Copper hexacyanoferrate (CuHCF) nanoparticles with Prussian blue structure present the ability to insert Al ions reversibly in aqueous solution.

Supercapacitors are the most promising energy storage devices by virtue of high power density, long cycle life, short charging time and environmental benignity. In order to enhance the energy density, rate capability and cycle stability for supercapacitors, a α-Ni(OH)2/graphite nanosheet composite is prepared via a homogeneous precipitation method. The morphology and microstructure of the as-prepared composite are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. It is demonstrated that after introducing the graphene oxide nanosheets into α-Ni(OH)2, a 3D hierarchical porous structure of fine α-Ni(OH)2 nanocrystals as building blocks is formed directly on the matrix of graphite nanosheets in the presence of urea as a mild reducing agent. The electrochemical performance of the as-prepared α-Ni(OH)2 and α-Ni(OH)2/graphite nanosheet composites as electro-active materials for supercapacitors is investigated by a galvanostatic charge–discharge method. As expected, the as-prepared α-Ni(OH)2/graphite nanosheet composite exhibits large specific capacitance, good rate capability and long cycle stability as compared to the pure α-Ni(OH)2. Apparently, the unique structure of fine α-Ni(OH)2 nanocrystals fabricated on the matrix of graphite nanosheets is responsible for the improvement of the reaction kinetics and subsequent electrochemical performance of the composite.

TiN nanotube arrays on the metallic Ti mesh, prepared by a simple nitridation of TiO2 nanotube arrays on the metallic Ti mesh in ammonia atmosphere, are introduced for the first time as low-cost electrocatalytic electrode for solar storable rechargeable battery. The microstructure of the as-prepared TiN nanotube arrays/Ti mesh is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that the obtained TiN retains its parent morphology of TiO2 nanotube arrays after the calcination in ammonia atmosphere. It is demonstrated from cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) that the highly ordered TiN nanotube arrays on the metallic Ti mesh substrate show an excellent electrocatalytic activity. Correspondingly, the rechargeable battery withWO(3)/carbon nanotubes as charge-storage electrode and TiN nanotube arrays/Ti mesh as electrocatalytic electrode presents reliable solar storable capability and reversible electrochemical conversion performance. Therefore, the TiN nanotube arrays/Timesh prepared in this work can be used as a potential low-cost alternative to the expensive noble metal Pt in future applications of the solar storable rechargeable battery. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.019211jes] All rights reserved.

The electrochemical aluminum storage of anatase TiO2 nanotube arrays in AlCl3 aqueous solution is investigated. It is firstly demonstrated that aluminum ions can be reversibly inserted/extracted into/from anatase TiO2 nanotube arrays in AlCl3 aqueous solution due to the small radius steric effect of aluminum ions, indicating a potential application in aluminum ion batteries.

Rechargeable aqueous TiO2/LiMn2O4 lithium-ion battery is fabricated by combining the TiO2 nanotube arrays on metallic titanium foil as anode and LiMn2O4 as cathode in aqueous solution with mixed lithium salts (LiCl and Li2SO4). It is shown from cyclic voltammograms that the lithium insertion/extraction peaks of the cathode are highly symmetrical before the oxygen evolution, which can ensure a good lithium utilization of the LiMn2O4. Importantly, a higher anodic hydrogen evolution overpotential in TiO2 anode is observed, which is essential for the facile lithium insertion in preference to the hydrogen evolution. Meanwhile, the gas (hydrogen and oxygen) evolution in the anodic and cathodic processes can be effectively suppressed in aqueous electrolyte with mixed lithium salts as compared with that in pure LiCl and Li2SO4 solution, respectively. Correspondingly, the fabricated TiO2/LiMn2O4 battery presents a high discharge voltage plateau of above 2 V, which is well beyond the average discharge voltage of current aqueous battery system. Therefore, the combination of the appropriate anode/cathode-active materials with a relatively large potential difference and high gas evolution overpotential is an ideal strategy for developing new aqueous battery system based on reversible lithium insertion/extraction reactions in aqueous electrolyte. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.094112jes]

Li4Ti5O12 nanorods are fabricated after calcination of the hydrated lithium titanate precursor, which is prepared from hydrothermal treatment of titanate nanorods in aqueous LiOH based on titanate nanorod reactivity. The morphology, composition, and phase transformation of the calcined samples at different temperatures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Titanate nanorods as starting materials exhibit higher chemical reactivity, regarded as a structure template for retaining the one-dimensional structure of final products after calcination. The formation of Li4Ti5O12 nanorods is related to ion-exchange reaction and Ostwald ripening process due to high chemical reactivity of titanate nanorods. The galvanostatic charge/discharge tests were conducted to measure the electrochemical performance of the Li4Ti5O12 nanorods. It is demonstrated that the Li4Ti5O12 nanorods calcined at 800 degrees C have excellent high rate discharge capability and good cycle stability during insertion and extraction processes, owing to the good crystallinity, unique structure, and the short diffusion distances originated from one-dimensional morphology. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3121216] All rights reserved.

