Enhanced Electrocatalysis via 3D Graphene Aerogel Engineered with a Silver Nanowire Network for Ultrahigh‐Rate Zinc–Air Batteries

3D graphene aerogel (GA) integrated with active metal or its derivatives has emerged as a novel class of multifunctional constructs with range of potential applications. However, GA fabricated by self‐assembly in the liquid phase still suffers from low conductivity and poor knowledge related to spatial active phase distribution and 3D structure. To address these issues, a facile approach involving in situ integration of 1D silver nanowire (AgNW) during gelation of graphene oxide flakes is presented. AgNWs prevent the restacking of graphene sheets and act as an efficient electron highway and Ag source for deposition of ultrasmall Ag nanocrystals (AgNCs). When applied as the cathodic electrocatalyst in a zinc–air battery, the 3D GA integrated with 0D AgNCs and 1D AgNWs permit ultrahigh discharge rates of up to 300 mA cm^?2. Moreover, for the first time, with the help of phase‐contrast X‐ray computed microtomography, the interconnected porous network of millimeter‐sized GA and a full‐field view of the macrodistribution of Ag is delivered, offering the vitally complementary macroscopic structure information, which has been missing in previous reports.     

Electromechanical Actuators Based on Graphene and Graphene/Fe3O4 Hybrid Paper

Exceptionally high specific surface area, mechanical strength, electrical conductivity, and a special two‐dimensional structure make graphene a highly promising material for electromechanical actuators. Electromechanical actuators are fabricated using flexible graphene‐based paper prepared via a filtration process, and the stroke of these graphene‐based actuators is directly measured during electrochemical double‐layer charge injection. Actuation strain up to 0.064% was obtained for pristine graphene paper in response to an applied potential of –1 V in 1 M NaCl solution. Double‐layer charge injection in graphene sheets is believed to induce actuation strain through a combination of coulombic and quantum‐chemical‐based expansion. To increase electrochemical‐double‐layer capacitance and actuator performance, Fe₃O₄ nanoparticles were used to partially prevent graphene sheets from restacking and allow the electrolyte ions to infiltrate the resulting magnetic graphene paper more easily. The magnetic graphene paper exhibits actuation strain as large as 0.1% at –1 V applied potential, which is about 56% higher than that of the pristine graphene paper.     

Battery Performance and Photocatalytic Activity of Mesoporous Anatase TiO2 Nanospheres/Graphene Composites by Template‐Free Self‐Assembly

Nanosized mesoporous anatase TiO₂ particles have important applications in high‐performance lithium ion batteries and efficient photocatalysis. In contrast to the conventional synthesis routes where various soft or hard templates are usually employed, the direct growth of uniform mesoporous anatase TiO₂ nanospheres on graphene sheets by a template‐free self‐assembly process is presented. Compared to the conventional mesoporous anatase particles consisting of polycrystalline TiO₂, the microstructure of obtained mesoporous anatase nanospheres on graphene sheets is single‐crystal‐like. The growth mechanism, lithium ion battery performance, and photocatalytic activity of the resultant mesoporous anatase TiO₂ nanospheres/graphene composites are thoroughly investigated. In comparison to the reference TiO₂, the composite shows substantial improvement in lithium specific capacity from 1 C to 50 C, and photocatalytic removing organic pollutant and hydrogen evolution. More strikingly, the specific capacity of the composite at the rate of 50 C is as high as 97 mA h g^?1, 6 times higher than that of the reference TiO₂.     

Smart Nanostructured Materials based on Self‐Assembly of Block Copolymers

Nanoscale fabrication of smart materials relying on the molecular self‐assembly of block copolymers (BCPs) has been recognized as a valuable platform for various next‐generation functional structures. In this Progress Report, the recent advances in the BCP self‐assembly process, which has paved the way for viable applications of emerging nanotechnologies, are highlighted. Effective light‐induced self‐assembly based on photothermal annealing of high‐χ BCPs and conformal 3D surface nanopatterning exploiting chemically modified graphene flexible substrates are reviewed as the typical instances of advanced BCP‐based nanofabrication methodologies. Additionally, relevant potential application fields are suggested, namely, graphene nanoribbon field effect transistors, highly tunable refractive index metasurfaces for visible light, high‐sensitivity surface‐enhanced Raman spectroscopy, 2D transition metal dichalcogenide nanopatterning, sequential infiltration synthesis, and organic photovoltaics. Finally, the future research direction as well as innovative applications of these smart nanostructured materials is proposed.     

