Hydrogen Exfoliated Graphene Research Articles

CuO/TiO2/ZnO NPs Anchored Hydrogen Exfoliated Graphene: To Comprehend the Role of Graphene in Catalytic Reduction of p-Nitrophenol.

The present study deals with sonochemically in situ synthesis of a novel functional catalyst using hydrogen exfoliated graphene (HEG) supported titanium dioxide (TiO2) and copper sulfate (CuSO4) doped with zinc oxide (ZnO) (abbreviated as Ti/Cu/Zn-HEG). The synthesis of the Ti/Cu/Zn-HEG nanocomposite (NCs) catalyst was confirmed through its characterizations by XRD, SEM-EDX, TEM, XPS, FTIR, and BET methods. It was assessed for catalytic conversion of a model aromatic compound para-nitrophenol (p-NP) in an aqueous solution. The p-NP is a nitroaromatic compound that has a toxic and mutagenic effect. Its removal from the water system is necessary to protect the environment and living being. The newly synthesized Ti/Cu/Zn-HEG NCs were applied for their higher stability and catalytic activity as a potential candidate for reducing p-NP in practice. The operating parameters, such as p-NP concentration, catalyst dosage, and operating time were optimized for 150 ppm, 400 ppm, and 10 min through response surface methodology (RSM) in Design-Expert software to obtain the maximum reduction p-NP up to 98.4% at its normal pH of 7.1 against the controls (using HEG, Ti/Cu-HEG, and Zn-HEG). Analysis of variance of the response suggested the regression equation to be significant for the process with a major impact on catalyst concentration and operating time. The model prediction data (from RSM) and experimental data were corroborated well as reflected through model's low relative error (RE < 0.10), high regression coefficient (R2 > 0.97), and Willmott d-index (dwill-index > 0.95) values.

Waterproof Flexible Polymer-Functionalized Graphene-Based Piezoresistive Strain Sensor for Structural Health Monitoring and Wearable Devices.

In recent times, flexible piezoresistive polymer nanocomposite-based strain sensors are in high demand in wearable devices and various new age applications. In the polymer nanocomposite-based strain sensor, the dispersion of conductive nanofiller remains challenging due to the competing requirements of homogenized dispersion of nanofillers in the polymer matrix and retaining of the inherent characteristics of nanofillers. In the present work, waterproof and flexible poly(vinylidene difluoride) (PVDF) with a polymer-functionalized hydrogen-exfoliated graphene (HEG)-based piezoresistive strain sensor is developed and demonstrated. The novelty of the work is the incorporation of polystyrene sulfonate sodium salt (PSS) polymer-functionalized HEG in a PVDF-based flexible piezoresistive strain sensor. The PSS-HEG provides stable dispersion in the hydrophobic PVDF polymer matrix without sacrificing its inherent characteristics. The electrical conductivity of the PVDF/PSS-HEG-based strain sensor is 0.3 S cm–1, which is two orders of magnitude higher than the PVDF/HEG-based strain sensor. Besides, near the percolation region, the PVDF/PSS-HEG shows a maximum gauge factor of 10, which is about two times higher than the PVDF/HEG-based flexible strain sensor and 5-fold higher than the commercially available metallic strain gauge. The enhancement in the gauge factor is due to the stable dispersion of PSS-HEG in the PVDF matrix and electron conjugation caused by the adherence of negatively charged sulfonate functional groups on the HEG. The developed waterproof flexible strain sensor is demonstrated using portable wireless interfacing device for various applications. This work shows that the waterproof flexible PVDF/PSS-HEG-based strain sensor can be a potential alternative to the commercially available metallic strain gauge.

2D MoSe2 sheetsembedded over ahigh surfacegraphene hybrid for the amperometric detection of NADH.

