Vertical Graphene Sheets Research Articles

Laser-Induced Vertical Graphene Nanosheets for Electrocatalytic Hydrogen Evolution.

Efficient and affordable electrocatalysts are fundamental for the sustainable production of hydrogen from water electrolysis. Here, an approach for the rapid production of laser-induced vertical graphene nanosheets (LIVGNs) through the exfoliation of the graphite foil under laser irradiation is presented. The density of the formed LIVGNs is ∼3 per 100 μm2. On leveraging the inherent flexibility and conductivity of the graphite foil substrate, the resulting LIVGNs exhibit a 2.2-fold increase in capacitance, making them promising candidates for electrode applications. The laser-induced surface reconstruction introduces abundant sharp edges to the LIVGNs, enhancing their electrocatalytic potential for hydrogen evolution. In electrocatalytic hydrogen evolution tests in acidic media, the LIVGNs demonstrate superior performance with a remarkable decrease in the required overpotential at 10 mA cm-2, from -555 mV for the pristine graphite foil to -348 mV for LIVGNs. This improvement is attributed to the active sites provided by the sharp edges, facilitating hydrogen species adsorption. Furthermore, the hydrophilic behavior of LIVGNs is enhanced through the anchoring of oxygen-containing groups, promoting the rapid release of the produced hydrogen bubbles. Importantly, the modified LIVGN electrode exhibits long-term stability across a wide range of current densities during chronoamperometry tests. This research introduces a transformative strategy for the efficient preparation of vertical graphene sheets on conductive graphite foils, showcasing their potential applications in electrocatalysis and energy storage.

Vertical graphene-decorated carbon nanofibers establishing robust conductive networks for fiber-based stretchable strain sensors

Stretchable strain sensors have great potential for diverse applications including human motion detection, soft robotics, and health monitoring. However, their practical implementation requires improved repeatability and stability along with high sensing performances. Here, we utilized spiky vertical graphene (VG) sheets decorated on carbon nanofibers (VG@CNFs) to establish reliable conductive networks for resistive strain sensing. Three-dimensional (3D) VG@CNFs combined with reduced graphene oxide (rGO) sheets were simply coated on stretchable spandex fibers by ultrasonication. Because of the spiky geometry of the VG sheets, VG@CNF and rGO exhibited enhanced interactions, which was confirmed by mode I fracture tests. Due to the robust conductive networks formed by the VG@CNF and rGO hybrid, the fiber strain sensor exhibited a significantly improved strain range of up to 522% (with a high gauge factor of 1358) and stable resistance changes with minimal variation even after 5000 stretching–releasing cycles under a strain of 50%. In addition, the textile strain sensor based on the VG@CNF/rGO hybrid showed even improved repeatability for various strain levels of 10% to 200%, enabling its implementation on leggings for monitoring of squat posture. This study demonstrates the high potential of the 3D VG@CNF for high-performance and reliable stretchable strain sensors.

Growth of Vertical Graphene Sheets on Silicon Nanoparticles Well-Dispersed on Graphite Particles for High-Performance Lithium-Ion Battery Anode.

With rapidly increasing demand for high energy density, silicon (Si) is greatly expected to play an important role as the anode material of lithium-ion batteries (LIBs) due to its high specific capacity. However, large volume expansion for silicon during the charging process is still a serious problem influencing its cycling stability. Here, a Si/C composite of vertical graphene sheets/silicon/carbon/graphite (VGSs@Si/C/G) is reported to address the electrochemical stability issues of Si/graphite anodes, which is prepared by adhering Si nanoparticles on graphite particles with chitosan and then in situ growing VGSs by thermal chemical vapor deposition. As a promising anode material, due to the buffering effect of VGSs and tight bonding between Si and graphite particles, the composite delivers a high reversible capacity of 782.2mAhg-1 after 1000 cycles with an initial coulombic efficiency of 87.2%. Furthermore, the VGSs@Si/C/G shows a diffusion coefficient of two orders higher than that without growing the VGSs. The full battery using VGSs@Si/C/G anode and LiNi0.8Co0.1Mn0.1O2 cathode achieves a high gravimetric energy density of 343.6Whkg-1, a high capacity retention of 91.5% after 500 cycles and an excellent average CE of 99.9%.

