Qilin Cheng

MnO2 nanoflake/polyaniline nanorod hybrid nanostructures on graphene paper for high-performance flexible supercapacitor electrodes

A facile two-step strategy is adopted to construct a free-standing composite paper of MnO2 nanoflake/polyaniline (PANI) nanorod hybrid nanostructures on reduced graphene oxide (RGO) for flexible supercapacitor electrode application. MnO2 nanoflakes are first grown on RGO paper via an electrodeposition method, followed by assembly of PANI nanorods between MnO2 nanoflakes by in situ polymerization using camphorsulfonic acid as a dopant. The morphology and structure of the composite paper are characterized and the electrochemical properties are systematically investigated. The interconnected PANI nanorods deposited on the interlaced MnO2 nanoflakes have a length of ∼100 nm and a diameter of ∼30 nm, creating plenty of open porous structures which are beneficial for ion penetration into the electrode. The RGO/MnO2/PANI composite paper shows a large specific capacitance of 636.5 F g−1 at 1.0 A g−1 in 1.0 M Na2SO4 electrolyte and excellent cycling stability (85% capacitance retention after 104 cycles). The optimized composite structure with more electroactive sites, fast ion and electron transfer, and strong structural integrity endows the ternary composite paper electrode with outstanding electrochemical performance.

Morphology-controllable synthesis of MnO2 hollow nanospheres and their supercapacitive performance

Uniform MnO2 hollow nanospheres with hierarchical (urchin-like and flower-like) and non-hierarchical structures have been synthesized via a dual-template assisted hydrothermal process. The morphology control of the MnO2 hollow spheres can be easily achieved by altering the mass ratio of Pluronic F-127 to silica spheres. Material characterizations reveal that urchin-like hollow spheres possess the highest BET surface area of 233.4 m2 g−1 among the diverse morphologies. A possible formation mechanism for the MnO2 hollow spheres with different morphologies is proposed. The supercapacitive performance of the MnO2 spheres was investigated by cyclic voltammetry and galvanostatic charge–discharge techniques. The urchin-like hollow spheres exhibit the highest specific capacitance of 266.6 F g−1 within the potential range of 0–1.0 V. The relationship between the specific capacitance and the morphology of the MnO2 hollow spheres is also discussed. The good capacitive behavior and cycling stability of the hierarchical MnO2 hollow spheres highlights the importance of the morphological design and control of materials in practical supercapacitor applications.

Ultrathin MnO2 nanoflakes grown on N-doped carbon nanoboxes for high-energy asymmetric supercapacitors

We demonstrate the synthesis of ultrathin MnO2 nanoflakes grown on N-doped carbon nanoboxes, forming an impressive hierarchical MnO2/C nanobox hybrid with an average size of 500 nm, which exhibits an excellent electrochemical performance due to the unique structure, N-doping and strong synergistic effects between them. In addition, we also assembled a green asymmetric supercapacitor (ASC) using the as-synthesized MnO2/C nanoboxes as a positive electrode and the corresponding N-doped carbon nanoboxes as a negative electrode in a neutral aqueous electrolyte, aiming to further enhance its energy density by extending the operating potential. More significantly, our ASC device is able to reversibly cycle within a wide operating voltage of 2.0 V and delivers a maximum energy density of 39.5 W h kg−1 with superior cycling stability (∼90.2% capacitance retention after 5000 cycles). These intriguing results show that hollow nanostructures will be promising electrode materials for advanced supercapacitors.

Dual Tuning of Biomass-Derived Hierarchical Carbon Nanostructures for Supercapacitors: the Role of Balanced Meso/Microporosity and Graphene.