Delaminated 2D sheets of MoSe2 were prepared by liquid phase exfoliation and were embedded over high surface area hydrogen exfoliated graphene (HEG) by a simple technique. The MoSe2/HEG hybrid composite exhibits fast heterogeneous electron-transfer (HET) anda high electrochemically active surface area compared to only HEG. When employed for detection of NADH, it exhibits electrooxidation at a low potential of 150mV (vs. Ag/AgCl) with high sensitivity of 0.0814µA⋅µM-1⋅cm2 over a wide linear range (1-280μM), good selectivity, and a low limit of detection (1μM). The good performance of the composite is due to the homogeneously dispersed 2D sheets of MoSe2 over large-surface area HEG, which retain its electrochemical activity, prevents restacking, and acts as anelectron transfer channel. On the basis of the above analytical requirements and itseasy synthesis, the hybrid composite represents a robust material for electrochemical sensing. Graphical abstract Schematic of the2D MoSe2/HEG composite for electrochemical detection of NADH.

Few layer graphene wrapped mixed phase TiO2 nanofiber as a potential electrode material for high performance supercapacitor applications

A combination of favorable composition and optimized anatase/rutile mixed-phase TiO2 (MPTNF)/Hydrogen exfoliated graphene (HEG) composite nanofibers (MPTNF/HEG) and anatase/rutile mixed-phase TiO2/reduced graphene oxide (rGO) composite nanofibers (MPTNF/rGO) have been reported to enhance the electrochemical properties for supercapacitor applications. These composite nanofibers have been synthesized by an efficient route of electrospinning together with the help of easy chemical methods. Both the composites exhibit good charge storage capability with enhanced pseudocapacitance and electric double-layer capacitance (EDLC) as confirmed by cyclic voltammetry studies. MPTNF/HEG composite showed maximum specific capacitance of 210.5 F/g at the current density of 1 A/g, which was mainly due to its availability of the more active sites for ions adsorption on a few layers of graphene wrapped TiO2 nanofiber surface. The synergistic effect of anatase/rutile mixed phase with one dimensional nanostructure and the electronic interaction between TiO2 and few layer graphene provided the subsequent improvement of ion adsorption capacity. Also exhibit excellent electrochemical performance to improve the capacitive properties of TiO2 electrode materials which is required for the development of flexible electrodes in energy storage devices and open up new opportunities for high performance supercapacitors.

Hydrogen Adsorption Studies on Platinum and Nickel Nanoparticles Decorated Functionalized Hydrogen-Exfoliated Graphene

Hydrogen Adsorption Studies on Platinum and Nickel Nanoparticles Decorated Functionalized Hydrogen-Exfoliated Graphene

Multi-edged wrinkled graphene-like carbon-wrapped carbon nanotubes and highly conductive Pt-free counter electrode for dye-sensitized solar cells

Multi-edged wrinkled graphene-like carbon-wrapped carbon nanotubes (GWC) is demonstrated as a Pt-free counter electrode for dye-sensitized solar cells (DSSCs). GWC, with wrinkled graphene-like surface and one-dimensional tubular structure, exhibits significant electrocatalytic activity toward the reduction of triiodide due to the highly defective multi-edges and good conductivity. Raman spectroscopy studies suggest the presence of significantly higher defects in the GWC sample in comparison to multi-walled carbon nanotubes (MWNTs) and hydrogen exfoliated graphene (HEG). Four-probe measurement studies show better specific resistance (11.30 Ω cm), sheet resistance (4.52 × 103 Ωsq−1), and conductivity (8.84 Sm−1) of GWC film compared to HEG, but less compared to MWNTs. The impact of GWC properties on DSSC performance is studied by cyclic voltammetry and electrochemical impedance spectroscopy. The GWC counter electrode shows enhanced catalytic activity and power conversion efficiency (6.15 %) compared to that of MWNTs (5.12 %) and HEG (5.42 %). We also compare the catalytic activity and power conversion efficiency of GWC with Pt and find approaching that of Pt (6.68 %).

