Search

Volumetric and areal capacitance are as important as gravimetric capacitance for small energy storage devices. However, achieving both a high volumetric and a high areal capacitance is still a big challenge. Here we report a dense redox organic molecules/graphene network, in which highly redox active sodium anthraquinone-2-sulfonate (AQS) molecules are anchored on interconnected and highly conductive graphene sheets by noncovalent π–π interactions to form high-performance supercapacitors (SCs). The AQS/graphene (AQS/G) has a high volumetric specific capacitance of up to 650 F cm−3 and an excellent rate capability (422 F cm−3 even at 30 A g−1), as well as a good cycling stability. A maximum areal specific capacitance of 13.3 F cm−2 is achieved at a high mass loading of 32 mg cm−2 (200 μm in thickness), which is amongst the highest values recorded for organic-based materials for SCs. An asymmetric SC constructed with AQS/G and RuO2/graphene delivers a maximum volumetric energy density of 44 W h L−1. This outstanding performance is attributed to the excellent electron conduction and ion transport provided by the dense but interconnected graphene network. This work suggests a new way for organic-based high-performance electrode materials to be used in electrochemical energy storage devices.

Conventional carbon materials cannot combine high density and high porosity, which are required in many applications, typically for energy storage under a limited space. A novel highly dense yet porous carbon has previously been produced from a three-dimensional (3D) reduced graphene oxide (r-GO) hydrogel by evaporation-induced drying. Here the mechanism of such a network shrinkage in r-GO hydrogel is specifically illustrated by the use of water and 1,4-dioxane, which have a sole difference in surface tension. As a result, the surface tension of the evaporating solvent determines the capillary forces in the nanochannels, which causes shrinkage of the r-GO network. More promisingly, the selection of a solvent with a known surface tension can precisely tune the microstructure associated with the density and porosity of the resulting porous carbon, rendering the porous carbon materials great potential in practical devices with high volumetric performance.

For lithium-ion capacitors (LICs), the electrode mass balancing and the electrode potential tuning are two techniques that have been widely used to maximize the gravimetric specific capacity and voltage to achieve a maximum gravimetric energy density. However, it is also great important to consider the volumetric performances of energy storage devices for the compact and portable applications. Herein, for achieving high-volumetric-performance LICs, we propose an electrode thickness matching strategy, which is to minimize the thickness of thick cathodes as close to the one of thin anodes as possible via increasing the gravimetric specific capacity and density of cathode materials. It is demonstrated that introducing a highly dense but porous activated carbon/graphene (AC/G) composite rather than the low-density traditional activated carbon as the cathode material, the volumetric energy density of the assembled AC/G//graphite LIC can be increased by 62% to reach a maximum of 98 Wh L-1, which represents one of the highest records for the contemporary LICs. We believe that the thickness matching should be a universal strategy for achieving high volumetric performances and can be applicable to other electrochemical energy storage devices.

Lithium-ion capacitors (LICs), constructed with a battery-type electrode and capacitor-type electrode in electrolytes containing a Li-salt, are designed to bridge the gap between lithium-ion batteries (LIBs) and supercapacitors (SCs). Such a configuration gives LICs a high energy density, high power density and long-term cycling stability. Hence, LICs are regarded as one of the most promising alternatives to present electrochemical energy storage (EES) devices. As the most important components of LICs, extensive efforts have been made to develop novel electrode materials during the past two decades. However, some critical issues including a kinetic imbalance between a battery-type electrode and a capacitor-type electrode, unsatisfactory energy and power densities and cycling stability still need to be effectively addressed. Two-dimensional (2D) materials, because of the unique advantages, including a high specific surface area, excellent electrical conductivity, a tunable layered structure, rich electrochemical active sites and mechanical flexibility, have been used as electrode materials and additives for LICs and great progress has been made in recent years. In this review, we summarize the recent progress in the use of 2D materials, including graphene, transition metal dichalcogenides (TMDs) and MXenes, as battery-type electrode materials, capacitor-type electrode materials and additives in LICs. The typical application of 2D materials in sodium-ion capacitors (NICs) is also briefly reviewed. Finally, an outlook for the future researches on achieving higher-performance LICs and NICs is presented.

