Solvent-Free Synthesis of Polymer Spheres and the Activation to Porous Carbon Spheres for Advanced Aluminum-Ion Hybrid Capacitors.

Porous carbon spheres (PCSs) characteristic of perfect symmetry and ideal rheological property have great potential in electrochemical energy storage (EES). However, conventional synthesis of PCSs heavily relies on solution-based methods that may lead to environmental issues. Herein, an environment-friendly solvent-free method toward the facile and mass production of m-phenylenediamine-formaldehyde (MPF) resin spheres, which can be converted into PCSs after carbonization and activation is reported. An ultrahigh productivity of 25.89 g in a 100-mL container and an impressive percent yield of 98.89% can be achieved for the MPF resin spheres, which are further converted into carbon spheres with a reasonable yield of 14.5% after carbonization. When employed as the cathode material for aluminum-ion hybrid capacitors, the obtained PCSs afford a double-layer capacity of ≈200 mAh g-1 , the highest value among reported porous carbon materials for Al-based EES devices. It is anticipated that the solvent-free synthesis method for PCSs developed here may play a significant role in other EES devices, such as magnesium-ion and calcium-ion hybrid capacitors.

High-performance supercapacitor based on three-dimensional flower-shaped Li4Ti5O12-graphene hybrid and pine needles derived honeycomb carbon.

A three-dimensional (3D) flower-shaped Li4Ti5O12-graphene (Gr) hybrid micro/nanostructures and pine needles derived carbon nanopores (PNDCN) has been prepared by using the effective hydrothermal process. Due to the unique micro/nanostructures which can provide abundant surface active sites, the obtained 3D Li4Ti5O12-Gr displays a high specific capacitance of 706.52 F g-1 at 1 A g-1. The prepared PNDCN also exhibits high specific capacitance of 314.50 F g-1 at 1 A g-1 benefiting from its interconnected honeycomb-like hierarchical and open structure, which facilitates the diffusion and reaction of electrolyte ions and enables an isotropic charging/discharging process. An asymmetric supercapacitor utilizing Li4Ti5O12-Gr as positive electrode and PNDCN as negative electrode has been fabricated, it delivers a high energy density of 35.06 Wh kg-1 at power density of 800.08 W kg-1 and outstanding cycling stability with 90.18% capacitance retention after 2000 cycles. The fabrication process presented in this work is facile, cost-effective, and environmentally benign, offering a feasible solution for manufacturing next-generation high-performance energy storage devices.

A yolk-shell V2O5 structure assembled from ultrathin nanosheets and coralline-shaped carbon as advanced electrodes for a high-performance asymmetric supercapacitor.

Various V2O5 three-dimensional nanostructures are synthesized using a facile template-free hydrothermal method and evaluated for use as supercapacitor electrode materials. As a result, the yolk-shell structure assembled from ultrathin nanosheets shows the best electrochemical performance, with a specific capacitance of 704.17 F g-1 at 1.0 A g-1 and a high capacity retention of 89% over 4000 cycles at 3.0 A g-1. In addition, a continuous three-dimensional porous coralline-shaped carbon is synthesized from osmanthus and has a large Brunauer-Emmett-Teller surface area of 2840.88 m2 g-1. Then, an asymmetric supercapacitor is developed using the as-prepared yolk-shell V2O5 as a positive electrode and the osmanthus derived coralline-shaped carbon as a negative electrode. This exhibits an energy density of 29.49 W h kg-1 at a power density of 800 W kg-1 with a good cycling performance that retains 90.6% of its initial capacity after 2000 cycles at 3.0 A g-1. Furthermore, two cells in series can easily brightly light up a light-emitting diode (3 V), further demonstrating the great potential of the prepared materials for high-performance supercapacitor devices.

Preparation of layered graphene and tungsten oxide hybrids for enhanced performance supercapacitors.

Tungsten oxide (WO3), which was originally poor in capacitive performance, is made into an excellent electrode material for supercapacitors by dispersing it on graphene (Gr). The obtained Gr-WO3 hybrids are characterized by X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy and scanning electron microscopy techniques, and evaluated as electrode materials for high-performance supercapacitors by cyclic voltammetry, galvanostatic charge-discharge curves and electrochemical impedance spectroscopy. A great improvement in specific capacitance is achieved with the present hybrids, from 255 F g-1 for WO3 nanoparticles to 580 F g-1 for Gr-WO3 hybrids (scanned at 1 A g-1 in 2 M KOH over a potential window of 0 to 0.45 V). The Gr-WO3 hybrid exhibits an excellent high rate capability and good cycling stability with more than 92% capacitance retention over 1000 cycles at a current density of 5 A g-1. The enhancement in supercapacitor performance of Gr-WO3 is not only attributed to its unique nanostructure with large specific surface area, but also its excellent electro-conductivity, which facilitates efficient charge transport and promotes electrolyte diffusion. As a whole, this work indicates that Gr-WO3 hybrids are a promising electrode material for high-performance supercapacitors.

Ultrasensitive electrochemical sensing platform for microRNA based on tungsten oxide-graphene composites coupling with catalyzed hairpin assembly target recycling and enzyme signal amplification.

An ultrasensitive electrochemical biosensor for microRNA (miRNA) is developed based on tungsten oxide-graphene composites coupling with catalyzed hairpin assembly target recycling and enzyme signal amplification. WO3-Gr is prepared by a simple hydrothermal method and then coupled with gold nanoparticles to act as a sensing platform. The thiol-terminated capture probe H1 is immobilized on electrode through Au-S interaction. In the presence of target miRNA, H1 opens its hairpin structure by hybridization with target miRNA. This hybridization can be displaced from the structure by another stable biotinylated hairpin DNA (H2), and target miRNA is released back to the sample solution for next cycle. Thus, a large amount of H1-H2 duplex is produced after the cyclic process. At this point, a lot of signal indicators streptavidin-conjugated alkaline phosphatase (SA-ALP) are immobilized on the electrode by the specific binding of avidin-biotin. Then, thousands of ascorbic acid, which is the enzymatic product of ALP, induces the electrochemical-chemical-chemical redox cycling to produce a strongly electrochemical response in the presence of ferrocene methanol and tris (2-carboxyethyl) phosphine. Under the optimal experimental conditions, the established biosensor can detect target miRNA down to 0.05fM (S/N=3) with a linear range from 0.1fM to 100pM, and discriminate target miRNA from mismatched miRNA with a high selectivity.