Abstract
A study was made to reveal the relation between the hydrogen evolution on and entry into nickel in an aqueous solution of 100 mol·m−3 sulfuric acid using an electrochemical technique.
Nickel foils were electrolytically charged with hydrogen kept at uniform concentrations in the ranges of hydrogen overpotentials 0.1-0.3 V and temperatures 298-343 K. The rates of hydrogen desorption from the hydrogen-charged foils were measured, immediately after the palladium plating following the cathodic charging, at a potential of 0.1 V against a saturated calomel electrode in an aqueous solution of 100 mol·m−3 sodium hydroxide at different temperatures ranging from 276.5 to 343 K. The diffusivity and solubility coefficients for hydrogen in nickel were calculated from the hydrogen desorption rate-time curves, and the values of hydrogen fugacity in conceptual cavities immediately below the cathodic surfaces were obtained from the solubility coefficients by using Sieverts’ law.
The internal hydrogen fugacity, fH2, of the cathodic surface is expressed experimentally as follows:
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oindentwhere η is the hydrogen overpotential, F the Faraday constant, R the gas constant, and T the absolute temperature. It seems that the hydrogen solubility at the reversible hydrogen potential is equivalent to that existing in equilibrium with a hydrogen fugacity of 101 kPa. The heat of solution of hydrogen for nickel changes by (0.655±0.003)ηF with hydrogen overpotential.
