THE DETERMINATION OF THE COVERAGE ON NICKEL AND STEEL DURING ELECTROLYTIC HYDROGEN EVOLUTION
PENNSYLVANIA UNIV PHILADELPHIA JOHN HARRISON LAB OF CHEMISTRY
Pagination or Media Count:
The galvanostatic double charging method was applied to determine the coverage of Ni cathodes with adsorbed atomic H in 2 N NaOH solutions. Anodic current densities were varied from 0.05 to 1.8 ampsq cm. The plateau indicating absence of readsorption was between 0.6 and 1.8 ampsq cm, for a constant cathodic c.d. of 110,000 ampsq cm. The variation of the adsorbed H over cathodic c.d.s ranging from 10 to the -6th power to 110 at a constant anodic c.d. of 1 ampsq cm were calculated and the coverage calculated. The mechanism of the H evolution reaction was elucidated. The rate determining step is discharge from a water molecules followed by rapid Tafel recombination. The rate constants for these processes and the rate constant for the ionisation, calculated with the extrapolated value of coverage for the reversible H electrode, were determined. A modification of the Tafel equation which takes into account both coverage and ionisation is in harmony with the results. A new method for the determination of coverage suitable for corrodible metals is described which involves the measurement of the rate of permeation of H by electrochemical techniques which enhances the sensitivity of the method.
- Metallurgy and Metallography