Palladium electrodeposits: Dependence of structure and sorption propertieson the deposition potential

A series of Pd electrodeposits (edPd) on Pt substrates is prepared at depos ition potentials of -0.05 to 0.55 V with respect to a reversible hydrogen e lectrode in 0.5 M H2SO4. Their nanostructure is characterized by scanning t unneling microscopy. The size distribution of particles is estimated, and d ependences of its maximum and half width on the deposition potential are de termined. A comparative coulometric study of adsorption of copper and oxyge n on edPd shows that real surface areas determined from these data substant ially 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 show n that the equilibrium hydrogen content in the alpha and beta hydrides is a nomalously high for the deposits whose growth was accompanied by deep hydro genation of Pd. At a given effective pressure, for the alpha-phase, this va lue is always substantially higher as compared with less defective material s. In the beta-phase, the hydrogen concentration can be either lower or hig her.