Preparation of graphene nanosheets/SnO2 composites by pre-reduction followed by in-situ reduction and their electrochemical performances

The Graphene nanosheets/SnO₂ composites were synthesized using stannous chloride to restore the semi-reduction graphene oxide (SRGO) under a simple hydrothermal reduction procedure. First graphene oxide was pre-reduced by glucose for a certain time to get SRGO, which keeps the good water-solubility of graphite oxide (GO) and has a good conductivity like graphene nanosheets. The higher electrostatic attraction between SRGO and Sn²⁺ makes SnO₂ nanoparticles tightly anchor on the graphene sheets in the hydrothermal reduction process. The formation mechanism of the composite was investigated by SEM, TEM, XRD, AFM and Raman. Moreover, the electrochemical behaviors of the Graphene nanosheets/SnO₂ nanocomposites were studied by cyclic voltammogram, electrical impedance spectroscopy (EIS) and chronopotentiometry. Results showed that the Graphene nanosheets/SnO₂ composites have excellent supercapacitor performances: the specific capacitance reached 368 F g⁻¹ at a current density of 5 mA cm⁻², and the energy density was much improved to 184 Wh kg⁻¹ with a power density of 16 kW kg⁻¹, and capacity retention was more than 95% after cycling 500 cycles with a constant current density of 50 mA cm⁻². The experimental results and the thorough analysis described in this work not only provide a potential electrode material for supercapacitors but also give us a new way to solve the reunification of the graphene sheets.     

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g⁻¹, remanent magnetization of 6.0 emu g⁻¹ and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.     

Graphene sheets anchored with ZnO nanocrystals as electrode materials for electrochemical capacitors

An efficient approach consisted of modified Hummers' method, pulse microwave heating, and homogenizing dispersion has been demonstrated to prepare ZnO/graphene hybrid as electrode material for electrochemical capacitors (ECs). Highly-crystalline ZnO nanoparticles are anchored with graphene sheets, forming three-dimensional framework. The electrochemical properties of ZnO/graphene hybrids are characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling. The EC equipped with ZnO/graphite hybrid (1:5 in w/w) exhibit the improved performance in terms of specific capacitance, high rate capability, and excellent cycling stability, as compared with blank graphene electrode. The maximum energy and power densities of ZnO/graphite capacitor can be obtained as high as 66 Wh kg⁻¹ and 15.2 kW kg⁻¹, respectively. The improved performance can be ascribed to the insertion of ZnO nanocrystals between individual graphite sheets, creating a conducting framework that provides more active sites for the formation of electric double layer. The unique framework allows the electrolyte ions to diffuse easily into the interior channels, leading to small inner resistance.     

The influence of Graphene quality on performance of a Si/Graphene nanocomposite anode

Si/Graphene nanoparticles represent attractive alternative anode materials for Lithium-ion batteries. Graphene nanosheets with different properties, including surface area, defect distance, and charge-transfer resistance, were fabricated and characterised in Si/Graphene nanocomposites formed by static-electric self-assembly then by an in-situ reduction process. Graphene nanosheets that exhibited the highest surface area, the shortest defect distance, and the lowest charge-transfer resistance demonstrated the best overall electrochemical performance, with a high initial discharge capacity of 2692?mAh?g^?1, good cycling performance of 1135?mAh?g^?1, at the 200th cycle at the current rate of 0.5?C. This work shows the preferable graphene quality for Si/Graphene nanocomposite anode and provides insights into the design of graphene nanocomposite electrodes, regardless of the graphene synthesis method.     

Graphene/MnO2 hybrid nanosheets as high performance electrode materials for supercapacitors

Graphene/MnO₂ hybrid nanosheets were prepared by incorporating graphene and MnO₂ nanosheets in ethylene glycol. Scanning electron microscopy and transmission electron microscopy analyses confirmed nanosheet morphology of the hybrid materials. Graphene/MnO₂ hybrid nanosheets with different ratios were investigated as electrode materials for supercapacitors by cyclic voltammetry (CV) and galvanostatic charge–discharge in 1 M Na₂SO₄ electrolyte. We found that the graphene/MnO₂ hybrid nanosheets with a weight ratio of 1:4 (graphene:MnO₂) delivered the highest specific capacitance of 320 F g⁻¹. Graphene/MnO₂ hybrid nanosheets also exhibited good capacitance retention on 2000 cycles.     

