The Langmuir adsorption isotherms of over-potentially deposited hydrogen ͑OPD H͒ for the cathodic hydrogen evolution reaction ͑HER͒ at poly-Au and Rh/0.5 M H 2 SO 4 aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift (0°р Ϫ р 90°) for the optimum intermediate frequency can be linearly related to that of the fractional surface coverage (1 у у 0) of OPD H for the cathodic HER at the interfaces. The phase-shift profile ͑Ϫ vs. E͒ for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm ͑ vs. E͒ of the OPD H for the cathodic HER at the interfaces. At the poly-Au/0.5 M H 2 SO 4 aqueous electrolyte interface, the equilibrium constant ͑K͒ and the standard free energy (⌬G ads ) of the OPD H are 2.3 ϫ 10 Ϫ6 and 32.2 kJ/mol, respectively. At the poly-Rh/0.5 M H 2 SO 4 aqueous electrolyte interface, K and ⌬G ads of the OPD H are 4.1 ϫ 10 Ϫ4 or 1.2 ϫ 10 Ϫ2 and 19.3 or 11.0 kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, two different Langmuir adsorption isotherms of OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of OPD H correspond to two different adsorption sites of OPD H on the poly-Rh electrode surface.

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The phase-shift method of the Frumkin adsorption isotherm of the over-potentially deposited hydrogen (OPD H) for the cathodic H2 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 false(0°⩽−ϕ⩽90°false) for the optimum intermediate frequency corresponds well to that of the fractional surface coverage false(1⩾θ⩾0false) at the interface. The phase-shift method, i.e., the phase-shift profile false(−ϕ vs. Efalse) for the optimum intermediate frequency, can be used as a new method to estimate and analyze the Frumkin adsorption isotherm (θ vs. Efalse) of the OPD H for the cathodic HER at the interface. At the poly-Ni/0.05 M KOH aqueous electrolyte interface, the rate false(rfalse) of change of the standard free energy of the OPD H with θ, the interaction parameter false(gfalse) for the Frumkin adsorption isotherm, the equilibrium constant false(Kfalse) for the OPD H with θ, and the standard free energy false(normalΔGθfalse) of the OPD H with θ are 24.8 kJ/mol, 10, 5.9×10−6⩽K⩽0.13, and 5.1⩽normalΔGθ⩽29.8 normalkJ/normalmol, respectively. The electrode kinetic and thermodynamic parameters false(r, g, K, normalΔGθfalse) depend strongly on θ false(0⩽θ⩽1false). © 2002 The Electrochemical Society. All rights reserved.

The phase-shift method f or the Frumkin adsorption isotherms at the Pd/acidic (H2SO4) and alkaline (KOH) solution interfaces has been studied using an ac impedance method. The phase shift (p) depends on the cathode potential (E < 0) and is inversely proportional to the fractional surface coverage (0) of the adsorbed hydrogen atom (Had,). The phase-shift profile (p vs. E) at the intermediate frequencies (ca. 130 Hz for the 0.1 M H2504 solution and ca. 63 Hz for the 0.1 M KOH solution) can be used as an experimental method to estimate or plot the Frumkin adsorption isotherm (0 vs. E). The rates (r) of change of the free energy of adsorption with 0 at the Pd/0.1 M H2S04 and 0.1 M KOH solution interfaces are 7.4 and 49.6 kJ/mol, respectively The equilibrium constant (K) and the standard free energy (AG9) of H, at the Pd/0.1 M H2S04 solution interface are 5.0 >< 10 < Kc 1.0 )< l0and 35.9 > AG9 > 28.5 kJ/mol, respectively The esuilibrium constant (K) and the standard free energy (AG9) of H9th at the Pd/0.1 M KOH solution interface are 2.1 x 10 ' AG0> 34.2 kJ/mol, respectively The electrode kinetic parameters (r, K, AG9) depend on 0 (0 <0 < 1).

The electrolytic decomposition effect of normalGaAs particles on electrochemical phenomena at the Pt/10−3 M normalKCl aqueous solution interface has been studied using voltammetric, time‐based, and electrochemical‐impedance techniques. The observed anodic decomposition effect of the normalGaAs particles on electrochemical phenomena was significant within the positive potential range (0 to 1.0 V vs. SCE). On the other hand, the cathodic decomposition effect of the normalGaAs particles was negligible in the negative potential range (0 to −1.0 V vs. SCE). The normalGaAs particles act as current activators or mediators during the anodic process and act as charge screens during the cathodic process. The solution resistance and related total impedance were increased due to the presence of the normalGaAs particles. The anodic decomposition of the normalGaAs particles can be used to increase the hydrogen evolution at the counterelectrode.