Properties of Pd–Ru–Rh electrodeposits studied by electrochemical, structural and spectroscopic methods

Pd–Ru–Rh electrodeposits were obtained potentiostatically from aqueous baths containing different concentrations of Pd, Ru and Rh ions. The formation of Pd–Ru–Rh alloys was confirmed electrochemically through the examination of sample properties in the acidic solution with the use of cyclic voltammetry. The alloy formation was also proved with the use of energy dispersive X-ray spectroscopy and X-ray diffraction. XRD and EDX measurements have certified the homogeneity of a single bulk alloy phase. The XRD results show that the lattice parameter of the Pd–Ru–Rh alloy is smaller than that of Pd, i.e. Pd, Ru and Rh form contracted alloys. This is also mirrored in the course of hydrogen absorption curves (H/M vs. E), with the α–β phase transition region shifted into lower potentials. Pd–Ru–Rh alloys with ca. 98.5% Pd in the bulk absorb by ca. 11% more hydrogen than pure Pd. In the process of electrochemical aging, the surface and bulk of Pd–Ru–Rh electrodes become enriched with Pd due to the preferential electrochemical dissolution of Ru and Rh.