Three-dimensional individual S-doped porous red-blood-cell-like graphene (SRBCG) microspheres with double concave-surface morphology duplicated from a template-directed chemical vapor deposition process in a fluidized bed reactor not only exhibit high porosity, good structural stability, and strong anticompression properties but also present superior capacitive energy-storage abilities with respect to a symmetric supercapacitor (great compatibility at different rates) and a Li ion capacitor (no capacitance loss after 3500 cycles at 2 A g–1). The well-kept integrity of the electrode configuration after cycling benefits from the intrinsic robust scaffold which acts as a structural buffer for volume expansion to inhibit structure collapse. The unique individual microarchitecture with well-developed pore channels of SRBCG can effectively prevent the obtained graphene from aggregation or restacking, expanding the contact area between electrolyte ions and the electrode. The excellent capacitive behaviors of SRBCG are guaranteed by the unique robust microarchitecture accompanied by the good structural stability. Additionally, the fluidized bed technology is conducive to the realization of the homogeneous growth and scalable production of SRBCG.

Porous carbon materials have been widely used as active materials, additives or substrates in energy storage devices using Li+ as the charge carrier. Fluctuations in cycling performance have been widely observed for Li storage by porous carbon materials, but the reason for such phenomena has not been clearly revealed. In this work, periodic variations of capacities and coulombic efficiencies are observed in the lithium insertion/extraction cycles of fibre-like graphene 3D networks. Volume expansion of nanopores in graphene networks caused by Li+ accumulation and their elastic compression that leads to Li+ release are considered as the key reasons for the periodic behavior. For the flexible few-layered graphene, the increase of the pore volume is retained, thus leading to a continuous increase of the Li storage capacity. Our results reveal a clear relationship between the elasticity of a porous carbon material and its Li storage performance.

We report on a chemical vapor deposition synthesis of graphene capsules (GCs) in sizes of tens to thousands of nanometers and their oil adsorption performance. MgO particles with different particle sizes are used as templates to produce GCs with different sizes. At a larger GC size and higher pore volume, a higher oil capacity is obtained. The highest oil adsorption capacity achieved by the GCs is 156 gdiesel gGC−1, which is much higher than that obtained by expanded graphite. The adsorption capacity proportionally increases as the viscosity of the fluid increases. Both the capsule structure and the viscosity of oil are relative to the adsorption capacity, showing that capillary adsorption with a limited entrance might have contributed to the high capacity oil adsorption by GCs.

•5Mg(OH)2·MgSO4·3H2O (513MOS) whiskers were synthesized by an atmospheric pressure reflux method.•Long reaction time and high MgSO4 concentration were necessary under gentle reaction conditions.•The growth of 513MOS whiskers is a relatively slow liquid phase deposition process.•Porous MgO whiskers were derived via 1,020 °C calcination from 513MOS whiskers.We have developed a one-step process for the synthesis of basic magnesium sulfate (5Mg(OH)2·MgSO4·3H2O, abbreviated as 513MOS) whiskers from MgSO4·7H2O and MgO by refluxing at atmospheric pressure. The process shows potential for the low-cost mass production of controlled-structure whiskers. Their 0.3–1.0 μm diameter and 40–80 μm length correspond to an aspect ratio of 40–260. The 513MOS whisker morphology is related closely to MgSO4 concentration and reflux time. The optimized MgSO4 concentration is 1.2–1.5 mol/L with a 25–30 h reflux time. X-ray diffractometry revealed that the b-axis is the predominant growth direction of the whiskers. Their growth mechanism is by the relatively slow liquid-phase deposition of Mg2+, OH–, and SO42–. The long reaction time and high MgSO4 concentration are conducive to the formation of 513MOS whiskers under gentle reaction conditions. Porous MgO whiskers with a fibrous structure were obtained after calcination of the 513MOS whiskers at 1020 °C.

S-doped carbon nanotubes (SCNTs) obtained by a post treatment approach are used as conductive additive for LiFePO4 (LFP) cathodes in Lithium ion batteries (LIBs). The SCNTs exhibit higher specific surface area, higher conductivity and better hydrophily as compared to the pristine CNTs because of S doping. Thus the SCNTs can be stably dispersed in water, forming an aqueous conductive slurry. The LFP cathode using the aqueous SCNTs slurry as conductive additive exhibits excellent electrochemical performances in terms of capacity (143 mA h g−1 at 2 C), rate capability and cycling stability (99.6% of initial capacity after 200 cycles) due to the uniform dispersibility of SCNTs in the bulk of electrodes forming a continuous conductive network. The full cell configuration with graphite as anode, affords a high reversible capability (150 mA h g−1 at 0.2 C), good cycling stability (capacity retention of 87.6% at 2 C), ultrahigh energy density of 163.7 W h kg−1 and power density of 296.8 W kg−1. Our results provide an easy approach to prepare high performance LIB cathodes using water as solvent, thus leading to lower cost and more secure for the electrode production.

