Determination of Adsorption Isotherms of Hydroxide and Deuteroxide on Pt—Ir Alloy in LiOH Solutions Using the Phase-Shift Method and Correlation Constants

The phase-shift method and correlation constants, that is, unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the behavior (−φ vs E) of the phase shift (90° ≥ −φ ≥ 0°) for the optimum intermediate frequency and that (θ vs E) of the fractional surface coverage (0 ≤ θ ≤ 1) of intermediates for sequential reactions, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On Pt−Ir (90:10 % (by weight)) alloy in 0.1 M LiOH (H2O) and 0.1 M LiOH (D2O) solutions, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants (K), interaction parameters (g), rates (r) of change of the standard Gibbs energies of hydroxide (OH) and hydroxide and deuteroxide (OH, OD) with θ, and standard Gibbs energies (ΔGθ0) of OH and (OH, OD) are determined and compared using the phase-shift method and correlation constants. Depending on θ (0 ≤ θ ≤ 1), the value of K for O...