Zhao Dongliang

Study on Hydrogen in Mixed Gas Separated by Rare Earth Hydrogen Storage Alloys

AB5-type rare-earth nickel (RE-Ni) based hydrogen storage alloys and AB3-type La-Mg-Ni based hydrogen storage alloys were prepared by vacuum medium-frequency induction melting in argon atmosphere. Industrial offgas was simulated by the mixed gas including H2, N2 and CH4. The purity of hydrogen separated by rare-earth hydrogen storage alloys and anti-poison and anti-pulverization properties of the alloys in the process of hydrogen absorption and desorption were studied. The results show that AB5-type RE-Ni based hydrogen storage alloys are possessed of the single structure with CaCu5-type, and AB3-type La-Mg-Ni based hydrogen storage alloys are possessed of the multi-phase structure with (La, Mg) Ni3, LaNi5 and LaNi2 phase. The hydrogen storage alloys will be poisoned by impurity gas in the separation of hydrogen, resulting in lower speed rate of hydrogen absorption and lesser capacity of hydrogen absorption. The anti-pulverization property of La-Mg-Ni based alloys is better than that of LaNi5 alloy and its complex alloy. LaNi3.7Mn0.4Al0.3Fe0.4Co0.2 alloy is considered as better alloy to separate hydrogen from the mixed gas, considering the purity of separated hydrogen, anti-poison and anti-pulverization property of the alloy. The hydrogen purity of 90.7% can be achieved.

Electrochemical Hydrogen Storage Characteristics of the as-Cast and Annealed La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0∼0.4) Electrode Alloys

Abstract The electrode alloys with the chemical compositions of La 0.8- x Pr x Mg 0.2 Ni 3.35 Al 0.1 Si 0.05 ( x =0, 0.1, 0.2, 0.3, 0.4) were prepared by casting and annealing. The effects of Pr substitution on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated. The results indicate that the as-cast and the annealed alloys consist of Ce 2 Ni 7 -type hexagonal (La, Mg) 2 Ni 7 phase and CaCu 5 -type hexagonal LaNi 5 phase as well as a little residual phase LaNi 3 . The substitution of Pr for La observably affects the electrochemical hydrogen storage characteristics of the alloys. The discharge capacity and the high rate discharge ability (HRD) of the as-cast and the annealed alloys first increase and then decline with the growing of Pr content. The as-cast and the annealed ( x =0.3) alloys yield the largest discharge capacities of 363.1 and 389.7 mAh/g, respectively. The electrochemical cycle stability of the as-cast and the annealed alloys markedly grows with the rising of Pr content. The capacity retaining rate ( S 100 ) at 100th charging and discharging cycle is enhanced from 64.96% to 77.94% for the as-cast alloy, and from 72.82% to 91.81% for the as-annealed alloy by raising Pr content from 0 to 0.4.

Electrochemical and Hydrogen Absorption/Desorption Properties of Nanocrystalline Mg2Ni-type Alloys Prepared by Melt Spinning

Abstract The nanocrystalline Mg2Ni-type alloys with the compositions of Mg20Ni10−xCux (x=0, 1, 2, 3, 4) were synthesized by melt spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system, and their hydriding and dehydriding kinetics were measured by an automatically controlled Sieverts apparatus. The results show that all the as-spun alloys hold a typical nanocrystalline structure. The substitution of Cu for Ni improves the electrochemical hydrogen storage performances of the alloys significantly, involving both the discharge capacity and the electrochemical cycle stability. Furthermore, the hydrogen absorption capacity of the alloy first increases and then decreases with the rising of Cu content, but the hydrogen desorption capacity grows dramatically for the same reason.

Influence of Melt Spinning on the Electrochemical Hydrogen Storage Kinetics of RE-Mg-Ni-Based A2B7-Type Alloys

Abstract In order to improve the electrochemical characteristics of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M=Pr, Zr) for La has been performed. The melt spinning technology was used to prepare the La0.65M0.1Mg0.25Ni3.2Co0.2Al0.1 (M=Pr, Zr) electrode alloys. The influences of the melt spinning and substithting La with M (M=Pr, Zr) on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The results obtained by XRD and TEM reveal that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun (M=Pr) alloy displays an entire nanocrystalline structure, while an amorphous-like structure is detected in the as-spun (M=Zr) alloy, implying that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurement indicates that the high rate discharge ability (HRD) of the alloys first mounts up and then falls with rising of spinning rate. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics first increase and then decreases with growing of spinning rate.

Effects of Rapid Quenching on Structure and Hydrogen Storage Characteristics of Mg20Ni10-xMnx (x=0-4) Alloys

Abstract In order to improve the hydrogen storage characteristics of the Mg 2 Ni-type alloys, Ni in the alloy was partially substituted by Mn. Rapid quenching technology was used to prepare the Mg 20 Ni 10- x Mn x ( x =0, 1, 2, 3, 4) hydrogen storage alloys. The microstructures of the as-cast and quenched alloys were characterized by XRD and HRTEM. The hydriding and dehydriding kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical performances were tested by an automatic galvanostatic system. The results show that, as the quenching rate reaches to 20 m/s, an amorphous phase can be detected in the ( x =4) alloy, and the amorphization degree of the alloy visibly increases with the growing of the quenching rate. The rapid quenching improves the hydrogen absorption and desorption characteristics of the alloy dramatically. Additionally, it also enhances the electrochemical hydrogen storage performances greatly, including the discharge capacity and cycle stability of the alloys substituted by Mn.

Investigation of Electrochemical Hydrogen Storage Kinetics of Melt Spun Nanocrystalline and Amorphous Mg2Ni-type Alloy

Abstract The Mg 2 Ni-type Mg 2 Ni 1− x Co x ( x =0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage kinetics of the as-spun alloy ribbons was tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves were plotted by an electrochemical workstation. The results show that the as-spun Co-free alloy exhibits a typical nanocrystalline structure, while the as-spun ( x =0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg 2 Ni-type alloy. The amorphization degree of the as-spun alloys substituted by Co visibly increases with the increase in the amount of Co replacement. The Co replacement for Ni notably improves the electrochemical hydrogen storage kinetics of the alloys. With a growth in the amount of Co replacement from 0 to 0.4, the high rate discharge ability of the as-spun (25 m/s) alloy increases from 65.3% to 75.3%, the hydrogen diffusion coefficient ( D ) from 2.22 to 3.34 cm 2 /s and the limiting current density I L from 247.8 to 712.4 mA/g, respectively.

Hydrogen Storage Behaviour of Nanocrystalline and Amorphous Mg20Ni10-xCox (x=0~4) Alloys by Melt-Spinning

Abstract In order to improve the hydriding and dehydriding behaviour of the Mg 2 Ni-type alloys, Ni in the alloy was partially substituted by Co, and melt-spinning technology was used to prepare the Mg 20 Ni 10− x Co x ( x =0, 1, 2, 3, 4) hydrogen storage alloys. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The hydriding and dehydriding kinetics as well as the electrochemical performances of the alloys were measured. The results show that no amorphous phase is detected in the as-spun Co-free alloy, but the as-spun alloys substituted by Co display the presence of an amorphous phase. The substitution of Co for Ni and the melt spinning significantly improve the hydrogen absorption and desorption performances of the as-cast and spun alloys. Meanwhile, the substitution of Co for Ni enhances the discharge capacity and cycle stability of the as-spun alloys dramatically.