EQCM studies on Pd-Ni alloy oxidation in basic solution

Processes of electrochemical oxidation of Pd-rich Pd-Ni alloys in basic solutions were studied with the aim of electrochemical quartz crystal microbalance. Potentials of current peaks of Ni(II)/Ni(III) redox couple are independent of alloy composition. On the other hand, Ni(II)/Ni(III) redox couples formed on Pd-Ni alloys and Ni differ in respect to the structure of involved compounds and the processes of transport of the species accompanying oxidation/reduction reaction. The process of oxidation of Pd exhibits some differences between pure Pd and Pd-Ni alloys. This concerns mainly on participation of adsorbed water/OH- in Pd oxidation process. In the initial stages of Pd oxidation, the source of oxygen is water/OH- from the bulk of the solution. At this stage of the process, the product of Pd oxidation could be described as Pd(OH)(2) or PdOH2O. With further progress in oxidation process, adsorbed species, water/OH-, start to play a decisive role. Hydrous species, i.e. Pd(OH)(2) or PdOH2O, are also reduced in the final stages of Pd(II) reduction process.