Study on the structure and hydrogen absorption–desorption characteristics of as-cast and annealed La0.78Mg0.22Ni3.48Co0.22Cu0.12 alloys

La0.78Mg0.22Ni3.48Co0.22Cu0.12 alloy is one kind of nonstoichiometric AB3.5 type hydrogen storage alloy with low cost and high capacity. In this paper, the effect of annealing treatment on the structure and hydrogen absorption–desorption characteristics of the alloy is discussed. The annealing temperature is determined by using thermogravimetry–differential scanning calorimetry (TG–DSC) tests. The structure of as-cast and annealed alloys is examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that the crystal cell volume decreases after annealing treatment. SEM tests reveal that the structure of the annealed alloys is more regular than that of the as-cast alloy. Influences of annealing treatment on maximum and reversible hydrogen storage capacity, hysteresis factor (Hf) between hydrogen absorption and desorption, sloping factor (Sf), enthalpy changes (ΔH) and entropy changes (ΔS) of hydrogen absorption are discussed in detail.

► Temperature of annealing treatment was ascertained by TG–DSC tests.
► The structure of hydrogen storage alloy was homogenized by annealing treatment.
► The hydrogen absorbing plateau pressure was elevated by the decreased crystal cell volume.
► The hysteresis between hydrogen absorption and desorption were enhanced by annealing treatment despite the improvement of plateau performance.