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The increasing demand for high-specific-energy batteries drives researchers to revisit Li metal anode. However, the formation and growth of Li-dendrite possibly leads to short-circuit of the battery, causing safety hazard of Li metal batteries. Therefore, it is quite necessary to regulate the plating/stripping behaviors of Li metal anodes to address this long-standing issue. Herein, we report the regulation of Li plating/striping behavior via manipulating the ratio of oxygen containing groups on reduced graphene oxide papers. It has been revealed that the electrochemical properties are highly dependent on the amount of carbonyl C O groups, which could associate Li+ and serve as a uniform nucleation site to guide Li plating. Furthermore, a high lithium ion diffusion coefficient of ∼2.09 × 10−14 m2 s−1 was enabled, around one magnitude higher than that of the Li lattice self-diffusivity (∼2 × 10−15 m2 s−1). As a result, stable dendrite-free Li metal anode is realized on the reduced graphene oxide paper with high C O group content (8.4%), which exhibits a low and stable overpotential of 50 mV for a long lifetime of 400 h. Our studies provide a fresh insight into the Li ion diffusion and its critical role in the regulation of the Li plating/stripping behaviors.

The sandwiched membrane which consists of the sulfonated holey graphene oxide paper with the deposition of the sulfonated poly(ether ether ketone) (SPEEK/SHGO/SPEEK) membrane on its both sides has been prepared. This membrane is reported to have higher proton conductivity (155.6 ± 1.6 mS cm −1 ), but lower methanol permeability (7.05 ± 0.21 × 10 −6 cm 2 s −1 ) than Nafion ® 112 at 80 °C, whose respective values are 138.6 ± 1.4 mS cm −1 and 15.40 ± 0.46 × 10 −6 cm 2 s −1 , respectively. The specific structure of the SHGO comprising the sulfonated and holey graphitic plane plays an important role in the high performance of the SPEEK/SHGO/SPEEK membrane. First, the sulfonated structure could increase the overall density of the sulfonic acid groups in the membranes, which increases the number of proton exchange groups participating in the proton transport. Second, the holey structure of the SHGO provides an additional path for the proton transport, which well avoids the blockage of the proton transport by the high aspect ratio graphitic planes. Third, the sulfonated and holey structure could also increase the interlayer spacing of the graphitic planes in the SHGO paper, which would promote the proton transport as well. Finally, the presence of the SHGO paper with the layer-by-layer stacked graphitic plane would effectively retard the diffusion of methanol through the membrane. When evaluated in the semi-passive direct methanol fuel cell (DMFC), the cell with the SPEEK/SHGO/SPEEK membrane shows higher stability and exhibits a maximum power density 61.1% higher than with Nafion ® 112, which strongly suggests that the SPEEK/SHGO/SPEEK membrane could be used as the proton exchange membrane for DMFCs.

In this work, we report a high-performance graphene flexible paper electrode composed of core-shell Gold@Prussian blue nanoparticles (Au@PB NPs) for real-time monitoring of living cell and biosensor platform. Core-shell Au@PB NPs with high stability, low cost, excellent biocompatibility and electrochemical activity was prepared. At the same time, combined with the robust mechanical properties of reduced graphene oxide (rGO) paper, an independent flexible graphene paper electrode was prepared and broadly characterized. Because of the unique structural properties and the combinational advantages of different components in the Au@PB NPs-rGO composite, the resultant nanohybrid paper electrode exhibits good electrochemical sensing performance toward hydrogen peroxide (H2O2) and it also displays a very short response time (1 s) in the tracking of H2O2 secretion by living HepG2 cells. Meanwhile, the as-prepared Au@PB NPs-rGO paper electrode can be further used as an enzyme-based biosensor. In this regard, glucose oxidase (GODx) used as an example for glucose detection and analysis, which proves its excellent performance as an enzyme sensing platform. The excellent properties of the kind of nanocomposites are expected to be further used in the field of flexible devices and Point-of-Care (POC).

Layered α-Co(OH)2 nanosheets have been widely investigated as one of the promising supercapacitor materials owing to its high theoretical specific capacitance (3,460 F g−1). However, their poor electrical conductivity, poor stability, and unclear charge storage mechanism limit their practical use in energy storage systems. To address the first two drawbacks of layered Co(OH)2, conductive silver nanoparticles (AgNPs) with a finely tuned loading content were for the first time incorporated to the layered Co(OH)2 structure coated on a flexible reduced graphene oxide (rGO)paper substrate. In situ electrochemical X-ray absorption spectroscopy (XAS) was also used to investigate the charge storage mechanism of AgNPs/Co(OH)2 electrode. It was found that the incorporation of AgNPs with an average diameter of

