Xiangfeng Liu

Facile Shape Control of Co3O4 and the Effect of the Crystal Plane on Electrochemical Performance

Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and {001} planes, and octahedra with exposed {111}planes - is synthesized using a very simple one-step hydrothermal method. The three kinds of Co(3)O(4) exhibit significantly different electrochemical performances and the effect of different exposed crystal planes on the electrochemical performance of Co(3)O(4) is comprehensively studied.

Facile Cycling of Ti-Doped LiAlH4 for High Performance Hydrogen Storage

LiH and Ti-doped Al react quantitatively with H(2) in Me(2)O solution to form LiAlH(4) under mild conditions. The solvent is easily vented along with excess H(2) on completion, leaving dry Ti-doped LiAlH(4); this releases approximately 7 wt % H(2) commencing at 80 degrees C with excellent kinetics.

Ti-doped LiAlH4 for hydrogen storage: synthesis, catalyst loading and cycling performance.

The direct synthesis of LiAlH(4) from commercially available LiH and Al powders in the presence of TiCl(3) and Me(2)O has been achieved for the first time. The effects of TiCl(3) loadings (Ti/Al = 0, 0.01, 0.05, 0.2, 0.5, 1.0 and 2.0%) and various other additives (TiCl(3)/Al(2)O(3), metallic Ti, Nb(2)O(5), and NbCl(5)) on the formation and stability of LiAlH(4) have been systematically investigated. The yield of LiAlH(4) initially increases, and then decreases, with increasing TiCl(3) loadings. LiH + Al → LiAlH(4) yields above 95% were obtained when the molar ratios of Ti/Al were 0.05 and 0.2%. In the presence of a very tiny amount of TiCl(3) (Ti/Al = 0.01%), LiAlH(4) is still generated, but the yield is lower. In the complete absence of TiCl(3), LiAlH(4) does not form. Addition of metallic Ti, Nb(2)O(5), and NbCl(5) to commercial LiH and Al does not result in the formation of LiAlH(4). Preliminary tests show that TiCl(3)-doped LiAlH(4) can be cycled, making it a suitable candidate for hydrogen storage.

LiCoO2 nanoplates with exposed (001) planes and high rate capability for lithium-ion batteries

AbstractWe report the synthesis of near-uniform LiCoO2 nanoplates by a two-step approach in which β-Co(OH)2 nanoplates are synthesized by co-precipitation and then transformed into LiCoO2 nanoplates by solid state reaction at 750 °C for 3 hours. Characterization by high-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED) reveal that the as-prepared LiCoO2 nanoplates are covered with many cracks and have exposed (001) planes. The electrochemical performance of the LiCoO2 nanoplates was investigated by galvanostatic tests. The capacity of LiCoO2 nanoplates stabilized at 123 mA·h/g at a rate of 100 mA/g and 113 mA·h/g at a rate of 1000 mA/g after 100 cycles. The excellent rate capability of the LiCoO2 nanoplates results from cracks which are perpendicular to the (001) plane and favor fast Li+ transportation. In addition, compared with other methods of synthesis of LiCoO2 the time of the solid reaction state is significantly shorter even at relatively low temperatures, which means the energy consumption in preparing LiCoO2 is greatly decreased. The controllable synthesis of LiCoO2 nanoplates with exposed (001) plane paves an effective way to develop layered cathode materials with high rate capabilities for use in Li-ion batteries.

The role of oxygen vacancies in improving the performance of CoO as a bifunctional cathode catalyst for rechargeable Li–O2 batteries

The design and facile synthesis of noble metal-free efficient cathode catalysts to accelerate the sluggish kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a big challenge for lithium–air batteries. In this study, oxygen vacancy-bearing CoO (CoO-A) has been successfully synthesized through a simple calcination of Co(Ac)2·4H2O in Ar, and the oxygen vacancies have been confirmed by Raman spectroscopy, HRTEM, X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS). In comparison with defect-free CoO-N, which is derived from the decomposition of Co(NO3)2·6H2O, an oxygen-deficient CoO-A based cathode shows much higher cycling stability, higher rate capability, higher coulombic efficiency, and lower charge–discharge overpotential. The enhanced performances of the CoO-A based cathode can be largely attributed to the synergetic effect of CoO itself and oxygen vacancies on the promotion of both ORR and OER. CoO provides catalytic activity for ORR, and at the same time the oxygen vacancies not only facilitate the electron and Li+ migration but also act as active sites binding to O2 and Li2O2, which accelerates the OER process. Furthermore, the formation and decomposition of Li2O2 during discharge–charge cycles have also been studied and the results indicate that CoO-A shows a high catalytic activity in the decomposition of Li2O2.

Microwave assisted one-pot synthesis of graphene quantum dots as highly sensitive fluorescent probes for detection of iron ions and pH value.

Recently, carbon nanomaterials have received considerable attention as fluorescent probes owing to their low toxicity, water solubility and stable photochemical properties. However, the development of graphene quantum dots (GQDs) is still on its early stage. In this work, GQDs were successfully synthesized by one-step microwave assisted pyrolysis of aspartic acid (Asp) and NH4HCO3 mixture. The as-prepared GQDs exhibited strongly blue fluorescence with high quantum yield up to 14%. Strong fluorescence quenching effect of Fe(3+) on GQDs can be used for its high selectivity detection among of general metal ions. The probe exhibited a wide linear response concentration range (0-50 μM) to Fe(3+) and the limit of detection (LOD) was calculated to be 0.26 μM. In addition, GQDs are also sensitive to the pH value in the range from 2 to 12 indicating a great potential as optical pH sensors. More importantly, the GQDs possess lower cellular toxicity and high photostability and can be directly used as fluorescent probes for cell imaging.

