Analysis of ultrasonically enhanced hydrogen evolution for Zn-NiCl₂ system

Abstract

Sonication has been found to influence significantly the rate of hydrogen evolution from a Zn/NiCl₂ (aqueous) system. The evolution of hydrogen is the result of pit corrosion experienced by zinc, and its rate is the net result of surface kinetics, ohmic resistance or mass transfer contribution both inside and outside the pit. Ultrasonication is shown to remove the mass transfer contribution and make the process ohmically controlled. This is confirmed by using solutions having different conductivities, which yield different rates of hydrogen evolution. In one case sonication results in the lowering of hydrogen evolution rate thus providing a rare example where sonication lowers the overall reaction rate. A model assuming the deposition of nickel patches on zinc surface followed by the growth of pits in zinc has been developed. The model requires the experimental evaluation of one lumped parameter from one set of data and is able to explain satisfactorily the remaining sets of data obtained under different experimental conditions.