Herein, an environmentally-benign, facile, efficient, low-cost, scalable fabrication process of achieving flexible graphene paper electrode at ambient conditions is reported. By means of high-shear exfoliation of graphite in aqueous polyvinyl alcohol (PVA), the graphene/PVA dispersion is prepared. Various characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, etc.) confirm that the resulting dispersion is with the presence of high-quality, single to few-layered graphene sheets with thickness up to 1.68 nm, lateral size of 0.5–2 μm, and low defect density (ID/IG = 0.09). Further, the applicability of the in-situ exfoliated graphene/PVA dispersion is demonstrated for the fabrication of flexible conductive paper electrodes through a simple intermittent soaking-drying approach. The graphene paper electrode possesses an electrical sheet resistance of 15 Ω sq−1, without any additional annealing treatment and conductive additives. Finally, the graphene paper electrode is integrated with ionic-liquid incorporated PVA polymer electrolyte to develop the all-solid-state supercapacitor. It imparts a considerable specific capacitance of 222.96 F g−1 along with ~60% capacitance retention and ~100% coulombic efficiency after 6000 charge–discharge cycles. Meanwhile, the polymer electrolyte exhibits a remarkable ionic conductivity (4.63 × 10−4 S cm−1) together with a wide electrochemical stability window (5.1 V), favorable for device applications. The unique interwoven nanoporous conductive network of PVA-stabilized exfoliated graphene provides fast diffusion pathways to electrolyte ions, thus significantly enhancing the charge-storage performance.

The development of polypyrrole (PPY) flexible supercapacitors has been recognized as one of the most effective strategies for preparing advanced flexible energy storage devices. However, they are still limited by low mass loading and poor areal capacitance during charge-discharge process. Here, freestanding conductive film is designed and prepared by PPY/bacterial cellulose (BC) nanofibers in combination with graphene (RGO) through a simple in situ polymerization and filtering method. The porous and flexible BC nanofiber is used as a substrate and template for successive polymerization of PPY, which is responsible for such a large areal mass of 13.5 mg cm −2 . Thus, the high areal capacitance of 3.66 F cm −2 at 1 mA cm −2 and 2.59 F cm −2 at 50 mA cm −2 are achieved. The assembled symmetric supercapacitor by coupling of two freestanding electrodes delivers high areal capacitance of 1.67 F cm −2 , high areal energy density of 0.23 mWh cm −2 and a maximum power density of 23.5 mW cm −2 . Therefore, it is believed that this strategy holds great promise for design of freestanding conductive polymer electrodes on high performance flexible supercapacitors.

Here we developed a free-standing reduced graphene oxide (rGO)-polypyrrole (PPy) hybrid paper via electropolymerization on a paper-like graphene gel. This flexible hybrid paper displayed a uniform layered structure with PPy coated onto the graphene layers. A high areal mass of 2.7 mg cm−2 could be obtained. It delivered a greatly enhanced areal capacitance of 440 mF cm−2 at 0.5 A g−1, in contrast to that 151∼198.5 mF cm−2 previously reported for graphene paper or polypyrrole-graphene paper. It can retain ∼81% of the initial capacitance at a high current density of 6 A g−1. The combined high flexibility with outstanding electrochemical performance, makes such novel hybrid paper a promising electrode for flexible supercapacitors.

Here, controlled growth of vertically aligned carbon nanotubes (VACNTs) on free-standing porous activated reduced graphene oxide (a-rGO) paper was fabricated using plasma-enhanced chemical vapor deposition method. The electrochemical performance of prepared film was investigated to provide effective electrode for 3D flexible high-performance lithium-ion batteries (LIBs) and supercapacitors. The results revealed that the prepared electrode exhibited a high specific capacitance of 347 F/g at 0.5 A/g in 1 M KOH electrolyte, 60% more than non-activated rGO-paper (218 F/g). The VACNTs on a-rGO have increased the accessible surface area and acted as efficient electrical conducting paths, which improved the power density. The free-standing flexible supercapacitor fabricated using such a film exhibited a sufficient electrochemical behaviour with high power density of 407 kW kg−1 at 5 Wh.kg−1 at a current density of 0.5 A/g. Since VACNTs with low sp2 hybridization defect lead to cyclic stability, suitable for high-performance LIB anodes. This 3D flexible anode electrode demonstrated a high initial discharge capacity of 1401 mAhg−1 with a large reversible charge capacity of 958 mAhg−1 at 150 mAg−1. The charge and discharge capacity have reached a stable value of 459 mAhg−1 after 100 cycles with a coulombic efficiency of ∼100% which is much higher than most carbon structures.

