Shougang Chen

N, O-codoped hierarchical porous carbons derived from algae for high-capacity supercapacitors and battery anodes

Nitrogen and oxygen codoped hierarchical porous carbons have been synthesized by using a direct carbonization/activation procedure of biomass algae – Enteromorpha. The proposed procedure allowed us to produce carbons with high surface area (up to 2073 m2 g−1), sponge-like 3D interconnected structure, combined macro/meso/micropores, and rich N (0.64–0.85 at%) and O (11.36–12.24 at%) doping. The application of the produced carbons in supercapacitors based on an ionic liquid electrolyte showed a high specific capacitance of 201 F g−1 (10.7 μF cm−2) at 1 A g−1 and 20 °C, a capacitance retention ratio of 61% at 100 A g−1 and a capacitance loss of 9% after 10u2006000 cycles. The devices were able to deliver an energy density of 24 or 35 W h kg−1 (on an active mass normalized basis) at an extremely high power density of 60 kW kg−1 at 20 or 60 °C. The application of the produced carbons in a lithium-ion battery anode based on the LiPF6 electrolyte exhibited a high specific capacity of 1347–1709 mA h g−1, a good initial coulombic efficiency of 61–64%, and a good cyclability up to 500 cycles. We believe that this simple precursor-synthesis route offers excellent potential for facile large-scale material production for supercapacitors and lithium ion batteries.

Tunable radio-frequency negative permittivity in nickel-alumina “natural” meta-composites

“Natural” metamaterials with intrinsic negative permittivity and permeability have attracted significant attention because of their wide promising applications and facile preparation processes. In order to match the negative permeability band which is usually located in the radio-frequency range, radio-frequency negative permittivity is desired. Moreover, the negative permittivity should be tunable to satisfy different application circumstances. Herein, nickel/alumina composites consisting of nickel particles homogeneously dispersed in alumina were prepared using a facile wet chemical process. A percolation phenomenon appears, and expected radio-frequency negative permittivity is obtained. Furthermore, the dependences of negative permittivity on the composites compositions and microstructures are investigated in detail. It is shown that higher nickel content results in higher negative permittivity magnitude and lower negative permittivity frequency. Besides, the addition of alumina particles leads to dec...

Extremely high-rate aqueous supercapacitor fabricated using doped carbon nanoflakes with large surface area and mesopores at near-commercial mass loading

Achieving a satisfactory energy–power combination in a supercapacitor that is based on all-carbon electrodes and operates in benign aqueous media instead of conventional organic electrolytes is a major challenge. For this purpose, we fabricated carbon nanoflakes (20–100 nm in thickness, 5-μm in width) containing an unparalleled combination of a large surface area (3,000 m2·g−1 range) and mesoporosity (up to 72%). These huge-surface area functionalized carbons (HSAFCs) also had a substantial oxygen and nitrogen content (~10 wt.% combined), with a significant fraction of redox-active carboxyl/phenol groups in an optimized specimen. Their unique structure and chemistry resulted from a tailored single-step carbonization-activation approach employing (2-benzimidazolyl) acetonitrile combined with potassium hydroxide (KOH). The HSAFCs exhibited specific capacitances of 474 F·g−1 at 0.5 A·g−1 and 285 F·g−1 at 100 A·g−1 (charging time < 3 s) in an aqueous 2 M KOH solution. These values are among the highest reported, especially at high currents. When tested with a stable 1.8-V window in a 1 M Na2SO4 electrolyte, a symmetric supercapacitor device using the fabricated nanoflakes as electrodes yielded a normalized active mass of 24.4 Wh·kg−1 at 223 W·kg−1 and 7.3 Wh·kg−1 at 9,360 W·kg−1. The latter value corresponds to a charge time of <3 s. The cyclability of the devices was excellent, with 93% capacitance retention after 10,000 cycles. All the electrochemical results were achieved by employing electrodes with near-commercial mass loadings of 8 mg·cm−2.

