In order to investigate the influences of the stoichiometric ratio of B/A (A: gross A-site elements, B: gross B-site elements) and the substitution of Co for Ni on the structures and electrochemical performances of th...In order to investigate the influences of the stoichiometric ratio of B/A (A: gross A-site elements, B: gross B-site elements) and the substitution of Co for Ni on the structures and electrochemical performances of the AB3.5-4.1-type electrode alloys, the La-Mg-Ni-Co system La0.75Mg0.25Ni3.5Mx (M=Ni, Co; x= 0, 0.2, 0.4, 0.6) alloys were prepared by induction melting in a helium atmosphere. The structures and electrochemical performances of the alloys were systemically measured. The results show that the structures and electrochemical performances of the alloys are closely relevant to the B/A ratio. All the alloys exhibit a multiphase structure, including two major phases, (La, Mg)2Ni7 and LaNi5, and a residual phase LaNi2, and with rising ratio B/A, the (La,Mg)2Ni7 phase decreases and the LaNi5 phase increases significantly. When ratio B/A=3.7, the alloys obtain the maximum discharge capacities. The high rate discharge(HRD) capability of the alloy (M=Ni) monotonously rises with growing B/A ratio, but that of the alloy (M=Co) first mounts up then declines. The cycle stability of the alloy (M=Co) monotonously increases with rising B/A ratio, but it first decreases slightly then increases for the alloy (M=Ni). The discharge potential of the alloy (M=Ni) declines with increasing B/A ratio (x>0.2), but for the alloy (M=Co), the result is contrary. The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed ratio B/A=3.7, the Co substitution enhances the discharge capacity from 365.7 to 401.8 mA·h/g, the capacity retention ratio (S100) after 100 charging-discharging cycles from 50.32% to 53.26% and the HRD from 88.65% to 90.69%.展开更多
The influences of annealing treatment on the electrochemical and structural properties of La 0.75Mg 0.25- Ni 2.8Co 0.5 hydrogen storage alloy were investigated by means of electrochemical studies and X-ray diffraction...The influences of annealing treatment on the electrochemical and structural properties of La 0.75Mg 0.25- Ni 2.8Co 0.5 hydrogen storage alloy were investigated by means of electrochemical studies and X-ray diffraction(XRD) analyses. The XRD results reveal that the peak width gets narrower with increasing annealing temperature, which can be ascribed to the structural change and more homogeneous composition after being annealed. Electrochemical studies show that the discharge capacity and the cycle stability of the alloy electrodes increase after being annealed. The maximum discharge capacity, exchange current density J 0 and limiting current density J L of the as-cast alloy are 388 mA·h/g, 340.5 mA/g and 3 068 mA/g, respectively, and they are increased to 400 mA·h/g, 372.1 mA/g and 3 399 mA/g for the alloy annealed at 1 123 K for 8 h, respectively. Meanwhile, as the discharge current density is 1 250 mA/g, the high rate dischargeability(HRD) increases from 77.4% for the as-cast alloy to 83.3% for the alloy annealed at 1 123 K.展开更多
基金Project(2006AA05Z132) supported by High-tech Research and Development Program of ChinaProject(50642033) supported by the National Natural Science Foundation of China+1 种基金Project(200711020703) supported by the Natural Science Foundation of Inner Mongolia, ChinaProject (20050205) supported by Science and Technology Planned Project of Inner Mongolia, China
文摘In order to investigate the influences of the stoichiometric ratio of B/A (A: gross A-site elements, B: gross B-site elements) and the substitution of Co for Ni on the structures and electrochemical performances of the AB3.5-4.1-type electrode alloys, the La-Mg-Ni-Co system La0.75Mg0.25Ni3.5Mx (M=Ni, Co; x= 0, 0.2, 0.4, 0.6) alloys were prepared by induction melting in a helium atmosphere. The structures and electrochemical performances of the alloys were systemically measured. The results show that the structures and electrochemical performances of the alloys are closely relevant to the B/A ratio. All the alloys exhibit a multiphase structure, including two major phases, (La, Mg)2Ni7 and LaNi5, and a residual phase LaNi2, and with rising ratio B/A, the (La,Mg)2Ni7 phase decreases and the LaNi5 phase increases significantly. When ratio B/A=3.7, the alloys obtain the maximum discharge capacities. The high rate discharge(HRD) capability of the alloy (M=Ni) monotonously rises with growing B/A ratio, but that of the alloy (M=Co) first mounts up then declines. The cycle stability of the alloy (M=Co) monotonously increases with rising B/A ratio, but it first decreases slightly then increases for the alloy (M=Ni). The discharge potential of the alloy (M=Ni) declines with increasing B/A ratio (x>0.2), but for the alloy (M=Co), the result is contrary. The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed ratio B/A=3.7, the Co substitution enhances the discharge capacity from 365.7 to 401.8 mA·h/g, the capacity retention ratio (S100) after 100 charging-discharging cycles from 50.32% to 53.26% and the HRD from 88.65% to 90.69%.
文摘The influences of annealing treatment on the electrochemical and structural properties of La 0.75Mg 0.25- Ni 2.8Co 0.5 hydrogen storage alloy were investigated by means of electrochemical studies and X-ray diffraction(XRD) analyses. The XRD results reveal that the peak width gets narrower with increasing annealing temperature, which can be ascribed to the structural change and more homogeneous composition after being annealed. Electrochemical studies show that the discharge capacity and the cycle stability of the alloy electrodes increase after being annealed. The maximum discharge capacity, exchange current density J 0 and limiting current density J L of the as-cast alloy are 388 mA·h/g, 340.5 mA/g and 3 068 mA/g, respectively, and they are increased to 400 mA·h/g, 372.1 mA/g and 3 399 mA/g for the alloy annealed at 1 123 K for 8 h, respectively. Meanwhile, as the discharge current density is 1 250 mA/g, the high rate dischargeability(HRD) increases from 77.4% for the as-cast alloy to 83.3% for the alloy annealed at 1 123 K.
