Unique Graphene Research Articles

Water Remediation Aided by a Graphene-Oxide-Anchored Metal Organic Framework through Pore- and Charge-Based Sieving of Ions

Herein, a unique reversible addition–fragmentation chain transfer (RAFT)-synthesized antibacterial copolymer was designed to target key requirements such as stringent and quick response toward bacteria and quick reversible response toward fouling using a multilayered assembly. In order to render the membrane assembly selective toward ions, a unique phosphonium-conjugated graphene oxide (P+GO)-anchored copper- and trimesic-acid-based metal organic framework (CuMOF) was sandwiched between the RAFT-synthesized polymer and a commercial reverse osmosis (RO) support. The sandwich architecture exhibited excellent antibacterial properties for both Gram-positive and Gram-negative bacterial cells. The membranes also retained an unimpeded flow of water even after longer continuous runs. The engineered active layer was excellent in rendering reversible antifouling against bovine serum albumin with 98.8% flux retention. The nanoexclusions/channels offered by the P+GO-anchored CuMOF, sandwiched as an interlayer, though...

Electrochemical performance of flexible graphene-based fibers as electrodes for wearable supercapacitors

The miniaturized supercapacitors are promising energy storage devices that can replace traditional batteries in portable electronics. Excellent graphene-based fibers have becoming a dominant role as electrode materials for supercapacitors. Unique and excellent carbon nanotubes and graphene composite fibers (G/CNTs) with outstanding mechanical properties and excellent capacitive behaviors were prepared by a facile, one-step and time-saving process. Scanning electron microscopy images displayed that the diameter of obtained G/CNTs was ∼150 μm, and showed a directional structure of graphene nanosheets and few-walled carbon nanotubes (FWNTs) along the specific direction of the as-prepared composite fibers. The electrochemical performances of the resultant fibers as flexible electrodes were estimated by a three-electrode system. The as-synthesized G/CNTs delivered a specific volumetric capacitance of 312.6 F g −1 at the current density of 200 mA g−1, and the capacitance of G10/CNTs could still remain at 89.6% of original capacitance after 10,000 cycles. Furthermore, the flexible G/CNTs could be fabricated into a stretchable and compressible fiber spring. The fiber supercapacitor displayed much efficient electrochemical capacitive behaviors, promising for being portable and wearable electronics, and this development can potentially promote its application in other fields.

A Cut-Resistant and Highly Restorable Graphene Foam.

High-pressure resistant and multidirectional compressible materials enable various applications but are often hindered by structure-derived collapse and weak elasticity. Here, a super-robust graphene foam with ladder shape microstructure capable of withstanding high pressure is presented. The multioriented ladder arrays architecture of the foam, consisting of thousands of identically sized square spaces, endow it with a great deal of elastic units. It can easily bear an iterative and multidirectional pressure of 44.5 MPa produced by a sharp blade, and may completely recover to its initial state by a load of 180 000 times their own weight even under 95% strain. More importantly, the foam can also maintain structural integrity after experiencing a pressure of 2.8 GPa through siphoning. Computational modeling of the "buckling of shells" mechanism reveals the unique ladder-shaped graphene foam contributes to the superior cut resistance and good resilience. Based on this finding, it can be widely used in cutting resistance sensors, monitoring of sea level, and the detection of oily contaminants in water delivery pipelines.

Rational design of unique graphene modified cobalt manganite hollow microcubes for supercapacitors

A novel reduced graphene oxide (rGO) modified ternary metal oxide electrode material with rational microstructure was successfully developed by the hydrothermal approach following the heat treatment, in which gauze-like rGO sheets were homogeneously decorated on the surfaces of uniform CoMn2O4 hollow microcubes. Benefitting from this special hybrid morphology possessing large specific surface area and good conductivity, the CoMn2O4@rGO composite gave rise to a greater specific capacitance of 1194.7 F g−1 at a low current density of 2 mA cm−2, longer cycle life (88.6% capacitance retention after 5000 cycles), and more excellent rate performance when fabricated into a promising electrode for electrochemical supercapacitors.

