Hollow Graphene Research Articles

Construction of highly-stable graphene hollow nanospheres and their application in supporting Pt as effective catalysts for oxygen reduction reaction

The construction and surface modification of three-dimensional (3D) graphene structures have been recognized as effective ways to prepare high-performance graphene-based composites in energy-related applications. Herein, on the basis of well-defined morphology and efficient electron conduction, the 3D highly-stable graphene hollow nanospheres have been synthesized by using sacrificial template method. The as-prepared 3D graphene nanospheres exhibit superior mechanical stability, electrochemical stability, and strong hydrophobicity, which may accelerate the emission of H2O in acidic medium-based ORR. Accordingly, the 3D highly-stable graphene nanospheres are used to confine tiny Pt nanoparticles (3D r-GO@Pt HNSs) for ORR in acidic medium, exhibiting superior activity with 4-electron-transfered pathway. Meanwhile, dramatically improved durability are achieved in terms of both ORR mass activity and electrochemically surface area compared to those of commercial Pt/C.

Hollow Graphene-Based Microspheres Adsorbents for Removal of Gaseous Formaldehyde

Two type of hollow graphene microspheres were investigated for the adsorption performance of gaseous formaldehyde. Hollow gently reduced graphene oxide microspheres (HgRGOS) were synthesized by using the polystyrene microspheres as sacrificial template and gently reducing graphene oxide with NH2NH2. Hollow amine modified graphene microspheres (DETA-HgRGOS) were synthesized by DETA-treatment following the before-mentioned steps. The materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, Fourier transform infrared and X-ray photoelectron spectroscopies. This was followed by formaldehyde adsorption tests. The results showed that HgRGOS and DETA-HgRGOS were characterized to have adsorption capacities of 24.54 and 17.18 mg/g. The amine-modified material can interacts with HCHO more easily than the material eith carboxyl and epoxy groups on the surface. The reaction mechanism was discussed according to FTIR and XPS analysis.

Isolated Fe Single Atomic Sites Anchored on Highly Steady Hollow Graphene Nanospheres as an Efficient Electrocatalyst for the Oxygen Reduction Reaction.

The rational design of economical and high‐performance nanocatalysts to substitute Pt for the oxygen reduction reaction (ORR) is extremely desirable for the advancement of sustainable energy‐conversion devices. Isolated single atom (ISA) catalysts have sparked tremendous interests in electrocatalysis due to their maximized atom utilization efficiency. Nevertheless, the fabrication of ISA catalysts remains a grand challenge. Here, a template‐assisted approach is demonstrated to synthesize isolated Fe single atomic sites anchoring on graphene hollow nanospheres (denoted as Fe ISAs/GHSs) by using Fe phthalocyanine (FePc) as Fe precursor. The rigid planar macrocycle structure of FePc molecules and the steric‐hindrance effect of graphene nanospheres are responsible for the dispersion of Fe–Nx species at an atomic level. The combination of atomically dispersed Fe active sites and highly steady hollow substrate affords the Fe ISAs/GHSs outstanding ORR performance with enhanced activity, long‐term stability, and better tolerance to methanol, SO2, and NOx in alkaline medium, outperforming the state‐of‐the‐art commercial Pt/C catalyst. This work highlights the great promises of cost‐effective Fe‐based ISA catalysts in electrocatalysis and provides a versatile strategy for the synthesis of other single metal atom catalysts with superior performance for diverse applications.

Novel design of Fe3O4/hollow graphene spheres composite for high performance lithium-ion battery anodes

On account of its high theoretical capacity and low cost, Fe3O4 is regarded as a promising anode material for lithium-ion batteries. Nevertheless, many problems such as poor conductivity and volume expansion during lithiation severely limit its practical application. In this work, we synthesized hollow graphene spheres (HGSs) by self-assembly and innovatively combined it with Fe3O4 particles to obtain a composite material. The Fe3O4/HGSs composite exhibits excellent electrochemical performances as an anode material, which behaves an initial discharge specific capacity of 1670.8 mA h g−1 at 50 mA g−1 and 1048.5 mA h g−1 after 50 cycles. Especially, the specific capacity can maintain as high as 617.1 mA h g−1 at the current density of 1000 mA g−1, which is much higher than that of commercial graphite. While largely inhibiting agglomeration between the particles of Fe3O4 particles, hollow spheres composed of conductive and flexible graphene layers also provide an interconnected conductive network. We believe that this design in structure will also provide a new perspective for the researches of other transition metal oxides for lithium-ion batteries.

