Interconnected Graphene Sheets Research Articles

Rapid photothermal reduction-derived Pt1.6Ni nanoalloys embedded in laser-induced graphene for hydrogen evolution reaction

Water electrolysis is one of the most intriguing technologies for hydrogen production because of its carbon-neutral nature, however the development of efficient electrocatalysts is required to improve the energy conversion efficiency of water splitting. In this study, we suggest a facile route for the fabrication of Pt1.6Ni nanoalloys on laser-induced graphene (Pt1.6Ni NAs/LIG) by the photothermal reduction using commercial CO2 laser which is irradiated on the surface of the LIG. The laser ablation process on the polyimide (PI) film resulted in porous and interconnected graphene sheets, while uniform nanoparticles with an average size of around 4.5 nm were decorated on their surface by the photothermal reduction effect. The overall process took only 60 s. Bonding structure investigation confirmed that PI film was successfully transformed into a graphene structure and the metal precursors were converted into bimetallic nanoalloy by using Raman spectroscopy and XPS, respectively. Electrochemical measurements for hydrogen evolution reaction discovered that the Pt1.6Ni NAs/LIG showed superior catalytic performance which required an overpotential of only 96 mV to achieve a current density of 10 mA cm−2. It exhibited superior catalytic activity compared to LIG (740 mV), Pt NPs/LIG (204 mV), and PtNi1.6 NAs/LIG (205 mV), as well as other previously reported catalysts at the same current density. Based on these results, the Pt1.6Ni NAs/LIG was employed for hydrogen gas collection and detection. The generated bubbles were collected separately from both electrodes, and their compositions with evolution rate were confirmed to be hydrogen using a commercial H2 sensor.

An Ultramicroporous Graphene-Based 3D Structure Derived from Cellulose-Based Biomass for High-Performance CO2 Capture.

The use of powered activated carbon is often limited by inconsistent particle sizes and porosities, leading to reduced adsorption efficiencies. In this study, we demonstrated a practical and environmentally friendly method for creating a 3D graphene nanostructure with highly uniform ultramicropores from wood-based biomass through a series of delignification, carbonization, and activation processes. In addition, we evaluated the capture characteristics of this structure for CO2, CH4, and N2 gases as well as its selectivity for binary-mixture gases. Based on textural and chemical analyses, the delignified monolith had a lamellar structure interconnected by cellulose-based fibers. Interestingly, applying the KOH vapor activation technique solely to the delignified samples led to the formation of a monolithic 3D network composed of interconnected graphene sheets with a high degree of crystallinity. Especially, the Act. 1000 sample exhibited a specific surface area of 1480 m2/g and a considerable pore volume of 0.581 cm3/g, featuring consistently uniform ultramicropores over 90% in the range of 3.5-11 Å. The monolithic graphene-based samples, predominantly composed of ultramicropores, demonstrated a notably heightened capture capacity of 6.934 mol/kg at 110 kPa for CO2, along with favorable selectivity within binary gas mixtures (CO2/N2, CO2/CH4, and CO2/CH4). Our findings suggest that this biomass-derived 3D structure has the potential to serve as a monolithic adsorbent in gas separation applications.

Nano-tablets and rods-shaped Fe and Ni oxide/hydroxide encapsulated graphene for asymmetric supercapacitor and OER applications

Ternary hybrid electrodes have been spotlighted in the energy storage and conversion domain due to their superior physicochemical and electrochemical attributes. Yet, elevating their electrochemical properties remains a challenge. Herein, gamma‑iron oxide nano-tablets and nickel hydroxide nano-rods encapsulated graphene sheets (γ-Fe2O3@Ni(OH)2@G/NF) nanocomposite (NC) electrodes are synthesized, using PVP as a surfactant by a simple, cost-effective and low-temperature synthesis procedure for supercapacitor (SC) and OER applications. These interconnected graphene sheets with γ-Fe2O3 and Ni(OH)2 are seen to enhance the electrical conductivity of NCs, leading to outstanding supercapacitive performances. The developed NC electrode displays the highest specific capacitance (Csp) of ∼937.5 F g−1 in the alkaline electrolyte. Moreover, Dunn's investigations, revealing the surface capacitive controlled contribution (77 %@10 mV s−1), predominates in the total capacitance, thus affirming the capacitor behavior of the electrodes. Using the NC electrode, an asymmetric supercapacitor (ASC) is constructed, and exhibits a maximum Csp of ∼120.3 F g−1 with an outstanding stability performance of 87.3 % capacitance retention. Moreover, the ASC displays an energy density of 22 Wh kg−1 under a power density of 1100 W kg−1. Overall, the results demonstrate that the developed ternary-hybrid composite shows promise as a worthy electrode for future energy demands.

