Liuzhang Ouyang

Monodisperse magnesium hydride nanoparticles uniformly self-assembled on graphene.

Monodisperse MgH2 nanoparticles with homogeneous distribution and a high loading percent are developed through hydrogenation-induced self-assembly under the structure-directing role of graphene. Graphene acts not only as a structural support, but also as a space barrier to prevent the growth of MgH2 nanoparticles and as a thermally conductive pathway, leading to outstanding performance.

Thermodynamic Tuning of Mg-Based Hydrogen Storage Alloys: A Review

Mg-based hydrides are one of the most promising hydrogen storage materials because of their relatively high storage capacity, abundance, and low cost. However, slow kinetics and stable thermodynamics hinder their practical application. In contrast to the substantial progress in the enhancement of the hydrogenation/dehydrogenation kinetics, thermodynamic tuning is still a great challenge for Mg-based alloys. At present, the main strategies to alter the thermodynamics of Mg/MgH2 are alloying, nanostructuring, and changing the reaction pathway. Using these approaches, thermodynamic tuning has been achieved to some extent, but it is still far from that required for practical application. In this article, we summarize the advantages and disadvantages of these strategies. Based on the current progress, finding reversible systems with high hydrogen capacity and effectively tailored reaction enthalpy offers a promising route for tuning the thermodynamics of Mg-based hydrogen storage alloys.

Express penetration of hydrogen on Mg(10͞13) along the close-packed-planes

Metal atoms often locate in energetically favorite close-packed planes, leading to a relatively high penetration barrier for other atoms. Naturally, the penetration would be much easier through non-close-packed planes, i.e. high-index planes. Hydrogen penetration from surface to the bulk (or reversely) across the packed planes is the key step for hydrogen diffusion, thus influences significantly hydrogen sorption behaviors. In this paper, we report a successful synthesis of Mg films in preferential orientations with both close- and non-close-packed planes, i.e. (0001) and a mix of (0001) and (103), by controlling the magnetron sputtering conditions. Experimental investigations confirmed a remarkable decrease in the hydrogen absorption temperature in the Mg (103), down to 392 K from 592 K of the Mg film (0001), determined by the pressure-composition-isothermal (PCI) measurement. The ab initio calculations reveal that non-close-packed Mg(103) slab is advantageous for hydrogen sorption, attributing to the tilted close-packed-planes in the Mg(103) slab.

Mg–TM (TM: Ti, Nb, V, Co, Mo or Ni) core–shell like nanostructures: synthesis, hydrogen storage performance and catalytic mechanism

Magnesium (Mg) was coated by different transition metals (TM: Ti, Nb, V, Co, Mo, or Ni) with a grain size in the nano-scale to form a core (Mg)–shell (TM) like structure by reaction of Mg powder in THF solution with TMClx. The thickness of the TM shell is less than 10 nm. TPD-MS results show the Mg–Ti sample can release hydrogen even under 200 °C. It is experimentally confirmed that the significance of the catalytic effect on dehydrogenation is in the sequence Mg–Ti, Mg–Nb, Mg–Ni, Mg–V, Mg–Co and Mg–Mo. This may be due to the decrease in electro-negativity (χ) from Ti to Mo. However, Ni is a special case with a high catalytic effect in spite of the electro-negativity. It is supposed that the formation of the Mg2Ni compound may play an important role in enhancing the hydrogen de/hydrogenation of the Mg–Ni system. It is also found that the larger the formation enthalpy, the worse the dehydrogenation kinetics.

Remarkable enhancement in dehydrogenation of MgH2 by a nano-coating of multi-valence Ti-based catalysts

A Ti-based multi-valence catalyst was coated on the surface of ball milled Mg powders (∼1 μm in diameter), aiming to decrease the desorption temperature and increase the kinetics of hydrogen release from MgH2 by its catalytic effect on thermodynamics. The catalysis coating was prepared by the chemical reaction between Mg powders and TiCl3 in THF solution, which is ∼10 nm in thickness and contains multiple valences in the form of Ti (0), TiH2 (+2), TiCl3 (+3) and TiO2 (+4). It is believed that the easier electron transfer among these different Ti valences plays a key role in enhancing the hydrogen recombination for the formation of a hydrogen molecule (e.g.). This recombination is generally regarded as the key barrier for hydrogen desorption of MgH2. Experimentally, temperature-programmed desorption (TPD) and isothermal dehydrogenation analysis demonstrate that the MgH2 – coated Ti based system (denoted as Mg–Ti) has excellent dehydrogenation properties, which can start to release H2 at about 175 °C and release 5 wt% H2 within 15 min at 250 °C. The dehydrogenation reaction entropy (ΔS) of the system is changed from 130.5 J K−1 mol−1 H2 to 136.1 J K−1 mol−1 H2, which reduces the Tplateau to 279 °C at an equilibrium pressure of 1 bar. A new mechanism has been proposed that multiple valence Ti sites act as the intermediate for electron transfers between Mg2+ and H−, which makes the recombination of H2 on Ti (in forms of compounds) surfaces much easier.