Electrochemically exfoliated graphene-graphite architecture with MnO2 for redox pseudocapacitive process

An electrochemical exfoliation-deposition strategy is provided to fabricate the MnO2-based electrode. After the efficient exfoliation in MnSO4 electrolyte, the stacked graphite expands into open structure, with vertical graphene sheets strongly bonded on the surface. This unique architecture not only provides sufficient surface areas for the anchoring of oxygen vacancy-enriched MnO2, but also ensures transportation pathways for the charge transfer and electrolyte ions diffusion. Thus, the resultant electrode exhibits an areal specific capacitance of 447.5 mF cm−2 at 0.5 mA cm−2 and promising cycling stability. It outperforms the analogues exfoliated in another Mn-based electrolyte because of the anion effect. In situ Raman spectra are taken to reveal the structural evolutions of the resultant electrode coupled with Na+ ions insertion-extraction behaviors in the redox pseudocapacitive process.

Surface functionalization of vertical graphene significantly enhances the energy storage capability for symmetric supercapacitors

Vertical graphene (VG) sheets, which consist of few-layer graphene vertically aligned on the substrate with three-dimensionally interconnected porous network, make them become one of the most promising energy storage electrodes, especially for SCs. Nevertheless, the intrinsic hydrophobic nature of pristine VG sheets severely limited its application in aqueous SCs. Here, electrochemical oxidation strategy is adopted to increase the hydrophilicity of VG sheets by introducing oxygen functional groups so that the aqueous electrolyte can fully be in contact with the VG sheets to improve charge storage performance. Our work demonstrated that the introduction of oxygen functional groups not only greatly improved the hydrophilicity but also generated a pseudocapacitance to increase the specific capacitance. The resulting capacitance of electrochemically oxidized VG for 7 min (denoted as EOVG-7) exhibited three orders of magnitude higher (1605 mF/cm2) compared to pristine VG sheets. Through assembled two EOVG-7 electrodes, a symmetric supercapacitor demonstrated high specific capacitance of 307.5 mF/cm2, high energy density of 138.3 μWh/cm2 as well as excellent cyclic stability (84% capacitance retention after 10000 cycles). This strategy provides a promising way for designing and engineering carbon-based aqueous supercapacitors with high performance.

Multilevel carbon architecture of subnanoscopic silicon for fast‐charging high‐energy‐density lithium‐ion batteries

AbstractSilicon (Si) is widely used as a lithium‐ion‐battery anode owing to its high capacity and abundant crustal reserves. However, large volume change upon cycling and poor conductivity of Si cause rapid capacity decay and poor fast‐charging capability limiting its commercial applications. Here, we propose a multilevel carbon architecture with vertical graphene sheets (VGSs) grown on surfaces of subnanoscopically and homogeneously dispersed Si–C composite nanospheres, which are subsequently embedded into a carbon matrix (C/VGSs@Si–C). Subnanoscopic C in the Si–C nanospheres, VGSs, and carbon matrix form a three‐dimensional conductive and robust network, which significantly improves the conductivity and suppresses the volume expansion of Si, thereby boosting charge transport and improving electrode stability. The VGSs with vast exposed edges considerably increase the contact area with the carbon matrix and supply directional transport channels through the entire material, which boosts charge transport. The carbon matrix encapsulates VGSs@Si–C to decrease the specific surface area and increase tap density, thus yielding high first Coulombic efficiency and electrode compaction density. Consequently, C/VGSs@Si–C delivers excellent Li‐ion storage performances under industrial electrode conditions. In particular, the full cells show high energy densities of 603.5 Wh kg−1 and 1685.5 Wh L−1 at 0.1 C and maintain 80.7% of the energy density at 3 C.