Toward Macroscale,Isotropic Carbons with Graphene‐Sheet‐Like Electrical and Mechanical Properties

Realization of macroscale three‐dimensional isotropic carbons that retain the exceptional electrical and mechanical properties of graphene sheets remains a challenge. Here, a method for fabricating graphene‐derived carbons (GDCs) with isotropic properties approaching those of individual graphene sheets is reported. This synthesis scheme relies on direct cross‐linking of graphene sheets via the functional groups in graphene oxide to maximize electronic transport and mechanical reinforcement between sheets and the partial restacking of the sheets to increase the material density to about 1 g cm^‐3. These GDCs exhibit properties 3–6 orders of magnitude higher than previously reported 3D graphene assemblies.     

Nanoscale Refractive Index Tuning of Siloxane‐Based Self‐Assembled Electro‐Optic Superlattices

The refractive indices of self‐assembled organic electro‐optic superlattices can be tuned by intercalating high‐Z optically transparent group 13 metal oxide sheets into the structures during the self‐assembly process. Microstructurally regular acentricity and sizable electro‐optic responses are retained in this straightforward synthetic procedure. This “one‐pot” all wet‐chemistry approach involves: i) layer‐by‐layer covalent self‐assembly of intrinsically acentric multilayers of high‐hyperpolarizability chromophores on inorganic oxide substrates, ii) protecting group cleavage to generate a large density of reactive surface hydroxyl sites, iii) self‐limiting capping of each chromophore layer with octachlorotrisiloxane, iv) deposition of metal oxide sheets derived from THF solutions of Ga(OⁱC₃H₇)₃ or In(OⁱC₃H₇)₃, and v) covalent capping of the resulting superlattices.     

Three‐Dimensionally Ordered Macroporous Polymeric Materials by Colloidal Crystal Templating for Reversible CO2 Capture

The design and preparation of porous materials with controlled structures and functionalities is crucial to a variety of absorption‐ or separation‐relevant applications, including CO₂ capture. Here, novel functional polymeric materials with three‐dimensionally ordered macroporous (3DOM) structures are prepared by using colloidal crystals as templates using relatively simple, rapid, and inexpensive approaches. These ordered structures are used for the reversible CO₂ capture from ambient air by humidity swing. Typically, the colloidal crystal template is synthesized from polymer latex particles of poly(methyl methacrylate) (PMMA) or polystyrene (PS). To maintain the functionality of the material, it is important to prevent the porous structure collapsing, which can occur by the hydrolysis of the ester bonds in conventional crosslinkers under basic conditions. This hydrolysis can be prevented by using a water‐soluble crosslinker containing two quaternary ammonium moieties, which can be used to prepare stable porous crosslinked polymers with the monomer (vinylbenzyl)trimethylammonium chloride (VBTMACl) and using a PMMA‐based colloidal crystal template. The hydroxide‐containing monomer and dicationic crosslinker are synthesized from their chloride precursors, avoiding the ion‐exchange step which causes shrinkage of the pores. An analysis of different methods for infiltrating the monomer solution into the colloidal crystal template shows that infiltration using capillary forces leads to fewer defects than infiltration under a partial vacuum. In addition, functional macroporous films with micrometer thickness are prepared from a template of PS‐based colloidal crystals in a thin film. In general, the colloidal crystal templated materials showed improved CO₂ absorption/desorption rates and swing sizes compared to a commercially available material with similar functional groups. This work could easily be extended to create a new generation of ordered macroporous polymeric materials with tunable functionalities for other applications.     