Si-Si3N4P (amorphous Si3N4 nanoparticles) and Si-Si3N4W (alpha-Si3N4 whiskers) composites as anode materials for lithium-ion batteries were synthesized by ball-milling. Ball-milling leads to the formation of inactive phases (Si(3)N(4)p and Si3N4W) that can be a buffer matrix to support active silicon particles avoiding the aggregation of silicon particles during cycling. The microstructure and electrochemical performance of the Si-Si(3)N(4)p and Si-Si(3)N(4)w composites with various silicon contents were investigated in detail. It is demonstrated that the composites with the amorphous Si3N4 nanoparticles as inactive materials have larger reversible capacities and improved cycle perfortuance due to active Si nanoparticles being supported in the buffer matrix. A high reversible (charge) capacity of 470 mA h/g is obtained for a Si-Si(3)N(4)p? composite containing 30 -,wt.% Si in the potential range from 0.02 to 1.2 (c) 2007 Elsevier B.V. All rights reserved.

Substituting small contents of aluminum for nickel in nickel hydroxides by a chemical coprecipitation and a subsequent hydrothermal process can yield stable positive electrode materials. Detailed studies on the structural evolution were conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The electrochemical properties of Al-substituted nickel hydroxides in alkaline solution were examined by charge-discharge experiments and cyclic voltammetric (CV) measurements. Hydrothermal treatments improved the crystallinity of Al-substituted nickel hydroxides, which exhibited much better electrode performance than the untreated samples. The sample with 10% (in mol) Al substitution having a mixture structure with alpha- and beta-phases after hydrothermal treatments showed the maximum discharge capacity of 333 mAh/g, corresponding to 1.46 exchanged electrons per Ni atom in alpha-phase nickel hydroxides. The phase distribution in the mixture has a great influence on the particle morphology, discharge capacity, potential plateau, and redox potentials of nickel hydroxide electrodes.

Aluminum-substituted cc-phase nickel hydroxide (Al-alpha-Ni(OH)2) microspheres with high structural stability are synthesized, and their surface modification by CoOOH nanoparticles is made subsequently in order to improve their electrochemical performance. The morphology, microstructure, and chemical state of the Al-alpha-Ni(OH)(2) microspheres, before and after coating, are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEIVI), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectra (FTIR). It is found that CoOOH nanoparticles with a rod-like morphology are either dispersed randomly on the surface or intercalated between nanosheets of the Al-a-Ni(OH)2 microspheres. The effect of CoOOH nanoparticles on the electrochemical performance of Al-a-Ni(OH)2 microspheres is investigated by galvanostatic charge- discharge experiments and cyclic voltammetry (CV). It is demonstrated that the Al-alpha-Ni(OH)(2) microspheres, coated with 7 wt % CoOOH nanoparticles, have an enhanced discharge capacity, high-rate discharge ability, discharge potential plateau, and cycle stability. The improvement of the electrochemical performance of Al-alpha-Ni(OH)(2) microspheres is mainly attributed to formation of highly conductive CoOOH nanoparticles on the surface of Al-oL-Ni(OH)(2) microspheres and good electrochemical accessibility of the microspherical aggregates of Al-alpha-Ni(OH)(2) nanosheets, which result in the good reversibility and high electrochemical activity of the positive materials.

The Si–AB5 (MmNi3.6Co0.7Al0.3Mn0.4 alloy) composites with a high tap density as anode materials for lithium-ion batteries were synthesized by ball-milling. Si nanoparticles are distributed homogeneously on the surface of the AB5 matrix. The electrochemical performance of the Si–AB5 composites as a function of Si content was investigated. It is demonstrated that the Si–AB5 composite delivers a larger reversible capacity and better cycle ability because the inactive AB5 alloy can accommodate the large volume changes of Si nanoparticles distributed on the surface of the Si–AB5 composite during cycling. In particular, the Si–AB5 composite containing 20wt% Si with the high tap density of 2.8g/cm3 obtained after ball-milling for 11h exhibits an initial and maximum reversible (charge) capacity of 370 and 385mAh/g. The high capacity retention can be achieved after 50 cycles in the potential range from 0.02 to 1.5V.

The titanium oxides with one-dimensional (ID) nanostructure are of significance in electrochemical lithium insertion owing to their high specific surface area and pore volume. In this study, nanorods with diameters of ca. 3-5 nm and lengths of 40-60 nm were prepared through the hydrothermal treatment of a hydrolysate obtained from TiCl4 with caustic soda as demonstrated by HRTEM. These nanorods are protonated titanate and can be converted into the anatase (TiO2) nanorods by a calcination at 400 degreesC. The anatase nanorods have a large specific surface area of 314 m(2)/g and a high pore volume of 1.514 cm(3)/g, respectively. The anatase TiO2 nanorods exhibit a large initial electrochemical lithium insertion capacity of 206 mAh/g and good reversibility. The splitting and multi peaks in cyclic voltammograms associated with differing site occupations are ascribed to the formation of the imperfection of the TiO2 nanorod lattice, which facilitates the transport of lithium in surface defects and bulk materials.