Hierarchically structured electrode materials derived from metal-organic framework/vertical graphene composite for high-performance flexible asymmetric supercapacitors

Low conductivity of metal-organic frameworks limits their applications in electrochemical energy storage and conversion. To overcome this shortcoming, we synthesized the zeolitic imidazolate framework-67 on the vertical graphene (VG) surface with abundant defects grown on carbon cloth (ZIF-67-VG-CC). Based on “one-for-two” strategy, the Co3O4 nanoparticles (Co3O4-VG-CC) and nanoporous carbon (NC-VG-CC) can be derived from ZIF-67-VG-CC via selective pyrolysis in the controlled atmospheres. In the hierarchically structured Co3O4-VG-CC and NC-VG-CC, the Co3O4 nanoparticles with a size of 20 nm and N-doped porous carbons were uniformly dispersed on the VG surface, as confirmed by electron microscopies. Both the Co3O4-VG-CC and NC-VG-CC yield high specific capacitance and excellent rate capability. After assembling these two electrodes to make an asymmetric supercapacitor, the Co3O4-VG-CC//NC-VG-CC delivered a maximum energy density of 43.75 Wh/kg at a power density of 5.2 kW/kg as well as excellent cycling stability with 91.5 % specific capacitance retained after 20,000 charge-discharge cycles. All these results should be ascribed to that the VG sheets possess their high electrical conductivity and 3D network structure, and provide the hierarchical supports for the uniform distribution of the ZIF-67-dervied Co3O4 nanoparticles and NC materials, which are beneficial to the fast electron and ion transfer in the electrodes.

Si-C nanocomposites supported on vertical graphene sheets grown on graphite for fast-charging lithium ion batteries

Silicon/carbon (Si/C) anodes have been successfully used in commercial lithium-ion batteries because of their high capacity and excellent safety. Nevertheless, their cycling stability and fast-charging capability are still unsatisfactory due to large volume expansion and slow charge transport capability under industrial electrode conditions. Here, we fabricate a Si/C anode via homogeneously depositing amorphous SiC nanolayers on graphite armored with N-doped porous flexible vertical graphene sheets (VGSs) (named as Si-C/VGSs/graphite). SiC nanolayers consist of homogeneously dispersed sub-nanometer Si particles in 3D carbon skeleton, which effectively alleviate the volume change of Si, and hugely accelerate electron and Li-ion transport. The N-doped VGSs possess porous structure, good flexibility, numerous exposed edges, and directional ion transport channels, which provide rational space for accommodating volume change of Si, buffer the stress caused by the volume change, increase the electrical contact points between Si-C/VGSs/graphite, and accelerate Li-ion transport, respectively. Consequently, Si-C/VGSs/graphite delivers superior rate capacity and long cycle life under industrial electrode conditions. When matched with the cathode of Li[Ni0.8Co0.1Mn0.1]O2, the full cell demonstrates a predominant fast-charging capability (180.8 Wh kg−1, charging for 8.2 min, 5C) accompanied by long cycle life.

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Vertical graphene on rice-husk-derived SiC/C composite for highly selective photocatalytic CO2 reduction into CO

Coupling graphene-based materials with SiC nanostructures is one of the most feasible strategies to improve the photocatalytic CO2 reduction performance. Here, we synthesized the vertical graphene (VG) sheets on the SiC nanowires achieved from rice husks to form the VG@SiC/C composite, in which the VG sheets possess high surface area, excellent electrical conductivity, and chemical stability, and the SiC nanowires have a suitable bandgap for sunlight absorption. The resulting VG@SiC/C composite provides an enhanced photocatalytic reduction of CO2 to CO and CH4, yielding CO and CH4 evolution yields of 25.5 and 2.3 μmol g−1 h−1, respectively. The achieved CO yield is maximal so far among the SiC-based photocatalysts. The defective VG sheets promote the absorption of sunlight, enhance the CO2 adsorption and activation, increase the separation of photogenerated electron-hole pairs, improve the activity of photocatalyst, and thereby prompt the photocatalytic reduction of CO2 to CO with high yield and selectivity.