Highlights Assembly strategies that reinforce the roles of carbon architectures as active materials, electrochemical reaction frameworks, and current collectors in high-energy and high-power lithium-ion batteries are summarized. To enhance structural stability and volumetric performance, the rational design of carbon architectures for high-capacity noncarbons in terms of the interface, network skeleton, void space, and densification, is discussed in detail. Designing carbon cages that protect the electroactive noncarbon is highlighted as a promising strategy that solves the challenges associated with future high-capacity noncarbon anode construction., Lithium-ion batteries (LIBs), which are high-energy-density and low-safety-risk secondary batteries, are underpinned to the rise in electrochemical energy storage devices that satisfy the urgent demands of the global energy storage market. With the aim of achieving high energy density and fast-charging performance, the exploitation of simple and low-cost approaches for the production of high capacity, high density, high mass loading, and kinetically ion-accessible electrodes that maximize charge storage and transport in LIBs, is a critical need. Toward the construction of high-performance electrodes, carbons are promisingly used in the enhanced roles of active materials, electrochemical reaction frameworks for high-capacity noncarbons, and lightweight current collectors. Here, we review recent advances in the carbon engineering of electrodes for excellent electrochemical performance and structural stability, which is enabled by assembled carbon architectures that guarantee sufficient charge delivery and volume fluctuation buffering inside the electrode during cycling. Some specific feasible assembly methods, synergism between structural design components of carbon assemblies, and electrochemical performance enhancement are highlighted. The precise design of carbon cages by the assembly of graphene units is potentially useful for the controlled preparation of high-capacity carbon-caged noncarbon anodes with volumetric capacities over 2100 mAh cm−3. Finally, insights are given on the prospects and challenges for designing carbon architectures for practical LIBs that simultaneously provide high energy densities (both gravimetric and volumetric) and high rate performance.

The practical application of lithium-sulfur batteries with a high energy density has been plagued by the poor cycling stability of the sulfur cathode, which is a result of the insulating nature of sulfur and the dissolution of polysulfides. Much work has been done to construct nanostructured or doped carbon as a porous or polar host for promising sulfur cathodes, although restricting the polysulfide shuttle effect by improving the redox reaction kinetics is more attractive. Herein, we present a well-designed strategy by introducing graphitic carbon nitride (g-C3N4) into a three-dimensional hierarchical porous graphene assembly to achieve a synergistic combination of confinement and catalyzation of polysulfides. The porous g-C3N4 nanosheets in situ formed inside the graphene network afford a highly accessible surface to catalyze the transformation of polysulfides, and the hierarchical porous graphene-assembled carbon can function as a conductive network and provide appropriate space for g-C3N4 catalysis in the sulfur cathode. Thus, this hybrid can effectively improve sulfur utilization and block the dissolution of polysulfides, achieving excellent cycling performance for sulfur cathodes in lithium-sulfur batteries.

Sulfur-functionalized graphene monoliths with a high sulfur fraction (16.8 wt%) were prepared to demonstrate a high capacity (∼400 mA h g-1 at 0.1 A g-1) and ultrafast (∼120 mA h g-1 at 5 A g-1) sodium ion storage. The reversible reaction of -C-Sx-C- with sodium ions contributes to the extra capacity while a 3D graphene network guarantees high rate capability.

Tin and its compounds hold promise for the development of high-capacity anode materials that could replace graphitic carbon used in current lithium-ion batteries. However, the introduced porosity in current electrode designs to buffer the volume changes of active materials during cycling does not afford high volumetric performance. Here, we show a strategy leveraging a sulfur sacrificial agent for controlled utility of void space in a tin oxide/graphene composite anode. In a typical synthesis using the capillary drying of graphene hydrogels, sulfur is employed with hard tin oxide nanoparticles inside the contraction hydrogels. The resultant graphene-caged tin oxide delivers an ultrahigh volumetric capacity of 2123 mAh cm–3 together with good cycling stability. Our results suggest not only a conversion-type composite anode that allows for good electrochemical characteristics, but also a general synthetic means to engineering the packing density of graphene nanosheets for high energy storage capabilities in small volumes., The excessive porous space in carbon anodes for lithium-ion batteries has to be utilized for high volumetric performance. Here the authors show an adaptable sulfur template strategy to yield graphene-caged noncarbon materials with a precisely controlled amount of void, enabling ultrahigh volumetric lithium storage.

This study investigated the characteristics of various graphene oxide (GO) nanohybrid membranes and their performance in algal organic matter (AOM) filtration. The membranes were fabricated by phase inversion method. The effect of GO and its nanohybrids embedded in membranes was investigated in terms of wettability, porosity, pore size, surface charge, composition, morphology, permeability, fouling resistance and antimicrobial ability. In addition, the rejection of protein and carbohydrate as critical foulants in AOM was studied. Based on the findings, all the composite membranes showed lower flux decline than PVDF membrane. Composite membranes maintained higher protein (81–86%) and carbohydrate (77–83%) rejection compared with PVDF membrane (64% for protein and 63% for carbohydrate). However, the reversible to irreversible fouling ratio of PVDF, ZnO/GO-PVDF, Ag/GO-PVDF and GO-PVDF membranes was 3.07, 1.53, 0.86 and 1.09, respectively. This scenario implied that more hydrophilic substances in small molecular weight (MW) contained in AOM had plugged the composite membranes' pores and resulted in irreversible fouling. On the other hand, ZnO/GO-PVDF and Ag/GO-PVDF membranes exhibited superior antimicrobial ability and showed great potential in anti-biofouling mitigation.