In this paper, carbon paper (CP) was modified by three-dimensional reduced graphene oxide (3DrGO/CP) and binders. Based on physical (field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy) and electrochemical tests (cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charging/discharging curves), the physical and chemical properties of 3GrGO/CP electrode were investigated. The physical characterization and electrochemical performance analysis indicated that the different binders significantly influenced the hydrophilicity and the wet surface area of electrode. Nitrogen doping three-dimensional reduced graphene oxide facilitates the electron transfer on electrode/electrolyte interface for both oxidation and reduction processes of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-HO-TEMPO), provides more reaction area and reduces concentration polarization. Therefore, the modified carbon paper electrode exhibits better electrochemical activity and reversibility compared with the pristine carbon paper electrode in a methyl viologen (MV)/4-HO-TEMPO redox flow battery (RFB).

The structural design and synthesis of sulfur-carbon composite materials with high performance is still a major challenge for rechargeable lithium-sulfur batteries. Interconnected three-dimensional frameworks comprising multi-walled carbon nanotubes, graphene, or carbon particles offer a combination of constituent advantages and can thus be used to achieve superior energy conversion and storage properties. Herein, we designed and prepared free-standing three-dimensional sulfur papers containing interconnected highly conductive carbon materials, which enable to be flexible binder-free cathodes for Li-S batteries. The resultant sulfur-carbon composite paper cathode exhibited high reversible specific capacity of 1386 mAhg−1, good rate capability up to 5C, and excellent cycling performance (a capacity retention 68% after 400 cycles), all of which are significantly improved from those of bare sulfur cathode or sulfur-GO composite only. Rational design of cathode composition, structure, and a simple fabrication process can give insight into the development of various advanced cathode materials for high-performance Li-S batteries.

Graphene paper that exhibits an excellent stabilized capacity, as high as 1300 mAh g −1 at a current rate of 60 mA g −1 , as a lithium ion battery anode is fabricated and evaluated. The few-layer graphene used to make the graphene paper is prepared via the thermal reduction of graphite oxide. The graphene is then modified by a novel method utilizing inherent defects, namely epoxy groups, on the graphene as active sites for a reaction with methanol, 1-butanol, 1-hexanol, and 1-octanol. The density values and X-ray diffraction patterns obtained for the graphene paper demonstrate that the alkyl brushes on the graphene sheets expand the d-spacing and hinder close restacking of the sheets, thereby inducing the formation of extra cavities within the paper. This loose packing due to the alkyl brushes increases sensitively as the alkyl chain length of the alcohol becomes longer. The lithium ion insertion capacity of a graphene paper electrode at the first cycle also increases with the alkyl chain length. However, fading of the capacity at early charge/discharge cycles is accelerated by the modification process because of electrolyte penetration into the gallery and the acceleration of protective solid electrolyte interface film formation due to looser packing. The paper composed of graphene modified with 1-butanol rather than shorter or longer alcohols exhibits the best reversible storage capacity, more than two-fold higher when compared to that of pristine graphene paper, due to a compromise between two conflicting effects on the reversible storage capacity by long alkyl brushes. The tensile properties and electrical conductivity of the graphene papers are also examined.

This paper focuses on an understanding of the influence of paper thickness on the electrochemical performances of graphene papers as an anode for lithium ion batteries. Three types of graphene papers, with thickness of ∼1.5, 3 and 10 μm, respectively, were fabricated by vacuum-assisted filtration of reduced graphene nanosheets suspended in water. These papers deliver evidently different lithium storage capacities, with thinner papers always outperform thicker ones. The 1.5 μm paper gives rise to initial reversible specific capacities (the first 10 cycles) of ∼200 mAh g −1 at a current density of 100 mA g −1 , while the 10 μm paper only presents ∼80 mAh g −1 at a current density of 50 mA g −1 . After 100 cycles, a specific capacity of ∼180 mAh g −1 is retained for the 1.5 μm paper; in contrast, only ∼65 mAh g −1 remains for the 10 μm paper. The capacity decline with the paper thickness is associated with the dense restacking of graphene nanosheets and a large aspect ratio of the paper. The effective Li + diffusion distance in graphene paper is mainly controlled by the thickness of the paper, and the diffusion proceeds mainly in in-plane direction, cross plane diffusion is restrained. As such, the effective contact of graphene nanosheets with electrolyte is limited and the efficiency of carbon utilization is very low in the thick papers.

Paper-based working electrodes were modified by the addition of nanomaterials (carbon nanofibers, gold nanoparticles, graphene and hybrids of them), with the aim to increase the conductivity and to obtain an electroactive platform with improved analytical behaviour. The effect of the nanostructures was evaluated by using cyclic voltammetry and dopamine as electrochemical probe. The modifications with in-situ generated nanomaterials such as gold nanoparticles (AuNPs) or others requiring treatment like graphene oxide (GO), were optimized by factorial design. The characterization of the cellulose based electrodes by scanning electron microscopy (SEM) showed the distribution of carbon nanofibers and the presence of AuNPs around the cellulose fibers. The partial modification made by the carbon ink was also monitored by attenuated total reflection (ATR) spectrometry. Electrodes modified with rGO and AuNPs exhibited higher intensity peaks with more reversibility and reproducibility than unmodified paper. The highest intensities and lowest limits of detection were achieved with paper electrodes modified with hybrid nanostructures composed by both CNFs and AuNPs.