Dry microwave heating enables scalable fabrication of pristine holey graphene nanoplatelets and their catalysis in reductive hydrogen atom transfer reactions

Current approaches for scalable production of holey graphene materials require graphene oxide or reduced graphene oxide as starting materials. The molecular basis fundamentally determines that the holey graphene materials thus generated still contain a large number of defects on their basal planes. The existence of these defects not only complicates fundamental studies but also influences practical applications due to the significance decrease in their conductivity and chemical stability. This work exploits microwave chemistry to enable rapid mass production of holey graphene nanoplatelets with their basal plane nearly intact. Interestingly, the unique chemistry also begets the generated nanoholes with edges rich in zigzag geometry. The near-pristine nature of the basal planes and the zigzag edges were clearly observed via atomic resolution TEM and further supported by the localized π-edge states studied via electron paramagnetic resonance (EPR) measurements. The holey graphene nanoplatelets were explored as metal free catalysts for hydrogen atom transfer reactions. These unique holey graphene nanoplatelets exhibited excellent catalytic activity, desired selectivity, and chemical stability for recyclability, which were not achievable by their counterpart holey graphene derivatives with basal plane defects.

Sensitivity Improvement of a Low-Invasive Type Amperometric Glucose Sensor

Implantable glucose biosensors for continuous glucose monitoring (CGM), are getting more attractive, since they can provide greater insight into the direction, magnitude, duration, frequency and possible causes of glucose fluctuations in response to meals, insulin injections, hypoglycemic episodes and exercise throughout the day. The current commercialized or presented conventional CGM sensor devise are required to have about 1.0 cm in length to be inserted inside the skin. Therefore, it is expected to develop lower invasive type glucose sensor in order to improve the life-quality of diabetic patients. We have previously reported that the sensor response of a fine tapered needle type glucose sensor, which has a sensing region at the tip, showed good correlation with blood glucose value, even it was implanted in the skin of a rabbit for a length of 1.0 mm [1]. This indicate that the glucose measurement in dermis may provide valuable information comparable to subcutaneous tissue glucose measurement. As part of our low-invasive improvement of the sensor, miniaturization of sensing region is essential, but it may lead to a decrease of response current to glucose. Therefore, at the same time, the improvement of sensor sensitivity is also indispensable. The sensitivity of an enzyme based glucose sensor can be improved by introduction of carbon nanomaterial or mediator, which can increase electrode surface area and the efficiency of electron or mass transport to the transducer. Due to their high chemical stability, high surface area, and unique electronic properties, carbon nanotubes (CNT) and graphene has greatly increased biosensor sensitivity and response speed. On the other hand, electroetching of the electrode surface is an effective method to obtain a higher surface area, which may be responsible for enhanced sensitivity. In this study, introduction of carbon nanomaterial and electroetching technique were introduced to improve the sensitivity of the proposed glucose sensor. [1] J. Li, P. Koinkar, Y. Fuchiwaki, M. Yasuzawa, Biosens. Bioelectron., 86 (2016) 90.

Wood-inspired multi-channel tubular graphene network for high-performance lithium-sulfur batteries

Hierarchical porous structure plays a vital role in various energy storage systems. Herein, a wood-inspired multi-channel tubular graphene (MCTG) architecture is fabricated by template-directed chemical vapor deposition (CVD). The multi-channel template is assembled via a facile hydrothermal and freeze-drying method with Si as precursor. The unique multi-channel tubular graphene architecture reveals distinct advantages for lithium-sulfur (Li-S) batteries. The curved tubular interior space with a pore volume of 2.141 cm3 g−1 can accommodate active sulfur and anchor soluble polysulfides, while the 3D multi-channel network favors rapid mass transport and ion diffusion. Furthermore, the CVD grown few-layer graphene offers good electron conductivity, while the enlarged (002) spacing (0.35–0.41 nm) of graphene layers provide more space for sulfur storage and Li+ diffusion. Benefiting from these merits, the MCTG/S cathode (loaded with 70 wt% sulfur) achieves a high initial discharge capacity of 1390 mAh g−1 at 0.1 C rate, excellent rate capability up to 8 C and a slow capacity decay rate of 0.078% per cycle during 500 cycles. This type of MCTG will also play an important role in gas adsorption, solar steam generation, catalysis, and so on.