Volumetric performance is highly important for evaluating the potential of supercapacitors, especially for the case where electrode space is limited. To achieve high space utilization, the less pores to be included the better. Along this direction, we showed previously a PANI/graphene composite almost free of porosity by shrinking the composite network to the most compact, which yet exhibited a high volumetric capacitance and a good rate capability. The PANI/graphene solid composite simultaneously enabled maximized space utilization of the electrode volume and achieved unimpeded ion transport, which seems counter to the general design principle of electrode materials where appropriate porous structure is highly desired. Here we propose the proton transport mechanism of PANI in the dense composite, which indicates that PANI is a dual electronic-ionic conductivity polymer that acts not only as a pseudo-capacitive active material for high energy storage but also as a proton conductor that realizes proton transport from the electrode/electrolyte interface to the inner of the dense micro-particles. More importantly, we further propose the design principle of non-porous carbon-based composites to achieve high volumetric performance, in which a good dual electronic-ionic conductor is selected as the best pseudo-capacitive filler. This work inspires new insights into better design and preparation of the composite electrodes for compact energy storage devices.

A dual functional CNTs@graphene/CNTs cathode for Li–Se battery was constructed by a CNTs@graphene network and a CNTs interlayer. CNTs were first integrated with graphene to form a three-dimensional (3D) framework and work together as a conductive matrix for Se confinement. The optimized composite cathode delivers a high initial capacity of 575 mAh·g−1 at 0.5 A·g−1 and good rate capacity with a retained capacity of 479 mAh·g−1 at 2.0 A·g−1 (73% of the capacity at 0.2 A·g−1). CNTs were further served as an interlayer to confine the diffusion of polyselenides by constructing a thin CNTs layer outside the CNTs@graphene network. An improved initial capacity of 616 mAh·g−1 at 0.5 A·g−1 is achieved with a retained capacity of 538 mAh·g−1 after 80 cycles, indicating the effective dual function of CNTs in this novel cathode construction and great application potential for Li–Se battery.

Graphene oxide (GO) was prepared by modified Hummer’s method, and reduced by solvothermal method using ethanol as the solvent and modified diethylene triamine (amine curing agent 593) as reducing agent and modifier. The effect of reduction time and temperature on the structure and conductive property of reduced graphene oxide (593-rGO) was investigated by SEM, FT-IR and XRD. The results show that the graphene modified by 593 is obviously improved in dispersibility and sedimentation stability in dichloromethane, as well as in conductivity. The optimal reduction processing is that the mass ratio of GO to 593 is 2:1, the reduction time and temperature is 6 h and 160°C, respectively.

In article number 1802355, Ying Tao, Quan‐Hong Yang, and co‐workers develop a densification strategy of activated carbons inspired by the dense structure of pomegranate grains. The carbon particles as “grains” are compactly packed in a capillary shrinking graphene network where reduced graphene oxides are “peels”.

Biohydrogen is a potential alternative for fossil fuels and it can be produced from POME fermentation. Membrane technology has been a prominent separation approach for H2 purification. However, membranes yield weakness in tradeoff between permeability and selectivity. The main objective of this project is to develop mixed matrix membrane with different polymeric bases of Polysulfone (PSF) and Polyimide (PI) with graphene oxide (GO) incorporation as inorganic filler for H2/CO2 separation. Gas permeability and selectivity results indicated that PI/GO membrane with 1 wt% of GO has the highest H2 and CO2 permeability at 501 GPU and 595 GPU at 1 bar, respectively, H2/CO2 selectivity of 1.01 at 5 bar and highest H2 purity of 83 %. FESEM analysis indicated changes in the pore size and top layer of membranes due to the presence of GO. Zeta potential analysis proved that PI/GO 1wt% membranes is highly negative-charged (-56 mV). Contact angle results showed a decrease in contact angle value with the addition of GO. It can be concluded that PI/GO 1 wt% membranes demonstrated better results in the aspects of permselectivity and physicochemical properties compared to PSF membranes.

