Determination of the Frumkin and Temkin Adsorption Isotherms of Hydrogen at Nickel/Acidic and Alkaline Aqueous Solution Interfaces Using the Phase-Shift Method and Correlation Constants

Abstract

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift (<TEX>$90^{\circ}{\geq}-{\varphi}{\geq}0^{\circ}$</TEX>) vs. potential (E) behavior for the optimum intermediate frequency (<TEX>$f_o$</TEX>) and the fractional surface coverage (<TEX>$0{\leq}{\theta}{\leq}1$</TEX>) vs. E behavior, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and the related electrode kinetic and thermodynamic parameters. At Ni/0.5 M <TEX>$H_2SO_4$</TEX> and 0.1M LiOH aqueous solution interfaces, the Frumkin and Temkin adsorption isotherms (<TEX>${\theta}$</TEX> vs. E) of H for the cathodic hydrogen (<TEX>$H_2$</TEX>) evolution, interaction parameters (g), equilibrium constants (K), standard Gibbs energies (<TEX>${\Delta}G^0_{\theta}$</TEX>) of H adsorption, and rates of change (r) of <TEX>${\Delta}G^0_{\theta}$</TEX> with <TEX>${\theta}$</TEX> have been determined using the phase-shift method and correlation constants. A lateral repulsive interaction (g>0) between the adsorbed H species appears. The value of K in the alkaline aqueous solution is much greater than that in the acidic aqueous solution.