Gengchao Wang

High-Performance Asymmetric Supercapacitor Based on Nanoarchitectured Polyaniline/Graphene/Carbon Nanotube and Activated Graphene Electrodes

Hierarchical sulfonated graphene nanosheet/carboxylated multiwalled carbon nanotube/polyaniline (sGNS/cMWCNT/PANI) nanocomposites were synthesized through an interfacial polymerization method. Activated porous graphene (aGNS) was prepared by combining chemical foaming, thermal reduction, and KOH activation. Furthermore, we have successfully fabricated an asymmetric supercapacitor (ASC) using sGNS/cMWCNT/PANI and aGNS as the positive and negative electrodes, respectively. Because of its unique structure, high capacitive performance, and complementary potential window, the ASC device can be cycled reversibly at a cell voltage of 1.6 V in a 1 M H2SO4 aqueous electrolyte, delivering a high energy density of 20.5 Wh kg(-1) at a power density of 25 kW kg(-1). Moreover, the ASC device also exhibits a superior long cycle life with 91% retention of the initial specific capacitance after 5000 cycles.

All-solid-state asymmetric supercapacitor based on reduced graphene oxide/carbon nanotube and carbon fiber paper/polypyrrole electrodes

Sandwich-like reduced graphene oxide/carboxylated multi-walled carbon nanotube (RGO/cMWCNT) hybrid film and the carbon fiber paper-supported polypyrrole (CFP/PPy) composite film were prepared by a vacuum-infiltration process and an electrochemical deposition method, respectively. Furthermore, a novel all-solid-state asymmetric supercapacitor (ASC) was fabricated using RGO/cMWCNT as the negative electrode and CFP/PPy as the positive electrode, separated with potassium polyacrylate/KCl gel electrolyte. Due to the unique structure, stable potential window and good capacitive performance of the two electrodes, the as-fabricated ASC can be cycled reversibly at a cell voltage of 1.6 V and displays outstanding performances with an energy density of 28.6 W h kg−1 and a power density of 15.1 kW kg−1. Additionally, our ASC device also presents a superior long cycle life with 93% capacitance retention after 2000 cycles.

Improving the performance of PEDOT-PSS coated sulfur@activated porous graphene composite cathodes for lithium–sulfur batteries

A novel PEDOT-PSS coated sulfur@activated porous graphene composite (PEDOT/S@aPG) is prepared by the impregnation of sulfur with aPG and encapsulation with PEDOT-PSS as the cathode material for lithium–sulfur batteries. The abundant nanopores and large surface area of aPG can provide an intimate contact and strong interaction with S species. Furthermore, the conductive PEDOT-PSS layer can facilitate the charge transportation and prevent the dissolution of polysulfides. As a result, the as-prepared PEDOT/S@aPG composite cathode with a sulfur content of about 60.1% shows a higher specific discharge capacity (1198 mA h g−1 at 0.1 C) in the first cycle and good cycling stability, retaining a reversible capacity of 845 mA h g−1 after 200 cycles. Moreover, the PEDOT/S@aPG cathode also exhibits excellent rate capability, showing a high reversible capacity of 718 mA h g−1 at 2 C.

The perfect matching between the low-cost Fe2O3 nanowire anode and the NiO nanoflake cathode significantly enhances the energy density of asymmetric supercapacitors

The real-world applications of supercapacitors are hindered by their relatively low energy density compared with rechargeable batteries. Even with tremendous efforts in developing cathodes for aqueous asymmetric supercapacitors (AASCs), their supercapacitive performance is still severely restricted by the low specific capacitance of anodes which mostly consist of carbonaceous materials. We developed a novel low-cost anode of homogenous Fe2O3 nanowires grown on carbon fiber paper (CFP) that achieves a high specific capacitance of 908 F g−1 at 2 A g−1 and excellent rate performance (90% capacitance retention up to 10 A g−1) in a wide negative potential window of 0 to −1.35 V. Such an excellent supercapacitive performance makes it a perfect anode compared with other reported ones. Matching it with the NiO nanoflake cathode (1520 F g−1 at 2 A g−1 in 0–0.45 V) on CFP, an extremely high energy density of 105 W h kg−1 is obtained at a power density of 1400 W kg−1 and still retains 72.6 W h kg−1 at 12 700 W kg−1 for the AASCs, which is much superior to previously reported AASCs and even exceeding those of Ni-MH batteries.

Improving thermal conductivity and decreasing supercooling of paraffin phase change materials by n-octadecylamine-functionalized multi-walled carbon nanotubes

Improving thermal conductivity and decreasing supercooling are essential for the utilization of paraffin phase change materials (PCMs). In this work, n-octadecylamine-functionalized multi-walled carbon nanotubes (f-MWCNTs) are obtained through a simple method of carboxylation of the MWCNTs with mixed acids of H2SO4 and HNO3 and then salt-forming reaction with n-octadecylamine. The paraffin/f-MWCNTs (paraffin/f-MWCNTs) composite PCMs are fabricated by mixing paraffin with f-MWCNTs under ultrasonication at 70 °C. It is found that the f-MWCNTs are homogenously dispersed in a toluene or paraffin matrix due to the existence of long chain alkanes in f-MWCNTs. As a result, the thermal conductivity and heat transfer of the paraffin/f-MWCNTs composite PCMs are significantly enhanced. Moreover, differential scanning calorimetry (DSC) analysis indicates that the incorporation of f-MWCNTs reduces the supercooling of paraffin, mainly due to the well-dispersed f-MWCNTs serving as nuclei to promote the heterogeneous nucleation and crystallization process of paraffin.