Blackberry-like hollow graphene spheres synthesized by spray drying for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries represent one of the most promising battery techniques in 21st century. However, the practical implementation of Li-S batteries is impeded by several intractable obstacles including the poor conductivity of sulfur, shuttling behaviour of polysulfides intermediates, and large volume change during sulfur lithiation. Thus, the rational design and morphological control of sulfur cathode paves the way to Li-S batteries practicalizations. Herein, we develop a blackberry-like hollow graphene sphere through spray drying method as a promising sulfur host for Li-S batteries. Attributed to the uniform sulfur distribution, fast reaction kinetics, and excellent sulfur immobilization, the S-HGS composite electrode achieves a highly reversible capacity of 780 mAh g−1, a great rate capability as well as cyclability without adding additives.

Constructing hollow graphene nano-spheres confined in porous amorphous carbon particles for achieving full X band microwave absorption

The development of high-performance carbonaceous microwave absorbers to achieve full X band (8.2–12.4 GHz) efficient microwave absorption with lower filler loading ratio is highly desirable but remains challenging. Here, a kind of hollow graphene nano-spheres uniformly confined in porous amorphous carbon particles (HGS@PAC) are fabricated via a facile pyrolysis of bi-metal organic framework (bi-MOF). The successful construction of hollow graphene nano-spheres (HGS) by the in situ catalysis of Co in the framework of bi-MOF significantly improve the interface polarization and conductive loss of HGS@PAC, which ensures the high enough absorption intensity with lower filler loading ratio when used as microwave absorbers. The optimal HGS@PAC demonstrate excellent microwave absorption performance, achieving an effective absorption bandwidth of 4.2 GHz which covers the whole X band with 10 wt.% loading content and the minimum reflection coefficient reaches −32.43 dB at 9.19 GHz. In addition, compared with other MOF derived absorbers (such as Co/C, C/TiO2 and CNTs/Co), the HGS@PAC exhibit broader effective absorption bandwidth and stronger absorption intensity. Therefore, this work provides a promising method for the design and synthesis of HGS uniformly confined in PAC with high-performance microwave absorption.

Synthesis of hierarchical hollow urchin-like HGRs/MoS2/MnO2 composite and its excellent supercapacitor performance

Hierarchical hollow urchin-like ternary composite which consists of hollow graphene spheres(HGRs), flowerlike molybdenum disulfide(MoS2) and manganese dioxide(MnO2) nanoflakes has been successfully synthesized by chemical vapor deposition(CVD) and two-step hydrothermal methods. The HGRs/MoS2/MnO2 composite was characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM), and its electrochemical properties were evaluated by cyclic voltammetry(CV), galvanostatic charge/discharge(GCD), and electrochemical impedance spectroscopy(EIS) measurements. The experimental results demonstrated that the specific capacitance of HGRs/MoS2/MnO2 composite is 608 F g−1 at a current density of 1 A·g−1, which is far higher than that of HGRs/MoS2 (300 F g−1) and HGRs/MnO2 (344 F g−1). In addition, 89.3% of the original capacitance of HGRs/MoS2/MnO2 composite is retained after 2500 cycles at a current density of 2 A·g−1, which keeps better cycle stability compared to HGRs/MnO2 composite. The excellent electrochemical performance can be ascribed to the synergistic effect of HGRs, flowerlike MoS2 and MnO2 nanoflakes. Flowerlike MoS2 as an ion buffer layer is beneficial to rapid ion diffusion and transportation from MnO2 into interior HGRs. Furthermore, HGRs/MoS2 composite as a three-dimensional(3D) matrix alleviates the volume change during charge/discharge cyclical process. The well-structured HGRs/MoS2/MnO2 composite with high performance has a great potential for advanced supercapacitors(SCs) applications.

Synthesis of interconnected graphene framework with two-dimensional protective layers for stable lithium metal anodes

Severe lithium (Li) dendrite growth during the plating/stripping process, which results in low Coulombic efficiency and safety issues, strongly hinders the practical applications of Li metal anodes. Herein, we propose a novel design of three-dimensional (3D) interconnected graphene (IG) framework synthesized with the help of nickel (Ni) microspheres for stable Li metal anodes. The as-prepared IG framework consists of multiple stacks of two-dimensional (2D) graphene layers and plenty of hollow graphene microspheres in between, and thus provides protective layers on the top to suppress lithium dendrites, sufficient surface area to reduce the effective current density, as well as ion channels for fast Li transport, which is confirmed by post-cycle morphology characterization. When Li foil was used as the counter electrode for Li deposition, the assembled coin cell maintained an average Coulombic efficiency of more than 97.5% for 100 cycles at current density of 1 mA cm−2 with a Li loading of 1 mAh cm−2. Furthermore, we achieved stable cycling for more than 300 h at a current density of 1 mA cm−2 with a Li loading of 2 mAh cm−2 when assembled as symmetric cells. This strategy of vertically stacking 2D materials provides a novel approach towards dendrite-free Li metal anodes for the next-generation energy storage systems.