Nanomaterials can be incorporated in the synthesis of membrane to obtain mixed-matrix membrane with marked improvement in properties and performance. However, stability and dispersion of the nanomaterials in the membrane matrix, as well as the need to use high ratio of nanomaterials for obvious improvement of membrane properties, remain a major hurdle for commercialization. Hence, this study aims to investigate the improvement of polyamide 6,6 membrane properties with the incorporation of silver nanoparticles decorated on graphene oxide (Ag-GO) nanoplates and at the same time focus is given to the issues above. Graphene oxide nanoplates were synthesized using the modified Hummers’ method and decorated with silver before embedded into the polyamide 6,6 matrix. Physicochemical characterizations were conducted on both nanoplates and the mixed-matrix Ag-GO polyamide 6,6 membrane. The issues of Ag agglomeration and leaching were not observed, which could be attributed to the decoration of Ag on GO that helped to disperse the nanomaterials and provided a better anchor point for the attachment of Ag nanoparticles. The synthesized membrane showed marked improvement regarding flux (135% increment) and antifouling (40% lower irreversible fouling), which could be ascribed to the more negative charge of membrane surface (−14 ± 6 to −31 ± 3.8 mV) and hydrophilicity (46% enhancement) of the membranes. With minimal embedment of Ag nanoparticles, the membrane showed superior antibacterial property where the E. coli bacteria could not form a single colony on the membrane surface. Overall, the decoration of Ag on GO nanoplates could be a promising approach to resolve the agglomeration and leaching issues as well as reduce the amount of precious Ag in the synthesis of Ag-GO polyamide 6,6 membrane.

Graphene-based materials have gained popularity recently for various applications. Most of the graphene-based composites have been developed using either graphene oxide (GO) or reduced-graphene oxide (rGO), using solvent processing, in situ polymerization, or melt processing method. The presence of GO can enhance the membrane surface charges, thus, higher rejection toward heavy metal ions. GO as additives in polyvinylidene fluoride composite membrane have improved membrane surface hydrophilicity, which is highly useful to reduce membrane fouling tendency in wastewater treatment. Layer-by-layer (LbL) approach (by constructing GO framework) has successfully produced composite nanofiltration membranes that can reject heavy metal ions (Pb2+, Ni2+, and Zn2+) higher than 95%. GO membrane interlinked with multiwalled carbon nanotubes were also fabricated on polyacrylonitrile support and recorded 93.4% of rejection for chelated strontium ions in an alkaline solution. Polyethersulfone/GO/polyacrylic acid membrane, on the other hand, has demonstrated a significant color removal efficiency of 54% with enhanced flux improvement, antifouling ability, and better color rejection capability. Separation membrane via LbL deposition of GO nanosheets, which were cross-linked by 1,3,5-benzenetricarbonyl trichloride, on a polydopamine-coated polysulfone support, showed membrane fluxes with approximately 4–10 times higher than most of the commercial nanofiltration membranes in addition to high rejection efficiency of 95% for Rhodamine WT, a moderate rejection rate of 66% for methylene blue and relatively low rejection (6%–46%) for monovalent and divalent salts. Undoubtedly, graphene-based membranes can be considered as highly promising materials to enhance the removal of hazardous contaminants, especially heavy metal ions and dyes, in wastewater treatments.

Supercapacitors are increasingly in demand among energy storage devices. Due to their abundant porosity and low cost, activated carbons are the most promising electrode materials and have been commercialized in supercapacitors for many years. However, their low packing density leads to an unsatisfactory volumetric performance, which is a big obstacle for their practical use where a high volumetric energy density is necessary. Inspired by the dense structure of irregular pomegranate grains, a simple yet effective approach to pack activated carbons into a compact graphene network with graphene as the “peels” is reported here. The capillary shrinkage of the graphene network sharply reduces the voids between the activated carbon particles through the microcosmic rearrangement while retaining their inner porosity. As a result, the electrode density increases from 0.41 to 0.76 g cm−3. When used as additive‐free electrodes for supercapacitors in an ionic liquid electrolyte, this porous yet dense electrode delivers a volumetric capacitance of up to 138 F cm−3, achieving high gravimetric and volumetric energy densities of 101 Wh kg−1 and 77 Wh L−1, respectively. Such a graphene‐assisted densification strategy can be extended to the densification of other carbon or noncarbon particles for energy devices requiring a high volumetric performance.

Organic electrode materials are usually highly soluble, less conductive and highly irreversible. These drawbacks result in the low utilization and poor performance of organic materials in sodium-ion batteries. In this work, a self-assembled graphene/disodium terephthalate (Na2TP) electrode with exceptionally high loadings of Na2TP (up to 88.60%) shows dramatically enhanced electrical conductivity and sodium storage performances in ether electrolytes. The strong confinement of Na2TP by graphene and the interfacial modification by ether combinationally improve the kinetics of sodiation/desodiation. This cooperative electrode/electrolyte configuration achieves a high reversible capacity of 245 mAh g−1 with an extraordinary initial Coulombic efficiency of 82.3%, which outperforms the state-of-the-art of organic anodes.

A controllable drying strategy is proposed for the precise and non-destructive control over the structure of a 3D graphene assembly. Such an assembly is used as a model carbon material to investigate the pore structure-dependent shuttle effect and cycling performance of the cathode of a Li-S battery.

