Thermodynamic Investigations of a Hydrogen Electrode Reaction in a Molten LiCl-KCl-LiH System

摘要

The equilibrium potential of the H_2/H~- couple has been measured in a molten LiCl-KCl-LiH system at 643-883 K. The Nernst relation holds for the potential at hydrogen pressure, P_(H_2) of 0.1-1.0 atm and H~- ion concentration, X_(H~-), of 0.002-0.080 (anion fraction). The standard formal potential of H_2/H~-, E_(H_2/H~-)~(0'), is evaluated to be 0.258 +- 0.002 V (vs. Li~+/Li) (p_(H_2) = 1 atm, X_(H~-) = 1) at 673 K. E_(H_2/H~-)~(0') changes linearly with temperature at 643-883 K, having the gradient of -0.575 +- 0.011 mV K~(-1). Thermodynamic quantities for formation of LiH in the melt are also estimated. When the activity coefficient of H~- ion, gamma_(H~-), is defined as unity in pure liquid LiH (X_(H~-) = 1), gamma_(H~-) in the dilute H~- region (0.002 <= X_(H~-) <= 0.080) is evaluated to be 7.1.