Monolithic Graphene Research Articles

Codoped Holey Graphene Aerogel by Selective Etching for High‐Performance Sodium‐Ion Storage

AbstractThe pursuit of more efficient carbon‐based anodes for sodium‐ion batteries (SIBs) prepared from facile and economical methods is a very important endeavor. Based on the crystallinity difference within carbon materials, herein, a low‐temperature selective burning method is developed for preparing oxygen and nitrogen codoped holey graphene aerogel as additive‐free anode for SIBs. By selective burning of a mixture of graphene and low‐crystallinity carbon at 450 °C in air, an elastic porous graphene monolith with abundant holes on graphene sheets and optimized crystallinity is obtained. These structural characteristics lead to an additive‐free electrode with fast charge (ions and electrons) transfer and more abundant Na+ storage active sites. Moreover, the heteroatom oxygen/nitrogen doping favors large interlayer distance for rapid Na+ insertion/extraction and provides more active sites for high capacitive contribution. The optimized sample exhibits superior sodium‐ion storage capability, i.e., high specific capacity (446 mAh g−1 at 0.1 A g−1), ultrahigh rate capability (189 mAh g−1 at 10 A g−1), and long cycle life (81.0% capacity retention after 2000 cycles at 5 A g−1). This facile and economic strategy might be extended to fabricating other superior carbon‐based energy storage materials.

3D Graphene‐Based H2‐Production Photocatalyst and Electrocatalyst

AbstractHydrogen (H2) has been deemed as the most promising and valuable alternative to nonrenewable fossil fuels. Photocatalytic and electrocatalytic water splitting are considered to be the most efficient and environmentally friendly approaches for the sustainable H2 evolution reaction (HER). Graphene with a 3D framework has been utilized for the HER due to its unique structure and properties, including its hierarchical network, large specific surface area, diverse pore distribution, outstanding light absorption ability, and excellent electrical conductivity. The large specific surface area and hierarchically porous structure of 3D graphene can not only maximize the exposure of active sites but also promote electron transfer and gas product diffusion. In addition, the free‐standing 3D graphene monolith is easily recycled compared with powder phase support, which can prevent the loss of active catalysts. By making full use of the aforementioned merits, 3D graphene‐based composite materials show great promise as high‐performance catalysts toward photocatalytic and electrocatalytic HER. In this review, recent advances in fabricating 3D graphene‐based composite materials and their applications in both photocatalytic and electrocatalytic HER are summarized and discussed. Furthermore, the current challenges and future vision associated with the design, fabrication, and integration of 3D graphene‐based composite materials toward HER are put forward.

Space-Confined Graphene Films for Pressure-Sensing Applications

Transferring the inherent physicochemical properties of monolithic graphene to its macroassemblies requires reasonable and controllable structural engineering. The elasticity has been considered to...

A dense graphene monolith with poloxamer prefunctionalization enabling aqueous redispersion to obtain solubilized graphene sheets

The realization of good aqueous dispersibility of commercial graphene products composed of exfoliated graphene sheets is of significance for downstream applications. However, the tap density of commercial graphene powder is quite low (0.03–0.1 kg/m3), meaning that 1 kg graphene powder occupies about 10–30 m3 in volume during transportation. And, the available content of commercial graphene dispersion/slurry in aqueous medium cannot exceed 5 wt%, although the density is high (≈ 1050 kg/m3). In this work, a graphene monolith was prepared by oven-drying of graphene sheets prefunctionalized with poloxamer surfactants. Our graphene monoliths not only have a high density (1500 kg/m3) and high graphene content (≈ 10 wt%), but also a full capability to be completely redispersed (≈ 100%) in water by bath sonication to obtain solubilized graphene sheets, whose lateral size and thickness are unchanged compared to as-exfoliated ones. Moreover, a simple empirical method was proposed to predict the redispersion capability of graphene monoliths using different poloxamers by contact angle measurements. Our results provide a universal approach to make exfoliated graphene-based products with better downstream availability and lower transportation cost.

