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.

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift (90° ≥ −φ ≥ 0°) versus electric potential (E) behavior for the optimum intermediate frequency 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 related electrode kinetic and thermodynamic parameters. On a Pt−Ir alloy (90:10 mass ratio) 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), standard Gibbs energies (ΔG θ °) of hydrogen (H) and deuterium (D) adsorption, and rates of change (r) of ΔG θ ° of H and D with θ have been determined and are compared using the phase-shift method and correlation constants. The value of K decreases in going from H2O to D2O. The values of K for both H and D increase with increasing E and θ. Over the θ range (i.e., 1 ≥ θ ≥ 0), the value of K for H is 3.7 to 4.1 times greater than that for D. For 0.2 < θ < 0.8, a lateral attractive (g < 0) or repulsive (g > 0) interaction between the adsorbed H or D species appears. The duality of the lateral attractive and repulsive interactions is a unique feature of the adsorbed H and D species on Pt, Ir, and Pt−Ir alloys in acidic and alkaline H2O and D2O solutions.

Due to its inherent reactivity, nitroxyl (HNO), must be generated in situ through the use of donor compounds, but very few physiologically useful HNO donors exist. Novel N-substituted hydroxylamines with carbon-based leaving groups have been synthesized, and their structures confirmed by X-ray crystallography. These compounds generate HNO under nonenzymatic, physiological conditions, with the rate and amount of HNO released being dependent mainly on the nature of the leaving group. A barbituric acid and a pyrazolone derivative have been developed as efficient HNO donors with half-lives at pH 7.4, 37 °C of 0.7 and 9.5 min, respectively.

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.