CHRONOPOTENTIOMETRIC DEPOSITION / DISSOLUTION KINETICS AND TEXTURAL ANALYSIS OF Ni-Fe OXY HYDROXIDE NANO FILMS

Nano oxy hydroxides of Ni and Fe are electrochemically deposited from sulfate-based bath via, hydrogen evolution and peroxide formation reactions. From chronopotentiometric and chronoamperometric transients, it can be noted that, non-faradaic, anomalous co-deposition occurs due to charge-transfer limitations, which in turn enhances the formation of β-Ni(OH)2. Unlike cathodic cycle, during anodic dissolution, iron rich films preferentially oxidized by two-electron-transfer with lower coulombic charge. Using self-designed computer simulation program, coded in MS-Visual Studio ‘Crystalsim’, {kkl} family planes are indexed along with d-spacing data. From FTIR, O-H stretching signal for both Ni and Fe hydroxides was observed. Transformation of acicular to nano-sphered morphology was noted in presence of NO3- rather than H+ with an average grain size is about 25 nm. With the increase in cathodic current density, grain growth rate is enhanced by diffusion limitations of Ni2+ and e- transfer rate of Fe2+ is enhanced. Deposition kinetics is under charge-transfer control at lower cathodic current density and becomes diffusion limited towards cathodic interface due to the change in concentration overpotential, at higher current density.