Optimization of AB2 type alloy composition with superior hydrogen storage properties for stationary applications

Improved hydrogen storage properties for an ambient temperature (30-35 degrees C) and moderate pressure (1-15 bar) stationary hydrogen storage application have been achieved for Laves phase AB(2) type alloys by introducing non-stoichiometry at the A site. A range of (Ti0.65Zr0.35)(1+x)MnCr0.8Fe0.2 (x = 0, 0.05, 0.075 and 0.1) C14 Laves phase AB(2) type alloys have been synthesized by levitation induction melting under an argon atmosphere. X-ray diffraction revealed formation of a single phase with a C14 Laves phase hexagonal structure with the space group of P63/mmc. From Pressure-Composition-Isotherm measurements, the maximum hydrogen storage capacity was found to be around 2.2 wt% at 35 bar and 32 degrees C for (Ti0.65Zr0.35)(1.1)MnCr0.8Fe0.2, which is approximately 16% higher than that of the commercially available Hydralloy C5. The (Ti0.65Zr0.35)(1.05)MnCr0.8Fe0.2 alloy has a hydrogenation Delta H of -26 +/- 2 kJ/mol H-2 and Delta S of -98 +/- 5 J/K/mol H-2. The hydrogenation kinetics of these alloys are relatively fast reaching full capacity within 10 min without any requirement for activation. The hydrogenation kinetics data for (Ti0.65Zr0.35)(1.05)MnCr0.8Fe0.2 at different temperatures were analysed using rate equations and the activation energy was found to be 19 +/- 1 kJ/mol in the alpha + beta phase and 29 +/- 2 kJ/mol in the beta phase. Pseudo van't Hoff plot from high pressure DSC data gave thermodynamic results comparable with that measured from the PCI, proving as a comparative screening method to determine this thermodynamic data. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.