Investigation of thermal conductivity, viscosity, and electrical conductivity of graphene based nanofluids

Stable and well dispersed functionalized graphene–ethylene glycol (EG) + distilled water nanofluids having graphene nano-sheets (GnS) volume concentration between 0.041 and 0.395 vol. % are prepared without any surfactant. Graphene nano-sheets are prepared from high purity graphite powder by Hummers method followed by exfoliation and reduction by hydrogen gas. Thus, obtained hydrogen exfoliated graphene (HEG) is then functionalized using acid. The graphene nano-sheets are characterized using XRD, TEM, Raman spectroscopy, and FTIR spectroscopy. Thermal conductivity and viscosity measurements are performed both as a function of graphene loading and temperature between 10 and 70 °C. Thermal conductivity enhancement of ∼15% for a loading of 0.395 vol. % f-HEG is observed at room temperature. The measured nanofluid's thermal conductivity is explained well in terms of the expression derived by Nan et al. (J. Appl. Phys. 81, 6692 (1997)), which considers matrix-additive interface contact resistance of mis-oriented ellipsoidal particles. The viscosity of the prepared f-HEG nanofluids and the base fluid (EG + distilled water) displays non-Newtonian behaviour with the appearance of shear thinning and nearly 100% enhancement compared to the base fluid (EG + DI water) with f-HEG loading of 0.395 vol. %. Known theoretical models for nanofluid's viscosity fail to explain the observed f-HEG volume concentration dependence of the nanofluid's viscosity. Temperature dependence of the studied nanofluid between 10 and 70 °C is explained well by the correlations proposed earlier for nanofluids with spherical nanoparticles. Electrical conductivity of the f-HEG nanofluids shows significant enhancement of ∼8620% for 0.395 vol. % loading of f-HEG in a base fluid of 70:30 mixture of EG and distilled water.

Synthesis of silver nanoparticle decorated multiwalled carbon nanotubes-graphene mixture and its heat transfer studies in nanofluid

The present study describes a novel synthesis procedure for a hybrid nanostructure consisting of multiwalled carbon nanotubes (MWNT), hydrogen exfoliated graphene (HEG) and silver nanoparticles. Moreover, synthesis of nanofluids using the above hybrid material and their heat transfer properties are discussed. The hybrid structure of MWNT and HEG (MWNT-HEG) has been synthesized by a simple mixing of MWNT and graphite oxide (GO) followed by exfoliation of this mixture in hydrogen atmosphere. The sample has been characterized with different experimental techniques. After surface functionalization, this hybrid material is decorated with silver nanoparticles (Ag/(MWNT-HEG)) and dispersed in ethylene glycol (EG) without any surfactant. The thermal conductivity and convective heat transfer properties are measured for different volume fractions. An enhancement of ∼8% in thermal conductivity is obtained for a volume fraction of 0.04% at 25°C. The convective heat transfer coefficient of these nanofluids is determined using an in-house fabricated setup. The enhancement in heat transfer coefficient is about 570% for 0.005% volume fraction at the entrance of the pipe for Re = 250.

Enhanced optical limiting in functionalized hydrogen exfoliated graphene and its metal hybrids

We present the mechanism and performance of optical limiting (OL) in hydrogen exfoliated graphene (HEG), functionalized HEG (f-HEG) and its metal hybrids. At the wavelengths used, the mechanism of nonlinear absorption (NLA) involves two-photon absorption and excited state absorption in the nanosecond excitation regime, and saturable absorption in combination with two-photon absorption in the femtosecond (ultrafast) excitation regime. The role of defects in the OL performance of HEG and f-HEG is investigated with the help of their Raman spectra. OL efficiency of f-HEG is found to improve with Pt and Pd nanoparticle decoration due to an enhanced NLA, which arises mainly from interband transitions between the d band and the s–p conduction band in the metal NPs, and charge transfer between f-HEG and metal NPs. Thermally induced light scattering is negligible in these water dispersed systems.

Novel Platinum–Cobalt Alloy Nanoparticles Dispersed on Nitrogen‐Doped Graphene as a Cathode Electrocatalyst for PEMFC Applications

AbstractA novel synthesis procedure is devised to obtain nitrogen‐doping in hydrogen‐exfoliated graphene (HEG) sheets. An anionic polyelectrolyte–conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen‐containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen‐doped graphene (N‐HEG) sheets are used as catalyst support for dispersing platinum and platinum–cobalt alloy nanoparticles synthesized by the modified‐polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt–Co/N‐HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt–Co alloy nanoparticles on the N‐HEG support, the alloying effect of Pt–Co, and the high electrocatalytic activity of the N‐HEG support. A stability study shows that Pt/N‐HEG and Pt–Co/N‐HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts.