Rich sulfur doped porous carbon materials derived from ginkgo leaves for multiple electrochemical energy storage devices

A strategy of utilizing biomass in energy applications has been highly sought after due to low cost, renewability and environmental friendliness. In this work, based on the unique multilayered structure of ginkgo leaves, an interconnected carbon nanosheet with rich micro/meso pores has been fabricated using hydrothermal treatment and a KOH activation process. Attractively, due to the intensive reactions between the rich organism components of the ginkgo leaves and sulfuric acid in the preparation process, the highest amount of sulfur doping (8.245 wt%) ever reported has been achieved in the as-obtained biomass derived carbons. Combined with the N doping derived from the proteins in ginkgo leaves, S,N dual-doping porous carbons with an interconnected sheet-like structure demonstrate excellent electrochemical performance in both EDLCs and NIBs. The application in EDLCs in aqueous electrolyte showed a high specific capacitance of 364 F g−1 at 0.5 A g−1 and only 2% capacitance loss after 30u2006000 cycles. In an ionic liquid electrolyte, the devices were able to deliver an energy density of 16 W h kg−1 at an extremely high power density of 50 kW kg−1. As a sodium-ion battery anode, it has the capacity of 200 mA h g−1 after 500 cycles (99% capacity retention) at 0.2 A g−1, which is superior or at least comparable to those of biomass derived carbons reported recently. Therefore, all these results exhibit the promising potential of the ginkgo leaves-derived carbon for wide applications in the field of energy storage devices.

Bilayer Polymer Metacomposites Containing Negative Permittivity Layer for New High-k Materials

Polymer matrix high-k composites are of considerable interest in various electronic devices, such as capacitors, antennas, actuators, etc. However, how to enhance the permittivity without elevating the loss remains a challenge for us. Here we present a novel design of bilayer high-k metacomposites consisting of two stacked single layers with positive permittivity and negative permittivity. Interestingly, the bilayer system shows an obvious permittivity boost effect with a permittivity improved by a 40-fold increase compared with the polymer matrix, while maintaining a loss tangent as low as 0.06. Further calculation results indicate that the permittivity of the bilayer composites could be enhanced by 4000-fold or even a greater increase as compared with the polymer matrix via balancing the dielectric properties of single layers. Insights into how the thickness ratios and dielectric properties of single layers interfere with the dielectric performances of bilayer composites were discussed. This study provides a new route for the design of high-k materials, and it will have great significance on the development of dielectric materials. Hopefully, multilayer high-k metacomposites with fascinating dielectric performances could be achieved via balancing the dielectric properties of single layers.

Ultra low percolation threshold and significantly enhanced permittivity in porous metal–ceramic composites

Iron–alumina composites consisting of different loadings of iron particles dispersed in an alumina matrix were prepared via a facile impregnation–calcination process. The frequency dispersions of conductivity and permittivity were investigated in detail. An ultra low percolation threshold of 2.3 vol%, which is much lower than that of dense metal–ceramic composites, was obtained. Meanwhile, a significant enhancement of permittivity e′ (from ∼7.5 to ∼800) was achieved when the iron content increases from 0 to 4.2 vol% at 10 MHz. The ultra low percolation threshold can be explained by the fact that the porous microstructure of the composites will facilitate the formation of a layer of two dimensional conductive networks on the pore wall of porous alumina. And the significant enhancement of permittivity should be attributed to the interfacial polarization phenomenon that takes place at the iron–alumina interfaces. This paper demonstrates that the loading of a conductive component into a porous matrix is an effective way to fabricate composites with simultaneously high permittivity and ultra-low percolation threshold. Hopefully, various porous metal–ceramic composites with tailored dielectric properties could be fabricated using the impregnation–calcination process.

Preparation, characterization and long-term antibacterial activity of Ag–poly(dopamine)–TiO2 nanotube composites

A simple and efficient approach for the loading of Ag nanoparticles on poly(dopamine)-modified TiO2 nanotubes (PDA–TNTs) was used to prepare a Ag nanoparticle–poly(dopamine)–TiO2 nanotube composite (Ag–PDA–TNTs) that was applied as a long-term antibacterial agent to inhibit the growth of bacterial cells. The features of the obtained Ag–PDA–TNTs were investigated by TEM, XRD, FT-IR and XPS analysis. Anatase TNTs were encapsulated in PDA layers with a thickness of about 3 nm on which about 20.4 wt% of single crystalline Ag nanoparticles anchored. XPS and FT-IR results indicated that the PDA layer not only served as a reduction reagent that could reduce Ag+ ions to Ag nanoparticles but also worked as an adhesive coating by tethering the Ag nanoparticles on the surface of PDA–TNTs. The long-term release profiles of the nanocomposites showed that PDA layers slowed the release rate of Ag nanoparticles, implying the possible long-term antibacterial activity of Ag–PDA–TNTs; and the antibacterial assays verified this point. Besides that, the antibacterial activity of Ag–PDA–TNTs under visible light was higher than that in the dark because of the synergistically antibacterial effects of Ag nanoparticles and ROS under visible light irradiation. Compared with the antibacterial activity of TiO2 nanotubes loaded with Ag nanoparticles (Ag–TNTs), Ag–PDA–TNTs had higher and longer-term antibacterial activity which is attributed to the effect of PDA layers tethering Ag nanoparticles on TNTs and slowing Ag+ ions release rate. This work provides a new method for the preparation of Ag-based antibacterial agents and facilitates their practical application in modern antifouling and biomedical fields.

