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 (90o ≥−ϕ≥ 0o) vs. potential (E) behavior for the optimum intermediate frequency (fo) and the fractional surface coverage (0 ≤θ≤ 1) 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/0.5M H2SO4 and 0.1M LiOH aqueous solution interfaces, the Frumkin and Temkin adsorption isotherms (θ vs. E) of H for the cathodic hydrogen (H2) evolution, interaction parameters (g), equilibrium constants (K), standard Gibbs energies (∆Gθ o) of H adsorption, and rates of change (r) of ∆Gθ o with θ 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.