Graphene nanosheets-poly(o-aminophenol) nanocomposite for supercapacitor applications

Graphene nanosheets-poly(o-aminophenol) (POAP/GNS) nanocomposite was fabricated on a platinum surface by potential cycling. Voltammograms of the POAP/GNS/Pt electrode showed an excellent capacitive behavior accompanied with a redox transition with a mid-peak potential of 295 mV. The POAP/GNS nanocomposite displayed a specific capacitance as high as 281.1 F g⁻¹ at 0.1 A g⁻¹ which is almost three times higher than that of pure graphene. The specific energy and power of the nanocomposite material were 25.0 Wh kg⁻¹ and 34.8 W kg⁻¹, respectively. The nanocomposite retained more than 99% of the initial capacitance after 1200 charge/discharge cycles.     

Nano iron oxide (Fe2O3)/carbon black electrodes as electrode material for electrochemical capacitors: Effect of the nanoparticles dispersion quality

In the present study, nano Fe₂O₃/carbon black electrodes are proposed for electrochemical capacitors and the effect of nanoparticles dispersion quality on the surface morphology, nature and electrochemical properties of the electrodes are investigated. Mechanical pressing is accompanied by different mixing (mechanical and sonication) processes to prepare the electrode. Electrochemical properties of the produced nanocomposites are studied using cyclic voltammetry and electrochemical impedance spectroscopy tests in 2 M KCl electrolyte. Scanning electron microscopy is used to characterize the microstructure and the nature of the nanoparticles on the nanocomposites produced. Results obtained show that the sonicated and unsonicated 10:80:10 (CB:Fe₂O₃:PTFE) electrodes have specific capacitance of 22.02 and 22.35 F g⁻¹ respectively, at scan rate of 10 mV s⁻¹. Sonication process breaks the agglomerated particles and disperses them on the electrode surface, uniformly. This increases the specific surface area and the electrical resistance of the electrodes. The sonicated electrodes show a higher charge separation capability at electrolyte/electrode interfaces, lower ratio of outer to total charge (q_O*/q_T*) of 0.13 and lower current response at end potentials. Energy density was increased after the sonication process from 0.686 to 1.498 (Wh kg⁻¹). Charge/discharge cycling results confirmed that the uniform dispersion of active material on the electrode surface postpones the electrolyte decomposition and improves the electrical conductivity during cycling.     

Low power and stable resistive switching in graphene oxide-based RRAM embedded with ZnO nanoparticles for nonvolatile memory applications

The present study reports the role of zinc oxide nanoparticles (ZnO NPs) embedded in graphene oxide (GO)-based RRAM for non-volatile memory applications. GO thin film embedded with different concentrations of ZnO NPs was deposited on bottom electrode, i.e., indium tin oxide (ITO) coated glass. Thermal evaporation technique was used for the fabrication of top electrodes for electrical measurements. Structural and morphological studies of synthesized GO and ZnO NPs were done by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Switching characteristics of the RRAM devices were investigated using electrical measurements. It has been observed that the optimized concentration of ZnO NPs (20%) shows stable switching behavior with low SET (??0.61 V) and RESET (+?0.65 V) voltages as compared to pure GO devices. The switching of the fabricated memory devices from high resistance state (HRS) to low resistance state (LRS) has been found due to conductive filament formed between top and bottom electrodes. This conductive filament has been confirmed by the change in resistance as a function of temperature. The Al/GO-ZnO(20%)/ITO devices show stable endurance behavior for >?50 cycles and retention behavior for >?4?×?10³ s. In HRS, the dominated conduction mechanism was found to be space-charge limited conduction (SCLC), whereas in LRS, the Ohmic conduction mechanism was observed. The incorporation of ZnO NPs increased the number of oxygen vacancies in switching layer which eventually enhanced the formation of conductive filament. This phenomenon has been confirmed using XPS characterization of the switching layer. These optimized concentrations of ZnO embedded in GO switching layers provide a way for future low power non-volatile memory devices.