Two-dimensional biomass-derived carbon nanosheets and MnO/carbon electrodes for high-performance Li-ion capacitors

Li-ion capacitors have been considered as next-generation advanced energy storage systems to meet the requirements of both high energy and high power due to the combination of rapid and long-term charge storage of supercapacitors and the high energy storage capacity of lithium ion batteries. Herein, we demonstrate the design of 2D nanostructured electrodes from low-cost biomass-kapok fiber for Li-ion capacitors: 2D carbon nanosheets with a high surface area and hierarchical porosity for the positive electrode, and 2D MnO/C nanocomposites with a large surface area and nanosized particles for the negative electrode. With the benefit of the structure of the Li-ion capacitor, the hybrid device can be operated at a high operating voltage of 4xa0V, exhibiting a high energy density of 100 W h kg−1 at 83 W kg−1, a high power density of 20 kW kg−1 at 30 W h kg−1 based on the active materials, and a capacity retention ratio of 70% after 5000 cycles. These results clearly demonstrate that biomass-derived electrodes are potential candidates for low-cost, fast and efficient energy storage systems in the future.

Preparation and long-term antibacterial activity of TiO2 nanotubes loaded with Ag nanoparticles and Ag ions

In this work anatase TiO2 nanotubes were prepared by hydrothermally treating a suspension of anatase TiO2 particles in alkaline solutions without the following calcination process. Ag nanoparticles and Ag ions were both loaded on TiO2 nanotubes by immersion in AgNO3 solutions followed by ultraviolet light radiation. The chemical and morphological features of the products, and the Ag release properties were investigated. The results demonstrated that the “open-ended” anatase TiO2 nanotubes with diameters of about 10 nm and lengths of over 100 nm were successfully prepared; 15.3 wt% of AgNO3 was loaded into the hollow tubular nanostructures and 9.2 wt% of Ag nanoparticles adhered uniformly to the walls of the nanotubes. The “open-ended” hollow tubular nanostructure of TiO2 nanotubes could act as a controller for the Ag release, and this endowed the Ag–TiO2 nanotubes with an extended antibacterial period. The long-term antibacterial activities of the resultant Ag–TiO2 nanotubes were examined against both Gram-negative bacteria and Gram-positive bacteria. It was confirmed that the “open-ended” hollow tubular nanostructure of TiO2 nanotubes and the dual action of Ag nanoparticles and Ag ions allowed the Ag–TiO2 nanotubes to attain long-term antibacterial activity, which enhanced the antibacterial performance of Ag-based antibacterial agents.

Metal ion-coordinated carboxymethylated chitosan grafted carbon nanotubes with enhanced antibacterial properties

Covalent bonding of multiwalled carbon nanotubes (MWCNTs) with carboxymethyl chitosan (CmCs) was prepared by the grafting method. The reaction products were confirmed by Fourier transform infrared spectroscopy (FTIR). The transmission electron microscopy (TEM) images and the thermogravimetric analysis (TGA) showed that the MWCNTs were coated by the CmCs uniformly, and the solubility and stability of the composites also increased in dimethyl sulfoxide (DMSO) and aqueous solutions. Multiwalled carbon nanotubes (MWCNTs) with carboxymethyl chitosan (CmCs) composites have been prepared in this work. It has been found that MWCNTs were coated by the CmCs uniformly and the solubility and stability of the composites also increased in dimethyl sulfoxide (DMSO) and aqueous solutions. The Cu and Zn ions were further coordinated to the MWCNT–CmCs composites. The MWCNT–CmCs metal complex showed a slower release rate than the CmCs metal complex by conductivity measurements. The results have confirmed the coordinated MWCNT–CmCs exhibited excellent antibacterial activity against Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Vibrio anguillarum. The susceptibility of MWCNT–CmCs–Cu against bacteria was more pronounced than that of MWCNT–CmCs–Zn, and all the complex materials illustrated more excellent antibacterial ability for S. aureus. The MWCNT–CmCs metals complex still illustrated good antibacterial property against S. aureus after 21 days. These results hinted that the composites possess great potential to be an alternative to other antifouling agents.