Kinetics analysis of Ni-TiO2 composite system during initial stages of electro-crystallization

Abstract

The initial stage of Ni-TiO2 composite system electrodeposition on glassy carbon electrode from an acidic solution of nickel sulfate was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). Analysis of current density-time transients was performed using the nonlinear fitting procedure and electrochemical impedance spectroscopy was simulated by Z-view software. Besides, the surface morphology of Ni-TiO2 co-deposition at the initial stage was observed by scanning electron microscopy (SEM). The results show that, in the case of low overpotential (−790 mV vs SCE), the presence of TiO2 particles in the plating bath makes the nucleation relaxation time tmax decreased clearly. Meanwhile, the electro-crystallization of Ni-TiO2 system follows a Scharifker-Hills (SH) progressive nucleation/growth mechanism. While in the case of higher overpotential, the presence of the TiO2 particles in solution makes the nucleation relaxation time tmax increased. At −850 mV (vs SCE), the co-deposition of Ni-TiO2 system meets SH instantaneous nucleation/growth mechanism. The results of impedance spectra show that the appearance of the characteristic inductive loops represents the nucleation/growth of nickel and the presence of TiO2 particles reduces the charge transfer resistance of solution. The SEM observation confirms that TiO2 particles can be considered as favorable sites for nickel nucleating.