     

Preparation and characterizations of polyaniline (PANI)/ZnO nanocomposites film using solution casting method

Polyaniline (PANI)-ZnO nanoparticles composites film has been successfully fabricated by solution casting technique on glass substrate in which ZnO nanopowder was prepared via auto combustion method and used as inorganic materials. The as-grown nanocomposites film has been characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Transmission electron microscopy (TEM) and Atomic Force Microscopy (AFM) for their structural and morphological characterizations. X-ray diffraction studies of as-grown film showed the reflection of ZnO nanoparticles along with a broad peak of PANI. The AFM study of the film shows the incorporation of ZnO nanoparticles into the polymer matrix which was further supported by roughness measurement. TEM images showed that the size of ZnO nanoparticles in the nanocomposites increase from ~ 35 nm to ~ 45 nm, indicating the interaction of nanoparticles with PANI molecular chains. FTIR spectra showed a band at 501 cm⁻¹ due to ZnO nanoparticles while the hydrogen bonding between the amine group of PANI and ZnO nanoparticles had been confirmed from the presence of the absorption band at 1148 cm⁻¹.     

A comparative study on electrochemical performances of the electrodes with different nanocarbon conductive additives for lithium ion batteries

Three nanocarbon materials (0 D acetylene black (AB), 1 D carbon nanotubes (CNTs) and 2 D reduced graphene oxide (RGO)) were used as conductive additives (CAs) in the mesocarbon microbead anodes for lithium ion batteries. The electrochemical performances of the electrodes were investigated. The results show that the CAs have a significant impact on the electrode performance because they can influence the electron conduction and lithium ion transportation within the electrode. The electrode with RGO achieves a maximum capacity of 387 mAh g⁻¹ after 50 cycles at a current density of 50 mA g⁻¹, much higher than those of the electrodes with AB (334 mAh g⁻¹) and CNTs (319 mAh g⁻¹). The improvement should be mainly ascribed to the “plane-to-point” conducting network formed in the electrode with 2 D RGO which can favor the electron conduction and enhance the lithium ion transportation.     

TiO2/石墨烯复合物的制备及其嵌脱锂行为研究

以钛酸丁酯为TiO₂前驱体, 通过水热法制得TiO₂/石墨烯复合物。使用X射线衍射(XRD)、热重分析(TG)、透射电镜(TEM)、扫描电镜(SEM)和电化学充放电等手段对材料进行了表征和分析。结果表明: TiO₂颗粒均匀地分散在石墨烯的表面, 复合物中石墨烯的含量为24.67%。当该材料用作锂离子电池负极材料时, 在2C的放电倍率下, 首次放电容量为384.35 mAh/g, 循环100次后的放电容量为130.26 mAh/g, 是纯TiO₂电极放电容量的2.93倍。与纯TiO₂电极相比, TiO₂/石墨烯复合物的电荷转移电阻较低。TiO₂/石墨烯复合物具有较好的倍率性能和较高的电化学反应活性。     

Sensitive and selective imprinted electrochemical sensor for p-nitrophenol based on ZnO nanoparticles/carbon nanotubes doped chitosan film

A sensitive and selective molecularly imprinted electrochemical sensor for p-nitrophenol detection has been developed based on ZnO nanoparticles/multiwall carbon nanotubes (MWNTs)-chitosan (CTS) nanocomposite. This nanocomposite was dripped onto an indium tin oxide electrode and then imprinted sol-gel solution was electrodeposited onto the modified electrode to construct the proposed sensor. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, X-ray diffraction, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry. The imprinted sensor displayed excellent selectivity towards the target molecule p-nitrophenol. Meanwhile, the introduced nanocomposite increased surface area and active sites for electron transfer, thus remarkably enhancing the sensitivity of the imprinted sensor. Under optimal conditions, the peak current was linear to p-nitrophenol concentration ranging from 1.0 × 10^− 8 to 2.0 × 10^− 4 mol·L^− 1 with a detection limits of 1.0 × 10^− 9 mol·L^− 1 (S/N = 3). This proposed sensor was applied to the detection of p-nitrophenol in various water samples successfully.     

