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We have demonstrated an extremely facile procedure for the preparation of 1D porous Ni@C nanostructures by pyrolysis of Ni-based coordination polymer nanorods. The highly aligned Ni-based polymer nanorods were prepared using nitrilotriacetic acid (NTA) as a chelating agent by a one-step solvothermal approach. The obtained precursors are demonstrated to have a well-designed 1D nanostructure and a 3D interconnected mesoporous texture. After thermal treatment, 1D porous Ni@C nanorods were obtained, which basically preserved the morphology of the precursors. In addition, the carbon in the porous Ni@C nanorods is in both crystalline and amorphous states. The as-prepared Ni@C sample displays nanorod-like morphology with about 3 μm length and about 200 nm diameter. With a large surface area of 161.4 m(2) g(-1), this novel material had a good catalytic effect on de/hydrogenation of MgH2. The desorption peak temperature of MgH2-5 wt% Ni@C composites can be lowered more than 57 °C than the pure as-milled MgH2. The MgH2-5 wt% Ni@C composite could desorb 6.4 wt% H2 within 10 min at 300 °C, in contrast, only 2.3 wt% H2 was desorbed even after 100 min for pure MgH2. In addition, an activation energy of 108 kJ mol(-1) for the as-milled MgH2-5 wt% Ni@C composites has been obtained, which exhibit an enhanced kinetics.

Highly crumpled graphene nanosheets (GNS) with a BET surface area as high as 1159 m(2) g(-1) was fabricated by a thermal exfoliation method. A systematic investigation was performed on the hydrogen sorption properties of MgH(2)-5 wt% GNS nanocomposites acquired by ball-milling. It was found that the as-synthesized GNS exhibited a superior catalytic effect on hydrogenation/dehydrogenation of MgH(2). Differential Scanning Calorimetry (DSC) and isothermal hydrogenation/dehydrogenation measurements indicated that both hydrogen sorption capacity and dehydrogenation/hydrogenation kinetics of the composites improved with increasing milling time. The composites MgH(2)-GNS milled for 20 h can absorb 6.6 wt% H(2) within 1 min at 300 °C and 6.3 wt% within 40 min at 200 °C, even at 150 °C, it can also absorb 6.0 wt% H(2) within 180 min. It was also demonstrated that MgH(2)-GNS-20 h could release 6.1 wt% H(2) at 300 °C within 40 min. In addition, microstructure measurements based on XRD, SEM, TEM as well as Raman spectra revealed that the grain size of thus-prepared MgH(2)-GNS nanocomposites decreased with increasing milling time, moreover, the graphene layers were broken into smaller graphene nanosheets in a disordered and irregular manner during milling. It was confirmed that these smaller graphene nanosheets on the composite surface, providing more edge sites and hydrogen diffusion channels, prevented the nanograins from sintering and agglomerating, thus, leading to promotion of the hydrogenation/dehydrogenation kinetics of MgH(2).

Abstract: To study the effect of CuO on the electrochemical properties of MgNi alloy, the MgNi–xCuO (x =3, 5 and 10wt%) composites were prepared by ball-milling method. The X-ray diffraction (XRD) analysis showed that the structures of the composites were amorphous. The cycle stability of the composites was improved compared to pure MgNi alloy due to the enhancement of the anti-corrosion property in the alkaline electrolyte, and the composite with 5wt% CuO ball-milled for 15h exhibited the best performance. Electrochemical impedance spectroscopy (EIS) and potential-step measurements indicated that the electrochemical kinetics of the composites was improved. [Copyright &y& Elsevier]

Abstract: Mg-based hydrogen storage alloys were successfully prepared by means of mechanical alloying (MA). The structure and the electrochemical characteristics of these Mg-based electrodes were also studied. The result of X-ray diffraction (XRD) shows that the main phases of the alloys exhibit amorphous structures. The charge–discharge cycle tests indicate these alloys have good electrochemical active characteristics. Among these alloys, the has the best cycle stability. After 50 cycles charge–discharge, the discharge capacity of alloy is 66.67% higher than MgNi alloy. The cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and anticorruption test (potentiodynamic polarization) were also studied, and the results show that the electrochemical cycle stability of these alloys was improved by Al and Ce substitutions. [Copyright &y& Elsevier]