Metal-Level Thermally Conductive yet Soft Graphene Thermal Interface Materials.

Along with the technology evolution for dense integration of high-power, high-frequency devices in electronics, the accompanying interfacial heat transfer problem leads to urgent demands for advanced thermal interface materials (TIMs) with both high through-plane thermal conductivity and good compressibility. Most metals have satisfactory thermal conductivity but relatively high compressive modulus, and soft silicones are typically thermal insulators (0.3 W m-1 K-1). Currently, it is a great challenge to develop a soft material with the thermal conductivity up to metal level for TIM application. This study solves this problem by constructing a graphene-based microstructure composed of mainly vertical graphene and a thin cap of horizontal graphene layers on both the top and bottom sides through a mechanical machining process to manipulate the stacked architecture of conventional graphene paper. The resultant graphene monolith has an ultrahigh through-plane thermal conductivity of 143 W m-1 K-1, exceeding that of many metals, and a low compressive modulus of 0.87 MPa, comparable to that of silicones. In the actual TIM performance measurement, the system cooling efficiency with our graphene monolith as TIM is 3 times as high as that of the state-of-the-art commercial TIM, demonstrating the superior ability to solve the interfacial heat transfer issues in electronic systems.

(Invited) Nano Carbon and Polymeric Materials for Energy Conversion and Storage

Green energy technologies have been highly demanded for a sustainable development. In this talk, our recent studies for the electricity conversion/storage using nano carbon and polymeric materials will be presented. These will include the material design, synthesis, and device fabrication, targeting for high energy efficiency and understanding the mechanism using simpler or cheap materials. Recent five references: "Polymeric Graphene Bulk Materials with a 3D Cross-Linked Monolithic Graphene Network", Wangqiao Chen, Peishuang Xiao, Honghui Chen, Hongtao Zhang, Qichun Zhang, and Yongsheng Chen*, Mater ., 2018, 1802403."Nonfullerene Tandem Organic Solar Cells with High Performance of 14.11%", Lingxian Meng, Yamin Zhang, Xiangjian Wan*, Chenxi Li, Xin Zhang, Yanbo Wang, Xin Ke, Zuo Xiao, Liming Ding*, Ruoxi Xia, Hin-Lap Yip, Yong Cao, Yongsheng Chen*, Science , 2018, 361, 1094-1098."Monolithic 3D Cross-linked Polymeric Graphene Materials and the Likes: Preparation and Their Redox Catalytic Applications",Yanhong Lu, Yanfeng Ma, Tengfei Zhang, Yang Yang, Lei Wei, and Yongsheng Chen , Am. Chem. Soc., 2018, 140 (37), pp 11538–11550."Ultra-Broadband Wide-Angle Terahertz Absorption Properties of 3D Graphene Foam",Zhiyu Huang, Honghui Chen, Yi Huang,* Zhen Ge, Ying Zhou, Yang Yang, Peishuang Xiao, Jiajie Liang, Tengfei Zhang, Qian Shi, Guanghao Li, and Yongsheng Chen, Funct. Mater. , 2017, 1704363“Macroscale light propulsion of 3D cross-linked graphene ”, Tengfei Zhang†, Huicong Chang†, Yingpeng Wu†, Peishuang Xiao, Ningbo Yi, Yanhong Lu, Yanfeng Ma, Yi Huang, Kai Zhao, Xiaoqing Yan, Zhibo Liu, Jianguo Tian and Yongsheng Chen*, Nature Photon., 2015, 9, 471-476

Direct assembly of micron-size porous graphene spheres with a high density as supercapacitor materials

A high volumetric energy density is extremely important in practical energy storage devices. Porous yet dense graphene monoliths obtained from a graphene hydrogel by capillary shrinkage are promising materials for achieving both high volumetric power and energy densities but they are hard to be further processed or ground into fine powders for use in industrial electrode fabrication. Here, by introducing an additional shaking process during the assembly, the bulk graphene hydrogel was broken into many graphene spheres of a much smaller size, and after capillary drying, micron-size graphene spheres were obtained with both a high density and high porosity. These microspheres were used to assemble an electrode with a higher density and give an improved volumetric energy density, which is very important for practical energy storage devices.

