Study of electrooxidation of binary electrolytic deposit palladium–bismuth deposited on graphite electrode surface

The phase structure of palladium–bismuth binary electrolytic deposit was studied. The electrodeposition of deposit components on the surface of a graphite electrode (GE) was carried out in situ. On current–voltage curves, the peak of bismuth electrooxidation, the peak of palladium electrooxidation and an additional peak at 0.15 V vs. Ag/AgCl are observed. The peak current at 0.15 V depends both on the concentration of palladium(II) ions and on that of bismuth(III) ions. The thermodynamic theory of alloys in the approximation of the theory of regular solutions was used for calculations. The mixing heat of the binary alloy components and the equilibrium potential of bismuth in the bismuth–palladium alloy are calculated. The calculated equilibrium potential of bismuth in an alloy with palladium is 0.12 V vs. Ag/AgCl which corresponds to the Bi₂Pd intermetallic compound (IMC). Investigation of the surface of a GE with a palladium–bismuth deposit with use of scanning electron microscope showed that the electrolytic deposit contains bismuth, palladium and the Bi₂Pd IMC. Peak at the potential of plus 0.15 V vs. Ag/AgCl is due to selective bismuth electrooxidation from the Bi₂Pd IMC.