Electrochemical PCT isotherm study of hydrogen absorption/desorption in AB5 type intermetallic compounds

The enthalpy (ΔH) and entropy (ΔS) of hydride formation/decomposition could be determined either experimentally or theoretically based on models proposed in the literature. The experimental pathway includes gas/solid-phase measurement of pressure–composition–temperature (PCT) isotherms at different temperatures. This measurement is followed by plotting of van't Hoff dependences and evaluation of the ΔH and ΔS from their slopes and intersects, respectively. In this study we demonstrate the applicability of electrochemical PCT isotherm measurements as an advanced method for thermodynamic analysis of hydrogen adsorption/desorption process. Experimentally this is done by electrochemical charging/discharging of an electrode, prepared from AB5 type alloy with MmNi4.6Co0.6Al0.8 composition (Mm – mischmetal). In addition, the hydride formation as a result of the electrochemical charging is independently confirmed by ex-situ XRD diffraction. Our work demonstrates that not only the electrochemical approach is a viable alternative of PCT gas/solid-phase measurement but it also represents a safer, cost-effective and faster protocol than its hydrogen gas–solid phase equivalent.