Metal oxide nanoparticles as the electrochemically active second phase were incorporated into the paper-like flexible graphene-based hybrid electrodes. Its size and dispersion are crucial factors for determining the rate capability and cycling stability of the flexible hybrid paper electrode. Herein, we employ in-situ formed ultrafine monodisperse TiO 2 quantum dots (QDs, ∼4.0 nm) as the electrochemically active second phase, which are uniformly incorporated into the flexible hybrid paper via a simple mixed solvothermal reaction together with a vacuum filtration, aiming at achieving a high-rate and long-cycle flexible TiO 2 -based anode in lithium ion batteries (LIBs). By combining the advantages of both ultrafine TiO 2 -QDs and three-dimensional (3D) conductive networks, the as-fabricated TiO 2 -QDs-reduced graphene oxide (TiO 2 -QDs-RGO) hybrid paper electrode shows high reversible capacity of 201 mA h g −1 after 100 cycles at 0.1 A g −1 and superior rate capability as well as long cycle life of 1500 cycles with ∼80.6% capacity retention at 2.0 A g −1 . Detailed electrochemical analysis shows that the improved capability and cyclability of the hybrid paper electrode results from the integrated intercalation-based and interfacial lithium storage behaviors as well as the 3D fast electron/ion transfer of materials, which is ascribed to the ultra-small size of TiO 2 -QDs and the 3D self-standing conductive networks of the hybrid paper electrode. The results demonstrate the distinct advantages of our material design strategy, and also might pave the way for further studies of other flexible metal oxide/graphene hybrid paper electrodes for fast and long-life flexible anodes in LIBs.

Free-standing graphene composite papers exhibit very high flexibility and stability. Therefore, these materials are preferred as modular electrodes for some electrochemical applications, e.g. electrochemical sensors, supercapacitors, and batteries. Graphene composite papers are usually doped with different substances to improve their electrical conductivity, electrochemical performance, and stability. This work describes the fabrication of flexible and free-standing reduced graphene oxide (rGO) papers doped with phenazine, phenothiazine, phenoxazine, xanthene, acridine, and thiazole class of dye molecules. Fabrication procedure was applied by two basic steps: vacuum filtration of a dispersion containing GO sheets and dye molecule through a membrane and reduction of free-standing GO/dye paper to rGO/dye paper by treatment with hydriodic acid. Characterization of these rGO/dye papers were achieved by using scanning electron microscopy, scanning tunneling microscopy, energy dispersive X-ray analysis, powder X-ray diffraction spectroscopy, Raman spectroscopy, fourier transform infrared spectroscopy, UV–vis. absorption spectroscopy, four-point probe conductivity measurement and cyclic voltammetry techniques. Electrical conductivity and electrochemical performance studies indicated that acriflavine (Acr) doped rGO paper electrode exhibited the best performance for electrocatalytical oxidation of nitrite. When rGO/dye paper was applied as amperometric sensor for nitrite, the sensor was very stable, flexible, and reproducible. rGO/Acr paper demonstrated good quality parameters with sensitivity of 0.40 μAμM−1cm−2, detection limit of 0.12 μM, and linear range of 0.40–3600 μM.

Graphitic layer of carbon has been deposited on the surface of cellulose paper by simple pencil drawing approach. The edges of exfoliated multilayer graphene sheets formed during pencil drawing on the rough paper surface causes the enhancement of electrochemical capacitance. One step chemical polymerization technique has been adopted to fabricate polyaniline nanofibers on hydrophobic pencil drawn graphitic layer on the cellulose paper. These polyaniline coated pencil drawn paper electrodes were used to fabricate all-solid-state symmetric supercpapcitors with superior performance in comparison to similar pencil drawn paper electrodes without polyaniline. All-solid-state symmetric supercapacitor with paper based multilayer graphene-polyaniline nanofiber electrodes exhibits specific capacitance of 28.37 F g−1, areal capacitance of 93.64 mF cm−2, energy density of 8.32 µW h cm−2, and power density of 39.97 µW cm−2. It also shows excellent cyclic stability with initial increment to a maximum value and then decrease to 91.5 % of the maximum value after 5000 cycles. It is interesting to note that it retains 134.28 % of initial areal capacitance after 5000 cycles.