A simplified electrophoretic deposition route for sandwiched structure-based Mn3O4/G composite electrodes as high-capacity anodes for lithium-ion batteries

Based on characteristic multielectron conversion reactions, transition-metal oxides are regarded as potential anode candidates for the new generation of lithium-ion batteries (LIBs) because they are endowed with high specific capacity. Nevertheless, the inferior electronic conductivity and larger volume change lead to fast capacity decay during cycling. Herein, we propose a novel electrophoretic deposition strategy to prepare binder-free Mn3O4/graphene hybrid electrodes and overcome these two obstacles simultaneously. In the rationally designed structure, Mn3O4 nanoparticles are well encapsulated in the conductive network constructed by interconnected graphene sheets. In the process of cycling, thanks to the excellent flexibility of graphene and the rich voids in this sandwiched structure, not only the structural integrity but also the unobstructed conductive network can be ensured. In addition, it is verified that electrode kinetics is a fast process for surface-controlled lithium storage. From this perspective, in addition to high reversible specific capacity (880 mAh g−1 at 0.1 A g−1), the prepared Mn3O4/graphene hybrid electrode possesses outstanding rate capability (678 mAh g−1 at 5 A g−1) and remarkable cycling stability (neglectable capacity decay after 500 cycles at 1 A g−1).

Conversion of silicon carbide fibers to continuous graphene fibers by vacuum annealing

Continuous graphene fibers (GFs) and graphene/SiC fibers (G/SiCFs) are fabricated from silicon carbide (SiC) fibers through vacuum annealing. The transformation gradually happens from the surface to the core of the fiber until complete conversion. Graphene sheets are in-situ formed after Si sublimation of 3C–SiC grains in the SiC fiber. Although porous structure is formed inevitably, the fiber shape is well maintained with circular cross section. The continuous GFs exhibit low density (1.63 g/cm3), excellent electric conductivity (53,900 S/m), high tensile strength (0.22 GPa) and elastic modulus (23 GPa, gauge length: 25 mm). Good properties can be probably attributed to interconnected graphene sheets. GFs have great electromagnetic interference shielding effectiveness of 62.8 dB, while G/SiCFs have outstanding microwave absorption properties. The minimum reflection loss (RL) value of −54.86 dB is achieved with sample thickness of 2.1 mm. When sample thickness is 1.4 mm, the effective absorption bandwidth of G/SiCFs can reach 4.4 GHz. Excellent flexibility is also possessed by a bundle of 1000 graphene filaments. Taking advantages of the facile conversion of silicon carbide fibers, the method demonstrated in this work can be further extended to prepare metal-containing GFs (Ti, Al, Zr, et.) and achieve large-scale production.

Electrochemically Derived Graphene‐Like Carbon Film as a Superb Substrate for High‐Performance Aqueous Zn‐Ion Batteries

Abstract3D graphene, as a light substrate for active loadings, is essential to achieve high energy density for aqueous Zn‐ion batteries, yet traditional synthesis routes are inefficient with high energy consumption. Reported here is a simplified procedure to transform the raw graphite paper directly into the graphene‐like carbon film (GCF). The electrochemically derived GCF contains a 2D–3D hybrid network with interconnected graphene sheets, and offers a highly porous structure. To realize high energy density, the Na:MnO2/GCF cathode and Zn/GCF anode are fabricated by electrochemical deposition. The GCF‐based Zn‐ion batteries deliver a high initial discharge capacity of 381.8 mA h g−1 at 100 mA g−1 and a reversible capacity of 188.0 mA h g−1 after 1000 cycles at 1000 mA g−1. Moreover, a recorded energy density of 511.9 Wh kg−1 is obtained at a power density of 137 W kg−1. The electrochemical kinetics measurement reveals the high capacitive contribution of the GCF and a co‐insertion/desertion mechanism of H+ and Zn2+ ions. First‐principles calculations are also carried out to investigate the effect of Na+ doping on the electrochemical performance of layered δ‐MnO2 cathodes. The results demonstrate the attractive potential of the GCF substrate in the application of the rechargeable batteries.

