Planar micro-supercapacitors (MSCs) have drawn extensive research attention owing to their unique structural design and size compatibility for microelectronic devices. Graphene has been widely used to improve the performance of microscale electrochemical capacitors. However, investigations of an intrinsic electrochemical mechanism for graphene-based microscale devices are still not sufficient. Here, micro-supercapacitors with various typical architectures are fabricated as models to study the graphene effect, and their electrochemical performance is also evaluated. The results show that ionic accessibility and adsorption are greatly improved after the introduction of the holey graphene intermediate layer. This study provides a new route to understand intrinsic electrochemical behaviors and possesses exciting potential for highly efficient on-chip micro-energy storage.
Recent experiments indicate that metal intercalation is a very effective method to manipulate the graphene-adatom interaction and control metal nanostructure formation on graphene. A key question is mass transport, i.e., how atoms deposited uniformly on graphene populate different areas depending on the local intercalation. Using first-principles calculations, we show that partially intercalated graphene, with a mixture of intercalated and pristine areas, can induce an alternating electric field because of the spatial variations in electron doping, and thus, an oscillatory electrostatic potential. This alternating field can change normal stochastic adatom diffusion to biased diffusion, leading to selective mass transport and consequent nucleation, on either the intercalated or pristine areas, depending on the charge state of the adatoms.
Three-dimensional (3D) graphene has recently attracted enormous attention for electrochemical energy storage applications. However, current methods suffer from an inability to simultaneously control and engineer the porosity and morphology of the graphene frameworks. Here, we report the designed synthesis of ordered mesoporous graphene spheres (OMGSs) by transformation of self-assembled Fe3O4 nanocrystal superlattices. The resultant OMGSs have an ultrathin framework comprising few-layered graphene, with highly ordered and interconnected mesoporosity and a high surface area. These advantageous structural and textural features, in combination with the excellent electrical conductivity of the graphitic frameworks, render the OMGSs an ideal and general platform for creating hybrid materials that are well suited for use as composite electrodes in lithium-ion batteries (LIBs). As a proof-of-concept demonstration, SnO2 and GeO2 nanoparticles are incorporated into the OMGSs to afford SnO2@OMGSs and GeO2@OMGSs, respectively, both of which exhibit outstanding lithium storage properties when used as LIB anodes.
A facile method was developed to fabricate nitrogen-doped graphene microtubes (N-GMT) with ultra-thin walls of 1–4 nm and large inner voids of 1–2 μm. The successful introduction of nitrogen dopants afforded N-GMT more active sites for significantly enhanced hydrogen evolution reaction (HER) activity, achieving a current density of 10 mA·cm–2 at overpotentials of 0.464 and 0.426 V vs. RHE in 0.1 and 6 M KOH solution, respectively. This HER performance surpassed that of the best metal-free catalyst reported in basic solution, further illustrating the great potential of N-GMT as an efficient HER catalyst for real applications in water splitting and chlor-alkali processes.
Nanoporous (NP) Si/Cu composites are fabricated by means of alloy refining followed by facile electroless dealloying in mild conditions. NP-Si/Cu composites with a three-dimensional porous network nanoarchitecture with different Cu contents are obtained by changing the feeding ratio of alloy precursors. Owing to the rich porosity and integration of conductive Cu into a nanoporous Si backbone, the NP-Si85Cu15 composite exhibits modified conductivity and reduced volumetric expansion/fracture during repeated charging-discharging processes in lithium-ion batteries (LIBs), thus exhibiting much higher cycling reversibility than NP-Si92Cu8 and pure NP-Si. With the advantages of unique performance and easy preparation, NP-Si/Cu composite has potential for application as an advanced anode material for LIBs.
Molecular dynamics simulations showed that a basal carbon nanotube can activate and guide the fabrication of single-walled carbon nanotubes (CNTs) on its internal surface by self-assembly of edge-unpassivated graphene nanoribbons with defects. Furthermore, the distribution of defects on self-assembled CNTs is controllable. The system temperature and defect fraction are two main factors that influence the success of self-assembly. Due to possible joint flaws formed at the boundaries under a relatively high constant temperature, a technique based on increasing the temperature is adopted. Self-assembly is always successful for graphene nanoribbons with relatively small defect fractions, while it will fail in cases with relatively large ones. Similar to the self-assembly of graphene nanoribbons with defects, graphene nanoribbons with different types of dopants can also be self-assembled into carbon nanotubes. The finding provides a possible fabrication technique not only for carbon nanotubes with metallic or semi-conductive properties but also for carbon nanotubes with electromagnetic induction characteristics.
Electronic properties of stanene, the Sn counterpart of graphene are theoretically studied using first-principles simulations. The topological to trivial insulating phase transition induced by an out-of-plane electric field or by quantum confinement effects is predicted. The results highlight the potential to use stanene nanoribbons in gate-voltage controlled dissipationless spin-based devices and are used to set the minimal nanoribbon width for such devices, which is typically approximately 5 nm.