3D Macroscopic Architectures from Self‐Assembled MXene Hydrogels

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.     

Highly Conductive Nanocomposites with Three‐Dimensional,Compactly Interconnected Graphene Networks via a Self‐Assembly Process

Polymer‐based materials with high electrical conductivity are of considerable interest because of their wide range of applications. The construction of a 3D, compactly interconnected graphene network can offer a huge increase in the electrical conductivity of polymer composites. However, it is still a great challenge to achieve desirable 3D architectures in the polymer matrix. Here, highly conductive polymer nanocomposites with 3D compactly interconnected graphene networks are obtained using a self‐assembly process. Polystyrene (PS) and ethylene vinyl acetate (EVA) are used as polymer matrixes. The obtained PS composite film with 4.8 vol% graphene shows a high electrical conductivity of 1083.3 S/m, which is superior to that of the graphene composite prepared by a solvent mixing method. The electrical conductivity of the composites is closely related to the compact contact between graphene sheets in the 3D structures and the high reduction level of graphene sheets. The obtained EVA composite films with the 3D graphene structure not only show high electrical conductivity but also exhibit high flexibility. Importantly, the method to fabricate 3D graphene structures in polymer matrix is facile, green, low‐cost, and scalable, providing a universal route for the rational design and engineering of highly conductive polymer composites.     

Constraining Si Particles within Graphene Foam Monolith: Interfacial Modification for High‐Performance Li+ Storage and Flexible Integrated Configuration

Pulverization of electrode materials and loss of electrical contact have been identified as the major causes for the performance deterioration of alloy anodes in Li‐ion batteries. This study presents the hierarchical arrangement of spatially confining silicon nanoparticles (Si NPs) within graphene foam (GF) for alleviating these issues. Through a freeze‐drying method, the highly oriented GF monolith is engineered to fully encapsulate the Si NPs, serving not only as a robust framework with the well‐accessible thoroughfares for electrolyte percolation but also a physical blocking layer to restrain Si from direct exposure to the electrolyte. In return, the pillar effect of Si NPs prevents the graphene sheets from restacking while preserving the highly efficient electron/Li⁺ transport channels. When evaluated as a binder‐free anode, impressive cycle performance is realized in both half‐cell and full‐cell configurations. Operando X‐ray diffraction and in‐house X‐ray photoelectron spectroscopy confirm the pivotal protection of GF to sheathe the most volume‐expanded lithiated phase (Li₁₅Si₄) at room temperature. Furthermore, a free‐standing composite film is developed through readjusting the pore size in GF/Si monolith and directly integrated with nanocellulose membrane (NCM) separator. Because of the good electrical conductivity and structural integrity of the GF monolith as well as the flexibility of the NCM separator, the as‐developed GF/Si‐NCM electrode showcases the potential use in the flexible electronic devices.     

Holey Graphene Nanomanufacturing: Structure,Composition, and Electrochemical Properties

Topology is critical for properties and function of 2D nanomaterials. Membranes and films from 2D nanomaterials usually suffer from large tortuosity as a result from dense restacking of the nanosheets and thus have limited utility in applications such as electrodes for supercapacitor and batteries, which require ion transport through the nanosheet thickness. In comparison with conventional porous 2D nanomaterials, introducing holes through the nanosheets to create holey 2D nanomaterials with retention of the 2D‐related properties is a more viable approach to improve molecular transport. Here, graphene is used as a model to study the fundamental structure‐property relationship as a result from defect‐enabled hole creation. Specifically, the correlation of electrochemical capacitive properties with structure and composition for holey graphene materials is prepared using a highly scalable controlled air oxidation process. The presence of holes on graphene sheets is not sufficient to account for the observed capacitance improvement. Rather, the improvement is achieved through the combination of an enhanced mesopore fraction with simultaneous oxygen doping while retaining the graphitic carbon network with minimal damage. The detailed understanding might be further applied to other 2D materials toward a broader range of both energy‐related and other applications.     