Electrohydrodynamic atomization approach to graphene/zinc oxide film fabrication for application in electronic devices

Graphene-based composites represent a new class of materials with potential for many applications. Metal, semiconductor, or any polymer properties can be tuned by attaching it to graphene. Here, a new route for fabrication of graphene based composites thin films has been explored. Graphene flakes (<4 layers) and a well-known semiconductor zinc oxide (ZnO) (<50 nm particle size) have been dispersed in N-methylpyrrolidone and ethanol, respectively. Thin film of graphene flakes is deposited and decorated with ZnO nanoparticles to fabricate graphene/ZnO composite thin film on silicon substrate by electro hydrodynamic atomization technique. Graphene/ZnO composite thin film has been characterized morphologically, structurally and chemically. To investigate electronic behavior of the composite thin film, it is deployed as cathode in a diode device i.e. indium tin oxide/poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate)/polydioctylfluorene-benzothiadiazole/(graphene/ZnO). The J–V analysis of diode device has shown that at voltage of 1 V, the current density in organic structure is at low value of 4.69 × 10^?3 A/cm² and when voltage applied voltage is further increased; the device current density has increased by the order of 200 that is 1.034 A/cm² at voltage of 12 V.     

CTAB assisted immobilization of RuO2 nanoparticles on graphene oxide for electrochemical sensing of hydrazine

A novel method has been presented to modify glassy carbon electrode (GCE) with graphene oxide (GO) nanocomposite without introducing any electrode binder such as chitosan and Nafion. First, modify GCE with RuO₂ nanoparticles which have been dispersed in cetyltrimethyl ammonium bromide (CTAB) aqueous solution. Then, highly adhesive RuO₂/CTAB/GO nanocomposite membrane formed on GCE by immersing RuO₂/CTAB modified GCE in GO suspension. CTAB plays significant roles not only in the preparation of the nanocomposite but also in the immobilization of nanocomposite on GCE surface. First, CTAB was used as the dispersant of RuO₂ nanoparticles. Second, CTAB acted as the molecular linker to bind RuO₂ nanoparticles on graphene sheets. Third, CTAB formed CTAB/GO nanocomposite which is highly adhesive on the surface of electrodes such as GCE and ITO (indium tin oxide). The obtained RuO₂/CTAB/GO/GCE shows excellent electrocatalytic ability towards the oxidation of hydrazine. The oxidation of hydrazine on RuO₂/CTAB/GO/GCE is an adsorption-controlled process and the oxidation current is linear with the concentration of hydrazine in the range of 1 × 10^?5～1 × 10^?3 M with a detection limit of 2.3 × 10^?6 M. The application of this sensor in the sensing of hydrazine in real water samples confirmed its reliability and accuracy.     

Room temperature ferromagnetism in Zn0.99La0.01O and pure ZnO nanoparticles

Room temperature ferromagnetism (RTFM) was observed in both La-doped and pure ZnO nanoparticles synthesized by the sol–gel method. RTFM is intrinsic according to the results of X-ray diffraction and X-ray photoelectron spectroscopy. The saturation magnetization (M_S), the remnant magnetization at zero field and coercive field are 5 × 10⁻³, 7 × 10⁻⁴ emu g⁻¹, 100 Oe for Zn_0.99La_0.01O nanoparticles and 1.5 × 10⁻⁴, 1 × 10⁻⁵ emu g⁻¹, 50 Oe for pure ZnO nanoparticles, respectively. The magnetization is enhanced greatly by doping of La. Furthermore, the M_S of Zn_0.99La_0.01O nanoparticles decreases from 0.005 to 0.001 emu g⁻¹ as the annealing temperature increases from 500 to 700 °C. The doping of La introduces more oxygen vacancies into ZnO. The decrease of annealing temperature also produces more oxygen vacancies in La-doped ZnO. These results indicate that the origin of the RTFM is related to oxygen vacancies.     