A self-healable and easily recyclable supramolecular hydrogel electrolyte for flexible supercapacitors

Although research on polymer hydrogel electrolytes has achieved great progress, their practical application is restricted due to their vulnerability and non-recyclability problems caused by covalent cross-linking effects. Herein, we report a ferric ion cross-linked supramolecular PAA hydrogel electrolyte (KCl–Fe3+/PAA), in which the ionic bond and hydrogen bond endow the KCl–Fe3+/PAA hydrogel electrolyte with favorable self-healing ability and easy-recyclability. In addition, considering the eco-friendly and cost effective properties of both ferric ion and polyacrylic acid, there would be great potential for this KCl–Fe3+/PAA hydrogel electrolyte to be broadly applied. Meanwhile, the hydrogel electrolyte maintained good mechanical performance (extensibility > 700%, and stress > 400 kPa) and excellent conductivity (0.09 S cm−1), which completely satisfy the demands of flexible supercapacitors. After being assembled with graphene foam supported polypyrrole electrodes, the electrochemical performance of this flexible supercapacitor is comparable to that of its liquid electrolyte counterpart.

Self-Assembly of Polyethylene Glycol-Grafted Carbon Nanotube/Sulfur Composite with Nest-like Structure for High-Performance Lithium–Sulfur Batteries

The novel polyethylene glycol-grafted multiwalled carbon nanotube/sulfur (PEG-CNT/S) composite cathodes with nest-like structure are fabricated through a facile combination process of liquid phase deposition and self-assembly, which consist of the active material core of sulfur particle and the conductive shell of PEG-CNT network. The unique architecture not only provides a short and rapid charge transfer pathway to improve the reaction kinetics but also alleviates the volume expansion of sulfur during lithiation and minimizes the diffusion of intermediate polysulfides. Such an encouraging electrochemical environment ensures the excellent rate capability and high cycle stability. As a result, the as-prepared PEG-CNT/S composite with sulfur content of 75.9 wt % delivers an initial discharge capacity of 1191 and 897 mAh g(-1) after 200 cycles at 0.2 C with an average Coulombic efficiency of 99.5%. Even at a high rate of 2 C, an appreciable capacity of 723 mAh g(-1) can still be obtained.

A graphene/carbon nanotube@π-conjugated polymer nanocomposite for high-performance organic supercapacitor electrodes

Supercapacitors based on π-conjugated conducting polymers have attracted attention due to their high pseudo-capacitance characteristics. However, the narrow window of their potential (<1 V) gives rise to low energy density, and this restricts their practical application. In the present study a novel hierarchical nanocomposite, graphene nanosheets/acid-treated multi-walled carbon nanotube-supported poly(1,5-diaminoanthraquinone) (GNS/aMWCNT@PDAA), has been successfully synthesized using cerium sulphate (Ce(SO4)2) as oxidant and camphor sulphonic acid as dopant. The nanocomposite exhibits a unique nanoporous morphology, a high π-conjugated degree and an excellent conductive interpenetrating network. With these intriguing features, in addition to its unique p- and n-doping characteristics, the supercapacitor in a 1 M tetraethylammonium tetrafluoroborate -acetonitrile (Et4NBF4-AN) electrolyte can be reversibly cycled within a potential window of 2.8 V. The supercapacitor achieves a high energy density of 86.4 W h kg−1 at a power density of 0.73 kW kg−1, and still retains energy density of 55.5 W h kg−1 at a power density of 153.9 kW kg−1. In addition, superior cycling stability is achieved, with only 7% capacitance loss after 10 000 cycles. This excellent performance surpasses that of other recently reported supercapacitors and represents a significant breakthrough in π-conjugated polymer-based supercapacitors.

Layer-by-layer assembly of aqueous dispersible, highly conductive poly(aniline-co-o-anisidine)/poly(sodium 4-styrenesulfonate)/MWNTs core-shell nanocomposites.

Poly(aniline-co- o-anisidine) (P(An-co- o-As)) ionomers and poly(sodium 4-styrenesulfonate) (PSS) were layer-by-layer (LbL) assembled on carboxylic acid-functionalized multiwalled carbon nanotubes (MWNTs). The multilayered polyelectrolyte greatly enhanced the dispersibility and stability of MWNTs in aqueous solutions. More importantly, the nanocomposites showed 3 orders of magnitude of conductivity increase, 4.2 S/cm, compared to that of neat ionomers, 0.004 S/cm. The deposition procedure was monitored with zeta (zeta) potential changes. Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis), and Raman spectra confirmed charge transfer from the quinoid units of the P(An-co- o-As) to MWNTs, which effectively delocalize the electrons. Further, we explored the pH response of the assembled P(An-co- o-As)/PSS/MWNTs multilayer nanocomposites. The sharp transition of the conductivity in the pH range of 2 to 6 makes the nanocomposites promising candidates for chemical-biological sensing.

A post-oxidation strategy for the synthesis of graphene/carbon nanotube-supported polyaniline nanocomposites as advanced supercapacitor electrodes

A post-oxidation strategy was proposed to synthesize sulfonated graphene nanosheets/carboxylated multi-walled carbon nanotube-supported PANI (sGNS/cMWCNT@PANI) hierarchical nanocomposites by an interfacial polymerization as advanced supercapacitor electrodes. Field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM) indicated that the morphology with a coexisting structure of sGNS supported PANI nanorod arrays and coaxial cMWCNT/PANI nanocables did not show significant differences through a post-oxidation process. X-ray diffraction (XRD) and thermogravimetic analysis (TGA) proved that the oligomers of PANI were eliminated during the post-oxidation process. The spectral analysis revealed that the post-oxidation led to an increasing content of quinoid structure in the nanocomposites. Electrochemical measurements showed that the sGNS/cMWCNT@PANI with a post-oxidation process exhibited improved cycling stability with 91.4% capacitance retention after 5000 cycles.