Effect of Electroplating Variables on Electrodeposition of Ni Rich Ni-Ir Alloys from Citrate Aqueous Solutions

Abstract

Nickel–iridium (Ni–Ir) alloy system is of great interest for catalytic and corrosive environment applications. In this study, Ni-Ir alloys were galvanostatically electrodeposited on copper substrates from citrate aqueous solutions in a three-electrode cell system. The effects of deposition variables, including pH, temperature and current density, on the faradaic efficiency (FE), chemical composition, surface morphology and crystallographic structure of the films were studied. The electrochemical behaviors of Ir, Ni and co-deposited alloys were investigated using cyclic voltammetric, chronopotentiometric and chronoamperometric techniques. The results show that Ni–Ir alloys as thick as 25.7 μm with Ir–content as high as 15 at% and the FE as high as 36% were obtained. By adjusting these deposition parameters, the optimum pH, temperature and current density for deposition of Ni-Ir alloys were 5.0, 70°C and 60 mA·cm−2, respectively. As the deposition variables were varied, the abundant of Ni-content in the deposit was obtained. The alloy was composed of nanocrystalline phase. The deposition of Ni ions was favored, and the co-deposition of Ni-Ir alloy was a normal deposition. The chronoamperometric transient nucleation at the potentials of −0.25 and −3.0 V were consistent with the model of diffusion-controlled 3D nucleation.