Effect of WFe substitution on microstructures and electrochemical hydrogen storage properties of LaNi3.70Co0.2–xMn0.30Al0.15Cu0.65(W0.42Fe0.58)x alloys

W0.42Fe0.58 alloy, instead of pure W and Fe, was used to substitute Co in LaNi3.70Co0.2Mn0.30Al0.15Cu0.65 alloy to improve the overall electrochemical properties with the decrement of the cost. Microstructures and electrochemical characteristics of LaNi3.70Co0.2–xMn0.30Al0.15Cu0.65(W0.42Fe0.58)x (x=0–0.20) hydrogen storage alloys were characterized. X-ray diffraction patterns and backscattered electron images indicated that the pristine alloy was LaNi5 phase, while the alloys containing W0.42Fe0.58 were made of LaNi5 matrix phase and W phase. The relatived abundance of W phase increased with the increase in x value. Lattice parameters a, c, c /a and cell volume V of LaNi5 phase increased with increasing x value. Activation property of the alloy electrodes was improved by substituting Co by W0.42Fe0.58. As x increased from 0 to 0.20, maximum discharge capacity of alloy electrodes decreased from 335.4 (x=0) to 320.7 mAh/g (x=0.20). The high-rate dischargeability at the discharge current density of 1200 mA increased from 59.8% (x=0) to 76.8% (x=0.10), and then decreased to 64.7% (x=0.20). The cycling capacity retention rate at the 100th cycle decreased from 80.4% (x=0) to 55.8% (x=0.20), which should be ascribed to the degradation of the corrosion resistance and electrochemical kinetics of alloy electrodes.

XRD patterns of LaNi3.70Co0.2–xMn0.30-Al0.15Cu0.65(W0.42Fe0.58)x alloys (a) XRD patterns for x=0–0.20; (b) Rietveld analysis pattern for x=0.15Figure optionsDownload as PowerPoint slide