Graphene based all-solid-state supercapacitors with ionic liquid incorporated polyacrylonitrile electrolyte
Herein, we report, the fabrication of a mechanically stable, flexible graphene based all-solid-state supercapacitor with ionic liquid incorporated polyacrylonitrile (PAN/[BMIM][TFSI]) electrolyte for electric vehicles (EVs). The PAN/[BMIM][TFSI] electrolyte shows high ionic conductivity (2.42 mS/cm at 28 °C) with high thermal stability. Solid-like layered phase of ionic liquid is observed on the surface of pores of PAN membrane along with liquid phase which made it possible to hold 400 wt% of mobile phase. This phase formation is facilitated by the ionic interaction of C. N moieties with the electrolyte ions. A supercapacitor device, comprised PAN/[BMIM][TFSI] electrolyte and graphene as electrode, is fabricated and the performance is demonstrated. Several parameters of the device, like, energy storage and discharge capacity, internal power dissipation, operating temperature, safe operation and mechanical stability, meet the requirements of future EVs. In addition, a good cyclic stability is observed even after 1000 cycles. © 2012 Elsevier Ltd.
Investigation of oxygen reduction and methanol oxidation reaction activity of PtAu nano-alloy on surface modified porous hybrid nanocarbon supports
Weinvestigate the electrocatalytic activity of PtAu alloy nanoparticles supported on various chemically modified carbon morphologies towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). The surface-modification of graphene nanosheets ( f-G), multi-walled carbon nanotubes ( f-MWNTs) and (graphene nanosheets-carbon nanotubes) hybrid support ( f-GMWNTs) were carried out by soft functionalization method using a cationic polyelectrolyte poly-(diallyldimethyl ammonium chloride). The Pt and PtAu alloy nanoparticles were dispersed over chemically modified carbon supports by sodium-borohydride assisted modified polyol reduction method. The electrochemical performance of all electrocatalysts were studied by half-and full-cell proton exchange membrane fuel cell (PEMFC) measurements and PtAu/f-G-MWNTs catalyst comparatively yielded the best catalytic performance. PEMFC full cell measurements of PtAu/f-GMWNTscathode electrocatalyst yield a maximum power density of 319mWcm2 at 60 °Cwithout any back pressure,which is 2.1 times higher than that of cathode electrocatalyst Pt on graphene support. The highORR andMORactivity of PtAu/f-G-MWNTs electrocatalyst is due to the alloying effect and inherent beneficial properties of porous hybrid nanocarbon support.
Modified graphene based molecular imprinted polymer for electrochemical non-enzymatic cholesterol biosensor
This work reports the development of cost effective sensor material prepared from modified graphene oxide based molecular imprinted polymer (GO-MIP). Firstly graphene oxide (GO) prepared from modified Hummers method undergoes acid functionalization to form GO[sbnd]COOH. It further undergoes surface modification with glycidyl methacrylate (GMA) in presence of N,N′-dicyclohexylcarbodiimide (DCC), dimethylaminopyridine (DMAP) and dimethyl sulfoxide (DMSO) to form GO[sbnd]CH[dbnd]CH2. The obtained GO[sbnd]CH[dbnd]CH2 undergoes molecular imprinting process with methacrylic acid (MAA) as the monomer and ethylene glycol dimethacrylate (EGDMA) as the cross–linker, α,α′-azobisisobutyronitrile (AIBN) as the initiator and cholesterol as the template molecule. The different preparatory stages of materials were characterized by FTIR, XRD, Raman and TEM techniques to understand the formation. The obtained GO-MIP used as an active material for cholesterol sensing where the sensor demonstrate a lower limit detection of 0.1 nM and response time of ∼2 min with maximum sensing performance at pH 5.0. The repeatability of the sensor is checked up to eight cycles and interference of cholesterol with ascorbic acid (AA), uric acid (UA) and glucose were also studied. The material shows a negligible (AA, UA), modest (Glucose) interference and better performance in human blood samples suggesting the real-time usability of the sensor.
Hydrogen exfoliated graphene as counter electrode for dye sensitized solar cells
In the present work, we demonstrate the use of few layered Graphene sheets (HEG) synthesized by hydrogen induced exfoliation technique as a novel counter electrode material for dye sensitized solar cells (DSSCs). The presence of wrinkles and low oxygen content gives a high surface area and good electrical conductivity to HEG, making it superior to other graphenes. Electrochemical impedance spectroscopy studies were carried out to determine the catalytic activity of HEG towards tri-iodide reduction. The effect of annealing temperature on HEG counter electrode was also studied. The DSSC fabricated with HEG as counter electrode shows excellent current density, comparable to that of Pt counter electrode and exhibits a power conversion efficiency of ∼ 3.6 % under one sun illumination. © 2011 IEEE.
Functionalized 2D graphene sheets as catalyst support for proton exchange membrane fuel cell electrodes
Functionalized graphene sheets have been investigated as catalyst supports for platinum electrocatalysts for use in PEMFC electrodes. Well-dispersed Pt nanoparticles with small particle size were impregnated on graphene sheets. The electrochemical tests showed that the Pt nanoparticles supported on graphene shows good electrochemical activity and much higher Electrochemical Surface Area (ECSA) of 24 m 2/g. The maximum current density was found to be 700 mA/cm 2 for electrodes having Pt/G catalysts on both electrodes, compared to electrodes where Pt/C is being used at the anode. This study reveals that Pt/G can be a good electro catalyst not only for oxygen reduction but also for hydrogen oxidation. The dispersion of the electrocatalyst on graphene has been found to be useful for achieving relatively better performance in fuel cells. Electrochemical experiments show that the Pt supported on graphene oxide have superior catalytic performance indicating that the graphene may have a splendid future as catalyst carrier in electrocatalyst and fuel cell. © 2012 American Scientific Publishers All rights reserved.