A new hybrid nanocatalyst Ni-CeO x /GNS (graphene nanosheets supported nanoscale Ni and CeO x , x = 1.69) of high surface area and porosity is synthesized by impregnation-reduction method. It is demonstrated that the Ni-CeO x /GNS nanocatalyst exhibits improved catalytic effect on the dehydrogenation performances of MgH 2 compares to individual Ni/GNS, CeO x /GNS, or GNS. Differential scanning calorimetry (DSC) measurement proved that both the onset and peak desorption temperature of MgH 2 -5 wt% Ni-CeO x /GNS (abbreviated as MgNCG) nanocomposites can be decreased by 90.2 and 60.1 °C, respectively. Isothermal desorption kinetic test confirmed that the dehydrogenation kinetics of MgNCG nanocomposites is dozens of times higher than the pure milled MgH 2 , e.g. MgNCG nanocomposites can release 6.50 wt% H 2 within 10 min at 300 °C with an initial hydrogen pressure of 5 KPa, superior to 0.16 wt% H 2 desorbed by MgH 2 under the same condition. Additionally, the activation energy (Ea) of MgNCG decreases significantly contrast with pure milled MgH 2 , it is proposed that the tri-component of Ni-CeO x /GNS nanocatalyst has a synergistic effect on the highly efficient dehydrogenation of MgH 2 . [ABSTRACT FROM AUTHOR]

Abstract: CoB alloy prepared by arc melting possesses excellent cyclic stability but low discharge capacity, while AB3 hydrogen storage alloy prepared by inductive melting exhibits high discharge capacity but poor cyclic stability as negative electrode materials of alkaline rechargeable nickel-based batteries. A series of CoB-x wt.% AB3 mixtures were synthesized by simple mixing of CoB alloy powders and AB3 alloy powders. Electrochemical measurements revealed that the reversible discharge capacity and cycle stability of the mixture electrodes were largely improved, compared with CoB alloy electrode and AB3 alloy electrode. The CoB-x wt.% AB3 (x =20) electrode displays the highest discharge capacity of the 40th cycle and the CoB-x wt.% AB3 (x =10) electrode displays the highest discharge capacity of the 100th cycle among all the mixture electrodes. The electrochemical effect of AB3 alloy on CoB alloy in mixture electrodes was also systematically investigated. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the cycle stability of MgNi alloy, the composites MgNi–x wt%NiP (x =5, 10, 15) were synthesized by ball milling the MgNi alloy with NiP alloy. The microstructure and electrochemical properties of the composites were investigated. Based on X-ray diffraction (XRD) patterns, the composites had better amorphous structures than pure-MgNi. Electrochemical studies showed that the cycle stability of the composite electrodes was improved due to the enhancement of the anti-corrosion property in the alkaline electrolyte. The MgNi–10wt%NiP electrode performed the best. At the discharge current density I d 500mAg−1, the HRD increased from 37.2% to 54.4% (x =10). Moreover, according to the electrochemical impedance spectroscopy (EIS), the charge-transfer resistance decreased, indicating that the electrochemical kinetics of the composite electrodes was improved. [Copyright &y& Elsevier]

Abstract: The influence of the surface treatment by KBH4 solution, alkaline solution, and alkaline solution containing KBH4 on the surface structure and electrochemical properties of the is investigated. It shows that all of the treatment methods improve the electrochemical properties of the hydrogen-storage alloy. In all the methods, the treatment by alkaline solution containing KBH4 shows the best overall electrochemical properties in this work. [Copyright &y& Elsevier]

Abstract: To improve the electrochemical performance of the MgNi-based alloys, different amounts of iron boride powder prepared by chemical reduction method were introduced by mechanical alloying. The results of powder X-ray diffraction showed these composites had amorphous structures. Cyclic charge–discharge tests showed the cycle stability of the MgNi alloy was improved by FeB. After 50 charge–discharge cycles, the discharge capacity of the MgNi–FeB composite was 60.99% higher than that of pure MgNi alloy. From the 1st cycle to 5th cycle, the discharge capacity faded rapidly; however, from the 6th to 100th cycle the discharge capacity was much more stable. The discharge capacity of cycle 100 remained , which was 93.53% of the 6th cycle. The corrosion resistance of the MgNi alloy in alkaline solution was also increased by FeB, which was confirmed by the results of electrochemical impedance spectroscopy and Tafel polarization tests. [Copyright &y& Elsevier]