Herein we reported a novel routine to easily access graphene/polyaniline paper (GPp) as supercapacitor electrodes through controlled in-situ polymerization followed by roll coating. According to this routine, the load fraction of PANI can be easily controlled by feed ratio of aniline to GO. In the resulting GPp, PANI nanoarrays anchored graphene nanosheets and PANI nanofibers throughout the bulk coexist, and the former construct a three-dimensional network. As a result, the GPp as a freestanding electrode exhibits excellent electrochemical properties. It can deliver a high capacitance up to 838 F/g at a current density of 1 A/g, while keeps high retention of 93.7% at 10 A/g over 5000 cycles. Kinetics analysis shows that the GPp stores both surface capacitance and diffusion capacitance, but the former dominates the latter.

A novel polyprrole (PPy)-decorated hierarchical NiCo2O4 nanoneedles was grown on highly conductive carbon fiber paper (CFP) for high performance asymmetric supercapacitor applications. The PPy-decorated hierarchical NiCo2O4 nanoneedle on CFP (PPy-NiCo2O4@CPF) was grown by two steps. At first, NiCo2O4 nanoneedle was grown by hydrothermal process and followed by the deposition of PPy through electrochemical method. The fabricated PPy-NiCo2O4@CPF electrode displayed the higher electrochemical performance. The specific capacitance was ∼910 F g-1 at a current density of 1 A g−1 and cyclic stability was ∼88% after 10,000 cycles. To explore real performance of the electrode, we have fabricated solid state asymmetric supercapacitor using PPy-NiCo2O4@CFP as positive and nitrogen doped reduced graphene oxide (N-rGO) as negative electrodes. The fabricated asymmetric device delivered a specific capacitance of 118.6 F g-1 at a current density of 1.0 A g−1 with a maximum energy density of 40.81 Wh Kg−1 (at a power density of 738.27 W Kg−1) and maximum power density of 3746.77 W Kg−1 (at an energy density of 13.53 Wh Kg−1). The impressive results suggest that flexible PPy-NiCo2O4@CFPs can be a promising electrode material for supercapacitor applications.

Manganese dioxide (α-MnO2)/reduced graphene oxide (RGO) nanocomposite paper was synthesized using a 3D precursor manganese benzoate dihydrazinate for supercapacitor and sensor applications. The new 3D precursor and residue-free synthesis are the advantages of this method. Transmission electron microscopy showed that MnO2 nanorods with a mean diameter of

To enhance Pd electro-catalysts in their electro-catalytic activity for C-C bond breaking and tolerance stability, Pd was electrodeposited on high-porosity 3D reduced graphene oxide (rGO) aerogel paper. For comparison, the Pd was also coated on other three different carbon material surfaces: bare carbon fiber paper (CFP), and CFP modified with either 2D graphene oxide (GO) and 2D rGO nanosheets. The Pd/3D rGO aerogel paper exhibits higher catalytic activity toward the electro-oxidation of ethylene glycol in alkaline media and higher excellent tolerance stability than other electrodes due to ultra-high porosity of the 3D rGO support leading to high active electrochemical surface area of the as-fabricated Pd catalyst electrode. In addition, the hydrodynamic diffusion of ethylene glycol to the cayalyst surface investigated in this work plays a major role to the catalytic activity of the as-prepared electrocatalyst. The Pd/3D rGO aerogel rotating disk electrode exhibits a high anodic current density of 267.8 mA cm −2 at 3000 rpm. This high-performance Pd/3D rGO aerogel may be practically used as the high-efficiency anode of direct ethylene glycol and other related alcohol fuel cells.

The composite of manganese dioxide (MnO2) with high theoretical capacity (1230 mAh g−1) and carbon nanofiber paper with high electrical conductivity is attracting attention as a next-generation battery anode material. This study proposes a facile route for coating mesoporous MnO2 on the carbon fiber by low-temperature reduction of KMnO4 and intercalating graphene into the carbon paper through vacuum filtration. The MnO2 coated carbon nanofiber (MOCNF) is synthesized in the form of paper, while maintaining the flexibility and strength with graphene intercalated between MOCNF papers. The resulting paper is applied for the lithium ion battery anode without any current collector, binder and conductor. This free-standing electrode has a discharge capacity of 945 mAh g−1 at 100 mA g−1 and shows a high discharge capacity of 545 mAh g−1 at 1000 mA g−1 even after 1000 cycles. This stable cycle performance originates from the mesoporosity of MnO2 and the intercalation of graphene, which accelerates the kinetics of redox reaction and mitigates the electrochemical isolation of MnO2 from the carbon nanofibers. This paper-type material can be a next-generation battery anode with considerable flexibility and capacity. Furthermore, the facile method of MnO2 coating and graphene intercalation can be applied to the other electrode synthesis.