Tailored Assembly of Carbon Nanostructures: Tailored Assembly of Carbon Nanotubes and Graphene (Adv. Funct. Mater. 8/2011)

This Feature Article reviews recent progress in the tailored assembly of carbon nanotubes and graphene into three‐dimensional architectures with particular emphasis on our own research employing self‐assembly principles. Carbon nanotubes and graphene can be assembled into macroporous films, hollow spherical capsules, or hollow nanotubes, via directed assembly from solvent dispersion. This approach is cost‐effective and beneficial for large‐scale assembly, but pre‐requests stable dispersion in a solvent medium. Directed growth from a nanopatterned catalyst array is another promising approach, which enables the control of morphology and properties of graphitic materials as well as their assembly. In addition, the aforementioned two approaches can be synergistically integrated to generate a carbon hybrid assembly consisting of vertical carbon nanotubes grown on flexible graphene films. Tailored assembly relying on scalable self‐assembly principles offer viable routes that are scalable for mass production towards the ultimate utilization of graphitic carbon materials in nanoelectronics, displays, sensors, energy storage/conversion devices, and so on, including future flexible devices.     

Tailored Assembly of Carbon Nanotubes and Graphene

This Feature Article reviews recent progress in the tailored assembly of carbon nanotubes and graphene into three‐dimensional architectures with particular emphasis on our own research employing self‐assembly principles. Carbon nanotubes and graphene can be assembled into macroporous films, hollow spherical capsules, or hollow nanotubes, via directed assembly from solvent dispersion. This approach is cost‐effective and beneficial for large‐scale assembly, but pre‐requests stable dispersion in a solvent medium. Directed growth from a nanopatterned catalyst array is another promising approach, which enables the control of morphology and properties of graphitic materials as well as their assembly. In addition, the aforementioned two approaches can be synergistically integrated to generate a carbon hybrid assembly consisting of vertical carbon nanotubes grown on flexible graphene films. Tailored assembly relying on scalable self‐assembly principles offer viable routes that are scalable for mass production towards the ultimate utilization of graphitic carbon materials in nanoelectronics, displays, sensors, energy storage/conversion devices, and so on, including future flexible devices.     

Dynamic application of novel electro-optic switchable device modulation by graphene oxide dispersed liquid crystal cell assembling CdS nanowires

In nanotechnology, the novel creation of nanostructures consistently feeds back into efforts to fabricate novel complex hybrid nanomaterials. Two-dimensional graphene oxide dispersed liquid crystalline materials (GDLC) module assembled with CdS nanowires(NW's) have received widespread unprecedented attention due to their exceptional mechanical, electrical, thermal properties. However, making macroscopic graphene oxide (GO) sheets with average diameter 2.1 μm, CdS nanowires (15–20 nm) requires novel technology to fabricate few layered graphene oxide (FGO)-sheets were uniformly distributed as macroscopically ordered structures. Aqueous GDLC-CdS nanowires are continuously twist to obtain macroscopic GO-sheets. Subsequently chemical reduction gave first macroscopic neat graphene sheets with high conductivity and good mechanical performance. Liquid crystal formation is the most viable approach to produce macroscopic, periodic self-assembled materials from oriented graphene sheets. We discovered well-soluble FLG-sheets can exhibit nematic liquid crystallinity into Dimethyl sulfoxide (DMSO), first established isotropic-nematic solid phase diagram demonstrated by optical microscopy textural evidences of switching and relevant spectroscopic characterizations. GO utilizes light absorption and nanoscale heat source to thermally induced phase transition with LC from homogeneous alignment to isotropic phase. Thus, volume contraction occurred over the surface area of the GDLC-nanowires hybrid complex module due to photothermal effect. Thus, an excellent conductor as well as high contrast electro-optic switchable cell also deserves most promising applications. These novel findings shed focus on microscopically assembled graphene-LC based semiconductor nanomaterial's textural phase behavior, which can only be realized as the field moves forward and makes more significant advances.     