Simultaneous solar-driven seawater desalination and continuous oil recovery

Oil spills and freshwater scarcity remain two worldwide challenging issues. Emerging efforts have been made either to recover oil from oil/water mixture or to extract freshwater from abundant seawater. However, almost all current devices focus on oil recovery or seawater desalination separately, which is lack of energy efficiency. Herein, we propose a design of mechanically robust, bi-functional graphene devices (BGDs), containing vertical graphene sheets decorated on inverted U-shaped graphene monoliths, to achieve simultaneous solar-driven vapor generation and continuous oil recovery from oil-contaminated seawater. Benefiting from the unique wettability design of the BGDs, water evaporates on the hydrophilic surfaces, and meanwhile oil can be spontaneously recovered through the hydrophobic/oleophilic interior channels due to siphon action. Moreover, the strong photothermal effect of vertical graphene can boost both the seawater desalination and oil recovery performance. As a result, a vapor generation rate of 2.04 kg m−2 h−1 and an oil recovery rate of 105.8 L m−2 h−1 are concurrently achieved under 1-sun irradiation. The design of bi-functional devices provides a new means to maximize the utilization of solar power and reduce the costs for multi-functional practical environmental engineering applications.

Effect of nitrogen doping on the structure and electrochemical properties of vertical graphene sheets prepared by HWP-CVD

3D nitrogen-doped vertically-oriented graphene nanosheets (3D N/VGs) were controllably prepared by helicon wave plasma chemical vapor deposition (HWP-CVD) employing argon, methane, and nitrogen by varying the N2 flow rate (RN2) without any catalyst and substrate heating during the growth. The effect of plasma gas phase species on the growth structure of N/VGs thin films was studied. The influence of nitrogen doping content on the structure and properties of VGs was analyzed. A growth model for the preparation of N/VGs by HWP-CVD was proposed. The results show that the elevated doping content of nitrogen atoms promotes enhanced CH4 dissociation and access to more H atoms, leading to an elevated nanosheet number density and a reduced growth rate. More excited N atoms could be embedded into the C vacancy to replace the missing C atom and restore the hexagonal network and increasing the nitrogen content. N/VGs with lower defect densities obtained with enhanced doping of nitrogen. The effective average distance between defects increases with nitrogen content, and the tunneling phenomenon is apparent, increasing resistance. Electrochemical performance tests showed that VGs with high nitrogen atomic content have higher specific capacitance and rate performance, up to 1340 μF/cm2 and 91.7%, respectively.

Superelastic, Highly Conductive, Superhydrophobic, and Powerful Electromagnetic Shielding Hybrid Aerogels Built from Orthogonal Graphene and Boron Nitride Nanoribbons.

Three-dimensional (3D) elastic aerogels enable diverse applications but are usually restricted by their low thermal and electrical transfer efficiency. Here, we demonstrate a strategy for fabricating the highly thermally and electrically conductive aerogels using hybrid carbon/ceramic structural units made of hexagonal boron nitride nanoribbons (BNNRs) with in situ-grown orthogonally structured graphene (OSG). High-aspect-ratio BNNRs are first interconnected into a 3D elastic and thermally conductive skeleton, in which the horizontal graphene layers of OSG provide additional hyperchannels for electron and phonon conduction, and the vertical graphene sheets of OSG greatly improve surface roughness and charge polarization ability of the entire skeleton. The resulting OSG/BNNR hybrid aerogel exhibits very high thermal and electrical conductivity (up to 7.84 W m-1 K-1 and 340 S m-1, respectively) at a low density of 45.8 mg cm-3, which should prove to be vastly advantageous as compared to the reported carbonic and/or ceramic aerogels. Moreover, the hybrid aerogel possesses integrated properties of wide temperature-invariant superelasticity (from -196 to 600 °C), low-voltage-driven Joule heating (up to 42-134 °C at 1-4 V), strong hydrophobicity (contact angel of up to 156.1°), and powerful broadband electromagnetic interference (EMI) shielding effectiveness (reaching 70.9 dB at 2 mm thickness), all of which can maintain very well under repeated mechanical deformations and long-term immersion in strong acid or alkali solution. Using these extraordinary comprehensive properties, we prove the great potential of OSG/BNNR hybrid aerogel in wearable electronics for regulating body temperature, proofing water and pollution, removing ice, and protecting human health against EMI.

