Inhibition of the hydrogen evolution reaction on nickel in acidic chloride solutions

The cathodic polarization of Ni in hydrochloric acid solutions has been investigated using the galvanostatic technique. The rate of hydrogen evolution reaction was found to depend on the concentration and pH of the solution. The reaction order with respect to hydrogen ion was found to be one. The rise of temperature enhances the rate of hydrogen evolution reaction. The activation energy, DeltaH{*}, for such process was found to be 10kcal. mol(-1). The effect of aniline and some of its derivatives (o-, m- and p-anisidine) on the cathodic polarization of nickel in 1M HCl solution was also studied. These compounds were found to inhibit the rate of hydrogen evolution reaction without affect on its mechanism. The inhibition efficiency depended on the concentration and type of the inhibitor. The inhibition efficiency ranged between 73 and 92 per cent at the highest concentration (10(-2) M), and ranged between 24 and 60 per cent at the lowest concentration (10(-4)M). This corresponded to surface coverage of the metal by the inhibitor. The degrees of surface coverage, theta, were calculated and found to increase with the inhibitor concentration. The results show also that, the inhibitors were adsorbed on the nickel surface according to Langmuir adsorption isotherm.