Xiongwei Wu

Graphitized Carbon Fibers as Multifunctional 3D Current Collectors for High Areal Capacity Li Anodes

The Li metal anode has long been considered as one of the most ideal anodes due to its high energy density. However, safety concerns, low efficiency, and huge volume change are severe hurdles to the practical application of Li metal anodes, especially in the case of high areal capacity. Here it is shown that that graphitized carbon fibers (GCF) electrode can serve as a multifunctional 3D current collector to enhance the Li storage capacity. The GCF electrode can store a huge amount of Li via intercalation and electrodeposition reactions. The as-obtained anode can deliver an areal capacity as high as 8 mA h cm-2 and exhibits no obvious dendritic formation. In addition, the enlarged surface area and porous framework of the GCF electrode result in lower local current density and mitigate high volume change during cycling. Thus, the Li composite anode displays low voltage hysteresis, high plating/stripping efficiency, and long lifespan. The multifunctional 3D current collector promisingly provides a new strategy for promoting the cycling lifespan of high areal capacity Li anodes.

Nanostructured positive electrode materials for post-lithium ion batteries

Nanotechnology has opened up new frontiers in materials science and engineering in the past several decades. Considerable efforts on nanostructured electrode materials have been made in recent years to fulfill the future requirements of electrochemical energy storage. Compared to bulk materials, most of these nanostructured electrode materials improve the thermodynamic and kinetic properties of electrochemical reactions for achieving high energy and power densities. Here we briefly review the state-of-the-art research activities in the area of nanostructured positive electrode materials for post-lithium ion batteries, including Li–S batteries, Li–Se batteries, aqueous rechargeable lithium batteries, Li–O2 batteries, Na-ion batteries, Mg-ion batteries and Al-ion batteries. These future rechargeable battery systems may offer increased energy densities, reduced cost, and more environmental benignity. A particular focus is directed to the design principles of these nanostructured positive electrode materials and how nanostructuring influences electrochemical performance. Moreover, the recent achievements in nanostructured positive electrode materials for some of the latest emerging rechargeable batteries are also summarized, such as Zn-ion batteries, F- and Cl-ion batteries, Na–, K– and Al–S batteries, Na– and K–O2 batteries, Li–CO2 batteries, novel Zn–air batteries, and hybrid redox flow batteries. To facilitate further research and development, some future research trends and directions are finally discussed.

A Quasi-Solid-State Sodium-Ion Capacitor with High Energy Density

A quasi-solid-state sodium-ion capacitor is demonstrated with nanoporous disordered carbon and macroporous graphene as the negative and positive electrodes, respectively, using a sodium-ion-conducting gel polymer electrolyte. It can operate at a cell voltage as high as 4.2 V with an energy density of record high 168 W h kg(-1).

Additive-free solvothermal synthesis of hierarchical flower-like LiFePO4/C mesocrystal and its electrochemical performance

Three dimensional hierarchical flower-like lithium iron phosphate (LiFePO4) mesocrystals were successfully synthesized via a solvothermal approach with the utilization of a mixture of water/ethylene glycol/dimethylacetamide (H2O/EG/DMAC) as co-solvent. No other surfactant or template agent was used and beautiful micro-sized LiFePO4 mesoporous structures with a special rose-like morphology were obtained. The hierarchical LiFePO4 mesocrystals were assembled by well crystallized nano-sized LiFePO4 thin plates with a thickness around 100 nm. The characteristics and electrochemical dynamics as well as performance of the obtained hierarchical flower-like LiFePO4 mesocrystals were carefully investigated. The flower-like hierarchical LiFePO4 mesocrystals showed a high initial lithium intercalation capability of 147 mA h g−1 at a current density of 17 mA g−1 (0.1 C), which should be attributed to the high specific surface area resulting from the mesoporous superstructure and well crystallized LiFePO4 nano-plate composition units. Polyvinylpyrrolidone (PVP) was introduced during the solvothermal synthesis as an in situ carbon coating source. The obtained flower-like C-coated LiFePO4 mesocrystals exhibited even better initial lithium intercalation capability of 161 mA h g−1 at 0.1 C and showed improved lithium storage performance at high rates as well as good cyclic stability.

A conductive polymer coated MoO3 anode enables an Al-ion capacitor with high performance

Electrochemical capacitors are becoming promising energy conversion/storage and power output devices. However, high cost and low energy density are two serious disadvantages. By integrating the advantages of Li-/Na-ion batteries and electrochemical capacitors, Li-/Na-ion capacitors have been explored recently. Al is very cheap and is the most abundant metal element on the earth. There are few reports on Al-ion capacitors due to the challenges in finding a suitable anode with large capacitance and good rate performance. Here, the feasibility of assembling an Al-ion capacitor with good electrochemical performance is demonstrated. The Al-ion capacitor is assembled by using a composite of MoO3 nanotubes coated by a conductive polypyrrole (PPy@MoO3) as an anode, which functions via a redox intercalation/deintercalation of Al3+ ions in aqueous solution. It delivers a capacitance of 693 F g−1, about 3 times higher than that of electrode materials for sodium-ion capacitors in aqueous solution. Combined with an activated carbon (AC) cathode, the Al-ion capacitor presents an energy density of 30 W h kg−1 and an excellent cycling life with 93% capacitance retention after 1800 cycles. This finding provides another energy storage device with low cost and promotes the application of capacitors.

