Nanotopography and electrochemical impedance spectroscopy of palladium deposited on different electrode materials

The objective of this work was to describe the characteristics of chemically and electrochemically deposited Pd surface layers on HOPG and polycrystalline gold electrode, using in situ ECSTM and EIS measurements, and SEM-EDX element analysis. Pd surface layers were deposited, in successive voltammetric cycles, and anodically dissolved in 0.01 M HCl+0.01 M (NH₄)₂PdCl₄ aqueous electrolyte. Both of the electrode materials used in the study were treated as standard testing electrodes: (i) HOPG for STM/ECSTM measurements, and (ii) polycrystalline Au as the well known working electrode in various electro-analytical applications. The elements surface analysis and nano-surface pictures were used to interpret the EIS diagrams and electrical equivalent circuits. Pd chemical and electrochemical deposition on the HOPG surface was compared with the same process on the polycrystalline gold electrode, on which palladium can be electrodeposited only by means of electrochemical cathodic deposition. Surface topographies of the electrodeposited palladium layers on HOPG and Au were completely different. The equivalent electrical circuits were fitted and the surface roughness of the investigated electrodes calculated. Relations between the surface topography, EIS and SEM-EDX, and interface model of the electrolyte solution electrodeposited Pd layer matrix electrode were proposed.