Micro‐Supercapacitors Based on Interdigital Electrodes of Reduced Graphene Oxide and Carbon Nanotube Composites with Ultrahigh Power Handling Performance

A novel method for fabricating micro‐patterned interdigitated electrodes based on reduced graphene oxide (rGO) and carbon nanotube (CNT) composites for ultra‐high power handling micro‐supercapacitor application is reported. The binder‐free microelectrodes were developed by combining electrostatic spray deposition (ESD) and photolithography lift‐off methods. Without typically used thermal or chemical reduction, GO sheets are readily reduced to rGO during the ESD deposition. Electrochemical measurements show that the in‐plane interdigital design of the microelectrodes is effective in increasing accessibility of electrolyte ions in‐between stacked rGO sheets through an electro‐activation process. Addition of CNTs results in reduced restacking of rGO sheets and improved energy and power density. Cyclic voltammetry (CV) measurements show that the specific capacitance of the micro‐supercapacitor based on rGO–CNT composites is 6.1 mF cm^?2 at 0.01 V s^?1. At a very high scan rate of 50 V s^?1, a specific capacitance of 2.8 mF cm^?2 (stack capacitance of 3.1 F cm^?3) is recorded, which is an unprecedented performance for supercapacitors. The addition of CNT, electrolyte‐accessible and binder‐free microelectrodes, as well as an interdigitated in‐plane design result in a high‐frequency response of the micro‐supercapacitors with resistive‐capacitive time constants as low as 4.8 ms. These characteristics suggest that interdigitated rGO–CNT composite electrodes are promising for on‐chip energy storage application with high power demands.     

Structure‐Properties Relationship in Iron Oxide‐Reduced Graphene Oxide Nanostructures for Li‐Ion Batteries

Non‐aqueous sol‐gel routes involving the reaction of metal oxide precursors in organic solvents (e.g., benzyl alcohol) at moderate temperature and pressure, offer advantages such as high purity, high reproducibility and the ability to control the crystal growth without the need of using additional ligands. In this paper, a study carried out on a series of iron oxide/reduced graphene oxide composites is presented to elucidate a structure‐properties relationship leading to an improved electrochemical performance of such composites. Moreover, it is demonstrated that the easy production of the composites in a variety of temperature and composition ranges, allows a fine control over the final particles size, density and distribution. The materials obtained are remarkable in terms of the particle's size homogeneity and dispersion onto the reduced graphene oxide surface. Moreover, the synthesis method used to obtain the graphene oxide clearly affects the performances of the final composites through the control of the restacking of the reduced graphene oxide sheets. It is shown that a homogeneous and less defective reduced graphene oxide enables good electrochemical performances even at high current densities (over 500 mAh/g delivered at current densities as high as 1600 mA/g). The electrochemical properties of improved samples reach the best compromise between specific capacity, rate capability and cycle stability reported so far.     

A Method for Fabricating an Ultrathin Multilayer Film Composed of Poly(p‐phenylenevinylene) and Reduced Graphene Oxide on a Plastic Substrate for Flexible Optoelectronic Applications

The photoconductive properties of a uniform ultrathin multilayer film composed of alternating poly(p‐phenylene vinylene) (PPV) and reduced graphene oxide (RGO) layers, fabricated on a poly(ethylene terephthalate) (PET) sheet are reported. The assembly of the two electron‐rich layer components on the temperature‐sensitive substrate is realized using a layer‐by‐layer‐deposition technique under mild conditions and HI/H₂O vapor treatment at 100 °C. This protocol is established to simultaneously convert the layer components to their conjugated counterparts, PPV and RGO in the multilayer films, whose total thicknesses shrinks to 50% of their original values due to lattice contraction. Furthermore, the surface roughness decreases significantly, in contrast to the results obtained from general chemical treatments. The PET sheets coated with (PPV/RGO)₁₅ films exhibit a photocurrent of 115 μA at an illumination intensity of 1.1 mW and a photoresponsivity of 111.1 mA W^?1 at an illumination intensity of 0.5 mW; these are among the best values yet achieved in carbon‐based materials. The establishment of a method for fabricating (PPV/RGO) films on a temperature‐sensitive transparent flexible sheet is crucial for the development of organic‐based portable electronic devices.     