Designing an advanced P2-Na0.67Mn0.65Ni0.2Co0.15O2 layered cathode material for Na-ion batteries

A high performance layered P2-Na0.67Mn0.65Ni0.2Co0.15O2 cathode material for sodium ion batteries with high rate capability and excellent long-life cyclic performance has been successfully designed and synthesized by a simple sol–gel method. In comparison with the reported Na0.7MnO2, the designed P2-Na0.67Mn0.65Ni0.2Co0.15O2 cathode material can be charged and discharged in an extended voltage range of 1.5–4.2 V and shows reversible capacities of 155, 144, 137, 132 and 126 mA h g−1 at different current densities of 12, 24, 48, 120 and 240 mA g−1, respectively. Even at high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C) it can still deliver capacities of 117, 93 and 70 mA h g−1, respectively, which are much higher than those of the recently reported Na0.5[Ni0.23Fe0.13Mn0.63]O2. In addition, the Na0.67Mn0.65Ni0.2Co0.15O2 cathode material also displays an excellent capacity retention ca. 85% and 78% after 100 cycles at 0.05C and 0.5C, respectively. It is also proposed that Mn4+ may be “activated” in a low voltage range, especially below 2.0 V, which contributes to the additional capacity. The Na-ion diffusion coefficient, DNa+, is ca. 10−14 cm2 s−1 as calculated by the PITT and the discharge diffusion coefficient is a little larger than the charge one. The designed Na0.67Mn0.65Ni0.2Co0.15O2 shows great potential as a cathode material for sodium ion batteries.

Controlled synthesis and enhanced electrochemical performance of Prussian blue analogue-derived hollow FeCo2O4 nanospheres as lithium-ion battery anodes

Porous metal oxides have attracted great interest as anode materials for lithium ion batteries owing to their improved electrochemical properties. In this study, we propose a Prussian blue analogue (PBA)-derived strategy to successfully prepare hollow porous FexCo3−xO4 (FCO) with controlled morphologies (nanospheres and nanocubes) using surfactants as “soft templates”. In comparison with FCO nanocubes (FCO-NCs) and FCO nanoparticles (FCO-NPs), FCO spheres (FCO-NSs) show a much better cycling stability and rate capability as an anode material for lithium ion batteries. The cycling capacity of FCO-NSs at the 50th cycle has been largely enhanced to 1060 mA h g−1 from only 721 (FCO-NCs) and 389 mA h g−1 (FCO-NPs). The capacity of FCO-NSs at a current density of 1000 mA g−1 has been considerably improved to 823 mA h g−1 from 504 and 152 mA h g−1 for FCO-NCs and FCO-NPs, respectively, indicating a much better rate capability. The greatly enhanced cycling stability and rate capability can be largely attributed to the hollow porous structure of FCO-NSs with a wider pore distribution, a slightly higher Co content (compared to FCO-NCs) and higher mechanical strength, which facilitates Li+ and electron diffusion and migration.

Microwave-assisted facile synthesis of yellow fluorescent carbon dots from o-phenylenediamine for cell imaging and sensitive detection of Fe3+ and H2O2

Strongly yellow fluorescent carbon dots (CDs) have been directly synthesized from o-phenylenediamine (o-PD) through a facile microwave-assisted method. The as-prepared o-CDs exhibit excitation-dependent photoluminescent behavior and excellent water-solubility due to some amino or hydroxy functional groups on the surface. An emission peak appears at 573 nm when the o-CDs solution is excited at 400 nm, and the quantum yield (QY) is 38.5%. Owing to their low toxicity and water solubility the as-prepared o-CDs can be directly used for cell imaging. More importantly, the as-prepared o-CDs solution also shows sensitivity for H2O2. The limits of detection (LOD) for Fe3+ and H2O2 are 16.1 nM and 28.1 nM, respectively, which is much lower than whats reported in previous studies. The fluorescence intensity also shows a dependence on pH and the strongest fluorescence intensity appears at pH 9. In addition, we also find that the fluorescent properties of CDs prepared from m-phenylenediamine (m-PDs) and p-phenylenediamine (p-PDs) are quite different from those of o-CDs.

New insights into designing high-rate performance cathode materials for sodium ion batteries by enlarging the slab-spacing of the Na-ion diffusion layer

Recently, the design and synthesis of high performance cathode materials for sodium ion batteries have attracted great interest. In this study, we propose a novel strategy to design high-rate performance cathode materials for sodium ion batteries through enlarging the d-spacing of the Na-ion diffusion layer. More importantly, some new insights into the expansion mechanism of the interplanar spacing for Na0.67Mn0.8Ni0.1Mg0.1O2 induced by Ni and Mg co-doping and the resulting high-rate capability have been presented for the first time. We find that Mg and Ni co-doping leads to the shortening of the TM–O (TM = transition metal) bond lengths and the shrinkage of the TMO6 octahedrons, which might be largely responsible for the expansion of the interplanar spacing of the Na-ion diffusion layer. In comparison with Na0.67Mn0.8Ni0.2O2 and Na0.67Mn0.8Mg0.2O2, Mg and Ni co-doped Na0.67Mn0.8Ni0.1Mg0.1O2 has a higher Na-ion diffusion coefficient and can deliver around 160, 145, 133 and 124 mA h g−1 at 24, 48, 120 and 240 mA g−1, respectively. In particular, at the high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C), MMN can still offer reversible capacities of 110, 66 and 37 mA h g−1, respectively. In addition, the cycling stability has also been enhanced via Mg and Ni co-doping at the same time, which means that Mg and Ni co-doping also has a positive effect on the stability of the layered structure.