Qualitative Analysis of the Frumkin Adsorption Isotherm of the Over-Potentially Deposited Hydrogen at the Poly-Ni/KOH Aqueous Electrolyte Interface Using the Phase-Shift Method

The phase-shift method of the Frumkin adsorption isotherm of the over-potentially deposited hydrogen (OPD H) for the cathodic H 2 evolution reaction (HER) at the poly-Ni/0.05 M KOH aqueous electrolyte interface has been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift (0° ≤ -Φ ≤ 90°) for the optimum intermediate frequency corresponds well to that of the fractional surface coverage ( 1 ≥ θ ≥ 0) at the interface. The phase-shift method, i.e., the phase-shift profile (-Φ vs. E) for the optimum intermediate frequency, can he used as a new method to estimate and analyze the Frumkin adsorption isotherm (θ vs, E) of the OPD H for the cathodic HER at the interface. At the poly-Ni/0.05 M KOH aqueous electrolyte interface, the rate (r) of change of the standard free energy of the OPD H with θ, the interaction parameter (g) for the Frumkin adsorption isotherm, the equilibrium constant (K) for the OPD H with θ, and the standard free energy (ΔG θ ) of the OPD H with θ are 24.8 kJ/mol, 10, 5.9 × 10 -6 ≤ K ≤ 0.13, and 5.1 ≤ ΔG θ ≤ 29.8 kJ/mol, respectively. The electrode kinetic and thermodynamic parameters (r, g, K. ΔG θ ) depend strongly on H (0 ≤ θ ≤ 1).