Poly(p-phenylenediamine)/graphene nanocomposites for supercapacitor applications

Herein, we report new nanocomposite materials based on poly(p-phenylenediamine) (PpPD) and hydrogen exfoliated graphene (HEG) sheets as efficient binder-free electrode materials for supercapacitors. The nanocomposites are synthesized via chemical oxidative polymerization of a para-phenyldiamine monomer in the presence of graphene sheets in acidic medium. The initial weight ratio of monomer to graphene is varied to get nanocomposites of different polymer to graphene weight ratios. The electrochemical performances of these nanocomposites as a supercapacitor electrode are investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) techniques in two electrode configuration. The nanocomposite with polymer to graphene weight ratio 1 : 2 shows a maximum specific capacitance of 248 F g−1 at a specific current density of 2 A g−1 and also demonstrates high rate capability. The maximum energy density of the fabricated symmetrical supercapacitor cells based on the mass of active electrodes is calculated to be 8.6 W h kg−1 and 5.8 W h kg−1 at a power density of 0.5 kW kg−1 and 5 kW kg−1, respectively. The nanocomposites retain 72% of their initial capacitance after 1000 cycles of charge–discharge at a high specific current density of 10 A g−1.

Cold field emission from hydrogen exfoliated graphene composites

In the present letter, field emission property of highly wrinkled hydrogen exfoliated graphene (HEG) was studied using an indigenously fabricated setup under ∼10−6 mbar pressure. Graphene was coated on a flexible carbon cloth by spin coating for the field emission study. The turn on voltage obtained for a HEG field emitter is around 1.18 V/μm. Further, the field emission property of HEG was improved by decorating metal oxide over HEG. The stability of the field emitter was tested and field enhancement factor was calculated using Fowler–Nordheim plot.

Enhanced convective heat transfer using graphene dispersed nanofluids

Nanofluids are having wide area of application in electronic and cooling industry. In the present work, hydrogen exfoliated graphene (HEG) dispersed deionized (DI) water, and ethylene glycol (EG) based nanofluids were developed. Further, thermal conductivity and heat transfer properties of these nanofluids were systematically investigated. HEG was synthesized by exfoliating graphite oxide in H2 atmosphere at 200°C. The nanofluids were prepared by dispersing functionalized HEG (f-HEG) in DI water and EG without the use of any surfactant. HEG and f-HEG were characterized by powder X-ray diffractometry, electron microscopy, Raman and FTIR spectroscopy. Thermal and electrical conductivities of f-HEG dispersed DI water and EG based nanofluids were measured for different volume fractions and at different temperatures. A 0.05% volume fraction of f-HEG dispersed DI water based nanofluid shows an enhancement in thermal conductivity of about 16% at 25°C and 75% at 50°C. The enhancement in Nusselts number for these nanofluids is more than that of thermal conductivity.

Experimental investigation of the thermal transport properties of a carbon nanohybrid dispersed nanofluid

A hybrid nanostructure consisting of 1D carbon nanotubes and 2D graphene was successfully synthesized. Nanofluids were made by dispersing the hybrid nanostructure in deionized (DI) water and ethylene glycol (EG) separately, without any surfactant. Later the thermal conductivity and heat transfer coefficient of the nanofluids were experimentally measured. Meanwhile, multiwalled carbon nanotubes (MWNT) were prepared by catalytic chemical vapor deposition (CCVD), and hydrogen exfoliated graphene (HEG) was synthesized by exfoliating graphite oxide in a hydrogen atmosphere. The hybrid nanostructure (f-MWNT+f-HEG) of functionalized MWNT (f-MWNT) and functionalized HEG (f-HEG) was prepared by a post mixing technique, and the sample was characterized by powder X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. Thermal conductivity of the nanofluids was measured for different volume fractions of f-MWNT+f-HEG at different temperatures. The hybrid nanostructure dispersed in the DI water based nanofluid shows a thermal conductivity enhancement of 20% for a volume fraction of 0.05%. Similarly, for a Reynolds number of 15,500, the enhancement of the heat transfer coefficient is about 289% for a 0.01% volume fraction of f-MWNT+f-HEG.