Xiaomiao Feng

The synthesis of shape-controlled MnO2/graphene composites via a facile one-step hydrothermal method and their application in supercapacitors

Novel MnO2 petal nanosheet and nanorod/graphene composites are successfully fabricated by a facile one-step hydrothermal method through changing the content of the Mn source. The formation mechanism of different morphologies of MnO2/graphene composites have been studied. The structure of the MnO2/graphene is “sandwich”-like, with MnO2 petal nanosheets and nanorods homogeneously anchored on each side of the graphene. Furthermore, the MnO2/graphene composites with different shapes can be used for supercapacitor electrode materials. The experimental results show that the MnO2 petal nanosheet/graphene composite has better capacitance performance than that of the MnO2 nanorod/graphene composite. The MnO2 petal nanosheet/graphene composite shows excellent specific capacitance as high as 516.8 F g−1 at a scan rate of 1 mV s−1 in 1 M Na2SO4 electrolyte and good long-term cycle stability, indicating its potential application to act as a promising electrode material for high-performance supercapacitors. This study provides a facile and in situ method to prepare metal oxide/graphene composite materials and a novel scaffold to construct other metal oxides with graphene for energy storage.

The self-assembly of shape controlled functionalized graphene–MnO2 composites for application as supercapacitors

Graphene–MnO2 nanocomposites with different morphologies were obtained by a facile self-assembly method. The formation mechanism of graphene–MnO2 composites with different shapes of MnO2 is discussed in detail. Nanostructured MnO2 with different morphologies was distributed on the surface of graphene uniformly. The prepared graphene–MnO2 composites could be used as electrode materials for supercapacitors. The graphene–MnO2 (flowerlike nanospheres) composite (405 F g−1) exhibited better capacitive performance than that of the graphene–MnO2 (nanowires) composite (318 F g−1) at a current density of 1.0 A g−1. The synergistic effect of graphene and MnO2 endowed the composite with high electrochemical capacitance. Moreover, the graphene–MnO2 (flowerlike nanospheres) composite showed a fast charge–discharge process and high cyclic stability.

Facile synthesis of shape-controlled graphene–polyaniline composites for high performance supercapacitor electrode materials

Graphene–polyaniline (PANI) nanocomposites with different morphologies were successfully fabricated by an effective one-step hydrothermal method. The morphologies of PANI could be controlled from nanowires to nanocones by adjusting the amount of aniline with the assistance of an ultrasonication process. By taking the advantages of the high conductivity of graphene and the pseudocapacitance of PANI, graphene–PANI composites were used as an example for the application to the supercapacitor electrode materials. The cyclic voltammograms (CV) and galvanostatic charge–discharge measurements demonstrate that the graphene–PANI shows excellent electrochemical properties. The graphene–PANI nanowire composite (724.6 F g−1) exhibited higher specific capacitance than that of the graphene–PANI nanocone composite (602.5 F g−1) at a current density of 1.0 A g−1. Furthermore, the graphene–PANI nanowire composite exhibited outstanding capacitive performance with a high specific capacitance of 957.1 F g−1 at 2 mV s−1 and a high cycle reversibility of 90% after charge–discharge 1000 cycles. The improved electrochemical properties of the graphene–PANI nanocomposites suggest their promising applications to high-performance supercapacitors.

Synthesis of a graphene/polyaniline/MCM-41 nanocomposite and its application as a supercapacitor

A ternary nanocomposite of graphene/polyaniline (PANI)/porous silica MCM-41 (MCM-41) was prepared by a hydrothermal method. The amount of graphene oxide (GO) in the graphene/PANI/MCM-41 nanocomposite had a strong effect on the supercapacitor performance. The experimental results showed that the specific capacitance of the graphene/PANI/MCM-41 nanocomposite could reach the highest value when the GO content was 50%. The specific capacitance of the nanocomposite was 405 F g−1 at a current density of 0.8 A g−1. Furthermore, over 91.4% of the original capacitance was retained after repeating the galvanostatic charge–discharge for 1000 cycles. The performance of the prepared supercapacitor containing different amounts of GO were studied in detail.

Preparation of graphene supported nickel nanoparticles and their application to methanol electrooxidation in alkaline medium

In this paper, we present the synthesis of Ni nanoparticles supported on graphene (Ni/G) using graphene oxide (GO) and Ni2+ ions as starting materials. GO is mixed with NiCl2 solution and treated by hydrazine. Hydrazine both reduces the GO and forms a complex with nickel(II). A treatment in the tubular furnace allows decomposing the nickel-hydrazine complex into Ni metallic nanoparticles as well as further reducing the GO into graphene. The materials are characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and thermogravimetry–mass spectrometry as well as tested for methanol electrooxidation in alkaline medium.