Rational design of advanced carbon nanomaterials with a balanced mesoporosity to microporosity is highly desirable for achieving high energy/power density for supercapacitors because the mesopore can allow better transport pathways for the solvated ions of larger than 1 nm. Inspired by the inherent meso/macroporous architecture and huge absorption ability to aqueous solution of auricularia biomass, we demonstrate a new biomass-derived synthesis process for the three-dimensional (3D) few-layered graphene nanosheets incorporated hierarchical porous carbon (GHPC) nanohybrids. The as-prepared GHPC nanohybrids possess a balanced mesoporosity to microporosity with much improved conductivity, which is highly desirable for achieving high energy/power density for supercapacitors. As we predicted, they delivered a high specific capacitance of 256 F g−1 at 1 A g−1 with excellent rate capability (120 F g−1 at 50 A g−1) and long cycle life (92% capacity retention after 10000 cycles) for symmetric supercapacitors in 1 M H2SO4. Based on the as-obtained carbon materials, a flexible and all-solid-state supercapacitor was also assembled, which can be fully recharged within 10 s and able to light an LED even under bended state. Such excellent performance is at least comparable to the best reports in the literature for two-electrode configuration under aqueous systems.

Synthesis and Structural and Electrical Characteristics of Polypyrrole Nanotube/TiO2 Hybrid Composites

Hybrid composites of conducting polypyrrole nanotubes with TiO2 nanoparticles were synthesized in the presence of β-naphthalenesulfonic acid by chemical oxidative polymerization. The morphology, structure, and electrical properties were investigated by several experimental techniques. The results indicated that the structural and electrical properties of the composites were influenced by the content of TiO2 nanoparticles. The DC conductivity of the composites increased by one order of magnitude when the concentration of TiO2 was 0.1 M compared with pure PPy nanotubes. AC conductivity of the composites showed the similar trend with the TiO2 content and obeyed the power law index in the 101–107 Hz range. The electrorheological properties of the composite under steady and oscillatory shear were also evaluated.

Synthesis, Characterization and Electrochemical Capacitance of Urchin-Like Hierarchical Polyaniline Microspheres

Urchin-like hierarchical polyaniline (PANI) microspheres were synthesized by a simple template-free method. The morphology and structure of the PANI microspheres were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The results indicated that the microspheres had sez-urchin-like architectures with their surfaces consisting of nanofibers with diameters of about 100 nm and length of 2 μm. Cyclic voltammetry and galvanostatic charge/discharge measurements in 1M H2SO4 solution revealed that the microspheres had typical electrochemical supercapacitor behavior but showed lower specific capacitance, due to low conductivity or doping level of the PANI microspheres, in comparison with conventional PANI or PANI nanofibers. The effect of experimental parameters on the morphology and electrochemical properties of PANI microspheres is also discussed.

Construction of Hierarchical CuO/Cu2O@NiCo2S4 Nanowire Arrays on Copper Foam for High Performance Supercapacitor Electrodes

Hierarchical copper oxide @ ternary nickel cobalt sulfide (CuO/Cu2O@NiCo2S4) core-shell nanowire arrays on Cu foam have been successfully constructed by a facile two-step strategy. Vertically aligned CuO/Cu2O nanowire arrays are firstly grown on Cu foam by one-step thermal oxidation of Cu foam, followed by electrodeposition of NiCo2S4 nanosheets on the surface of CuO/Cu2O nanowires to form the CuO/Cu2O@NiCo2S4 core-shell nanostructures. Structural and morphological characterizations indicate that the average thickness of the NiCo2S4 nanosheets is ~20 nm and the diameter of CuO/Cu2O core is ~50 nm. Electrochemical properties of the hierarchical composites as integrated binder-free electrodes for supercapacitor were evaluated by various electrochemical methods. The hierarchical composite electrodes could achieve ultrahigh specific capacitance of 3.186 F cm−2 at 10 mA cm−2, good rate capability (82.06% capacitance retention at the current density from 2 to 50 mA cm−2) and excellent cycling stability, with capacitance retention of 96.73% after 2000 cycles at 10 mA cm−2. These results demonstrate the significance of optimized design and fabrication of electrode materials with more sufficient electrolyte-electrode interface, robust structural integrity and fast ion/electron transfer.