Removal of mercury by adsorption: a review

Due to natural and production activities, mercury contamination has become one of the major environmental problems over the world. Mercury contamination is a serious threat to human health. Among the existing technologies available for mercury pollution control, the adsorption process can get excellent separation effects and has been further studied. This review is attempted to cover a wide range of adsorbents that were developed for the removal of mercury from the year 2011. Various adsorbents, including the latest adsorbents, are presented along with highlighting and discussing the key advancements on their preparation, modification technologies, and strategies. By comparing their adsorption capacities, it is evident from the literature survey that some adsorbents have shown excellent potential for the removal of mercury. However, there is still a need to develop novel, efficient adsorbents with low cost, high stability, and easy production and manufacture for practical utility.

Surface fluorinated LiNi0.8Co0.15Al0.05O2 as a positive electrode material for lithium ion batteries

LiNi0.8Co0.15Al0.05O2 is considered as an alternative to the commercial LiCoO2 positive electrode material for lithium ion batteries because of its excellent cycling performance. However, its capacity fading and potential safety hazard still need to be improved. In this study, fluorination has been introduced for the first time to modify the surface of LiNi0.8Co0.15Al0.05O2 by a one-step facile and dry method. The crystalline structure, morphology, surface information and electrochemical performance were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectronic spectroscopy and electrochemical tests. The surface-fluorinated LiNi0.8Co0.15Al0.05O2 exhibits a reversible capacitance up to 220.5 mA h g−1 at 0.1 C, good rate capability, and an excellent long-term cycling stability with 93.6% capacity retention after 80 cycles at 0.1 C, which is much better than that of the pristine commercial LiNi0.8Co0.15Al0.05O2. The main reason is that metal-fluorine (M–F) bond partially replaces the metal–oxygen (M–O) bond at the surface, enhancing the entire bond energy as well as the structure stability. In addition, the interfacial conductivity between the electrolyte and the positive electrode has been increased, leading to a faster kinetic process. These results show that fluorinated LiNi0.8Co0.15Al0.05O2 is a promising positive electrode material for high performance lithium ion batteries.

Chiral electrochemical recognition of tryptophan enantiomers at a multi-walled carbon nanotube–chitosan composite modified glassy carbon electrode

A multi-walled carbon nanotube–chitosan composite modified glassy carbon electrode (MWCNT–CS/GCE) was prepared and used for the chiral recognition of tryptophan (Trp) enantiomers. Cyclic voltammetry (CV) was employed to characterize the electrical conductivity of the modified electrode. Differential-pulse voltammetry (DPV) was employed to observe the oxidation peak potentials (Ep) of L- and D-Trp at the modified electrode. Different Ep of L- and D-Trp at the modified GCE were observed in the solutions containing only L- or D-Trp enantiomers. As for a mixed aqueous solution containing both L- and D-Trp, only one Ep peak would appear. However, the Ep of the peak was found to shift positively and linearly with an increasing percentage of L-isomer in the racemic Trp mixture solution, making it possible to determine the percentage of L- and D-Trp enantiomers in a racemic Trp mixture.

A quasi-solid-state Li-ion capacitor with high energy density based on Li3VO4/carbon nanofibers and electrochemically-exfoliated graphene sheets

Electrochemical capacitors are playing increasing roles in our daily life but their low energy densities limit their wide applications. The appearance of Li-ion capacitors (LICs) is regarded as the beginning of a new era of increased energy densities in the field of electrochemical capacitors. However, it is a great challenge to find a suitable anode material with superior electrochemical performance. In addition, the intrinsic instability of the liquid electrolytes used in LICs can easily result in leakage of the electrolyte and causes a serious safety issue. Here, a quasi-solid-state LIC is fabricated by applying Li3VO4/carbon nanofibers as the anode and electrochemically-exfoliated graphene sheets as the cathode in a gel polymer electrolyte. It achieves an energy density of 110 W h kg−1 and a good cycling performance. Our results demonstrate that quasi-solid-state LICs provide a key system acting as a bridge between conventional Li-ion batteries and supercapacitors, while meeting the high safety demands of electronic devices.

Soluble starch functionalized graphene oxide as an efficient adsorbent for aqueous removal of Cd(II): The adsorption thermodynamic, kinetics and isotherms

Soluble starch-functionalized graphene oxide composite (GO-starch) was prepared by a facile esterification reaction. And the composite was used as a novel adsorbent for the removal of Cd(II) from aqueous solution. The chemical composition and morphology of the GO-starch was investigated by fourier transform infrared spectroscopy, scanning electron microscopy and Raman spectroscopy. To evaluate the effects of the adsorption of Cd(II) by GO-starch, batch adsorption studies were performed to optimize the major parameters such as contact time, pH, initial concentration and temperature. The maximum uptake capacity of Cd(II) was 43.20 mg/g under the optimal conditions. Furthermore, the adsorption kinetics, isotherms and thermodynamics of Cd(II) on GO-starch were also investigated. The experimental data indicated that the adsorption kinetics and adsorption isotherms of Cd(II) on GO-starch were well fitted by pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The adsorption thermodynamic parameters were calculated as ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0, respectively. The thermodynamic parameters indicated that the adsorption process was endothermic, feasible and spontaneous. Due to its high adsorption capacity for Cd(II), the GO-starch might have considerable potential for the aqueous removal of metal ions.Graphical AbstractSoluble starch-functionalized graphene oxide composite (GO-starch) was prepared and used as a novel adsorbent for the aqueous removal of Cd(II). The chemical composition and morphology of the GO-starch was characterized by fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and Raman spectroscopy. Batch adsorption experiments were performed to optimize the major parameters such as contact time, pH, initial concentration and temperature. The maximum uptake capacity of Cd(II) was 43.20 mg/g under the optimal conditions. The adsorption kinetics and adsorption isotherms were well fitted by pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The adsorption thermodynamic parameters were ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0, indicating that the Cd(II) adsorption process was spontaneous, endothermic and feasible.