The hyperstoichiometric ZrMn1 + xFe1 + y− H2 system I: Hydrogen storage characteristics

Abstract

The ZrMn 1 + x Fe 1 + y −H 2 systems with x, y = 0.11-0.53 and x + y ⩽ 0.64 were studied as a function of composition, temperature (0–200 °C) and hydrogen dissociation pressure (0.01–50 atm). The hyperstoichiometric manganese and iron appear to substitute at the zirconium sites with a net effect of raising the vapor pressure of their hydrides to 500–1500 times that of ZrMn 2 hydride. The ZrMn 1.27Fe 1.58 alloy does not absorb measurable quantities of hydrogen, presumably because of the very high vapor pressure of its hypothetical hydride. The hydrides of ZrMn 1.22Fe 1.11 and ZrMn 1.11Fe 1.22 alloys have dissociation pressures in the range of 1–2 atm at room temperature. The hydrogen capacities of these alloys are quite high, e.g. about 185 cm 3 g −1. Enthalpies and entropies of dehydrogenation, obtained from a van't Hoff plot of ln p H 2 versus 1/ T, are very low, being 9.8–13.4 kJ (mol H 2) −1 and 42–53 J (mol H 2) −1 K −1 respectively. The kinetics of hydrogen absorption and desorption are extremely fast.