Novel Hollow Graphene Flowers Synthesized by Cu‐Assisted Chemical Vapor Deposition

AbstractNovel hollow graphene flowers (HGFs) are synthesized by a Cu‐assisted chemical vapor deposition. Multilayer graphene films and vertical‐oriented graphene nanosheets are grown on hollow silica spheres successively by controlling the CH4/H2 flow and growth time. After graphene growth, HSS templates are removed to achieve HGFs. The π‐conjugated systems and unique morphology of HGFs lead to apparent adsorption ability for dyes and phenol molecules. This work provides a facile way to produce unique hollow structure graphene with massive edges for different applications in the future.

High Rate Production of Clean Water Based on the Combined Photo-Electro-Thermal Effect of Graphene Architecture.

The use of abundant solar energy for regeneration and desalination of water is a promising strategy to address the challenge of a global shortage of clean water. Progress has been made to develop photothermal materials to improve the solar steam generation performance. However, the mass production rate of water is still low. Herein, by a rational combination of photo-electro-thermal effect on an all-graphene hybrid architecture, solar energy can not only be absorbed fully and transferred into heat, but also converted into electric power to further heat up the graphene skeleton frame for a much enhanced generation of water vapor. As a result, the unique graphene evaporator reaches a record high water production rate of 2.01-2.61 kg m-2 h-1 under solar illumination of 1 kW m-2 even without system optimization. Several square meters of the graphene evaporators will provide a daily water supply that is enough for tens of people. The combination of photo-electro-thermal effect on graphene materials offers a new strategy to build a fast and scalable solar steam generation system, which makes an important step towards a solution for the scarcity of clean water.

Bulk Polymer-Derived Ceramic Composites of Graphene Oxide.

Bulk polymer-derived ceramic (PDC) composites of SiCO with an embedded graphene network were produced using graphene-coated poly(vinyl alcohol) (PVA) foams as templates. The pyrolysis of green bodies containing cross-linked polysiloxane, PVA foams, and graphene oxide (GO) resulted in the decomposition of PVA foams, compression of GO layers, and formation of graphitic domains adjacent to GO within the SiCO composite, leading to SiCO composites with an embedded graphene network. The SiCO/GO composite, with about 1.5% GO in the ceramic matrix, offered an increase in the electrical conductivity by more than 4 orders of magnitude compared to that of pure SiCO ceramics. Additionally, the unique graphene network in the SiCO demonstrated a drop in the observed thermal conductivity of the composite (∼0.8 W m–1 K–1). Young’s modulus of the as-fabricated SiCO/GO composites was found to be around 210 MPa, which is notably higher than the reported values for similar composites fabricated from only ceramic precursors and PVA foams. The present approach demonstrates a facile and cost-effective method of producing bulk PDC composites with high electrical conductivity, good thermal stability, and low thermal conductivity.

Ultrathin Active Layer for Transparent Electromagnetic Shielding Window

Recently, electromagnetic (EM) shielding (EMS) window, especially the ultrathin, transparent EMS active layer, has been the primary objective of extensive studies because of its widely potential applications in stealth technology, high radiation pollution, and others. However, several defects, including opacity and large thickness, have severely restricted the application in optical EMS devices. Herein, we developed an ultrathin and highly transparent EMS active layer on a rigid glass and a flexible polyethylene terephthalate substrate by chemical doping CVD (chemical vapor deposition) graphene with nitric acid (HNO3) as the P-type dopant, which has a 91% transmittance and 1/1000 thickness compared to the conventional EMS active layer. The HNO3-treated graphene shows excellent EMS efficiency by a factor of 4.5, significantly compensating for the adverse effects of the grain boundaries between CVD graphene crystals. Additionally, 55% HNO3 is the most suitable for achieving high EMS effectiveness, which can be significantly improved by treating for only 5 min. This unique chemical-doping CVD graphene holds potential for being exploited as a transparent active layer in numerous EMS applications.

