Effect of the substitution of PR for LA on the microstructure and electrochemical properties of La_(0.7_x)Pr_xMg_(0.3)Ni_(2.45)Co_(0.75)Mn_(0.1) Al_(0.2) (x =0.0-0.3) hydrogen storage electrode alloys

摘要

In this paper, the effects of substitution of Pr for La on the microstructure and electrochemical properties of La_(0.7-x)Pr_xMg_(0.3)Ni_(2.45)Co_(0.75) Mn_(0.1)Al_(0.2) (x = 0.00-0.30) hydrogen storage alloys have been studied systematically. XRD Rietveld analyses showed that all alloys consisted of (La, Mg)Ni_3 phase and LaNi_5 phase. With the increase in Pr content, the lattice parameters and cell volumes of the component phases all decreased. The electrochemical studies showed that the maximum discharge capacity decreased from 366 to 346 mAh/g when x increased from 0.00 to 0.30. However, the cycling stability of the alloy electrodes was improved with the increase in Pr content. Moreover, the high rate dischargeability, the exchange current density I_0, the limiting current density I_L and the hydrogen diffusion coefficient D of the alloy electrodes all increased first then decreased with increasing x, reaching an extreme when x is 0.15, which indicated that the alloys' kinetics of hydriding/dehydriding increased first up to x = 0.15 and then decreased with further increasing x to x = 0.30.