•RBC-like basic magnesium carbonate microspheres were synthesized via a hydrothermal method.•The formation of microspheres was attributed to amphiphilic surfactant-participated self-assembly.•The method can be applied to the synthesis of other carbonate or metallic oxide self-assemblies.Basic magnesium carbonate microspheres with a red blood cell (RBC)-like appearance and diameters of ∼3 μm were synthesized by amphiphilic molecule-participated self-assembly under hydrothermal conditions. In the self-assembly, sodium dodecyl benzene sulfonate served as a template for the formation of Mg(OH)2 spherical micelles and also as a reactant precursor that releases CO2 to react with Mg(OH)2. The growth of the microspheres is driven by the continuous generation of new hydrophobic centers because of the consumption of hydrophilic poles (SO3−). The surfactant-directed self-assembly can be applied to the synthesis of other carbonate or metallic oxide self-assemblies, indicating that it is a universal self-assembly method for amphiphilic molecules.

Nanostructured Fe2O3-nanomesh graphene (NMG) composites containing ∼3 nm Fe2O3 nanoparticles (NPs) uniformly distributed in the nanopores of NMG are synthesized by an adsorption–precipitation process. As anodes for Li ion batteries (LIBs), the 10%Fe2O3–NMG composite exhibits an upward trend in the capacity and delivers a reversible specific capacity of 1567 mA h g–1 after 50 cycles at 150 mA g–1, and 883 mA h g–1 after 100 cycles at 1000 mA g–1, much higher than the corresponding values for the NMG electrode. The significant capacity enhancement of the 10%Fe-NMG composite is attributed to the positive synergistic effect between NMG and Fe2O3 NPs due to the catalytic activity of Fe2O3 NPs for decomposition of the solid electrolyte interface film. Our results indicate that decoration of ultrasmall Fe2O3 NPs can significantly change the surface condition of graphene. This synthesis strategy is simple, effective, and broadly applicable for constructing other electrode materials for LIBs.Keywords: catalytic activity; composite; electrochemistry; iron oxide; lithium batteries; nanomesh graphene; synergistic effect;

Few-layered graphene networks composed of phosphorus and nitrogen dual-doped porous graphene (PNG) are synthesized via a MgO-templated chemical vapor deposition (CVD) using (NH4)3PO4 as N and P source. P and N atoms have been substitutionally doped in graphene networks since the doping takes place at the same time with the graphene growth in the CVD process. Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks. The doping levels of P and N measured by X-ray photoelectron spectroscopy are 0.6 and 2.6 at %, respectively. As anodes for Li ion batteries (LIBs), the PNG electrode exhibits high reversible capacity (2250 mA h g–1 at the current density of 50 mA g–1), excellent rate capability (750 mA h g–1 at 1000 mA g–1), and satisfactory cycling stability (no capacity decay after 1500 cycles), showing much enhanced electrode performance as compared to the undoped few-layered porous graphene. Our results show that the PNG is a promising candidate for anode materials in high-rate LIBs.Keywords: anode; chemical vapor deposition; lithium-ion battery; phosphorus doping; porous graphene

Here, we report a new approach to synthesizing S-doped porous carbons and achieving both a high capacity and a high Coulombic efficiency in the first cycle for carbon nanostructures as anodes for Li ion batteries. S-doped porous carbons (S-PCs) were synthesized by carbonization of pitch using magnesium sulfate whiskers as both templates and S source, and a S doping up to 10.1 atom % (corresponding to 22.5 wt %) was obtained via a S doping reaction. Removal of functional groups or highly active C atoms during the S doping has led to formation of much thinner solid-electrolyte interface layer and hence significantly enhanced the Coulombic efficiency in the first cycle from 39.6% (for the undoped porous carbon) to 81.0%. The Li storage capacity of the S-PCs is up to 1781 mA h g–1 at the current density of 50 mA g–1, more than doubling that of the undoped porous carbon. Due to the enhanced conductivity, the hierarchically porous structure and the excellent stability, the S-PC anodes exhibit excellent rate capability and reliable cycling stability. Our results indicate that S doping can efficiently promote the Li storage capacity and reduce the irreversible Li combination for carbon nanostructures.Keywords: anode; carbon nanostructure; Coulombic efficiency; Li ion battery; sulfur doping; synthesis

