A new method of determining the thermodynamic parameters of metal hydride electrode materials

Thermodynamic parameters of the hydriding reaction of a hydride electrode can be obtained by two different methods. The results show that the change of enthalpy ΔH, change of entropy ΔS and hydrogen pressure calculated from e-c-T curves of electrochemical reactions have much larger inherent errors compared with those obtained from p-c-T curves of alloys in hydriding reactions with hydrogen gas (gaseous method). The hydrogen storage capacities determined by gaseous and electrochemical methods are also different, owing to the low utilization factor, and diffusion of hydrogen into air and formation of hydrogen gas bubbles in electrolyte in an unsealed battery. ΔHe0 and ΔSe0 as well as the relations between ΔHe0, ΔSe0 of the electrochemical reaction and gaseous ΔHp0, ΔSp0 have also been derived on the basis of the Nernst equation. Much more accurate results have thus been assured.