Heterostructural Graphene Quantum Dot/MnO2 Nanosheets toward High-Potential Window Electrodes for High-Performance Supercapacitors.

The potential window of aqueous supercapacitors is limited by the theoretical value (≈1.23 V) and is usually lower than ≈1 V, which hinders further improvements for energy density. Here, a simple and scalable method is developed to fabricate unique graphene quantum dot (GQD)/MnO2 heterostructural electrodes to extend the potential window to 0–1.3 V for high‐performance aqueous supercapacitor. The GQD/MnO2 heterostructural electrode is fabricated by GQDs in situ formed on the surface of MnO2 nanosheet arrays with good interface bonding by the formation of Mn—O—C bonds. Further, it is interesting to find that the potential window can be extended to 1.3 V by a potential drop in the built‐in electric field of the GQD/MnO2 heterostructural region. Additionally, the specific capacitance up to 1170 F g−1 at a scan rate of 5 mV s−1 (1094 F g−1 at 0–1 V) and cycle performance (92.7%@10 000 cycles) between 0 and 1.3 V are observed. A 2.3 V aqueous GQD/MnO2‐3//nitrogen‐doped graphene ASC is assembled, which exhibits the high energy density of 118 Wh kg−1 at the power density of 923 W kg−1. This work opens new opportunities for developing high‐voltage aqueous supercapacitors using in situ formed heterostructures to further increase energy density.

Correction: Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach.

Correction for 'Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach' by Rajendra P. Panmand et al., Nanoscale, 2017, 9, 4801-4809.

Rational design of a 3D MoS2/dual-channel graphene framework hybrid as a free-standing electrode for enhanced lithium storage

The unique 3D dual-channel graphene framework could improve electron transport by GF channels possessing high electrical conductivity and facilitate Li ion diffusion by GA channels shortening the diffusion pathways.

Hierarchical three-dimensional Fe3O4@porous carbon matrix/graphene anodes for high performance lithium ion batteries

In the present paper, the hierarchical three-dimensional Fe3O4@porous carbon matrix (PCM) and Fe3O4@PCM/graphene are synthesized by a facile annealing of Mil-53(Fe) templates. Their electrochemical performances are evaluated as anode materials for lithium ion batteries. In comparison with Fe3O4@PCM, the Fe3O4@PCM/graphene electrode exhibits a much better cycling performance with the reversible capacity high up to 1000 mAh g−1 after 500 cycles at 1 C. The improved performance can be ascribed to the high conductivity and structure stability provided by the unique graphene based hierarchical three-dimensional nanostructure.

Fine-sized Pt nanoparticles dispersed on PdPt bimetallic nanocrystals with non-covalently functionalized graphene toward synergistic effects on the oxygen reduction reaction

To data, combination of Pt-based bimetallic nanocrysatals and the graphene support have significantly contributed to enhance the oxygen reduction reaction (ORR) performance relative to electrocatalysts based on monometallic Pt nanoparticles (NPs) primarily due to the unique ligand effects and benefits of the carbon support. In this study, we propose a new structure of bimetallic electrocatalysts to realize the synergistic effects on the ORR performance through effective integration of the fine-sized Pt NPs, PdPt bimetallic nanocrystals, and non-covalently functionalized graphene with ionic polymers. The facile wet-chemical methods were applied to synthesize fine-sized (2–5nm) spherical Pt NPs doped large-sized (20–50nm) non-spherical PdPt bimetallic NPs on the electronically negative ionic polymer-functionalized graphene support (Pt-on-PdPt/fG). This Pt-on-PdPt/fG with synergistic effects based on enlarged active surface area, ligand, and interfacial linking effects, exhibits substantially enhanced ORR activity (specific activity: 1.89mA cmPt−2 at 0.9VRHE) and durability in comparison to the commercial Pt/C (specific activity: 0.23mA cmPt−2 at 0.9VRHE). To this end, the effective integration of newly designed fine-sized Pt NPs doped bimetallic nanocrystals and unique graphene supports with the well-interactive ability could be a good platform to develop the advanced electrocatalysts for the efficient ORR.