Compact energy storage with high volumetric performance is highly important. However, the state-of-the-art electrodes and devices remain far from the requirements due to the lack of consideration from a device perspective, which not only demands a high specific gravimetric capacity, but also needs to take into account operation voltage, material density and electrode thickness. We develop a novel approach to fabricate a monolithic ultra-thick and dense carbon electrode for symmetric supercapacitors, starting with graphene assembly and taking all the above factors into consideration. We found that zinc chloride is an ideal sacrificial pore former, and taken together with capillary drying can tune the specific surface area of the monolithic graphene from 370 to over 1000 m2 g−1 while the monoliths maintain a high density from 1.6 to 0.6 g cm−3. Having a good balance of porosity and density, the directly sliced graphene pellet electrode with a thickness up to 400 μm delivers a capacitance of 150 F cm−3 in an ionic liquid electrolyte, corresponding to a volumetric energy density of ∼65 W h L−1 for a symmetrical supercapacitor device, the highest value reported to date for supercapacitors. This study presents a design principle for electrode materials towards next-generation energy storage devices, not limited to supercapacitors, which are becoming smaller, lighter but more energetic.

Graphite intercalation compounds are promising anode materials for potassium-ion batteries, but still have problems of sluggish kinetics and a large volume expansion upon potassiation. Porous carbons with a large ion-accessible area used as anode materials can have a high gravimetric capacity and structural stability. However, to avoid a low volumetric performance in porous carbons, an electrode must have both a high density and fast ion-transport channels and these pose stringent requirements for the pore structure. Here we use a flowable sulfur template to produce continually- and precisely-tunable pores in three-dimensional graphene assemblies. During capillary drying of graphene hydrogel, sulfur accompanied with the shrinking graphene sheets controls the formation of pores with precise sizes by tuning the usage. The pores formed are open and interlinked due to the existence of a flowable sulfur template in the graphene network. This obtained graphene-assembly with well-controlled interconnected pores is used as potassium-ion battery anodes and gives a stable cycling performance (500 cycles) and an ultrahigh volumetric capacity.

Gelation is an effective way to realize the self-assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene-based carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g-1 at 1 V s-1 ). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene-based structures and develop different applications.

This work presents a new class of porous graphene particles with a three-dimensional microscale network and an ultrahigh specific surface area (2590 m(2) g(-1)), which is obtained by the KOH activation of a compact graphene hydrogel. As supercapacitor electrodes, such porous graphene particles show high compressibility and little capacitance loss when subjected to a compressive force up to 40 MPa, yielding an excellent volumetric performance with an ionic liquid electrolyte. Such carbon materials show great promise for applications needing high volumetric energy.

Graphene is a basic unit for various types of sp2 carbon forms and its emergence brings new opportunities to construct carbonaceous materials with desired structure and function. Controlled preparation of novel carbonaceous functionalized materials can be achieved by graphene/graphene oxide assembly in solution and texture tuning. That is, solid carbon materials can be directly constructed from graphene sheets in liquid by solution-processing methods. Conventional carbonization of solids focuses on tuning macroscale morphology (e.g., carbon fiber), while vapor deposition to prepare nanocarbons allows structural control at the microscale (e.g., carbon nanotubes). In comparison, solution-processing methods to construct graphene macroassemblies bridge between micro- and macrosystems, so have the evident advantage of mesoscale texture control of final materials. Combined with our recent work, this review summarizes the development of solution-processed assemblies and texture tuning of graphene-based macroforms with emphasis on several novel graphene-based porous materials, and is concluded by discussing the prospects of this field.

Zinc oxide nanoparticles were well-known for the enhanced antifouling and antibacterial properties which could be beneficial for membrane processes in desalination. The functionalization of ZnO onto graphene oxide nanoplates was targeted for better distribution. Both ZnO and ZnO-GO NPs were synthesized using sol-gel method. The nanoparticles characteristics were checked with XRD, TEM, and FESEM. The nanohybrid membranes were fabricated via wet phase inversion technique and embedded with various percentage of ZnO (1, 2, 3 wt%) and ZnO-GO (0.1, 0.3, 0.6 wt%) nanoparticles. All the membranes with nanoparticles incorporation exhibited improved membrane properties in comparison with the pristine PSF membrane. The best membrane performance was shown in membrane with 2 wt% of ZnO and 0.6 wt% of ZnO-GO. These two membranes presented significantly improved performance such as enhanced hydrophilicity, high permeability and porosity, improved humic acid rejection rate as well as good antifouling and antibacterial control. To an extent, the excellent antimicrobial ability of these nanohybrid membranes appeared as appropriate candidate to contribute or overcome bio-fouling issues in applications such as brackish water or seawater desalination. Hence, ZnO and ZnO-GO NPs were superb nanomaterials in the fabrication of PSF-nanohybrid membranes. The use of GO nanoplates allowed reduction of ZnO composition by up to 5 times while showing similar performances. This study was financially supported by the NPRP grant # [ 5-1425-2-607 ] from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. In addition, the authors wish to acknowledge the Ministry of Education Malaysia for sponsoring the postgraduate study of Y.T. Chung through the MyBrain15 program. The CRIM (Centre for Research and Instrumentation Management, UKM) is also acknowledged for XRD, FESEM and TEM analyses. Scopus

