Optimization of the hydrogen evolution activity on zinc-nickel deposits using experimental strategies

The experimental strategies including the fractional factorial design (FFD), path of the steepest ascent study, and the central composite design (CCD) coupled with the response surface methodology (RSM) was adopted to optimize the hydrogen evolution activity of Zn-Ni deposits. The key deposition variables, pH, the Zn/Ni ionic ratio and the TEPA concentration in the plating solutions, influencing the hydrogen evolution activity of Zn-Ni cathodes were found in the FFD investigation. These variables were subjected to the steepest ascent study to approach the vicinity of the optimal deposition conditions for plating the Zn-Ni deposits with the highest hydrogen evolution activity. In the CCD investigation, the optimal deposition settings, where the temperature of 50 degreesC, the current density of 2500 A m(-2), pH of 13.0, the Zn/Ni ionic ratio of 0.89 and the TEPA concentration of 0.58 M, were obtained by means of a regression model. This highest activity of the Zn-Ni deposits mainly consisting of the gamma phase structure for hydrogen evolution is due to a combination of their good electrocatalytic activity and relatively high surface area. The electrocatalytic activity of these cathodes mainly composed of the gamma phase Zn-Ni alloy was damaged by the selective dissolution of Zn from the deposits in 5 M KOH. (C) 2002 Elsevier Science Ltd. All rights reserved.