Solution-processed copper nanowire flexible transparent electrodes with PEDOT:PSS as binder, protector and oxide-layer scavenger for polymer solar cells

The easy oxidation and surface roughness of Cu nanowire (NW) films are the main bottlenecks for their usage in transparent conductive electrodes (TCEs). Herein, we have developed a facile and scaled-up solution route to prepare Cu NW-based TCEs by embedding Cu NWs into pre-coated smooth poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films on poly(ethylene terephthalate) (PET) substrates. The so obtained Cu NW-PEDOT:PSS/PET films have low surface roughness (∼70 nm in height), high stability toward oxidation and good flexibility. The optimal TCEs show a typical sheet resistance of 15 Ω·sq−1 at high transparency (76% at λ = 550 nm) and have been used successfully to make polymer (poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester) solar cells, giving an efficiency of 1.4%. The overall properties of Cu NW-PEDOT:PSS/PET films demonstrate their potential application as a replacement for indium tin oxide in flexible solar cells.

Synthesis of shape-controlled NiO–graphene nanocomposites with enhanced supercapacitive properties

Flowerlike and polyhedral NiO–graphene nanocomposites have been successfully synthesized using a facile hydrothermal method. The formation mechanism of the two nanocomposites with different morphologies has been studied. The resulting products are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopic analysis (XPS), thermogravimetry (TG), and the Brunauer–Emmett–Teller (BET) method. The prepared NiO–graphene nanocomposites with different shapes can be used for supercapacitor electrode materials. Through electrochemical tests, the flowerlike NiO–graphene composite shows higher specific capacitance than that of the polyhedral one with a specific capacitance as high as 500 F g−1 at a scan rate of 5 mV s−1 while the polyhedral NiO–graphene composite delivers better long-term cycle stability with 84% specific capacitance remaining after 3000 cycles in a 1 M KOH electrolyte.

The synthesis of shape-controlled α-MoO3/graphene nanocomposites for high performance supercapacitors

Novel nanoflake-like and nanobelt-like α-MoO3/graphene nanocomposites were synthesized by a facile hydrothermal method through tailoring the content of Mo source. The formation mechanisms of α-MoO3/graphene nanocomposites with different morphologies has been investigated. As a model, the α-MoO3/graphene nanocomposites were studied for electrochemical energy storage supercapacitor devices. The results showed that α-MoO3 nanoflakes/graphene displayed better supercapacitive performances than that of α-MoO3 nanobelts/graphene, arising from the structural superiority and optimum compositions. The best composite exhibited a high specific capacitance (up to 360 F g−1) at a current density of 0.2 A g−1, good rate capability, and a nearly 100% long-term cycle stability. This study provided a facile and optimal experimental design to prepare α-MoO3/graphene composite materials which act as promising electrode materials for high-performance supercapacitors.

The synthesis of shape-controlled polypyrrole/graphene and the study of its capacitance properties

Polypyrrole (PPy)/graphene nainocomposite was prepared by methyl orange (MO) reactive template. By changing the amount of MO, the morphology of PPy can be controlled to range from nanoparticle to nanowire. Transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction results demonstrated that the composites were successfully synthesized. The different morphologies of PPy/graphene nanocomposites had certain effects on the supercapacitor performance. The experimental results showed that the capacitance of PPy (nanoparticle)/graphene was higher than that of PPy (nanowire)/graphene. As a model, PPy (nanoparticle)/graphene was used to construct a supercapacitor. By changing the amount of pyrrole monomer, the performance of the supercapacitor prepared from different PPy content was studied in detail.

Self-degradable template synthesis of polyaniline nanotubes and their high performance in the detection of dopamine

Polyaniline (PANI) nanotubes with improved electrochemical activity were synthesized by using a self-degradable MnO2 template and were developed as electrode materials for biosensors. The morphology, composition, and optical properties of the resulting products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and cyclic voltammetry (CV). The results confirmed that the obtained PANI nanotubes had a perfect tubular structure with uniform diameters and lengths. Furthermore, PANI nanotubes were immobilized onto the surface of a glassy carbon electrode (GCE) and applied to construct a sensor. The obtained PANI-modified GCE showed high catalytic activity in the electrochemical oxidation of dopamine (DA) in a near neutral environment. Differential pulse voltammogram (DPV) results illustrated that the fabricated DA biosensor had high anti-interference ability towards uric acid (UA), ascorbic acid (AA), and glucose (GC). In addition, the fabricated biosensor showed superior performance with two wide linear ranges from 7 × 10−5 to 3 × 10−4 M and 3 × 10−4 to 5 × 10−3 M with a lower limit of detection of 0.5 × 10−9 M.