Ultrahigh mechanical robustness of vertical graphene sheets covalently bonded to diamond

Vertical graphene sheets (VGs), covalently bonded to diamond substrate, can exhibit ultra-high mechanical robustness against scratching, friction, and compression. In this study, AFM tests with a diamond probe were preformed to investigate the interfacial mechanical properties of VGs film fabricated on diamond substrate. The unique bonding structure between VGs and diamond, featured with an ultra-strong C–C covalent bonds, effectively inhibited VGs being uprooted from diamond substrate even under a contact pressure as high as 53.7 GPa. Despite the inevitable breakage of graphene sheets under a contact pressure exceeds 25 GPa, the fractured graphene sheets residuals, which retain their covalent bonds to diamond substrate, could still act as a mechanically robust VGs film. Furthermore, in a long-duration AFM friction test, the VGs exhibited a highly stabilized coefficient of friction around 0.03 and a nearly ignorable specific wear rate as low as 2.0 × 10−4 mm3/Nm. Due to the relative slipping between adjacent graphene sheets was inhibited by the interfacial covalent C–C bonds between VGs and diamond substrate, the compressed VGs film transformed into a scale-like structure that consist of compactly stacked graphene sheets with a certain concentration of sp3 bonds (up to 8%) forming inside. This structure, characterized with extremely high elastic modulus and compressive strength, substantially attributed to the ultrahigh stability and sustainability exhibited by VGs upon friction and compression. The findings presented here is expected to boost utilizations of VGs and diamond combined in electronics, optical, mechanical, and tribological fields.

Porous composites of vertical graphene sheets and Fe3O4 nanorods grown on Fe/Fe3C particle embedded graphene-structured carbon walls for highly efficient microwave absorption

It is significantly important but remains challenging to prepare high performance microwave absorption materials in civil and military fields. Here, the Fe/Fe3C particles embedded in graphene-structured porous carbon (FGPC) served as a three-dimensional framework is prepared by simple carbothermal reduction, then vertical graphene nanosheets (VGSs) and Fe3O4 nanorods are successively grown on FGPC (FGPC/VGSs and FGPC/VGSs/Fe3O4) by thermal chemical vapor deposition, solution method, and subsequent heat treatment. As for comparison, VGSs and Fe3O4 nanorods grown on GPC without Fe/Fe3C particles (GPC/VGSs and GPC/VGSs/Fe3O4) are also prepared. The microwave absorption properties of them are investigated. Benefiting from the multi-component integration and well-designed structure, the FGPC/VGSs/Fe3O4 exhibits impressive microwave absorption performance with an optimal reflection loss of −64.7 dB at 15.3 GHz, a matching thickness of 1.7 mm, filler loading of 12 wt%, and effective absorption bandwidth of over 4.8 GHz. This results from the balance of impedance match and attenuation capability. In detail, the introduction of magnetic particles and nanorods improves the impedance match. The multiple reflections and scatterings, moderate conductive loss and magnetic loss enhance the attenuation of microwaves. Thus, this work might open an avenue to design a highly efficient and lightweight multi-dimensional multiple component microwave absorbers.

Preparation and electrochemical properties of nano-diamond/vertical graphene composite three-dimensional electrodes

Diamond/graphene composite three-dimensional electrode has attracted extensive attention because of its low background current, wide potential window from diamond component, and high electrochemical activity from graphite component. In this work, by using the hot wire chemical vapor deposition method, nano diamonds are embedded in the vertical graphene sheet on the surface of single particle layer of nano diamond by regulating the short-term growth time to form a composite three-dimensional electrode. The results show that the electrode exhibits a wide potential window (3.59 V) and a very low background current (1.27 mA/cm<sup>2</sup>) when nano-diamond crystals grow on the top of the vertical graphene sheet. The composite structure of nano-diamond crystals coated with graphite on the top of the graphene sheet is the key to broadening the potential window and reducing the background current. With the increase of growth time, the vertical graphene sheet grows and nano-diamond grains are embedded into the lamellae, and a novel nano-diamond/graphene composite vertical lamellae structure is constructed. The ordered graphite structure increases the electrochemical active area to 677.19 μC/cm<sup>2</sup> and the specific capacitance to 627.34 μF/cm<sup>2</sup>. The increase of graphite components makes the potential window narrow, and the embedded nano-diamond crystals effectively reduce the background current. This study provides a new method for preparing three-dimensional nanodiamond/graphene composite electrodes by hot wire chemical vapor deposition, and provides a new idea for fully exploiting the synergistic effect of diamond/graphene composite films.