Most recently, aqueous zinc-ion batteries (AZIBs) are the research focus because of their low cost, high safety, and eco-friendliness. In this respect, flexible binder-free electrodes have been investigated by several studies to keep pace with the development of wearable electronics. However, the mass loading of active materials in these electrodes is usually below 2 mg cm−2, considerably limiting the areal capacity. Herein, we report a paper electrode prepared via a facile vacuum filtration technique with a high mass loading of 5 mg cm−2 for the active material, namely, reduced graphene oxide (rGO)/δ-NaxV2O5·nH2O nanocomposite. Thanks to the homogeneous distribution and synergistic effect of the active material, carbon nanotubes, and cellulose fibers, the electrode not only exhibits good mechanical property and high electrical conductivity but also displays impressive performances for AZIBs. It achieves an admirable areal specific capacity of 1.87 mAh cm−2 (corresponding to 374.9 mAh g−1 for the active material), substantially higher than that of other flexible binder-free electrodes for (hybrid) AZIBs. Meanwhile, this electrode also shows good rate capability and excellent long-term cyclability (with a capacity retention of 92% over 4000 cycles). This work opens new opportunities towards flexible free-standing electrodes.

A composite material of reduced graphene oxide (rGO) and Hong Kong University of Science and Technology-1 (HKUST-1) metal organic framework (MOF) was produced and used as the supercapacitor electrode material. Pure HKUST-1 has a microporous structure with poor conductivity limiting its electrochemical applications while loading rGO to HKUST-1 leads to a novel composite with a mesoporous structure and good electrochemical properties. 10 wt.% rGO/HKUST-1 has a high BET surface area of 1241 m 2 g −1 , a specific pore volume of 0.78 cm 3 g −1 , and an average pore diameter of 8.2 nm, which is a proper pore size to allow uptaking and releasing of electrolytes. A half-cell electrode of 10 wt.% rGO/HKUST-1 coated on flexible carbon fiber paper (CFP) exhibits a high specific capacitance of 385 F g −1 at 1 A g −1 while pure HKUST-1 stores only 0.5 F g −1 . A 1.8″ × 4.0″ symmetric solid-type supercapacitor of the 10 wt.%rGO/HKUST-1 exhibits a specific power of 3100 W kg −1 and a specific energy of 42 Wh kg −1 . The supercapacitor can practically supply electricity to a spinning 3-V motor over 9-min discharging time.

A novel strategy was reported for the preparation of TiO2 nanobelts by the acid-assisted hydrothermal method. Complex nanopaper based on the TiO2 nanobelts and graphene was fabricated via a modified paper-making process. The as-prepared TiO2–graphene structure inherited the excellent electron transport of graphene and facilitated the spatial separation of photo-generated charge carrier, therefore resulting in the enhanced photocurrent, and making it a promising candidate for developing photoelectrochemical (PEC) biosensors. Thus, an advanced PEC biosensing platform for the detection of carcinoembryonic antigen was proposed at relatively low applied potential on screen-printed working paper-electrode using the as-prepared TiO2–graphene complex nanopaper. The complex nanopaper with good biocompatibility showed high PEC intensity and satisfactory stability, all of which held great promise for the fabrication of PEC biosensors with improved sensitivity. Furthermore, the TiO2–graphene complex nanopaper based PEC biosensor in this study was anticipated to provide the chance for the design of high-performance PEC biosensors for the detection of other enzymes and biomolecules.

In this work, a sensitive microfluidic origami electrochemical immunodevice (denoted as μ-OECI in this work) has been developed, based on polyaniline-Au nanoparticles (AuNPs) modified paper working electrode (PANI/Au-PWE) as sensor platform and different redox substrates as tracers. Au-PWE was fabricated through the growth of an AuNPs layer on the surfaces of cellulose fibers in the PWE. Through electropolymerization of aniline in an Au-PWE, the effective surface area and the sensitivity of the PANI/Au-PWE were enhanced remarkably. 3D graphene sheets (GS) with high surface-to-volume reaction and good in-plane conductivity were used as matrices to immobilize the redox probes and antibodies. Each biorecognition event yielded a distinct voltammetric peak, whose position and size reflected the identity and level of the corresponding antigen. The large amount of redox probes on the 3D GS greatly amplified the detection signals, and the good biocompatibility of PANI/Au-PWE retained good stability for the sandwich-type immunoassay. Using carcinoembryonic antigen and α-fetoprotein as model analytes, the simultaneous multiplex immunoassay showed linear ranges of over 4 orders of magnitude with the detection limits down to 0.5 and 0.8 pg·mL−1, respectively. This facile biosensing μ-OECI exhibited high sensitivity and specificity, and it was applied in point-of-care testing of other cancer markers for remote regions and developing countries.