The single crystalline nanostructure of organic semiconductors provides a very promising class of materials for applications in modern optoelectronic devices. However, morphology control and optoelectronic property modulation of high quality single crystalline samples remain a challenge. Here, we report the morphology-controlled growth of single crystalline nanorod arrays of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). We demonstrate that, unlike PTCDA film, PTCDA nanorods exhibits optical waveguide features, enhanced absorption, and Frenkel excitation emission in the visible region. Additionally, we measured the electrical properties of PTCDA nanorods, including the conductivity along the growth direction of the nanorod, which is roughly 0.61 S·m–1 (much higher than that of pure crystalline PTCDA films).
Densely packed and ordered “suprastructures” are new types of nanomaterials exhibiting broad applications. The direct self-assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanotriangles to form “suprastructures” was systematically investigated by varying the temperature and tilt angle of the silicon wafer used in the assembly process. Under optimal conditions, nanotriangles form into regular patterns, maintain their integrity, and form edge-to-edge, point-to-point, and face-to-face connections to form ordered “suprastructures” within an area of hundreds of square microns, achieving a high level of regularity. The formation of the “suprastructures” under optimal conditions could be mainly attributed to the complex balance between multiple temperature-dependent factors, including the atom diffusion rate, solvent evaporation rate, self-assembly rate, and the time for which the nanoparticle stays in the wet medium.
The assembly of hybrid nanomaterials has opened up a new direction for the construction of high-performance anodes for lithium-ion batteries (LIBs). In this work, we present a straightforward, eco-friendly, one-step hydrothermal protocol for the synthesis of a new type of Fe2O3-SnO2/graphene hybrid, in which zero-dimensional (0D) SnO2 nanoparticles with an average diameter of 8 nm and one-dimensional (1D) Fe2O3 nanorods with a length of ~150 nm are homogeneously attached onto two-dimensional (2D) reduced graphene oxide nanosheets, generating a unique point-line-plane (0D-1D-2D) architecture. The achieved Fe2O3-SnO2/graphene exhibits a well-defined morphology, a uniform size, and good monodispersity. As anode materials for LIBs, the hybrids exhibit a remarkable reversible capacity of 1,530 mA·g?1 at a current density of 100 mA·g?1 after 200 cycles, as well as a high rate capability of 615 mAh·g?1 at 2,000 mA·g?1. Detailed characterizations reveal that the superior lithium-storage capacity and good cycle stability of the hybrids arise from their peculiar hybrid nanostructure and conductive graphene matrix, as well as the synergistic interaction among the components.
In this work, we developed a novel triboelectricity-assisted polymer-free method for the transfer of large-area chemical vapor deposited graphene films. With the assistance of electrostatic forces from friction-generated charges, graphene sheets were successfully transferred from copper foils to flexible polymer substrates. Characterization results confirmed the presence of high quality graphene with less defects and contaminations, compared to graphene transferred by conventional poly(methyl methacrylate)-mediated processes. In addition, the graphene samples possessed outstanding electrical transport capabilities and mechanical stability, when studied as electron transfer matrixes in graphene/ZnO hybrid flexible photodetectors. Our results showed a broad application potential for this transfer method in future flexible electronics and optoelectronics.
The development of rechargeable lithium-ion batteries (LIBs) is being driven by the ever-increasing demand for high energy density and excellent rate performance. Charge transfer kinetics and polarization theory, considered as basic principles for charge regulation in the LIBs, indicate that the rapid transfer of both electrons and ions is vital to the electrochemical reaction process. Graphene, a promising candidate for charge regulation in high-performance LIBs, has received extensive investigations due to its excellent carrier mobility, large specific surface area and structure tunability, etc. Recent progresses on the structural design and interfacial modification of graphene to regulate the charge transport in LIBs have been summarized. Besides, the structure-performance relationships between the structure of the graphene and its dedicated applications for LIBs have also been clarified in detail. Taking graphene as a typical example to explore the mechanism of charge regulation will outline ways to further understand and improve carbon-based nanomaterials towards the next generation of electrochemical energy storage devices.
Manipulating materials at the nanometer scale is challenging, particularly if alignment with nanoscale electrodes is desired. Here, we describe a lithography-free, self-aligned nanotrench ablation (SANTA) technique to create nanoscale “trenches” in a polymer like poly(methyl methacrylate) (PMMA). The nanotrenches are self-aligned with carbon nanotube (CNT) or graphene ribbon electrodes through a simple Joule heating process. Using simulations and experiments we investigated how the Joule power, ambient temperature, PMMA thickness, and substrate properties affect the spatial resolution of this technique. We achieved sub-20 nm nanotrenches, for the first time, by lowering the ambient temperature and reducing the PMMA thickness. We also demonstrated a functioning nanoscale resistive memory (RRAM) bit selfaligned with a CNT control device, achieved through the SANTA approach. This technique provides an elegant and inexpensive method to probe nanoscale devices using self-aligned electrodes, without the use of conventional alignment or lithography steps.
