Abstract:

La_0.8-xGd_0.2Mg_xNi_3.1Co_0.3Al_0.1(x=0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4) alloys were prepared by induction melting followed by annealing treatment at 1173 K for 8 h in Ar atmosphere. Phase structure analyses show that main phase is the Ce₂Ni₇-type phase and the phase abundance of Ce₂Ni₇- and Gd₂Co₇-type is 98.8% at the lower Mg content. When x≥0.25, the alloys are mainly composed of A₂B₇-type, CaCu₅-type and PuNi₃-type structure. The phase abundance of the PuNi₃- and CaCu₅-type phase increase with the high content of Mg. The unit cell parameters of main phases decrease and hydrogen absorption plateau rises with the increasing content of Mg. Electrochemical measurements show that as the Mg content increases, the discharge capacity and cyclic stability of alloy electrodes both first increase and then decrease. La_0.65Gd_0.2Mg_0.15·Ni_3.1Co_0.3Al_0.1 alloy electrode exhibits the maximum electrochemical discharge capacity(393 mA·h/g) and the best cyclic stability(S₁₀₀=92.82%). The high rate dischargeability first decreases then increases and final decreases. The appropriate Mg content improves electrochemical kinetics property of alloy electrodes.

Key words: Rare earth-Mg-Ni-based hydrogen storage alloy, Magnesium, Phase structure, Hydrogen absorption property, Electrochemical property