Adsorption of thiourea and formation of nickel-thiourea complexes at initial stage of nickel deposition

Abstract

The effect of thiourea(TU) on the nickel deposition process was analyzed by means of linear-sweep voltammetry. Raman spectroscopy and infrared reflectance spectroscopy were used to investigate the adsorption of TU and the formation of nickel-TU complexes on copper surface. The experimental results indicate that the nucleation and the preceding conversion step are involved in the deposition of nickel on copper electrodes. TU makes the onset nucleation potential negative due to the formation of nickel-TU complexes, which can accelerate the nickel deposition. Moreover, the S atom in the TU molecule adsorbed on copper surface facilitates the coordination of TU to Ni2+. Meanwhile, TU might be adsorbed at a flatter orientation if no Ni2+ is on the surface, while at a perpendicular orientation when Ni2+ is coadsorbed.