Sandwich-type ordered mesoporous carbon/graphene nanocomposites were successfully synthesized using 2D ordered mesoporous silica/graphene nanocomposites as the hard template and an ionic liquid as a N-rich carbon source. We used an ionic liquid of 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide containing nitrile groups (–CN) in the cation and anion as a carbon precursor for the preparation of the nanocomposites. Nitriles do not decompose under thermal treatment in an inert gas atmosphere, but leave significant amounts of N-rich carbon materials. The nanocomposites had a large surface area (1,316 m2·g–1), an average pore diameter of 5.9 nm, and high electrical conductivity. The nanocomposite electrode showed a high specific capacitance of 190 F·g–1 at 0.5 A·g–1 in 1 M TEABF4/AN electrolyte and a good rate capability between 0 and 2.7 V for supercapacitor (or ultracapacitor) applications.
Nanomaterials with electrochemical activity are always suffering from aggregations, particularly during the high-temperature synthesis processes, which will lead to decreased energy-storage performance. Here, hierarchically structured lithium titanate/nitrogen-doped porous graphene fiber nanocomposites were synthesized by using confined growth of Li4Ti5O12 (LTO) nanoparticles in nitrogen-doped mesoporous graphene fibers (NPGF). NPGFs with uniform pore structure are used as templates for hosting LTO precursors, followed by high-temperature treatment at 800 °C under argon (Ar). LTO nanoparticles with size of several nanometers are successfully synthesized in the mesopores of NPGFs, forming nanostructured LTO/NPGF composite fibers. As an anode material for lithium-ion batteries, such nanocomposite architecture offers effective electron and ion transport, and robust structure. Such nanocomposites in the electrodes delivered a high reversible capacity (164 mAh·g–1 at 0.3 C), excellent rate capability (102 mAh·g–1 at 10 C), and long cycling stability.
The persistent need for a sustainable energy economy has led researchers to focus on novel energy conversion and storage technologies, inspiring the discovery of smart material designs such as hierarchical nanocomposites. These nanocomposites have proven effective in the advancement of energy-based technologies. The synergistic properties of hierarchical nanocomposites composed of two types of two-dimensional layered materials, layered double hydroxides and graphene, have resulted in improved electrochemical as well as photocatalytic performance. Synthetic strategies and their effect on the electrochemical and photocatalytic performance of these nanocomposites as high-performance supercapacitors and water oxidation catalysts are discussed in detail in this review.
In this study, macroscopic graphene-wrapped melamine foams (MF-G) were fabricated by an MF-templated layer-by-layer (LBL) assembly using graphene oxide as building blocks, followed by solution-processed reduction. By concisely duplicating sponge-like, highly ordered three-dimensional architectures from MF, the resulting MF-G with an interconnected graphene-based scaffold and tunable nanostructure was explored as compressible, robust electrodes for efficient energy storage. A thin layer of pseudocapacitive polypyrrole (PPy) was then attached and uniformly coated on MF-G, resulting in a well-defined core–double-shell configuration of the MF-G-PPy ternary composite sponges. The as-assembled devices exhibited enhancement of supercapacitor performance, with a high specific capacitance of 427 F·g?1 under a compressive strain of 75% and an excellent cycling stability with only 18% degradation after 5,000 charge–discharge cycles. Besides, the MF-G-PPy electrode maintained stable capacitance up to 100 compression–release cycles, with a compressive strain of 75%. These encouraging results thus provide a new route towards the low-cost, easily scalable fabrication of lightweight and deformation-tolerant electrodes.
Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition (CVD) approach for the high-efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2–4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined-flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.
In this study, a potentially universal new strategy is reported for the large-scale, low-cost fabrication of visible-light-active highly ordered heteronanostructures based on the spontaneous photoelectric-field-enhancement effect inherent in pyramidal morphology. The hierarchical vertically oriented arrayed structures comprise an active molecular co-catalyst at the apex of a visible-light-active large band gap semiconductor for low-cost solar water splitting in a neutral aqueous medium without the use of a sacrificial agent.
Bottom-up synthesis of graphene nanoribbons (GNRs) by surface-assisted polymerization and cyclodehydrogenation of specifically designed precursor monomers has been shown to yield precise edges and doping. Here we use a precursor monomer containing sulfur atoms to fabricate nanostructures on a Au(111) surface at different annealing temperatures. The nanostructures have distinct configurations, varying from sulfur-doped polymers to sulfur-doped chevron-type GNRs (CGNRs) and, finally, pristine graphene nanoribbons with specific edges of periodic five-member carbon rings. Non-contact atomic force microscopy provides clear evidence for the cleavage of C–S bonds and formation of pristine CGNRs at elevated annealing temperatures. First-principles calculations show that the CGNRs exhibit negative differential resistance.
