Yanping Fan

Phase structure and electrochemical properties of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-xFex hydrogen storage alloys

Abstract La 0.7 Ce 0.3 Ni 3.75 Mn 0.35 Al 0.15 Cu 0.75- x Fe x ( x =0–0.20) hydrogen storage alloys were synthesized by induction melting and subsequent annealing treatment, and phase structure and electrochemical characteristics were investigated. All alloys consist of a single LaNi 5 phase with CaCu 5 structure, and the lattice constant a and the cell volume ( V ) of the LaNi 5 phase increase with increasing x value. The maximum discharge capacity gradually decreases from 319.0 mA·h/g ( x =0) to 291.9 mA·h/g ( x =0.20) with the increase in x value. The high-rate dischargeability at the discharge current density of 1200 mA/g decreases monotonically from 53.1% ( x =0) to 44.2% ( x =0.20). The cycling stability increases with increasing x from 0 to 0.20, which is mainly ascribed to the improvement of the pulverization resistance.

Microstructures and hydrogen storage properties of as-cast and copper-mould-cast LaMg4Ni alloys

Phase compositions, morphologies and hydrogen storage properties of the as-cast and copper-mould-cast LaMg4Ni alloys were studied. The dehydriding onset temperature of the as-cast alloy hydride was about 500 K, which was at least 50 K higher than that of the copper-mould-cast one, and the copper-mould-cast alloy hydride had a faster dehydriding rate compared with as-cast one. Additionally, the copper-mould-cast alloy could uptake 2.85 wt.% hydrogen, which was 95.0% of saturated hydrogen storage capacity at room temperature. While only 1.80 wt.% hydrogen (60% of saturated capacity) was absorbed for the as-cast alloy under the same conditions. The reversible hydrogen storage capacities and plateau hydrogen pressures of the two alloys were close. X-ray diffractions and scanning electron microscopy results indicated that similar thermodynamic property of the two alloys should be ascribed to the same hydrogen storage phase, Mg and Mg2Ni. The better hydrogen sorption kinetics of copper-mould-cast alloy should be ascribed to the more uniform phase distribution compared with that of the as-cast one.

Phase structure and electrochemical properties of non-stoichiometric La0.7Ce0.3(Ni3.65Cu0.75Mn0.35Al0.15(Fe0.43B0.57)0.10)x hydrogen storage alloys

Abstract Phase structure and electrochemical characteristics of Co-free La0.7Ce0.3(Ni3.65Cu0.75Mn0.35Al0.15(Fe0.43B0.57)0.10)x (0.90≤x≤1.10) alloys were investigated. When x was 0.90, the alloy was composed of LaNi5, La3Ni13B2 and Ce2Ni7 phases. The Ce2Ni7 phase disappeared, and the abundant of La3Ni13B2 phase decreased when x increased to 0.95. When x was 1.00 or higher the alloys consisted of LaNi5 phase. The lattice parameter a and the cell volume V of the LaNi5 phase decreased, and the c/a ratio of the LaNi5 phase increased with x value increasing. Maximum discharge capacity of the alloy electrodes first increased and then decreased with x value increasing from 0.90 to 1.10, and the highest value was obtained when x was 1.00. High-rate dischargeability at the discharge current density of 1200 mA/g increased from 50.7% (x= 0.90) to 64.1% (x=1.10). Both the charge-transfer reaction at the electrode/electrolyte interface and the hydrogen diffusion in the alloy were responsible for the high-rate dischargeability. Cycling capacity retention rate at 100th cycle (S100) gradually increased from 77.3% (x= 0.90) to 84.6% (x=1.10), which resulted from the increase in Ni content and the c/a ratio of the LaNi5 phase with x value increasing.

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

Abstract W 0.42 Fe 0.58 alloy, instead of pure W and Fe, was used to substitute Co in LaNi 3.70 Co 0.2 Mn 0.30 Al 0.15 Cu 0.65 alloy to improve the overall electrochemical properties with the decrement of the cost. Microstructures and electrochemical characteristics of LaNi 3.70 Co 0.2– x Mn 0.30 Al 0.15 Cu 0.65 (W 0.42 Fe 0.58 ) x ( x =0–0.20) hydrogen storage alloys were characterized. X-ray diffraction patterns and backscattered electron images indicated that the pristine alloy was LaNi 5 phase, while the alloys containing W 0.42 Fe 0.58 were made of LaNi 5 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 LaNi 5 phase increased with increasing x value. Activation property of the alloy electrodes was improved by substituting Co by W 0.42 Fe 0.58 . 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.