Hydrogen storage properties of as-cast and annealed low-Co La1.8Ti0.2MgNi8.9Co0.1 alloys

Low-Co La1.8Ti0.2MgNi8.9Co0.1 alloys were prepared by magnetic levitation melting followed by annealing treatment. The effect of annealing on the hydrogen storage properties of the alloys was investigated systematically by X-ray diffraction (XRD), pressure-composition isotherm (PCI), and electrochemical measurements. The results show that all samples contain LaNi5 and LaMg2Ni9 phases. LaCo5 phase appears at 1,000 degrees C. The enthalpy change of all hydrides is close to -30.6 kJ.mol(-1) H-2 of LaNi5 compound. Annealing not only increases hydrogen capacity and improves cycling stability but also decreases plateau pressure at 800 and 900 degrees C. After annealing, the contraction of cell volume and the increase of hydride stability cause the high rate dischargeability to reduce slightly. The optimum alloy is found to be one annealed at 900 degrees C, with its hydrogen capacity reaching up to 1.53 wt%, and discharge capacity remaining 225.1 mAh.g(-1) after 140 charge-discharge cycles.