An approach as “hydroxylamine diffusion induced assembly” has been developed to fabricate N-doped graphene paper-like films (NG-P) and composite films containing multiwalled carbon nanotubes (NG-MWCNT-P). The obtained films have been characterized by using X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy and scanning electron microscopy. The results indicate that the N atoms have doped into the graphene sheets and the interplanar distance between the graphene sheets decreases with the increment of the thermally treated temperature. The films of NG-P prepared at 100 °C are flexible and exhibit a maximum tensile stress of about 70.5 MPa and a Young's modulus of about 17.7 GPa, and the films of NG-P thermally treated at 300 °C (NG-P300) have high thermal conductivity of about 3403 W m-1 K−1. However, the NG-MWCNT-P film exhibits a relatively weaker tensile stress compared with NG-P. The electrochemical measurements show that the NG-P300 possesses excellent ultrahigh-rate capacitive properties, and that the specific capacitance and the impedance phase angle of the capacitor can reach to about 318 μF cm−2 and -77.1° respectively at frequency of 120 Hz. Simple measurements on NG-MWCNT-P show that it has specific capacitance of about 90 F g−1 based on one electrode and the capacitor possesses the high-rate capability.

The development of low-cost, accurate and sensitive diagnostic tests is crucial to many clinical, laboratory, and field applications, including forensics and medical diagnostics. Cellulose fiber-based paper is an inexpensive, biodegradable, and renewable resource, the use of which as a diagnostic device confers several advantages compared to traditional substrate. In this work, wax printer was used to produce collapsible microfluidic paper-based analytical devices (μPADs), which were combined with screen-printed electrodes (SPEs) to create simple, low-cost, disposal devices in bulk. Herein, an electrochemical DNA sensor was introduced for the first time into a folding paper based on the AuNPs/graphene modified screen-printed working paper electrode (SPWPE). Thionine (TH) bound to double stranded DNA(dsDNA) as signal tags (TH/D1), together with Complementary ssDNA (S3) immobilized on Nanoporous gold (NPG) forming a S3-TH/D1-NPG bioconjugates. Owing to the chain structure of dsDNA and large specific surface area of NPG, the bioconjugates proved to be an excellent amplification label. Under optimal conditions, the folding μPADs DNA sensor showed high sensitivity, good precision, acceptable stability, reproducibility and excellent performance in human serum assay. In addition, the simple, low-cost, sensitive device can be easily applied for point-of-care testing (POCT), public health and environmental monitoring in remote regions, developing or developed countries.

Paper-like flexible electrode becomes one of the most important research objects in energy storage. In the present work, sandwich-structured S-doped reduced graphene oxide/carbon nanotubes/polyaniline (S-rGO/CNTs/PANI) composite membranes were designed as free-standing electrodes for high-performance supercapacitors, by electro-deposition of polyaniline (PANI) onto the flexible and robust sandwich structured S-doped reduced graphene oxide/carbon nanotubes (S-rGO/CNTs) composite films as highly conductive supports, which were prepared through a mild hydrothermal reduction and doping reaction of graphene oxide (GO) nanosheets in presence of multi-walled carbon nanotubes (MW-CNTs), with Na2S as not only a sulfur precursor, but also a high-efficient reducing agent. The S-rGO/CNTs/PANI composite membrane electrode possessed high specific capacitance (812 F/g) in 1.0 M H2SO4 aqueous solution, with excellent rate capability and cycling stability for supercapacitors without the need of current collectors and binders, showing significant potential in flexible energy storage devices. (C) 2017 Elsevier Ltd. All rights reserved.

A novel graphene/riboflavin (RF) composite electrode was developed and its potential application as microbial fuel cell (MFC) anode was demonstrated. Graphene layers were first grown on the surface of graphite electrode by a one-step in-situ electrochemical exfoliation approach. Then, noncovalent functionalization of the graphene layers with RF was achieved by a simple spontaneous adsorption process. The graphene/RF electrode was extensively characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, Raman analysis, and cyclic voltammetry analysis. Remarkably, when applied as the anode of Shewanella oneidensis MR-1 inoculated MFCs, the graphene/RF electrode significantly decreased charge transfer over-potential and enhanced cell attachment, which in turn delivered about 5.3- and 2.5-fold higher power output, when compared with that produced by the bare graphite paper electrode and graphene electrode, respectively. These results demonstrated that electron shuttle immobilization on the electrode surface could be a promising and practical strategy for improving the performance of microbial electrochemical systems.

A zeolitic imidazolate framework (ZIF)/graphene composite was prepared by the solvothermal reaction using different concentrations of graphene oxide to investigate the effect of graphene addition on the electroactivity of the composite. Field emission scanning electron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM), and X-ray diffraction (XRD) were conducted to determine the morphology and micro-structure of the composite. Electrochemical characterizations were measured using the CR2016 type coin cell test. Based on the electrochemical properties and structural characteristics of the composite, the roles and effects of graphene in ZIF/graphene composite were studied. The concentration of graphene oxide used during the synthesis process affect the initial specific capacity and cycle performance of the composite.