Enhanced lubricity of CVD diamond films by in-situ synthetization of top-layered graphene sheets

In the present study, we demonstrated a novel process of in-situ fabrication of graphene sheets by adopting the chemical vapor deposition (CVD) method. Fabricating such a layer of vertical graphene sheets (VGs) on the surface of microcrystalline diamond (MCD) films could decrease the stable coefficient of friction (COF) by 20–30%. Besides, such lubricity showed excellent load capacity and durability. With normal loads ranging from 3 N to 9 N (Hertz contact pressure of 2.1–3.1 GPa), the MCD-VGs films exhibited COFs stabilized at 0.105 and wear rates less than 5 × 10−6 mm3 N−1 m−1. Additionally, the produced VGs displayed an excellent service lifetime with 72,000 sliding cycles. During the friction tests, an equilibrium graphene self-mated contact formed on the sliding interface as graphene fragments adhered onto the counterpart ball and resulted in the reduction of friction and low wear rates. Additionally, the mixtures of Si3N4/SiO2 particles and graphene sheets residual within the wear tracks would promote the transformation of the sliding regime to three-body abrasion, beneficial for friction reduction. The findings presented in this study provide a novel and effective approach to enhance the lubricity of any engineering diamond surface.

High yield production of 3D graphene powders by thermal chemical vapor deposition and application as highly efficient conductive additive of lithium ion battery electrodes

With respect to the application of powdered graphene sheets, agglomeration is a troublesome problem. Another problem is that the conventional production method generates a huge amount of harmful wastewater, which brings about unbearable environmental and cost problems. It is thus of great significance to explore novel structure and massive production methods of powdered graphene. Here, we report growth of vertical graphene sheets (VGSs) on carbon black (CB) by thermal chemical vapor deposition, which forms a novel three-dimensional graphene powders (3DGPs). High yield growth of the VGSs at kilograms scale is achieved by increasing the substrate area. As a demonstration, the 3DGPs are used as conductive additive of lithium ion battery electrodes, which show excellent electrochemical performance. The rate performance of LiFePO4 electrode with 1.0 wt% 3DGPs is even better than that with 10.0 wt% CB measured in half-cells. The soft-pack full cells assembled using commercial LiFePO4 and graphite electrodes with 1.3 wt% 3DGPs possess 542.8 mAh with 93.3% retention after 400 cycles at 0.2C, and 85.4% retention after 1000 cycles at 1C. The novel 3DGPs also hold high promise in many other applications such as various composite materials, coatings, and electrochemical electrodes.

Growing vertical graphene sheets on natural graphite for fast charging lithium-ion batteries

A goal of extreme fast charging less than 15 min recharge time while maintaining high energy density has been pursued to meet fast-charging and high-energy-density demand on lithium ion batteries used in electric vehicles, which is still a challenge. Here, in order to realize the goal vertical graphene sheets are grown on surface of graphite by thermal chemical vapor deposition. The vertical graphene sheets not only can greatly boost lithium-ion transport rate due to its intrinsically high electrical conductivity but also can significantly reduce tortuosity of lithium ion transport due to its highly preferential lithium-ion insertion paths. In half cells, the vertical graphene sheets/graphite can endure 3000 cycles in 3 min of charge time per cycle. More remarkably, a full cell with vertical graphene sheets/graphite anode and LiFePO4 cathode exhibits an ultrahigh energy density of 312.1 Wh kg−1 in 10 min of charge time per cycle at 4 C, indicating that the vertical graphene sheets/graphite anode possesses ability of extreme fast charging while maintaining high energy density.

Nitrogen-Doped Few-Layer Graphene Grown Vertically on a Cu Substrate via C60/Nitrogen Microwave Plasma and Its Field Emission Properties

Vertical few-layer graphene (V-FLG) sheet is expected to be a high field emitter due to its electrical properties and open surface with sharp edges. However, the complicated and tedious preparation...