One-step hydrothermal reduction synthesis of tiny Sn/SnO2 nanoparticles sandwiching between spherical graphene with excellent lithium storage cycling performances

The reunion of Sn is always a troublesome issue when it’s used as the energy storage materials, on the one hand it comes from the preparation process due to its low melting point, and on the other hand it comes from the Li-Sn alloying process because of its natural tendency of migration. The Sn/SnO2/spherical graphene composite prepared by one-step low temperature hydrothermal reduction method can effectively solve this problem. In the composite, Sn/SnO2 tiny nanoparticles with average diameter of 5 nm distribute evenly between multilayers of graphene sheets presenting a hollow spherical structure. The introduction of SnO2 can effectively restrain the agglomeration of Sn nanoparticles during alloying process since an amorphous Li2O matrix is formed to separate the adjacent active particles. The sandwich graphene hollow sphere skeleton effectively buffers the volume expansion of Sn/SnO2 and further restricts their migration and agglomeration. Due to the above advantages, the nano-Li2O generating from the decomposition of SnO2 can contact closely with excessive nano-Sn in restricted area, promoting facile conversed conversion reaction. Therefore, the composite exhibits high reversible capacity and excellent cycle performance. A stable and high specific capacity of 843.8 mAh g−1 is obtained after 100 cycles at 0.1 C.

Innovative N-doped graphene-coated WS2 nanosheets on graphene hollow spheres anode with double-sided protective structure for Li-Ion storage

By skillfully designing the double-sided protective structure, WS2 nanosheets in situ grow on reduced graphene oxide hollow spheres (Hs-rGO). Then nitrogen doped graphene (NG) is coated on the outer layer to obtained NG@WS2@Hs-rGO. Double-sided protective structure of NG@WS2@Hs-rGO is successfully fabricated via a facile synthesis strategy. When evaluated as an anode material for Lithium-ion batteries (LIBs), NG@WS2@Hs-rGO exhibits a high specific capacity of 1309.4 mAh g−1 at 100 mA g−1 and excellent rate capability (166.1 mAh g−1 at a high current density of 4000 mA g−1). More strikingly, at a high current density of 1000 mA g−1, the NG@WS2@Hs-rGO electrode delivers a discharge capacity of 300.9 mAh g−1 after 320 cycles. The capacity retention of the electrode material reaches as high as 106% of the discharge capacity after the 10th cycle. Internally, the elastic Hs-rGO provides space for the bulk expansion of WS2. Externally, the outer layer of WS2 coated with NG not only improves the conductivity, but also provides more active sites for Li ion storage. The double-sided protective structure makes NG@WS2@Hs-rGO a potential anode material for light and high-performance LIBs.

One-component fermion plasma on a sphere at finite temperature

We study through a computer experiment, using the restricted path integral Monte Carlo method, a one-component fermion plasma on a sphere at finite, nonzero, temperature. We extract thermodynamic properties like the kinetic and internal energy per particle and structural properties like the radial distribution function. This study could be relevant for the characterization and better understanding of the electronic properties of hollow graphene spheres.

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

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

Preparation of three-dimensional hollow graphene balls and simultaneous electrochemical determination of dopamine and uric acid

Nickel nanoparticles (Ni-NPs) were synthesized by the reduction reaction of NiCl2·6H2O, N2H4·H2O and NaOH, and then the graphene layers were coated on the surface of Ni-NPs by the carbide cladding method while triethylene glycol was used as carbon source. After etching Ni, the obtained 3D hollow graphene balls (HGBs) were sprayed onto the ITO coated glass to fabricate 3D HGBs/ITO electrode, which acted as a working electrode for determining dopamine and uric acid simultaneously. The results indicate that the multi-layered 3D HGBs maintain the original size of Ni-NPs (the diameter of ~ 100 nm) and have few defects. The 3D HGBs/ITO electrode exhibits a high sensitivity of 1.16 and 0.94 μA μM− 1 for detecting dopamine and uric acid, respectively. Also, it shows a low measured limit of detection, excellent selectivity, reproducibility and stability. It is potential for use in clinical research.