A novel, rapid, one-step electron-beam (EB) based method for both reduction of graphene oxide (GO) and co-doping of nitrogen and sulfur to prepare N, S-codoped graphene layers (NSG) has been achieved. This synthesis process relies on the interaction of high energy EB rays from an electron accelerator with the water in the aqueous solutions containing l -cysteine as the precursor of nitrogen and sulfur, leading to the generation of highly reducing species that not only reduce the GO to reduced graphene oxide (rGO), but also dope nitrogen and sulfur into graphene. The as-prepared heteroatom doped graphene materials own a better dual-doping and reduction of the GO. The range of nitrogen and sulfur doping content could achieve 4.88–10.88 at% and 2.08–4.59 at%, respectively. The sample prepared under the irradiation dose of 210 kGy (NSG-210) exhibits the highest specific capacitance of 227.94 F g −1 at a scan rate of 10 mV s −1 and stable cycling performance with a capacitance retention of 83% after 25,000 cycles at a current density of 10 A g −1 . These results exhibit an eco-friendly and simple design of electrode materials for high performance supercapacitors.

Much focus with regards to graphene oxide (GO) reduction has been on reducing the oxygen:carbon ratio with little focus on other associated chemical transformations. The current work presents an enlightening physical and chemical transformation study of reduced graphene oxide (RGO) samples with regards to use of ascorbic acid, hydrazine hydrate and sodium borohydride as reducing agents and their associated appropriateness in electrochemical capacitors. The physical and chemical characteristics of RGO were compared by means of elemental analysis, infra-red spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, powder X-ray diffraction, textural characteristics, scanning and transmission electron microscopies, electron impedance spectroscopy and cyclic voltammetry. Hydrazine hydrate was the most effective reducing agent with the highest nitrogen at.% (4.07), surface area of 390.55 m2 g−1 and was increased to 599.67 m2 g−1 upon thermal treatment at 750 °C. The nitrogen functionalities observed in pristine-GO, ascorbic acid and hydrazine hydrate reduced GO were sp3 N C, pyrrolic and pyridinic, respectively. Whereas sodium borohydride RGO were B-doped with at.% of 2.49 during the reduction reaction. The N-doped RGO samples were more effective in charge storage than B-doped counterparts (76-fold better) and pyrrolic-N-doped was more effective than pyridinic- N-doped-RGO (1.35 times better).

A 3D spray-dried micro/mesoporous LiFePO4/porous graphene oxide/C (denoted as SP-LFP/PGO/C) composite material is synthesized via a three-step process, i.e., hydrothermal process, carbon coating, and spray dry method in sequence. The 2D porous graphene oxide (denoted as PGO) material is first prepared through an activation method. The galvanostatic charge-discharge measurements of LFP composites without graphene oxide, with 1 wt% graphene oxide, and 1 wt% PGO are conducted in the potential range of 2–3.8 V at various rates (0.1–10C). It is revealed that the SP-LFP/PGO/C material shows the best performance among three samples. The discharge capacities of the SP-LFP/PGO/C composites are observed to 160, 152, 151, 149, 144, 139, 127 mAh g−1 at 0.1C, 0.2C, 0.5C, 1C, 3C, 5C and 10C rate. In particular, the discharge capacity of the SP-LFP/PGO/C composite with 1 wt% PGO is 107 mAh g−1 after 1000 cycles at a 10C rate, and its capacity retention is ca. 97%. It is due to the unique structural and geometrical feature of SP-LFP/PGO/C composite, there the diamond-like (rhombus) LFP nanoparticles are embedded in porous GO matrix which forming a porous three-dimensional network for fast electronic and ionic transport channels.

A narrow size distribution of graphene sheets is critical to there application. Although several strategies have been demonstrated to classify the polydispere graphene oxide (GO), a precursor of graphene sheets, into various specified monodisperse fractions, few reports have revealed the size separation of graphene sheets straightly. Herein, a straightforward and efficient approach for size separation of mechanically exfoliated graphene sheets is proposed. The original graphene sheets (S0) have been separated into two portions with smaller (S1) or larger (S2) lateral dimensions in a weak alkaline buffer via electrophoresis, based on the zeta potential of graphene colloid under different pH values. It was found that the electrophoresis velocities of graphene colloids increase when their diameters decrease. In this way, graphene sheets of different sizes and properties can be separated successfully. Further study on the as-separated components indicated that small-size graphene sheets (S1) display blue shift signals in both ultraviolet–visible and raman spectroscopy, as well as a distinct fluorescent compared with large-size (S2) and original ones (S0). As electrode materials, S2 had a faster charge transfer and higher specific capacitance than that of S1 and S0. The feasible and effective method provided in this work to classify mechanically exfoliated graphene sheets are potentially beneficial to the broad applications of graphene.