Electrochemical Quartz Crystal Microbalance Study on the Kinetics of Nickel Monolayer and Multilayer Electrodeposition on (111)-Oriented Gold Films

The electrodeposition of nickel on (111)-oriented gold films has been studied in electrolytes with different Ni 2+ concentrations and/or pH values using the electrochemical quartz crystal microbalance (EQCM). In all solutions, potential step experiments reveal two regimes with different deposition rates, which can be assigned to the deposition of the first Ni layer on the Au substrate and to the growth of subsequent Ni layers, respectively. Deposition of the monolayer is 10−20 times faster than Ni multilayer growth, indicating that the charge-transfer reaction is enhanced on the gold surface as compared to that on the already deposited Ni. For Ni multilayer deposition, we find Tafel slopes of 88−104 mV/decade, in good agreement with previous data, whereas, in the (sub-)monolayer regime, we obtain a slope of ≈40 mV/decade. This indicates a change in the rate-limiting step, which is attributed to the inhibiting effects of coadsorbates on the Ni surface. Furthermore, the studies revealed an increasing current efficiency of the Ni electrodeposition with increasing overpotential. In contrast to the case of Ni deposition, preliminary EQCM results on Co and Fe electrodeposition show a reduced deposition rate in the monolayer range as compared to that at multilayer coverages.