Enhanced dielectric permittivity and suppressed electrical conductivity in polyvinylidene fluoride nanocomposites filled with 4,4′-oxydiphenol-functionalized graphene

Plastic film capacitors suffer from low charge storage capacity due to the low dielectric constant of the polymer (<10). We have devised a polyvinylidene fluoride (PVDF) composite film filled with small graphene oxide (GO) sheets that have aromatic molecules attached to their surfaces. The use of 4,4′-oxydiphenol molecules to functionalize graphene sheets is found to have a remarkable effect on enhancing the dielectric permittivity as well as reducing the electrical conductivity of the nanocomposite. When under an electric field, these molecules with an angled molecular geometry act as aligned electric dipoles to largely enhance the dielectric permittivity of the composite, reaching a level two orders of magnitude higher than that of the counterpart filled with blank graphene sheets. Also, the aromatic molecules on the graphene surface act as resistive barriers that block charge transfer between interconnected graphene sheets. As a consequence, the electric conductivity of the composite can be decreased by two orders of magnitude. The PVDF composite filled with functionalized graphene shows a percolation threshold of 13 wt% and a high dielectric constant of 1091 at 100 Hz at this point.

Mechanochemical Reinforcement of Graphene Sheets into Alkyd Resin Matrix for the Development of Electrically Conductive Paints

AbstractIn this work, we are reporting the preparation of graphene‐based conductive paints using mechanochemically prepared graphene nanosheets as a conductive pigment and alkyd resin as the binder with non‐toxic additives. The surface morphology and intermolecular interactions between the graphene pigments and alkyd resin in the prepared graphene nanopaint are studied using field emission scanning electron microscope, X‐ray photoelectron spectroscopy, and Raman spectroscopic analysis, respectively. The formation of percolation pathways owing to the interconnected graphene sheets in the paint matrix resulted in an excellent conductive behavior of the as‐prepared graphene paint, thus ensuring its applications in conductive paint technology. Furthermore, Raman mapping analysis (including intensity maps and peak position maps) was used to understand the spatial distribution of graphene sheets in the alkyd resin matrix of the paint.

Self-supporting porous CoS2/rGO sulfur host prepared by bottom-up assembly for lithium-sulfur batteries

Cobalt disulfide (CoS2) has been revealed as strong adsorption and activation sites for polar polysulfides, which effectively accelerates the redox reactions of polysulfides in lithium-sulfur (Li-S) batteries. As an ideal sulfur host, a three-dimensional (3D) graphene framework is adopted for high-performance Li-S batteries. Considering the special function of the CoS2 nanoparticles and the advantages of a 3D porous graphene framework, a porous CoS2/reduced graphene oxide (CoS2/rGO) binder-free sulfur host is prepared by a bottom-up assembly and hydrothermal treatment. The porous rGO film is stacked by interconnected graphene sheets, and the CoS2 nanoparticles are dispersed on the graphene sheets uniformly, which effectively obstructs the stacking of graphene sheets. As a binder-free sulfur host, the porous CoS2/rGO sulfur host combines the sufficient electron conductivity of the porous rGO framework and the sulfur immobilization interaction of the CoS2 nanoparticles. This host material demonstrates an initial discharge capacity of 993.5 mAh g−1 and a capacity of 806.7 mAh g−1 after 110 cycles at 0.5 C. Both the capacity and cycling stability of the CoS2/rGO cathode were greatly improved over that of rGO. Furthermore, the bottom-up assembly approach provides a novel opportunity for preparing self-supporting graphene-based nanocomposite electrodes.

Atomistic and Coarse-Grained Modeling of the Adsorption of Graphene Nanoflakes at the Oil-Water Interface.

The high interfacial tension between two immiscible liquids can provide the necessary driving force for the self-assembly of nanoparticles at the interface. Particularly, the interface between water and oily liquids (hydrocarbon chains) has been exploited to prepare networks of highly interconnected graphene sheets of only a few layers thickness, which are well suited for industrial applications. Studying such complex systems through particle-based simulations could greatly enhance the understanding of the various driving forces in action and could possibly give more control over the self-assembly process. However, the interaction potentials used in particle-based simulations are typically derived by reproducing bulk properties and are therefore not suitable for describing systems dominated by interfaces. To address this issue, we introduce a methodology to derive solid-liquid interaction potentials that yield an accurate representation of the balance between interfacial interactions at atomistic and coarse-grained resolutions. Our approach is validated through its ability to lead to the adsorption of graphene nanoflakes at the interface between water and n-hexane. The development of accurate coarse-grained potentials that our approach enables will allow us to perform large-scale simulations to study the assembly of graphene nanoparticles at the interface between immiscible liquids. Our methodology is illustrated through a simulation of many graphene nanoflakes adsorbing at the interface.

