귀금속(Au, Rh) 전극계면에서 Langmuir 흡착등온식에 관한 위상이동방법

Abstract

The Langmuir adsorption isotherms of the over-potentially deposited hydrogen (OPD H) fur the cathodic <TEX>$H_2$</TEX> evolution reaction (HER) at the poly-Au and <TEX>$Rh|0.5M\;H_2SO_4$</TEX> aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift <TEX>$(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$</TEX> for the optimum intermediate frequency corresponds well to that of the fractional surface coverage <TEX>$(1{\geq}{\theta}{\geq}0)$</TEX> at the interfaces. The phase-shift profile <TEX>$({-\phi}\;vs.\;E)$</TEX> 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 <TEX>$({\theta}\;vs.\;E)$</TEX> of the OPD H for the cathodic HER at the interfaces. At the poly-Au|0.5M <TEX>$H_2SO_4$</TEX> aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy <TEX>$({\Delta}G_{ads})$</TEX> of the OPD H are <TEX>$2.3\times10^{-6}$</TEX> and 32.2kJ/mol, respectively. At the poly-Rh|0.5M <TEX>$H_2SO_4$</TEX> aqueous electrolyte interface, K and <TEX>${\Delta}G_{ads}$</TEX> of the OPD H are <TEX>$4.1\times10^4\;or\;1.2\times10^{-2}$</TEX> and 19.3 or 11.0kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, the two different Langmuir adsorption isotherms of the OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of the OPD H correspond to the two different adsorption sites of the OPD H on the poly-Rh electrode surface.