Co3O4@CoS Core-Shell Nanosheets on Carbon Cloth for High Performance Supercapacitor Electrodes

In this work, a two-step electrodeposition strategy is developed for the synthesis of core-shell Co3O4@CoS nanosheet arrays on carbon cloth (CC) for supercapacitor applications. Porous Co3O4 nanosheet arrays are first directly grown on CC by electrodeposition, followed by the coating of a thin layer of CoS on the surface of Co3O4 nanosheets via the secondary electrodeposition. The morphology control of the ternary composites can be easily achieved by altering the number of cyclic voltammetry (CV) cycles of CoS deposition. Electrochemical performance of the composite electrodes was evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The results demonstrate that the Co3O4@CoS/CC with 4 CV cycles of CoS deposition possesses the largest specific capacitance 887.5 F·g−1 at a scan rate of 10 mV·s−1 (764.2 F·g−1 at a current density of 1.0 A·g−1), and excellent cycling stability (78.1% capacitance retention) at high current density of 5.0 A·g−1 after 5000 cycles. The porous nanostructures on CC not only provide large accessible surface area for fast ions diffusion, electron transport and efficient utilization of active CoS and Co3O4, but also reduce the internal resistance of electrodes, which leads to superior electrochemical performance of Co3O4@CoS/CC composite at 4 cycles of CoS deposition.

High-performance stretchable supercapacitors based on intrinsically stretchable acrylate rubber/MWCNTs@conductive polymer composite electrodes

The key to fabricating high-performance stretchable supercapacitors (SSCs) is the design of intrinsically stretchable electrodes. However, there are few reports focusing on this, especially in organic electrolytes with a broader potential window. In this work, we have fabricated novel intrinsically stretchable electrodes made of acrylate rubber/multiwall carbon nanotube (ACM/MWCNT) composite film supported poly(1,5-diaminoanthraquinone) or polyaniline (ACM/MWCNTs@PDAA and ACM/MWCNTs@PANI). The ACM/MWCNT film with 35 wt% MWCNTs shows a high conductivity (9.6 S cm−1), high stretchability (155%) and good elastic resilience (11.7% plastic deformation after 500 stretching cycles at 50% strain). The ACM/MWCNTs@PDAA anode and ACM/MWCNTs@PANI cathode exhibit a high volumetric specific capacitance of 20.2 and 17.2 F cm−3 at 1 mA cm−2, respectively. To demonstrate the good performance of the as-prepared stretchable electrodes, an organic asymmetric stretchable supercapacitor (oASSC) is assembled conveniently by using ACM/MWCNTs@PANI as the cathode, ACM/MWCNTs@PDAA as the anode, and ACM/Et4NBF4–AN as the quasi-solid-state polymer electrolyte (QPE). The oASSC delivers an outstanding energy density of 2.14 mW h cm−3 and good cycling stability under static and 50% strain conditions, which makes it superior to most reported stretchable supercapacitors.

A Highly Flexible Supercapacitor Based on MnO2/RGO Nanosheets and Bacterial Cellulose-Filled Gel Electrolyte

The flexible supercapacitors (SCs) of the conventional sandwich-type structure have poor flexibility due to the large thickness of the final entire device. Herein, we have fabricated a highly flexible asymmetric SC using manganese dioxide (MnO2) and reduced graphene oxide (RGO) nanosheet-piled hydrogel films and a novel bacterial cellulose (BC)-filled polyacrylic acid sodium salt-Na2SO4 (BC/PAAS-Na2SO4) neutral gel electrolyte. Apart from being environmentally friendly, this BC/PAAS-Na2SO4 gel electrolyte has high viscosity and a sticky property, which enables it to combine two electrodes together. Meanwhile, the intertangling of the filled BC in the gel electrolyte hinders the decrease of the viscosity with temperature, and forms a separator to prevent the two electrodes from short-circuiting. Using these materials, the total thickness of the fabricated device does not exceed 120 μm. This SC device demonstrates high flexibility, where bending and even rolling have no obvious effect on the electrochemical performance. In addition, owing to the asymmetric configuration, the cell voltage of this flexible SC has been extended to 1.8 V, and the energy density can reach up to 11.7 Wh kg−1 at the power density of 441 W kg−1. This SC also exhibits a good cycling stability, with a capacitance retention of 85.5% over 5000 cycles.