Template-free fabrication of graphene-wrapped mesoporous ZnMn2O4 nanorings as anode materials for lithium-ion batteries

We rationally designed a facile two-step approach to synthesize ZnMn2O4@G composite anode material for lithium-ion batteries (LIBs), involving a template-free fabrication of ZnMn2O4 nanorings and subsequent coating of graphene sheets. Notably, it is the first time that ring-like ZnMn2O4 nanostructure is reported. Moreover, our system has been demonstrated to be quite powerful in producing ZnMn2O4 nanorings regardless of the types of Zn and Mn-containing metal salts reactants. The well-known inside-out Ostwald ripening process is tentatively proposed to clarify the formation mechanism of the hollow nanorings. When evaluated as anode material for LIBs, the resulting ZnMn2O4@G hybrid displays significantly improved lithium-storage performance with high specific capacity, good rate capability, and excellent cyclability. After 500 cycles, the ZnMn2O4@G hybrid can still deliver a reversible capacity of 958 mAh g−1 at a current density of 200 mA g−1, much higher than the theoretical capacity of 784 mAh g−1 for pure ZnMn2O4. The outstanding electrochemical performance should be reasonably ascribed to the synergistic interaction between hollow and porous ZnMn2O4 nanorings and the three-dimensional interconnected graphene sheets.

Unique interconnected graphene/SnO2 nanoparticle spherical multilayers for lithium-ion battery applications.

We have designed and synthesized a unique structured graphene/SnO2 composite, where SnO2 nanoparticles are inserted in between interconnected graphene sheets which form hollow spherical multilayers. The hollow spherical multilayered structure provides much flexibility to accommodate the configuration and volume changes of SnO2 in the material. When it is used as an anode material for lithium-ion batteries, such a novel nanostructure can not only provide a stable conductive matrix and suppress the mechanical stress, but also eliminate the need of any binders for constructing electrodes. Electrochemical tests show that the unique graphene/SnO2 composite electrode as designed could exhibit a large reversible capacity over 1000 mA h g-1 and long cycling life with 88% retention after 100 cycles. These results indicate the great potential of the composite for being used as a high performance anode material for lithium-ion batteries.

Confined synthesis of graphene wrapped LiMn0.5Fe0.5PO4 composite via two step solution phase method as high performance cathode for Li-ion batteries

A novel strategy for confined synthesis of graphene wrapped nano-sized LiMn0.5Fe0.5PO4 hybrid composite has been developed, including co-precipitation and solvothermal reactions. The LiMn0.5Fe0.5PO4 nanoparticles with a constrained diameter of 20 nm are homogeneously wrapped by a continuous interconnected graphene sheets. The mechanism and composite structure evolution during the process are carefully investigated and discussed. With the shortened Li+ diffusion paths and enhanced electron conductivity, the hybrid composite shows high discharge capacity and superior rate performance with the discharge capacities of 166 mA h g−1 at 0.1 C and 90 mA h g−1 at 20 C. Excellent cycle stability is also demonstrated with only about 7.8% capacity decay after 500 cycles at 1 C.

Ultrahigh Performance of Novel Capacitive Deionization Electrodes based on A Three-Dimensional Graphene Architecture with Nanopores.

In order to achieve optimal desalination during capacitive deionization (CDI), CDI electrodes should possess high electrical conductivity, large surface area, good wettability to water, narrow pore size distribution and efficient pathways for ion and electron transportation. In this work, we fabricated a novel CDI electrode based on a three-dimensional graphene (3DG) architecture by constructing interconnected graphene sheets with in-plane nanopores (NP-3DG). As compared to 3DG, NP-3DG features a larger specific surface area of 445 m2 g−1 and therefore the higher specific capacitance. The ultrahigh electrosorptive capacity of NP-3DG predicted from Langmuir isotherm is 17.1 mg g−1 at a cell potential of 1.6 V. This can be attributed to the interconnected macropores within the graphene networks and nanopores on graphene sheets. Both of macropores and nanopores are favorable for enhancing CDI peroformance by buffering ions to reduce the diffusion distances from the external electrolyte to the interior surfaces and enlarging the surface area.

Solar-thermal conversion and thermal energy storage of graphene foam-based composites.

