Optimization of Ti-Zr-Cr-Fe alloys for 45 MPa metal hydride hydrogen compressors using orthogonal analysis

Abstract A series of (Ti1-xZrx)yCr2-zFez (x=0.1, 0.2, 0.3; y=1, 1.05, 1.1; z=0.9, 1, 1.1) alloys has been designed by orthogonal experiments for a three-stage metal hydride hydrogen compressor. XRD results show that such alloys exist as a single C14 Laves phase, and SEM with energy-dispersive spectroscopy reveals a uniform distribution of the elements. The effects of substitution of Ti by Zr, of Cr by Fe, and over-stoichiometry on the hydrogen storage properties of the Ti-Zr-Cr-Fe alloys have been investigated by orthogonal analysis. With increasing Zr content and 2A/B ratio (1, 1.05, 1.1), the cell volume and enthalpy gradually increase, while the plateau pressure and hysteresis decrease. With increasing Fe content, the cell volume and enthalpy decrease, while the plateau pressure, plateau slope, and hysteresis all dramatically increase. The (Ti0.85Zr0.15)yCr2-zFez (y=1, 1.05, 1.1; z=0.9, 1, 1.1) alloys show the largest average hydrogen storage capacity at 1.73 wt%. Besides, a simple model is proposed to predict enthalpy, which is based on the unit cell volume and average electronegativity difference with hydrogen. Finally, the (Ti0.85Zr0.15)1.05Cr1.1Fe0.9 alloy has been selected for a three-stage metal hydride hydrogen compressor. Its maximum and usable storage capacities were evaluated as 1.75 wt% and 1.40 wt%, respectively, with a dissociation plateau pressure derived from the van’t Hoff equation of 45.5 MPa at 90 °C.