Synthesis of transfer-free graphene on cemented carbide surface

Direct growth of spherical graphene with large surface area is important for various applications in sensor technology. However, the preparation of transfer-free graphene on different substrates is still a challenge. This study presents a novel approach for the transfer-free graphene growth directly on cemented carbide. The used simple thermal annealing induces an in-situ transformation of magnetron-sputtered amorphous silicon carbide films into the graphene matrix. The study reveals the role of Co, a binding phase in cemented carbides, in Si sublimation process, and its interplay with the annealing temperature in development of the graphene matrix. A detailed physico-chemical characterisation was performed by structural (XRD analysis and Raman spectroscopy with mapping studies), morphological (SEM) and chemical (EDS) analyses. The optimal bilayer graphene matrix with hollow graphene spheres on top readily grows at 1000 °C. Higher annealing temperature critically decreases the amount of Si, which yields an increased number of the graphene layers and formation of multi-layer graphene (MLG). The proposed action mechanism involves silicidation of Co during thermal treatment, which influences the existing chemical form of Co, and thus, the graphene formation and variations in a number of the formed graphene layers.

Three-dimensional hollow graphene efficiently promotes electron transfer of Ag3PO4 for photocatalytically eliminating phenol

The effective transport of photo-induced carriers over semiconductor photocatalyst is critical for enhancing the photocatalytic performance under light excitation. Although oxidized graphene (GO) and/or reduced graphene oxide (rGO) has been used as cocatalyst to promote the transfer and utilization of electrons, however, random diffusion and transfer of photo-induced charges are inevitable from all sides over these actual graphene owing to the limitation of the preparation process and theory. Herein, we utilized three-dimensional hollow carbon graphene (HCG) to promote the efficient electron transfer of Ag3PO4 in the photocatalytic process. Owing to the confinement-induced electron field of HCG, the constructed HCG-Ag3PO4 photocatalytic system demonstrated the enhanced visible-light adsorption, improved transfer of photo-induced charges, and suitable redox potentials as revealed by transient photo-current spectroscopic, surface photovoltage spectroscopy, and electron paramagnetic resonance (EPR). EPR spectra of oxygen species and gas chromatography-mass spectra exhibited high efficiency activity over HCG-Ag3PO4 with Z-scheme photocatalytic mechanism for phenol decomposition by reaction between hexanoic acid and OH and O2−. It is noteworthy that photocatalytic performance over optimal HCG-Ag3PO4 is 6, 3.43, 1.92 times of pristine Ag3PO4, GO-Ag3PO4, and rGO-Ag3PO4, respectively. The results may supply a novel perspective to enhance transfer of photo-induced charges for the promotion of photocatalytic technology.

One-step synthesis of graphene hollow nanoballs with various nitrogen-doped states for electrocatalysis in dye-sensitized solar cells

Nitrogen-doped graphene hollow nanoballs (N-GHBs) were synthesized in chemical vapor deposition (CVD) reaction using melamine as a chemical precursor via an in situ nitrogen-doping approach. In the CVD reaction, N-GHBs were deposited directly on carbon cloth (CC) to be used as an efficient metal-free electrocatalyst for dye-sensitized solar cell (DSSC) applications. The highly curved N-GHBs could avoid the self-assembly restacking of planar graphene sheets, which usually occurred during the film preparation. Keeping oxygen contaminations from N-GHBs, the characteristic electrical conductivity of graphene was preserved in the as-synthesized N-GHBs. By controlling the evaporation temperature of melamine, the nitrogen-doping content of 8.7–14.0% and different nitrogen-doped configurations in N-GHBs could be adjusted. The catalytic activities of different nitrogen-doped states in N-GHBs toward the triiodide (I3−) reduction in DSSCs were investigated, revealing that the pyridinic and quaternary nitrogens, rather than the total nitrogen doping level, in N-GHBs are mainly responsible for their catalytic activities in DSSCs. For solar cell applications, the high surface area and heteroatomic nitrogens of GHBs can remarkably improve the catalytic activity toward the triiodide reduction, lower the charge-transfer resistance, and enhance the corresponding photovoltaic performance (7.53%), which is comparable to that (7.70%) of a standard sputtered Pt counter electrode-based cell. These exceptional properties allow N-GHBs/CC to act as a promising electrocatalytic electrode for DSSC and other electrochemical energy applications.