We report a novel monolithic porous carbon constructed by the hydrothermal self-assembly of graphene oxide sheets with poly (vinyl alcohol) as the linker in the formation process of a three-dimensional (3D) structure. All the pores in this carbon have circular cross-sections and range from micropores to mesopores to macropores and are formed by the gradual removal of trapped water. This 3D graphene network together with unique spheroidal and hierarchical pore structure with macropore openings at the surface allows fast ion and electron transport into the innermost micropores. The carbon not only exhibits excellent capability for removal of dye pollutants and oils but also shows a good performance as an electrode material in lithium ion batteries. Moreover, it is also proved to be an ideal buffer for expanded active materials in electrochemical energy storage.

International audience; Assembly of 2D MXene sheets into a 3D macroscopic architecture is highly desirable to overcome the severe restacking problem of 2D MXene sheets and develop MXene‐based functional materials. However, unlike graphene, 3D MXene macroassembly directly from the individual 2D sheets is hard to achieve for the intrinsic property of MXene. Here a new gelation method is reported to prepare a 3D structured hydrogel from 2D MXene sheets that is assisted by graphene oxide and a suitable reductant. As a supercapacitor electrode, the hydrogel delivers a superb capacitance up to 370 F g−1 at 5 A g−1, and more promisingly, demonstrates an exceptionally high rate performance with the capacitance of 165 F g−1 even at 1000 A g−1. Moreover, using controllable drying processes, MXene hydrogels are transformed into different monoliths with structures ranging from a loosely organized porous aerogel to a dense solid. As a result, a 3D porous MXene aerogel shows excellent adsorption capacity to simultaneously remove various classes of organic liquids and heavy metal ions while the dense solid has excellent mechanical performance with a high Young's modulus and hardness.

It is essential to understand the size scaling effects on the mechanical properties of graphene networks to realize the potential mechanical applications of graphene assemblies. Here, a “highly dense-yet-nanoporous graphene monolith (HPGM)” is used as a model material of graphene networks to investigate the dependence of mechanical properties on the intrinsic interplanar interactions and the extrinsic specimen size effects. The interactions between graphene sheets could be enhanced by heat treatment and the plastic HPGM is transformed into a highly elastic network. A strong size effect is revealed by in situ compression of micro- and nanopillars inside electron microscopes. Both the modulus and strength are drastically increased as the specimen size reduces to ≈100 nm, because of the reduced weak links in a small volume. Molecular dynamics simulations reveal the deformation mechanism involving slip-stick sliding, bending, buckling of graphene sheets, collapsing, and densification of graphene cells. In addition, a size-dependent brittle-to-ductile transition of the HPGM nanopillars is discovered and understood by the competition between volumetric deformation energy and critical dilation energy.

A metal-free supercapacitor electrode material is prepared by the hybridization of graphene and polyaniline in a very compact way without sacrificing their gravimetric capacitance. It exhibits a record high volumetric capacitance over 800 F cm(-3).

Substituted graphenes without centrosymmetry can be considered as a new acceptor-graphene model for NLO materials and exhibit large static first hyperpolarizabilities ( β 0 ). Especially, three interesting relationships between the defect structure and β 0 value are observed. We found that the defects (for example, the Stone–Wales and 585 defects) in graphenes can greatly enhance β 0 values up to 1.4 × 10 5 au (about 1200 × 10 −30 esu), which shows that the defect is a new factor for enhancing β 0 value. Meanwhile, large HOMO–LUMO gaps (4.595–5.982 eV) and vertical ionization potential values (8.059–13.572 eV) indicate that those substituted graphenes molecules have chemical stabilities.

A porous, yet compact, RuO2/graphene hybrid is successfully prepared by using a disassembly–reassembly strategy, achieving effective and uniform loading of RuO2 nanoparticles inside compact graphene monolith. The disassembly process ensures the uniform loading of RuO2 nanoparticles into graphene monolith, while the reassembly process guarantees a high density yet simultaneously unimpeded ion transport channel in the composite. The resulting RuO2/graphene hybrid possesses a density of 2.63 g cm−3, leading to a record high volumetric capacitance of 1485 F cm−3 at the current density of 0.1 A g−1. When the current density is increased to 20 A g−1, it remains a high volumetric capacitance of 1188 F cm−3. More importantly, when the single electrode mass loading is increased to 12 mg cm−2, it still delivers a high volumetric capacitance of 1415 F cm−3 at the current density of 0.1 A g−1, demonstrating the promise of this disassembly–reassembly approach to create high volumetric performance materials for energy storage applications.