A mechanical-force-driven physical vapour deposition approach to fabricating complex hydride nanostructures

Nanoscale hydrides desorb and absorb hydrogen at faster rates and lower temperatures than bulk hydrides because of their high surface areas, abundant grain boundaries and short diffusion distances. No current methods exist for the direct fabrication of nanoscale complex hydrides (for example, alanates, borohydrides) with unique morphologies because of their extremely high reducibility, relatively low thermodynamic stability and complicated elemental composition. Here, we demonstrate a mechanical-force-driven physical vapour deposition procedure for preparing nanoscale complex hydrides without scaffolds or supports. Magnesium alanate nanorods measuring 20-40 nm in diameter and lithium borohydride nanobelts measuring 10-40 nm in width are successfully synthesised on the basis of the one-dimensional structure of the corresponding organic coordination polymers. The dehydrogenation kinetics of the magnesium alanate nanorods are improved, and the nanorod morphology persists through the dehydrogenation-hydrogenation process. Our findings may facilitate the fabrication of such hydrides with improved hydrogen storage properties for practical applications.

(Nd1.5Mg0.5)Ni-7-Based Compounds: Structural and Hydrogen Storage Properties

The structural and hydrogen storage properties of (Nd(1.5)Mg(0.5))Ni(7)-based alloys (i.e., A(2)B(7)-type) with a coexistence of two structures (hexagonal 2H and rhombohedral 3R) are investigated in this study. In both 2H- and 3R-type A(2)B(7) structures, Mg atoms occupy Nd sites of Laves-type AB(2) subunits rather than those of AB(5) subunits because Mg substitution for Nd in the AB(2) subunits more significantly strengthens the ionic bond in the system. An increase in the A-atomic radius or the B-atomic radius stabilizes the 2H structure, but a decrease in the A-atomic radius or the B-atomic radius is favorable for formation of the 3R structure. The 2H-A(2)B(7) and 3R-A(2)B(7) phases in each alloy have quite similar equilibrium pressures upon hydrogen absorption and desorption, which show a linear relationship with the average subunit volume. The hydriding enthalpy for the (Nd(1.5)Mg(0.5))Ni(7) compound is about -29.4 kJ/mol H(2) and becomes more negative with partial substitution of La for Nd and Co/Cu for Ni but less negative with partial substitution of Y for Nd.

Sandwich-like SnS/Polypyrrole Ultrathin Nanosheets as High-Performance Anode Materials for Li-Ion Batteries.

Sandwich-like SnS/polypyrrole ultrathin nanosheets were synthesized via a pyrrole reduction and in situ polymerization route, in which room-temperature synthesized ZnSn(OH)6 microcubes were used as the tin source. As anode materials for Li-ion batteries, they exhibit an extremely high reversible capacity (about 1000 mA h g(-1) at 0.1C), outstanding rate capability (with reversible capabilities of 878, 805, 747, 652, and 576 mA h g(-1) at 0.2C, 0.5C, 1C, 2C, and 5C, respectively), stable cycling performance, and high capacity retention (a high capacity of 703 mA h g(-1) at 1C after long 500 cycles).

Robust Pitaya-Structured Pyrite as High Energy Density Cathode for High-Rate Lithium Batteries

To solve the serious problems (the agglomeration of nano-Fe0, dissolution of polysulfide, and low electronic conductivity of Li2S) of earth-abundant pyrite (FeS2) cathodes for lithium batteries, a simple in situ encapsulation and transformation route has been successfully developed to synthesis pitaya-structured porous carbon embedded with FeS2 nanoparticles. Due to such a hierarchical architecture design, this cathode of pitaya-structured FeS2@C can effectively avoid the serious agglomeration and coarsening of small Fe nanoparticles, reduce the dissolution of polysulfide, and provide superior kinetics toward lithium storage, resulting in enhanced reversibility and rate capability. Cycling in the voltage region of 1.0-3.0 V at 0.3 A g-1, the current conversion-based FeS2@C cathode displays a high and stable energy density (about 1100 Wh kg-1), ultrahigh rate capability (a reversible capability of 660, 609, 554, 499, 449, and 400 mA h g-1 at 0.2, 0.5, 1.0, 2.0, 5.0, and 10 A g-1, respectively), and stable cycling performance.

Facile synthesis of Ge@FLG composites by plasma assisted ball milling for lithium ion battery anodes

Efficient production of graphene or its germanium (Ge) composites remains a challenge, although Ge nanoparticles (NPs) wrapped with graphene are suitable for preventing the large volume change of anodes for lithium ion batteries during Li uptake and release processes. This work is the first simple, efficient in situ synthesis of Ge NPs, with an excellent structure, wrapped with few-layer graphene sheets (abbreviated as Ge@FLG) from commercial Ge powders and natural graphite by a one-step ball-milling process assisted by dielectric-barrier discharge plasma. Because of their unique structure, Ge@FLG electrodes exhibit better electrical conductivity, low initial capacity loss, good cycling capability, and rate resilience compared with Ge@C electrodes prepared by conventional milling. This work highlights a new method for the efficient production of Ge@FLG composites and their applications in lithium ion batteries and in other technologies.