Development of metal hydride with high dissociation pressure

The effective hydrogen capacity of Ti1.1CrMn exhibited the maximum value of 1.8 wt% in the pressure range of 33 and 0.1 MPa at 296 K (dissociation pressure: 11 MPa), and the alloy provided over 10% more capacity than conventional TiCrMn (Ti1.2CrMn: 1.6 wt%, Ti1.2Cr1.9Mn0.1: 1.3 wt%). At the low temperature of 233 K, the alloy absorbed 2.0 wt% of hydrogen and the hydrogen desorption capacity at 0.1 MPa was 1.6 wt%. The desorption capacity of conventional TiCrV was 0 at 233 K due to the low dissociation pressure. The dissociation pressure decreased with the Ti and the Mn contents and was explained by the function of the bulk modulus and the cell volume. According to the Van’t Hoff plots, the standard enthalpy difference (heat of formation) of the Ti1.1CrMn hydride was −22 kJ/mol H2. The absolute value was about 10 kJ/mol H2 smaller than those of LaNi5 and TiCrV. The alloy had sufficient hydriding and dehydriding kinetics. In the pressure range of 33 and 0.1 MPa at 296 K, the alloy absorbed and desorbed 1.8 wt% of hydrogen in 60 and 300 s, respectively. The hydrogen capacity changed gradually over many cycles and that after 1000 cycles was 94% of the initial capacity. Thus, Ti1.1CrMn can be utilized for a high-pressure MH tank, which contains a hydrogen-absorbing alloy with high dissociation pressure and compressed hydrogen.