Jiangwen Liu

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 392u2009K from 592u2009K 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.

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.

Enhancing the performance of Sn–C nanocomposite as lithium ion anode by discharge plasma assisted milling

An efficient synthesis method, namely dielectric barrier discharge plasma assisted milling (P-milling), is used for the first time to prepare Sn–C anode materials for lithium ion batteries. By short-time P-milling, a unique Sn–C nanocomposite is obtained with a microstructure of multi-scale Sn particles homogeneously dispersed in a graphite matrix. The P-milled Sn–C nanocomposite anodes exhibit much better electrochemical performance with higher reversible capacity and better cyclability in comparison with those obtained by conventional milling (C-milling). Our results demonstrate that discharge plasma assisted milling is a simple and efficient method to prepare Sn–C composite anodes on a large scale with good performance for lithium ion battery applications.

Mesoporous Mo2C/N-doped carbon heteronanowires as high-rate and long-life anode materials for Li-ion batteries

Transition metal carbides are an emerging class of anode materials for Li-ion batteries (LIBs), which have recently drawn attention because of their good conductivity and high capacity after rational nano-engineering. In this work, we have developed Mo2C/N-doped carbon mesoporous heteronanowires (Mo2C/N–C MHNWs) with enhanced capacitive behaviour as high-performance anode materials for LIBs. With the heterostructure, the Mo2C nanocrystallites offer short paths for Li+ diffusion, while the N-doped carbon matrix facilitates fast electron transportation and buffers the volume change of Mo2C during the discharge/charge cycles. When evaluated as anodes for LIBs, the Mo2C/N–C MHNWs exhibited high capacity and high rate capability, as well as a long-term cycle life. In particular, a reversible capacity of 744.6 mA h g−1 was achieved in the first cycle, and 732.9 mA h g−1 was preserved after 700 cycles at a current density of 2 A g−1. The outstanding performance stems from fast kinetics enhanced by the pseudocapacitive effect, which was evidenced in the further analysis based on electrochemical impedance spectra and cyclic voltammetry. Our results elucidate the attractive Li+ storage performance of Mo2C-based nanocomposites, which may shed some light on the development of high-performance materials for energy storage and utilization.

Deformable fibrous carbon supported ultrafine nano-SnO2 as a high volumetric capacity and cyclic durable anode for Li storage

Multidimensional fibrous carbon scaffolds, derived from carbonized filter papers (CFPs), were used to support SnO2 nanocrystals (NCs, with a size of 4–5 nm) to form a free-standing SnO2NC@CFP hybrid anode for Li-ion batteries. The SnO2NC particles are well accreted on the surfaces of 1D carbon fibers and 2D ultrathin carbon sheets while maintaining 3D interconnected pores of the carbon matrices for fast ionic transport. The SnO2NC@CFP hybrid electrode exhibits long-term higher energy density than the commercial graphite anode, and excellent rate capability, mainly due to good dispersion of SnO2 in the multidimensional conductive carbon. In particular, the reversible deformation of the flexible fibrous carbon matrices, as inferred from in situ Raman spectroscopy and SEM image analysis, facilitates stress release from the active SnO2NCs during discharge–charge cycling while maintaining the structural integrity of the self-supported SnO2NC@CFP anode. These demonstrate that the rational combination of the multidimensional architecture of deformable carbon with nanoscale active materials is ideally suited for high-performance Li-ion batteries.

Hydrogen generation via hydrolysis of magnesium with seawater using Mo, MoO2, MoO3 and MoS2 as catalysts

Hydrogen generation is one of the enabling technologies for realization of hydrogen economy. In this study, we developed a high-performance hydrogen generation system using the transition metal Mo and its compounds (MoS2, MoO2, and MoO3) for catalyzing the hydrolysis of Mg composites in seawater. These Mg-based composites for the hydrolysis process were synthesized through a simple planetary ball mill technique. The results demonstrate that small amounts of added MoS2 could significantly accelerate and enhance the hydrolysis reaction of Mg in seawater. In particular, the Mg–10 wt% MoS2 composite releases 838 mL g−1 hydrogen in 10 min (about 89.8% of the theoretical hydrogen generation yield), and the recycled catalysts exhibit high cycle stability, which is the most significant achievement in this study. In addition, Mo, MoO2, and MoO3 also showed similar enhancement in the hydrolysis reaction of Mg. The activation energies for the hydrolysis of Mg decreased from 63.9 kJ mol−1 to 27.6 kJ mol−1, 20.4 kJ mol−1, 14.3 kJ mol−1, and 12.1 kJ mol−1 on introducing Mo, MoS2, MoO2, and MoO3, respectively. The attractive hydrolysis performance of the composites of Mg milled with Mo and its compounds in seawater may shed light on future developments of hydrogen generation technologies.

Microsized Sn supported by NiTi alloy as a high-performance film anode for Li-ion batteries

A novel Sn–NiTi composite thin film has been prepared by directly co-sputtering a mixture of pure Sn and NiTi shape memory alloy and has been used as an anode for an Li-ion battery for the first time. The thin film has a unique microstructure of microsized Sn particles and microsized Sn grooves uniformly dispersed in an amorphous NiTi (a-NiTi) matrix. The a-NiTi matrix covers the Sn phase and effectively accommodates the volume change resulting from Li–Sn reactions. It also protects the surface of the Sn particles, thus ensuring good cycle performance of the Sn–NiTi composite thin film electrode, with excellent high-rate capability and a low initial irreversible capacity. It delivered a stable capacity of 503 mAh g−1 at 1 C and a high value of 372 mAh g−1 at 15 C, thus demonstrating a significant improvement of the anode performance through the protection of the Sn by the NiTi alloy matrix.

An amorphous wrapped nanorod LiV3O8 electrode with enhanced performance for lithium ion batteries

To achieve a good combination of high capacity, cyclability and rate capability in an electrode is still a great challenge for lithium-ion batteries, especially those used for electric vehicles. The present work has developed a simple and effective strategy to solve this problem in the layer structured LiV3O8 positive electrode. This has the highest theoretical capacity of the currently available positive electrodes but it has not yet been achieved in practice along with high rate capability. In our approach, an amorphous wrapped [100] orientated nanorod structure has been fabricated in a LiV3O8 thin film by adjusting the oxygen partial pressure in the deposition process using radio frequency (RF) magnetron sputtering. With this structure, a record combination of high capacity and superior high-rate capability, namely 388 mA h g−1 at C/5 and 102 mA h g−1 at 40 C, has been achieved along with stable cycle life. The result revealed that the orientated nanorods provide additional ionic transport channels and their amorphous wrapping layer can withstand the anisotropy of the surface during the intercalation of Li ions.