Rational design of self-supporting graphene - Polypyrrole/sulfur - Graphene sandwich as structural paper electrode for lithium sulfur batteries

Lithium sulfur batteries have been regarded as next-generation battery technology due to its high energy density, environmental benignity and abundance. However, the poor electric/ionic conductivity of sulfur limits the practical use of sulfur in an electrode. The main problem is the high solubility of long-chain polysulfides, which are the intermediates of the electrochemical processes in the liquid electrolyte. The dissolved polysulfide ions shuttle between the cathode and anode, thus causing precipitation of insulating Li2S2/Li2S on the surface of the electrode. The unavoidable phenomenon results in loss of active materials and fast capacity fading. In this regard, we show one simple method to prepare free-standing paper electrode used as cathode material for lithium sulfur batteries. Binder-free graphene-polypyrrole (PPy)/S-graphene (G-PPy/S-G) paper-like sandwich structural electrode was prepared by using the vacuum filtration method. In this structure, the unique graphene layers of sandwich-like framework not only serve as a conductive film, but also effectively block the diffusion of polysulfides, leading to suppression of the shuttle effect and low self-discharge behaviour. In addition, the middle layer, the PPy nanofibers can limit the diffusion of dissolved polysulfides due to the special bond with sulfur, and furthermore maintain the structural stability of the paper electrode because the nanofibers can serve as elastic springs to accommodate the huge volume changes in charging-discharging processes. When tested as cathode for Li-S batteries, the as-prepared sample G-PPy/S-G exhibits excellent electrochemical performance. We believe that our strategy could provide a useful pathway towards commercial utilizing of sulfur.

Imidazoles-Derived PGM-Free Cathode Catalysts for Oxygen Reduction Reaction

Conventionally platinum based catalysts are most commonly used cathodic catalysts in fuel cells. The high cost of platinum is a serious limiting factor for the widespread deployment of fuel cell technology. Fe-N-C materials have been explored to be some of the best performing substitutes. However the cost of synthesis, activity and durability are issues that still need to be addressed. In this work we explore the use of novel synthesis techniques with small organic molecules to synthesize Fe-N-C catalysts. Hydrothermal and pyrolysis synthesis strategies are used on templated and template free precursors to obtain the desired catalytic materials. Benzimidazole carboxylic acid is treated with a dual templating protocol that involves sodium salt formation and sacrificial silica hard template. The process then involves high temperature pyrolysis followed by template removal to yield the final product. A highly active and stable Fe-N-C electrocatalyst possessing a unique 3D porous graphene “nano-stack” morphology is thus synthesized. Control experiments with single template were performed to prove the advantage of the dual template. The oxygen reduction catalytic activity of these benzimidazole derived catalysts in alkaline electrolyte is studied rotating disk electrode methods. The dual templated catalyst shows an improvement over the commercial Pt/C catalyst along with excellent stability (as performed under the Department of Energy- Durability Working Group protocols). Furthermore, template-free synthesis of an Fe-N-C ORR catalyst is achieved by the direct pyrolysis of ethylenediaminetetraacetic acid ferric sodium salt. Detailed physical characterization of the catalyst is performed by surface area measurement, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. Rotating Ring Disk Electrode measurements. A detailed analysis of the effects of synthesis temperature on graphitization, surface area and their concurrent effects on the catalytic performance is brought forth in this work. Finally, we also establish a novel hydrothermal-pyrolysis approach to generate an active Fe-N-C catalyst from molecules like glucose and methyl-imidazole. The process simultaneously involves formation of metal-nitrogen bonds and partial carbonization resulting in in-situ active site formation. The glucose-imidazole catalysts termed as GLU-IMID-C exhibit good ORR activity in acidic and alkaline electrolyte. We perform detailed structural analysis of these catalysts using such techniques as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area analysis and Transmission Electron Microscopy (TEM). The electrocatalytic behavior of the catalysts towards oxygen reduction is studied separately in acidic and alkaline electrolytes by using rotating ring disk electrode measurements. A general precursor-structure-performance relationship of these catalysts and their individual performance trends in both electrolytes has been established in this work.