Selenium is a novel and promising cathode material in lithium ion batteries owing to its high electronic conductivity and a theoretical volumetric capacity comparable to that of S.As a congener of sulfur (S), Se has a similar lithiation mechanism to S in charge/discharge when used as the cathode material of a Li-Se battery. However, similar to the Li-S battery, the Li-Se battery suffers from a shuttle effect that leads to poor cycle performance and low Coulombic efficiency. This review summarizes recent developments, highlights the excellent performance of Li-Se batteries and focuses on improvements to the carbon/Se composite electrode. The main obstacles are also discussed. The use of porous carbons, especially graphene-based materials, for improving the performance of the Se electrode in high performance Li-Se batteries is highlighted and discussed.

A 3D hollow Sn@C-graphene hybrid material (HSCG) with high capacity and excellent cyclic and rate performance is fabricated by a one-pot assembly method. Due to the fast electron and ion transfer as well as the efficient carbon buffer structure, the hybrid material is promising in high-performance lithium-ion battery.

A small volumetric capacitance resulting from a low packing density is one of the major limitations for novel nanocarbons finding real applications in commercial electrochemical energy storage devices. Here we report a carbon with a density of 1.58 g cm(-3), 70% of the density of graphite, constructed of compactly interlinked graphene nanosheets, which is produced by an evaporation-induced drying of a graphene hydrogel. Such a carbon balances two seemingly incompatible characteristics: a porous microstructure and a high density, and therefore has a volumetric capacitance for electrochemical capacitors (ECs) up to 376 F cm(-3), which is the highest value so far reported for carbon materials in an aqueous electrolyte. More promising, the carbon is conductive and moldable, and thus could be used directly as a well-shaped electrode sheet for the assembly of a supercapacitor device free of any additives, resulting in device-level high energy density ECs.

We investigate valley-dependent transport through a graphene sheet modulated by both the substrate strain and the fringe field of two parallel ferromagnetic metal (FM) stripes. When the magnetizations of the two FM stripes are switched from the parallel to the antiparallel alignment, the total conductance, valley polarization and valley conductance excess change greatly over a wide range of Fermi energy, which results from the dependence of the valley-related transmission suppression on the polarity configuration of inhomogeneous magnetic fields. Thus the proposed structure exhibits the significant features of a valley-filtering switch and a magnetoresistance device.

We study the band and transport features of zigzag graphene nanoribbon with an antidot lattice. It is found that an antidot lattice could turn semi-metal graphene into a semiconductor. The size of the band gap can be tuned by the position of the antidots and the distance D between the two nearest antidots. For a finite superlattice with N antidots and a large D, a group of (N - 1) splitting resonant peaks and transmission-blockade regions appear alternately in the conductance spectrum. This indicates the formation of minibands and minigaps. In addition, Fano resonances can be observed when the antidots are localized near one edge of the nanoribbon. These features provide potential applications for graphene-based electronic and optoelectronic devices.

We investigate spin-dependent electron transport through a zigzag graphene nanoribbon sample with two ferromagnetic strips deposit on two sides of the graphene ribbon. Our results show that, for the antiparallel configurations of ferromagnetic strips, the conductance exhibits zero conductance plateau when the Fermi energy locates around the Dirac point and the sample shows the properties of a semiconductor. But for the parallel configurations, the energy band spectrum is metallic and the conductance is always equal to or larger than ${e}^{2}/h$. Thus the huge giant magnetoresistance effect can be achieved by altering the configurations of the ferromagnetic strips. Moreover, we study the spin-dependent conductance for the parallel configuration. It is found that the device shows half-metal behavior, in which it acts as a conductor to carriers of one spin orientation but as an insulator to those of the opposite spin orientation. So the present device can be applied as a spin filter. In addition, we study the consequence of the short-range Anderson disorder and find that the spin filtering effect and magnetoresistance effect still remain even in the strong disorder limit.