Selective Proton/Deuteron Transport through Nafion|Graphene|Nafion Sandwich Structures at High Current Density.

Ion current densities near 1 A cm-2 at modest bias voltages (<200 mV) are reported for proton and deuteron transmission across single-layer graphene in polyelectrolyte-membrane (PEM)-style hydrogen pump cells. The graphene is sandwiched between two Nafion membranes and covers the entire area between two platinum-carbon electrodes, such that proton transfer is forced to occur through the graphene layer. Raman spectroscopy confirms that buried graphene layers are single-layer and relatively free of defects following the hot-press procedure used to make the sandwich structures. Area-normalized ion conductance values of approximately 29 and 2.1 S cm-2 are obtained for proton and deuteron transport, respectively, through single-layer graphene, following correction for contributions to series resistance from Nafion resistance, contact resistance, etc. These ion conductance values are several hundred to several thousand times larger than in previous reports on similar phenomena. A ratio of proton to deuteron conductance of 14 to 1 is obtained, in good agreement with but slightly larger than those in prior reports on related cells. Potassium ion transfer rates were also measured and are attenuated by a factor of many thousands by graphene, whereas proton transfer is attenuated by graphene by only a small amount. Rates for hydrogen and deuterium ion exchange across graphene were analyzed using a model whereby each hexagonal graphene hollow site is assumed to transmit ions with a specific per-site ion-transfer self-exchange rate constant. Rate constant values of approximately 2500 s-1 for proton transfer and 180 s-1 for deuteron transfer per site through graphene are reported.

Nitrogen-rich graphene hollow microspheres as anode materials for sodium-ion batteries with super-high cycling and rate performance

Nitrogen-rich graphene hollow microspheres (NGHMs) have been synthesized by simply calcining the core@shell polystyrene@graphene oxide (PS@GO) microspheres in the presence of melamine. These NGHMs are highly active as the anode for sodium ion batteries (SIBs) and can deliver a stable reversible capacity of 253.8 mAh g−1 at 100 mA g−1, which is much higher than that of the conventional nitrogen doped graphene (102.3 mAh g−1). Additionally, the NGHMs exhibit excellent rate and cycling performance. A high stable discharge capacity of 77.8 mAh g−1 could be observed when the NGHMs are cycled for 8000 cycles at 10 A g−1. At 20 A g−1, the NGHMs can still deliver a reversible capacity of 66.7 mAh g−1. The capacities of the NGHMs are higher than those of most carbonaceous materials reported. These results strongly suggest that the NGHMs are usable as the anode for the SIBs with high-rate performance and super-long life time. The specific hollow structure is found to play an important role in the high performance of the NGHMs. It does not only increase specific surface area of the NGHMs, allowing for more active sites available to the Na+ storage, but also allows a ready diffusion of the Na+ ions.

3-Dimensional hollow graphene balls for voltammetric sensing of levodopa in the presence of uric acid.

The development of novel nanomaterials brings new opportunity and challenge for high sensing detection of biomolecules. The authors describe the preparation of 3-dimentional hollow graphene balls (3D HGBs) using nickel nanoparticles (Ni-NPs) as the template. The Ni-NPs were synthesized by chemical reduction of nickel chloride and then graphene was coated onto their surface via carburization and carbonization. After etching Ni-NPs, 3D HGBs with few layers and a typical size of 100nm were obtained. They were sprayed onto indium tin oxide glass to obtain a working electrode for electrochemical determination of levodopa in the presence of uric acid. Due to the unique hollow porous structure of the 3D HGBs, the electrode exhibits a sensitivity of 0.69μA·μM-1·cm-2 and a 1 μM limit of detection. It is selective, reproducible and stable. It was applied to the determination of levodopa in spiked human plasma samples and it isof potential use in clinical research. Graphical abstract Schematic presentation of the preparation of 3-dimensional hollow graphene balls (HGBs) by using nickel nanoparticles as a template that can be removed by etching. The HGBs were sprayed onto indium tin oxide (ITO) glass to obtain a working electrode that hasa sensitivity of 0.69 μA⋅μM-1·cm-2 and a 1 μM limit of detection for the determination of levodopa.

Highly interconnected hollow graphene nanospheres as an advanced high energy and high power cathode for sodium metal batteries

Developing sodium based energy storage systems that retain high energy density at high power along with stable cycling is of paramount importance to meet the energy demands of next generation applications.