Effect of praseodymium substitution for lanthanum on structure and properties of La0.65–xPrxNd0.12Mg0.23Ni3.4Al0.1(x=0.00–0.20) hydrogen storage alloys

In order to investigate the effect of substituting La with Pr on structural and hydrogen storage properties of La-Mg-Ni system (AB3.5-type) hydrogen storage alloys, a series of La0.65–xPrxNd0.12Mg0.23Ni3.4Al0.1 (x=0, 0.10, 0.15, 0.2) hydrogen storage alloys were prepared. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) analyses revealed that two alloys (x=0.0 and 0.10) were composed of (La, Mg)2(Ni, Al)7 phase, La(Ni, Al)5 phase and (La, Mg)Ni2 phase, while other alloys (x=0.15 and 0.20) consisted of (La, Mg)2(Ni, Al)7 phase, La(Ni, Al)5 phase, (La, Mg)Ni2 phase and (La, Mg)(Ni, Al)3 phase. All alloys showed, however, only one pressure plateau in P-C isotherms. The Pr/La ratio in alloy composition influenced hydrogen storage capacity and kinetics properties. Electrochemical studies showed that the discharge capacity decreased from 360 mAh/g (x=0.00) to 335 mAh/g (x=0.20) as x increased. But the high-rate dischargeability (HRD) of alloy electrodes increased from 26% (x=0.00) to 56% (x=0.20) at a discharge current density of Id=1800 mA/g. Anode polarization measurements were done to further understand the electrochemical kinetics properties after Pr substitution.