DOI: 10.1002/aenm.201301565 The increasing demand for environmentally friendly industries and effective pollution control has attracted great attention from both academic and industrial organizations for the development of new processes and novel materials. As a major air pollutant, hydrogen sulfi de (H 2 S), originating from various sources (natural gas processing, the refi ning and consumption of fossil fuel, etc.) must urgently be removed and reused due to its high toxicity towards the environment (acid rain) and living organisms. [ 1 ] Great efforts have been made to explore the effective removal of H 2 S and in most cases transitionmetal oxides and mixed oxides are used as adsorbents and/or catalysts for the oxidation of H 2 S, whereas others use zeolite, activated carbon (AC), and carbon nanotubes (CNTs) as adsorbents. [ 2,3 ] Carbon materials have appealing properties as adsorbents or catalyst supports for the removal of H 2 S. For instance, AC or CNTs have been widely used as supports of catalysts (ZnO, NiS 2 , etc.) for the catalytic oxidation of H 2 S. [ 3 ] Nevertheless, the regeneration and full utilization of the H 2 S and the development of high-performance adsorbents are still hard to realize. Thus, it is necessary to develop an appropriate approach to eliminate and recycle H 2 S to realize its regeneration and environmental protection. As a fascinating carbon material, graphene possesses excellent electrical, thermal, and mechanical properties due to its unique 2D structure, making it versatile in fundamental science and various applications, such as energy storage, sensors, adsorption, etc. [ 4 ] Due to its large and fully accessible surface and excellent conductivity, the use of graphene in the removal of H 2 S has been examined both experimentally and theoretically. [ 1a, 2, 5 ] Density functional theory (DFT) studies show that H 2 S molecules are physisorbed only on the surface of graphene, thus, in most cases, graphene has a low catalytic activity for H 2 S oxidation and also a low adsorption capacity. Graphene oxide (GO), the most important derivative of graphene, is decorated by abundant oxygen-containing groups on the graphene layer, and these help improve the reactivity and processability due to their hydrophilic nature. Although GO suffers from poor conductivity due to the destruction of the continuous sp 2

Graphene oxide hydrogel is used as a reactive template to prepare nanoporous materials with a 3D microstructure. The as-prepared porous MnO2 shows a capacitance retention of ~70.6% at a current density as high as 15 A g(-1), resulting from the 3D interconnected ion transport channel replicated from the graphene oxide hydrogel.

We investigate spin polarization and valley-dependent transport in bulk graphene in the presence of the exchange splitting field, the pseudo magnetic field, and Rashba spin-orbit coupling (SOC). It is demonstrated that Rashba SOC and the pseudo magnetic field cannot produce a spin polarization component perpendicular to the graphene sheet, but the exchange field can. However, the Rashba SOC leads to a finite in-plane spin polarization, which can be modulated by the pseudo magnetic field. Furthermore, it is also demonstrated that the valley polarization current cannot be produced in the considered system due to the mirror symmetry property of transmission probability for valley K and K′.

We investigate the electron transport through a zigzag graphene nanoribbon with a staggered sublattice potential and a certain asymmetric boundary potential. By using the tight binding model to combine with the nonequilibrium Green’s function theory and the Landauer–Buttiker formalism, the energy band structure, conductance, and conductance fluctuation are calculated. We find that an energy gap opens up due to the inversion symmetry breaking by the staggered sublattice potential. By further tuning the boundary potential, the gapless valley-dependent edge states are achieved in which the carriers with the different valleys on a given boundary propagate in opposite directions. Furthermore, we study the effect of long range disorder on the transport properties of the valley-dependent edge states. The results show that the conductance plateau 4e2/h contributed by the edge states can be maintained well in a broad range of disorder strength for low-density disorder, indicating the robustness of the valley-depen...

Free-standing graphene-based macroscopic membranes, which are characterized by a layered structure and tunable conductivity, are prepared by a self-assembly process at a liquid–air interface. Since the preliminary results indicate that it is hard to construct macroscopic graphene membranes solely by low-temperature exfoliated graphene nanosheets (LGNs) at the liquid–air interface, graphene oxide nanosheets (GONs), as the stacking template and sticking component, are introduced into the assembly process of graphene layers to promote the formation of layer-by-layer stacking structure and help form a conductive macroscopic membrane. The conductivity of such a graphene-based membrane can be tuned by changing the GON fraction in the LGN/GON hybrid membrane.

The innate character of graphene, defined as the basic unit of sp2carbon materials, provides opportunities for the design and construction of carbon nanostructures with tuned properties. Here, we report a novel three-dimensional graphene macroassembly with a core–shell structure starting from reduced graphene oxides (RGO) by a one-pot self-assembly process under very mild conditions. In the presence of KMnO4, such an assembly process is initiated by low-temperature heating below 100 °C at atmospheric pressure and is totally free from a severe hydrothermal process. Such a core–shell structure is characterized by a porous core and layered membrane shell, and the macro-morphology and infrastructure of the macroassembly are well controllable and tunable. The macroassembly presented here and its self-assembly preparation directly from graphene nanosheets present the first example of the simultaneous formation of a coaxial hybrid infrastructure in a graphene-based nanostructured material, and such a core–shell structured macroassembly shows potential for use in energy storage and other applications.