Making a wearable supercapacitor based on highly porous 3D nitrogen-doped graphene

In this paper, based on the hydrothermal method and using a non-toxic organic molecule, as a spacer (and nitrogen source), we synthesized a highly conductive and porous 3D graphene. Then, graphene is used as an electrode material to make a supercapacitor on the surface of activated carbon cloth electrode. The graphene is characterized by different methods, such as Fourier-transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, X-ray diffraction, energy-dispersive and transmission electron microscopy, energy-dispersive X-Ray spectroscopy, emission scanning electron microscopy, Barrett–Joyner–Halenda, and Brunauer–Emmett–Teller methods. The supercapacitor (2 and 3 electrodes) is studied by different electrochemical techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge. The 3-electrode system shows a specific capacity 101 F g^? 1 at the current density of 1.7 A g^? 1 (or 0.5 mA cm^? 2). The 2-electrode system (symmetric capacitor) has a power density of about 8000 W kg^? 1 and a maximum energy density of 12.85 Wh kg^? 1.

     

Preparation of reduced graphene oxide-NiFe2O4 nanocomposites for the electrocatalytic oxidation of hydrazine

A reduced graphene oxide (RGO)-NiFe₂O₄ nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe₂O₄ nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni³⁺ and Ni²⁺, and Fe²⁺ and Fe³⁺, respectively. Further, the electrochemical activity of the RGO-NiFe₂O₄ nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe₂O₄ modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe₂O₄ and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe₂O₄. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe₂O₄ modified GCE. Therefore, the RGO-NiFe₂O₄ modified GCE can be used for the electrochemical oxidation of hydrazine.     

High-yield synthesis of carbon nanotube–porous nickel oxide nanosheet hybrid and its electrochemical capacitance performance

This study reports an easy chemical conversion route toward large-scale fabrication of carbon nanotube (CNT)–porous nickel oxide (NiO) hybrid nanocomposites as supercapacitor electrode materials. The electrocapacitive performance of CNT–porous NiO hybrids is evaluated by cyclic voltammetry and galvanostatic charge–discharge measurements. The synthesized CNT–NiO hybrid nanocomposite electrode presents a high specific capacitance of 759 F g⁻¹ at 0.5 A g⁻¹ in 6 M KOH aqueous electrolyte, which is almost twice that of pure NiO nanoparticle (388 F g⁻¹) electrodes and nine times of that of commercial NiO particle (88.4 F g⁻¹) electrodes. Furthermore, good capacitance retention is achieved after 1000 cycles of galvanostatic charge–discharge. The synergistic effects from the pseudocapacitance of porous NiO particles, good electrical conductivity, and open tip CNTs attribute to the high capacitance performance.     

Rapid synthesis, characterization and optical properties of TiO2 coated ZnO nanocomposite particles by a novel microwave irradiation method

A novel and rapid microwave method was used to prepare TiO₂ coated ZnO nanocomposite particles. The resulted particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Results show that ZnO nanoparticles were coated with 6-10 nm amorphous TiO₂ layers. In addition, zeta potential analysis demonstrated the presence of TiO₂ layer on the surface of ZnO nanoparticles. Photoluminescence (PL) spectroscopy and UV-visible spectroscopy were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnO nanoparticles, the TiO₂ coated ZnO nanoparticles showed enhanced UV emission. The UV-visible diffuse reflectance study revealed the significant UV shielding characteristics of the nanocomposite particles. Moreover, amorphous TiO₂ coating effectively reduced the photocatalytic activity of ZnO nanoparticles as evidenced by the photodegradation of Orange G with uncoated and TiO₂ coated ZnO nanoparticles under UV radiation.     

Performance of Eu2O3 coated ZnO nanoparticles-based DSSC

To provide an inherent energy barrier between the electrode and electrolyte interface, the surface of the ZnO nanoparticles has been modified by Eu₂O₃ layer. The synthesis of ZnO, Eu₂O₃ coated ZnO nanoparticles have been carried out by chemical precipitation method and solvothermal treatment. The synthesized samples were characterized by XRD and the diffraction plane (222) of Eu₂O₃ detected, demonstrating the existence of Eu₂O₃ on the surface of ZnO, which is further verified using energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The strong quenching in photoluminescence emission, in case of Eu₂O₃/ZnO nanoparticles, has been attributed to the decrease in recombination rate of photo-generated electron–hole pairs. Compared to ZnO electrodes, Eu₂O₃ coated ZnO electrodes adsorbed more dye. The photoelectrochemical properties of the Eu₂O₃/ZnO electrodes have been found to improve and the energy conversion efficiency increase from 0.44 to 1.45 % under the illumination of simulated light of 100 mW/cm².