Among various utilizations of solar energy, solar-thermal conversion has recently gained renewed research interest due to its extremely high energy efficiency. However, one limiting factor common to all solar-based energy conversion technologies is the intermittent nature of solar irradiation, which makes them unable to stand-alone to satisfy the continuous energy need. Herein, we report a three-dimensional (3D) graphene foam and phase change material (PCM) composite for the seamlessly combined solar-thermal conversion and thermal storage for sustained energy release. The composite is obtained by infiltrating the 3D graphene foam with a commonly used PCM, paraffin wax. The high macroporosity and low density of the graphene foam allow for high weight fraction of the PCM to be incorporated, which enhances the heat storage capacity of the composite. The interconnected graphene sheets in the composite provide (1) the solar-thermal conversion capability, (2) high thermal conductivity and (3) form stability of the composite. Under light irradiation, the composite effectively collects and converts the light energy into thermal energy, and the converted thermal energy is stored in the PCM and released in an elongated period of time for sustained utilization. This study provides a promising route for sustainable utilization of solar energy.

One-pot self-assembly of graphene/carbon nanotube/sulfur hybrid with three dimensionally interconnected structure for lithium–sulfur batteries

A graphene/carbon nanotube (CNT)/sulfur (denoted GCS) hybrid with interconnected structure is prepared through a one-pot self-assembly approach initiated by l-ascorbic acid reduction under a mild condition. In such a solution-based assembly process, the formation of an interconnected graphene/CNT conductive network is accompanied by the uniform loading of sulfur, whose fraction is as high as of 70 wt%. The as-prepared GCS hybrid delivers an initial capacity of 1008 mAh g−1 at 0.3C and maintains 704 mAh g−1 after 100 cycles. Remarkably, at a high rate of 1.0C, the cathode shows an excellent cyclic performance with a capacity of 657 mAh g−1 after 450 ycles and the capacity decay is only 0.04% per cycle. Moreover, the superior rate performance of GCS hybrid is attributed to the conductive network formed by interconnected graphene sheets and CNT, which supply an unimpeded and continuous path for electron and Li ion transfer and accommodate the volume variation of sulfur during charge/discharge cycling. In addition, the residual functional groups on GCS can retain intimate contact of the conducting matrix with sulfur and effectively confine the diffusion of polysulfides. This study gives an eco-friendly and highly effective solution-based approach for carbon–sulfur electrode for lithium–sulfur battery.

Microspherical polyaniline/graphene nanocomposites for high performance supercapacitors

Polyaniline/graphene nanocomposites with microspherical morphology and porous structure are prepared as electrode materials for supercapacitors. Using few-layer graphene obtained by liquid phase exfoliation of graphite as the raw material, porous graphene microspheres are produced by spray drying, and are then employed as the substrates for the growth of polyaniline nanowire arrays by in situ polymerization. In the composite, interconnected graphene sheets with few structural defects constitute a high-efficient conductive network to improve the electrical conductivity of polyaniline. Furthermore, the microspherical architecture prevents restacking of polyaniline/graphene composite nanosheets, thus facilitates fast diffusion of electrolytes. Consequently, the nanocomposite exhibits excellent electrochemical performance. A specific capacitance of 338 F g−1 is reached in 1 M H2SO4 at a scan rate of 20 mV s−1, and a high capacity retention rate of 87.4% after 10,000 cycles at a current density of 3 A g−1 can be achieved, which suggests that the polyaniline/graphene composite with such kind of 3D architecture is a promising electrode material for high-performance supercapacitors.

Preparation of MoS2‐Coated Three‐Dimensional Graphene Networks for High‐Performance Anode Material in Lithium‐Ion Batteries

A novel composite, MoS2 -coated three-dimensional graphene network (3DGN), referred to as MoS2 /3DGN, is synthesized by a facile CVD method. The 3DGN, composed of interconnected graphene sheets, not only serves as template for the deposition of MoS2 , but also provides good electrical contact between the current collector and deposited MoS2 . As a proof of concept, the MoS2 /3DGN composite, used as an anode material for lithium-ion batteries, shows excellent electrochemical performance, which exhibits reversible capacities of 877 and 665 mAh g(-1) during the 50(th) cycle at current densities of 100 and 500 mA g(-1) , respectively, indicating its good cycling performance. Furthermore, the MoS2 /3DGN composite also shows excellent high-current-density performance, e.g., depicts a 10(th) -cycle capacity of 466 mAh g(-1) at a high current density of 4 A g(-1).