Abstract: In the present study, hydrogen storage composite electrodes were prepared by mechanical milling the powder mixtures of Ni-free Laves phase alloy Ti0.9Zr0.2Mn1.5Cr0.3V0.3 (AB2) with LaNi3.8Mn0.3Al0.4Co0.5 (AB5) and La0.7Mg0.25Zr0.05Ni2.975Co0.525 (AB3.5), respectively. X-ray diffraction (XRD) measurements found that the basic phase structure (hexagonal C14) was still maintained in TiMn2-based alloy after short-time mechanical milling with additional La-based alloys. The fine particles of La-based alloy were found dispersing over the bulk particle of TiMn2-based alloy by observations of scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The electrochemical studies showed that the additional La-based alloys greatly improved the discharge capacity of the composite electrode. The maximum discharge capacity reached 310.4mAh/g and 314.0mAh/g for AB2–10wt.% AB5 and AB2–10wt.% AB3.5 electrodes, respectively, which was much higher than the maximum 48.6mAh/g of original Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements suggests that AB3.5-type alloy as a surface-modifier is beneficial to the decrease of the charge-transfer reaction resistance. The mechanical milling with AB5-type alloy was found improving the hydrogen diffusion in the bulk of the alloy from the results of anodic polarization measurement. [Copyright &y& Elsevier]

Abstract: A series of AB3/PANI composites were prepared by adding polyaniline (PANI) into La0.7Mg0.25Ti0.05Ni2.975Co0.525 (AB3) hydrogen storage alloy, which was prepared by magnetic levitation melting, and the composites were investigated by XRD and SEM. The effects of PANI concentration on the hydrogen absorption–desorption properties and discharge capacities of AB3 alloy were systematically studied by P–C–T isotherms and LAND battery test system, respectively. The results indicated that the addition of PANI did not change the hydrogen absorption capacity of AB3 alloy distinctly, while the hydrogen desorption plateau pressure of AB3 alloy decreased firstly, and then increased with the increase in the PANI concentration, the minimum plateau pressures of 0.022, 0.1, 0.321 and 0.55MPa were obtained with PANI concentration of 2 wt% at 25, 50, 80 and 100°C, respectively. It was theoretically verified by the changes in enthalpy and entropy of AB3/PANI hydrides dehydrogenation which were calculated by Van’t Hoff equation. In the present paper, the phenomenon that PANI improved the hydrogen absorption kinetics of AB3 alloy was found; the influence of PANI concentration on hydrogen absorption kinetics of AB3 alloy was more apparent at higher temperature. The activation energies of dissolved hydrogen in AB3/PANI hydrides were calculated from hydrogen absorption kinetics and the Arrhenius equation. LAND experiments demonstrated that, the AB3/PANI electrodes composites possessed higher cycling discharge capacity retention rates than AB3 electrode alloy. [Copyright &y& Elsevier]

Abstract: The alloys Co2B were prepared by two ways of high temperature solid phase process and arc melting, the structure of the alloys was characterized by XRD and SEM. It showed that it was structure of tetragonal Co2B.The electrochemical experimental results demonstrated that the Co2B prepared by two means both showed excellent cycling stability. The initial discharge capacity of Co2B prepared by the high temperature solid phase process was 480.3mAhg−1, there was no distinct declination after 70 charge–discharge cycles and the capacity kept about 195mAhg−1. Co2B prepared by the high temperature solid phase process showed very good electrochemical reversibility in CV curves. The hydrogen storage mechanism was also discussed, it confirmed that the high initial capacity of Co2B prepared by the high temperature solid phase process was due to the oxidation of Co and B2O3, and it was irreversible. [Copyright &y& Elsevier]

A mixture of commercial NaAlH4 and 2 wt.% of nanocrystalline TiN is subjected to ball milling (stainless steel vessel, 450 rpm, 1 h, Ar atmosphere). [ABSTRACT FROM AUTHOR]

Abstract: A novel catalyst TiB2 is used in preparing TiB2-doped sodium aluminium hydride under a low hydrogen pressure. NaAlH4 can be directly synthesized by using TiB2 as catalyst in about 5h at 2MPa hydrogen pressure. It shows that TiB2 has a remarkable catalytic effect and can enhance the performance of hydrogen release. The highest hydrogen desorption capacity of the sample doped with 8mol% TiB2 is 5.02wt.%. Thus, TiB2 particles synthesized is a promising catalyst for synthesizing and catalysing the hydrogen absorption and desorption in light-metal complex hydrides. [Copyright &y& Elsevier]