Building a Novel Chemically Modified Polyaniline/Thermally Reduced Graphene Oxide Hybrid through π-π Interaction for Fabricating Acrylic Resin Elastomer-Based Composites with Enhanced Dielectric Property.

Sustainability urgently demands low dielectric loss and low elastic modulus as fostering high permittivity (Hi-K) conductor/polymer composites. This work introduces a ternary composite system, consisting of acrylic resin elastomer (AR), chemically modified polyaniline (HBSiPA), and the thermally reduced graphene oxides (TrGOs), for applying to actuators, of which AR was fabricated by free radical polymerization. The unique hybridized graphene (HBSiPA-TrGO) was prepared by a two-step procedure, including the doped polyaniline modified by the hyperbranched polysiloxane via a ring opening reaction, followed by the decoration of HBSiPA on the surface of TrGO, the conductivity of which is desired to be the same as that of graphene. Afterward, diverse filler contents of HBSiPA-TrGO were put into the AR matrix to fabricate composites with the solution casting method and TrGO/AR composites were fabricated as well for comparison. Unlike TrGO, HBSiPA has plenty of polyaniline chain segments that ensure better dispersion of graphene hybrids in the AR, and thus the composites inherit the excellent electrical property of graphene. The permittivity and dielectric loss of the HBSiPA-TrGO/AR composite at 100 Hz are 3.5 and 0.27 times that of the TrGO/AR composite, respectively, when the loading of fillers approaches the percolation threshold (fc), which originates from the HBSiPA anchored onto the graphene serving as spacer and thus decreases the leakage currents induced by the contact of graphene sheets. Besides, the elastic modulus of 2.83 vol % HBSiPA-TrGO/AR composite was lower than 5 MPa.

Enhanced transport properties of graphene-based, thin Nafion® membrane for polymer electrolyte membrane fuel cells

A polymer electrolyte membrane fuel cell (PEMFC) is one of the promising renewable energy conversion systems; however, its performance is considerably limited by the sluggish transport properties and/or reaction kinetics of the catalyst layers, especially at a high current density. In this study, graphene-based, thin Nafion® membranes are prepared using 0 to 4 wt% of graphene nanoflakes, and the effects of the graphene are examined for enhanced transport properties. The electrical conductivity and dielectric constant are drastically enhanced to 0.4 mS/cm and 26 at 4 wt% of graphene nanoflakes, respectively, while the thermal conductivity linearly increases to 3 W/m-K. The proton conductivity also significantly increases with the aid of graphene nanoflakes at >2 wt% of graphene nanoflakes, and the enhancement doubles compared with those of the carbon-black (CB)-based and carbon nanotube (CNT)-based, thin Nafion® membranes, perhaps due to unique graphene structures. Additionally, the quasi-steady-state water contact angle increases from 113° to ~130° with the addition of graphene nanoflakes, showing that a hydrophobic-like water wetting change may be related to the significant proton conductivity enhancement. This work provides an optimal material design guideline for the transport-enhanced cathode catalyst layer using graphene-based materials for polymer electrolyte membrane fuel cell applications.