The partially aligned carbon nanotubes are successfully prepared by catalytic decomposition of methane at the surface of wafer consisting of the oxidized and reduced product of LaNi5 hydrogen storage alloy with Ni powder. The CNTs are straight with a larger inner hollow core of 20–30nm, whereas the long CNFs are curved with an inner hollow core of 6–10nm. In addition, the long continuous metallic Ni nanowires with several microns in length are observed inside nanotubes after purification in concentrated hydrochloric acid. The purified partially aligned carbon nanotubes show a high electrochemical discharging capacity up to 267mAh/g, corresponding to a hydrogen storage capacity of 1.0wt%, while the maximal discharge capacity of carbon nanofiber electrode is 64mAh/g, indicating that the partially aligned carbon nanotubes with open tips obtained provide a potential way to improve their electrochemical hydrogen storage due to the different structure.

Rotor-like ZnO was grown from a mixture of rod-like ZnO powder and a saturated Zn(OH)(4)(2-) solution under moderate hydrothermal conditions at 100 degree C, in which the precursor rod-like ZnO crystal plane acts as a matrix core, and the branched nanorods showed fast epitaxial growth on the six directions around the prism core.

A simple and efficient approach is developed for the synthesis of copper oxide nanorods with different morphology and crystallographic structure. Polycrystalline fine rods 10-20 nm thick and several hundred nanometers long and single crystalline thick rods 60-100 nm thick and up to 1 mum long were obtained from the reactions of copper hydrate with caustic soda solution at room temperature and 100 degreesC, respectively. The fine CuO nanorods as anode materials for Li ion battery exhibit a high electrochemical capacity of 766 mA h/g and relatively poor capacity retention as compared to thick nanorods with the single crystalline structure. The correlation between the structural features of the nanorods and their electrode performance is discussed in detail.

Some compounds of LiCo1-xRExO2 (RE=rare earth elements and x=0.01～0.03) were prepared by doping rare earth elements to LiCoO2 via solid state synthesis. The microstructure characteristics of the LiCo1-xRExO2 were investigated by XRD. It was found that the lattice parameters c are increased and the lattice volumes are enlarged compared to that of LiCoO2. Moreover, the performance of LiCo1-xRExO2 as the cathode material in lithium ion battery is improved, especially LiCo1-xYxO2 and LiCo1-xLaxO2. The initial charge/discharge capacities of LiCo0.99Y0.01O2 and LiCo0.99La0.01O2 are 174/154 (mAh*g-1) and 159/149 (mAh*g-1) respectively, while those for LiCoO2 working in the same way are only 139/131 (mAh*g-1).

A facile method is proposed to use LaNi2 hydrogen storage alloy as a catalyst precursor to produce metallic nickel filled carbon nanotubes. Multi-walled carbon nanotubes filled with long continuous nickel nanowire with several microns in length are synthesized through chemical vapor deposition at low temperature (550 °C). It is more efficient to fill Ni nanowires into nanotubes after the oxidation treatment of LaNi2 alloy at low temperatures, while the oxidation treatment at high temperature results in the forming of herringbone carbon nanofibers with tips of Ni nanoparticles. The metallic Ni nanowires inside the cores of carbon nanotubes could not be eliminated during the purification process in concentrated hydrochloric acid. The analysis of transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD) reveals that the metallic nickel nanowires filled inside carbon nanotubes exist as a single crystalline with fcc structure.

MgNi-carbon nanotube composites were prepared by ballmilling the MgNi alloy and multiwalled carbon nanotubes (CNTs, 10 wt %) at various periods of time. It was confirmed by scanning electron microscope images that the MgNi alloy surface was modified by shorter and broken CNTs. The MgNi-CNT composites prepared by ballmilling after 60 min were found to show improved electrochemical properties with respect to the original MgNi alloy. In particular, the discharge capacity of the composite electrode increased from 400 to 480 mAh/g by surface modification with CNTs. The electrochemical reaction activity of the composite electrode was improved as confirmed by cyclic voltammogram. The analysis of the electrochemical impedance spectra showed that the double layer capacitance of the composite electrode increased under steady-state condition, which related to surface area of the particles. On the contrary, however, the improvement of the electrode cycle life was unsatisfactory, which probably attributed to the further generation of a new MgNi-CNT interface. (C) 2002 The Electrochemical Society.

The electrochemical properties of an electrode of carbon nanotubes decorated with metallic nickel particles were investigated. A high initial discharge capacity of 297 mAh g(-1) of the decorated carbon nanotubes was obtained under a discharge current density of 1000 mA/g, after eliminating the capacity of Ni-P alloy, due to the improvement of the electrocatalytic, activity and the hydrogen adsorption of the surface Ni-P alloy. However, the electrode of decorated carbon nanotubes was found to show a poor charge/discharge cycle life owing to the dramatic increase of surface reaction resistance measured by means of electrochemical impedance spectra, which arose probably from destruction of the structure at the interface of the carbon nanotubes and the coating layer and the passivation of nanoscale-size metallic nickel particles during cycling. (C) 2001 The Electrochemical Society.