Highly Conductive Porous Graphene/Ceramic Composites for Heat Transfer and Thermal Energy Storage

A novel architecture of 3D graphene growth on porous Al₂O₃ ceramics is proposed for thermal management using ambient pressure chemical vapor deposition. The formation mechanism of graphene is attributed to the carbothermic reduction occurring at the Al₂O₃ surface to initialize the nucleation and growth of graphene. The graphene films are coated on insulating anodic aluminum oxide (AAO) templates and porous Al₂O₃ ceramic substrates. The graphene coated AAO possesses one‐dimensional isolated graphene tubes, which can act as the media for directional thermal transport. The graphene/Al₂O₃ composite (G‐Al₂O₃) contains an interconnected macroporous graphene framework with an extremely low sheet electrical resistance down to 0.11 Ω sq^?1 and thermal conductivity with 8.28 W m^?1 K^?1. The G‐Al₂O₃ provides enormous conductive pathways for electronic and heat transfer, suitable for application as heat sinks. Such a porous composite is also attractive as a highly thermally conductive reservoir to hold phase change materials (stearic acid) for thermal energy storage. This work displays the great potential of CVD direct growth of graphene on dielectric porous substrates for thermal conduction and electronic applications.     

Multifunctional Three‐Dimensional T‐Junction Graphene Micro‐Wells: Energy‐Efficient,Plasma‐Enabled Growth and Instant Water‐Based Transfer for Flexible Device Applications

The “third‐generation” 3D graphene structures, T‐junction graphene micro‐wells (T‐GMWs) are produced on cheap polycrystalline Cu foils in a single‐step, low‐temperature (270 °C), energy‐efficient, and environment‐friendly dry plasma‐enabled process. T‐GMWs comprise vertical graphene (VG) petal‐like sheets that seemlessly integrate with each other and the underlying horizontal graphene sheets by forming T‐junctions. The microwells have the pico‐to‐femto‐liter storage capacity and precipitate compartmentalized PBS crystals. The T‐GMW films are transferred from the Cu substrates, without damage to the both, in de‐ionized or tap water, at room temperature, and without commonly used sacrificial materials or hazardous chemicals. The Cu substrates are then re‐used to produce similar‐quality T‐GMWs after a simple plasma conditioning. The isolated T‐GMW films are transferred to diverse substrates and devices and show remarkable recovery of their electrical, optical, and hazardous NO₂ gas sensing properties upon repeated bending (down to 1 mm radius) and release of flexible trasparent display plastic substrates. The plasma‐enabled mechanism of T‐GMW isolation in water is proposed and supported by the Cu plasma surface modification analysis. Our GMWs are suitable for various optoelectronic, sesning, energy, and biomedical applications while the growth approach is potentially scalable for future pilot‐scale industrial production.     

Tailoring Microstructure of Graphene‐Based Membrane by Controlled Removal of Trapped Water Inspired by the Phase Diagram

As an important form of graphene assembled in macroscale, the graphene‐based membrane attracts much attention due to its easy manipulation and various potential applications. However, tailoring the microstructure of these membranes is hard to achieve and the surface utilization of graphene layers is low. By analyzing the drying process for the wet graphene oxide membrane (GOM), it is found that the trapped water in freshly formed GOM actually provides potential forces to tune its microstructure. According to the phase diagram of pure water, with a reduced pressure, the trapped water boils seriously and then transforms into ice crystal instantaneously around the triple point. This sudden phase change across the triple point provides strong forces to change and fix the microstructure of GOM. In this study, the ordinary evaporation drying process for the wet GOM is replaced with a two‐stage drying process and the tightly layered structure of graphene membrane is turned into an open and grade structure. The obtained membrane shows high surface utilization. Thus, after reduction, the membrane possesses high adsorption capability towards various molecules, especially for heavy oil and lithium polysulfide products in the cathode of Li–S battery. Furthermore, the membrane shows high rate performance as the electrodes for supercapacitors.