposition potential are determined. A comparative coulometric study of adsorption of copper and oxygen on edPd shows that real surface areas determined from these data substantially differ. The average size of particles for edPd, estimated within the model of equal-size spheres, is shown to be incorrect. The assumption that particles in the deposits essentially coalesce is substantiated. It is shown that the equilibrium hydrogen content in thea and β hydrides is anomalously high for the deposits whose growth was accompanied by deep hydrogenation of Pd. At a given effective pressure, for the α-phase, this value is always substantially higher as compared with less defective materials. In the β-phase, the hydrogen concentration can be either lower or higher