Three-dimensional (3D) networks composing of S and N dual-doped graphene (SNG) were synthesized by a chemical vapor deposition approach using MgSO4-containing whiskers as templates and S source and NH3 as N source. Energy dispersive spectrometer mapping and X-ray photoelectron spectroscopy coupled with Raman analysis have revealed that S and N atoms with concentrations of 5.2 and 1.8 atom%, respectively, have been substitutionally incorporated into the graphene networks via covalent bonds. The SNG, as an anode material for lithium ion batteries (LIBs), exhibits extremely high capacity (3525 mAh/g at the current density of 50 mA/g) and superior rate capability (870 mAh/g at 1000 mA/g) with excellent cycling stability (remaining a reversible capacity of 400 mAh/g at 10 A/g after 2500 cycles). The enhanced conductivity, the 3D porous network with many disorders and the intrinsically high Li storage capacity of S and N-doped carbon segments have led to the excellent electrode performance of the SNG networks. The effects of binder content and calendaring pressure on the electrode performance have been investigated. The full LIB with SNG as anode and LiCoO2 as cathode can afford a high reversible capability (164 mAh/g at 0.2 C) and good cycling stability.

Here, we report a novel Co3O4–graphene hybrid electrode material with high density Co3O4 nanoparticles (NPs) in a size range of 2–3 nm confined in a few-layered porous graphene nanomesh (PGN) framework driven by an electrochemical process. Raman spectra indicate that Co species preferentially anchor on the defective sites of the PGN, which results in markedly reduced irreversible Li storage and therefore significantly enhanced coulombic efficiency. The ultra-small Co3O4 NPs provide a large surface area and a short solid-state diffusion length, which is propitious to achieving a high Li ion capacity at high rate. Also, the few-layered graphene network with high electronic conductivity not only permits easy access to the high surface area of the Co3O4 NPs for the electrolyte ions, but also serves as a reservoir for high capacity Li storage. As a result, the Co3O4–PGN composite layers deliver an ultra-high capacity (1543 mA h g−1 at 150 mA g−1) and excellent rate capability (1075 mA h g−1 at 1000 mA g−1) with good cycling stability.

We present a novel approach to fabricate flexible graphene papers using chemical vapor deposition (CVD) derived graphene. Expanded vermiculite was used as a layered template in the CVD process to produce bulk materials containing graphene sheets of the order of hundreds of microns at a gram scale. Meshes or carbon nanotubes can be introduced into the graphene sheets by template pretreating. Owing to the large sheet size, the as-obtained graphene sheets were easily fabricated into flexible graphene papers with low surface density and good conductivity, which exhibited greatly enhanced reversible capacity (1350 mA h g−1 at 50 mA g−1) and cycling performance as anodes for lithium rechargeable batteries as compared to the graphene papers fabricated using reduced graphene oxide.

The strategy to regularly arrange and join the polycyclic aromatic hydrocarbons of asphalt into graphene was explored. Expanded vermiculite with a multi-layered structure was used to adsorb asphaltene molecules onto its surfaces or into its interstices, and graphene sheets with 8–10 graphene layers and a width of tens of microns were obtained by carbonization of the regularly-arranged asphalt molecules. The formation of graphene layers is ascribed to not only the regular arrangement of asphaltene molecules due to the adsorption by vermiculite layers but also the joining of the asphaltene molecules catalyzed by the Fe-containing vermiculite surfaces. By the preabsorption of melamine on vermiculite, a nitrogen-doped graphene–carbon nanotube hybrid was produced from asphalt. As anodes for Li-ion batteries, the obtained graphene materials exhibited increased capacities and rate performance as compared to the widely-used reduced graphene oxide, indicating that the asphalt-derived graphene materials have a reasonable quality.

A nanomesh graphene (NMG) was produced by a chemical vapor deposition using porous MgO layers as templates, and its magnetic properties were measured and compared with those of reduced graphene oxide (rGO). Extraordinary ferromagnetism with a saturation magnetization of 0.04 emu/g at room temperature was found in the NMG, four times of that of rGO (0.01 emu/g). The mesh structure with remarkable corrugations indicates the possible existence of a high density of defects in the NMG, which is believed to contribute to the origin of the ferromagnetism. Our results present a direct connection between the mesh structure and the ferromagnetism, which provides valuable clues to explore the essential origination of carbon magnetism.