Hydrothermal synthesis of RuO 2.xH 2O/graphene hybrid nanocomposite for supercapacitor application
Herein we report a facile approach for synthesis of well dispersed hydrated ruthenium oxide nanoparticles onto the surface of hydrogen exfoliated graphene (HEG) sheets via hydrothermal synthesis route. The as prepared hybrid nanocomposite (RuO 2·xH 2O/HEG) was characterized by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). A symmetrical supercapacitor was fabricated and the electrochemical performance of this model supercapacitor cell was investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and impedance spectroscopy (EIS) in 1.0 M H 2SO 4 solution. The hybrid nanocomposite shows a maximum specific capacitance of 154 F/g and energy density of about 11Wh/kg at a specific discharge current of 1 A/g (20 wt% Ru loading). The composite also shows a maximum power density of 5 kW/kg and coulombic efficiency of 97% for a specific discharge current of 10 A/g. © 2011 IEEE.
Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: A surfactant free laser ablation approach
A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine gold's electronic relay and π-π stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants.© 2014 Elsevier B.V. All rights reserved.
One-step in situ hydrothermal preparation of graphene–SnO2 nanohybrid for superior dopamine detection
Abstract: In this work, we report a facile and one -step hydrothermal method to decorate SnO2 nanostructures on few-layered graphene for superior dopamine detection. The structural and morphological properties of the prepared nanohybrids illustrated the tetragonal crystal system of SnO2, reconstruction of graphene layers with oxygen containing functional groups, increased ID/IG ratio, and uniform decoration of SnO2 nanostructures on graphene layers. The prepared nanohybrids exhibited a high electrochemical activity toward dopamine oxidation in comparison with individual graphene sheets. This enhanced performance can be due to the presence of SnO2 nanostructures between the graphene layers, which efficiently avoid the restacking and increase the surface area accessibility. The fabricated nanohybrid-based sensor showed an increase in current with respect to the increased analyte concentration over the wide range of 0.005–0.20 × 10−6 M. The sensor exhibits excellent catalytic activity toward dopamine with the lowest detection limit of 6.3 nm. Further, the modified electrode exhibited good stability, reproducibility, and better recovery of 99 % in human urine samples suggesting the real-time usability of the sensor. Graphical Abstract: Schematic representation of SnO2 nanohybrids formation. The modified electrode exhibits superior catalytic activity. The oxidation peak current increased linearly in the concentration range of 0.005–0.019 × 10−6 M with LOD of 6.3 nm.[Figure not available: see fulltext.]
Catalytic performance of non-platinum-based hybrid carbon hetero-structure for oxygen reduction and hydrogen oxidation reactions in proton exchange membrane fuel cell
The present work describes the potential of a hybrid carbon hetero-structure having the unique properties of one-dimensional carbon nanotubes and two-dimensional graphene as a catalyst support material for platinum-free electrocatalysts in polymer electrolyte membrane fuel cell (PEMFC) for hydrogen oxidation reaction (HOR) or oxygen reduction reaction (ORR). Partially exfoliated carbon nanotubes (PCNT), which have the synergistic effect of good electrical conductivity and high surface area, have been used as the support material for Pd3Co alloy catalysts. This provides more active sites for the dispersion of catalyst particles along with quick electron transport through the carbon structure. This unique characteristic increases the catalytic activity of the electrocatalysts. The electrochemical half-cell studies confirm that, ORR on Pd3Co/PCNT proceeds via a four-electron process. The single cell measurements were carried out by preparing a membrane electrode assembly (MEA) using Pd3Co/PCNT at the anode, cathode separately as well as simultaneously at both the anode and cathode. A maximum power density of 327 mW cm−2, 240 mW cm−2 and 96 mW cm−2 is attained from the use of Pd3Co/PCNT nanocomposite at anode, cathode and at both electrodes simultaneously in a PEMFC at 60 °C, respectively.
Effect of complex formation on nonlinear optical parameters of dye-graphene system
The effect of saturable absorption in a dye decreases significantly in the presence of functionalized hydrogen-induced exfoliated wrinkled graphene (f-HEG). The absorption spectra give strong evidence of complex formation in the ground state. The fluorescence spectra and nonlinear optical properties of the dye are affected by f-HEG and silver decorated graphene (Ag-f-HEG) by various degrees. The open aperture Z-scan and degenerate four wave mixing (DFWM) techniques have been used to record the drastic changes in the nonlinear optical parameters of dye in presence of f-HEG and Ag-f-HEG. The results indicate a reduction in the average value of the nonlinearity due to formation of the non-fluorescent ground-state charge-transfer complex. At high input irradiance the optical limiting capability of the dye-f-HEG system has been found to be enhanced. The pre-existing charge transfer between silver nanoparticles and f-HEG reduces the strength of dye-f-HEG complex formation.