The Frumkin adsorption isotherm of the over-potentially deposited hydrogen (OPD H) for the cathodic $H_2$ evolution reaction (HER) at the poly-Ni|0.05M KOH aqueous electrolyte interface has been studied using the phase-shift method. The behavior of the phase shift $(0^{circ}leq{phi}leq90^{circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1geq{ heta}geq0)$ at the interface. The phase-shift method, i.e., the Phase-shift profile $(-{phi};vs.;E)$ for the optimum intermediate frequency, can be used as a new method to estimate the Frumkin adsorption isotherm $( heta;vs.;E)$ of the OPD H for the cathodic HER at the interface. At the poly-Ni|0.05M KOH aqueous electrolyte interface, the rate (r) of change of the standard free energy of the OPD H with $ heta$, the interaction parameter (g) for the Frumkin adsorption isotherm, the equilibrium constant (K) for the OPD H with $ heta$, and the standard free energy $({Delta}G_{ heta})$ of the OPD H with ${ heta}$ are $24.8kJ mol^{-1},;10,;5.9 imes10^{-6}{leq}K{leq}0.13,;and;5.1leq{Delta}G_{ heta}leq29.8kJ;mol^{-1}$. The electrode kinetic parameters $(r,;g,;K,;{Delta}G_{ heta})$ depend strongly on ${ heta} (0{leq}{ heta}{leq}1)$