•Nanomesh graphene (NMG) was synthesized by template chemical vapor deposition.•Binder-free graphene monoliths were prepared from loosely stacking NMG by tablet pressing.•Graphene monoliths have obvious elasticity and a porous structure.•Methane capacity of the graphene monolith was up to 236 (v/v) at 9 MPa.Nanomesh graphene (NMG) obtained by template chemical vapor deposition was used to synthesize the binder-free graphene monoliths by simple tablet pressing. The stacking manner of the NMG sheets was crucial to the cohesion interaction between the graphene sheets, only the NMG materials with a loosely stacking manner could be pressed into binder-free monoliths. At the tableting pressure of 2–8 MPa, both the bulk densities and the specific surface areas of the monoliths keep nearly constant as the tableting pressure increases, indicating that the NMG monoliths have obvious elasticity and a porous structure due to the large corrugations and the mesh structures of the graphene sheets. As a result, an extraordinary methane storage capacity of 236 (v/v) at 9 MPa was obtained in the graphene monolith prepared by tableting at 4 MPa.Nanomesh graphene synthesized and graphene monoliths prepared.

Graphene-carbon nanotube (G-CNT) hybrids were synthesized by a one-step chemical vapor deposition process using a mixed catalyst of MgO and Fe/MgO. MgO layers acted as templates for the growth of graphene, and Fe particles on the MgO layers catalyzed the growth of single or double-walled CNTs. The G-CNT hybrids had porous structures with hierarchical pore distributions due to the composition of graphene with CNT network. Superparamagnetism with a saturation magnetization of 2.7 emu/g was found in the G-CNT hybrids due to the existence of Fe3C nanoparticles of size ∼3 nm. The graphene to CNT ratio was conveniently changed by varying the MgO to Fe/MgO ratio, as characterized by Raman analysis and specific surface area measurements. Furthermore, a simplified synthesis of G-CNT hybrids was demonstrated by using MgO supported Fe or Ni catalysts with a low metal concentration.

Graphene that had nanomeshes, only one to two graphene layers, and specific surface areas of up to 1654 m2 g−1 was produced on gram-scale by template growth on porous MgO layers. Its unique porous structure gave excellent electrochemical capacitance (up to 255 F g−1), cycle stability and rate performance.

We present a novel approach to fabricate flexible graphene papers using chemical vapor deposition (CVD) derived graphene. Expanded vermiculite was used as a layered template in the CVD process to produce bulk materials containing graphene sheets of the order of hundreds of microns at a gram scale. Meshes or carbon nanotubes can be introduced into the graphene sheets by template pretreating. Owing to the large sheet size, the as-obtained graphene sheets were easily fabricated into flexible graphene papers with low surface density and good conductivity, which exhibited greatly enhanced reversible capacity (1350 mA h g−1 at 50 mA g−1) and cycling performance as anodes for lithium rechargeable batteries as compared to the graphene papers fabricated using reduced graphene oxide.

Porous carbon materials have been widely used as active materials, additives or substrates in energy storage devices using Li+ as the charge carrier. Fluctuations in cycling performance have been widely observed for Li storage by porous carbon materials, but the reason for such phenomena has not been clearly revealed. In this work, periodic variations of capacities and coulombic efficiencies are observed in the lithium insertion/extraction cycles of fibre-like graphene 3D networks. Volume expansion of nanopores in graphene networks caused by Li+ accumulation and their elastic compression that leads to Li+ release are considered as the key reasons for the periodic behavior. For the flexible few-layered graphene, the increase of the pore volume is retained, thus leading to a continuous increase of the Li storage capacity. Our results reveal a clear relationship between the elasticity of a porous carbon material and its Li storage performance.

Graphene that had nanomeshes, only one to two graphene layers, and specific surface areas of up to 1654 m2 g−1 was produced on gram-scale by template growth on porous MgO layers. Its unique porous structure gave excellent electrochemical capacitance (up to 255 F g−1), cycle stability and rate performance.

Here, we report a novel Co3O4–graphene hybrid electrode material with high density Co3O4 nanoparticles (NPs) in a size range of 2–3 nm confined in a few-layered porous graphene nanomesh (PGN) framework driven by an electrochemical process. Raman spectra indicate that Co species preferentially anchor on the defective sites of the PGN, which results in markedly reduced irreversible Li storage and therefore significantly enhanced coulombic efficiency. The ultra-small Co3O4 NPs provide a large surface area and a short solid-state diffusion length, which is propitious to achieving a high Li ion capacity at high rate. Also, the few-layered graphene network with high electronic conductivity not only permits easy access to the high surface area of the Co3O4 NPs for the electrolyte ions, but also serves as a reservoir for high capacity Li storage. As a result, the Co3O4–PGN composite layers deliver an ultra-high capacity (1543 mA h g−1 at 150 mA g−1) and excellent rate capability (1075 mA h g−1 at 1000 mA g−1) with good cycling stability.