Size Effects on the Mechanical Properties of Nanoporous Graphene Networks

AbstractIt 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.

High performance broadband acoustic absorption and sound sensing of a bubbled graphene monolith

A bubbled graphene monolith exhibits a superhigh normalized absorption coefficient of up to 0.9 within a wide frequency range.

The adsorptive potential of graphene monolith for organic pollutant treatment: kinetics, isotherms, and thermodynamics of interactions

The adsorptive potential of graphene monolith for organic pollutant treatment: kinetics, isotherms, and thermodynamics of interactions

Flexible and transparent graphene complementary logic gates

Flexible and transparent monolithic graphene transistors and complementary logic gates were fabricated using chemically doped graphene.

Amphiphilic cellulose nanofiber-interwoven graphene aerogel monolith for dyes and silicon oil removal

Monolithic graphene oxide (GO) and reduced GO (rGO) aerogel is recently receiving a great deal of concern as a promising adsorbent, whose structure and surface properties, however, are anticipated to be improved and adapted to the adsorption of organic contaminants with various polarities and ionic properties. Herein, super strong and hydrophilic cellulose nanofiber (CNF) was exploited as a cross-linker to interweave in between rGO layers so as to tune and balance the structural and surface properties (hydrophilicity and hydrophobicity) of the monolith. It was found that mechanical property of the monolith changes stepwise with the addition of CNF and can be greatly improved by proportion with CNF irrespective of a little sacrifice in electrical conductivity. Filling and further formation of aggregating bundle structure of CNFs in rGO monolith gradually decreases porosity at compensation of a slight increase in monolithic volume. CNF plays a critical role in separating rGO layers, leading to formation of the exposed and uniformly dispersed rGO layers in the monoliths. It can increase the amount of oxygen containing groups at the same time to generate carbonized moieties, thus ameliorating both hydrophilicity and hydrophobicity of the monolithic aerogel. The unique structural change and improved amphiphile surface property due to the addition of CNF can greatly enhance affinity of the hybridized monolith toward the adsorption of not only hydrophilic (both anionic and cationic) dyes but also hydrophobic organic oil.

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

AbstractCarbon materials are the most promising anodes for sodium‐ion batteries (SIBs), but low initial Coulombic efficiency (ICE) and poor cyclic stability hinder their practical use. It is shown herein, that an effective but simple remedy for these problems can be achieved by deactivating defects in the carbon with Al2O3 nanocluster coverage. A 3D porous graphene monolith (PGM) is used as the model material and Al2O3 nanoclusters around 1 nm are grown on the defects of graphene. It is shown that these Al2O3 nanoclusters suppress the decomposition of conductive sodium salt in the electrolyte, resulting in the formation of a thin and homogenous solid electrolyte interphase (SEI). In addition, Al2O3 nanoclusters appear to reduce the detrimental etching of the SEI by hydrogen fluoride (HF) and improve its stability. Therefore, after the introduction of Al2O3 nanoclusters, the ICE, cyclic stability, and rate capability of the PGM are greatly improved. A higher ICE (70.2%) and capacity retention (82.9% after 500 cycles at 0.5 A g−1) than those of normally reported for large surface area carbons are achieved. This work indicates a new way to deactivate defects and modify the SEI of carbon materials, and hopefully accelerate the commercialization of carbon materials as anode materials for SIBs.

Highly conductive, mechanically strong graphene monolith assembled by three-dimensional printing of large graphene oxide

The manufacturing of three-dimensional (3D) graphene monolith with high mechanical and electrical performance has become an urgent issue in view of their potential applications in energy and electronics fields. Due to the structure rigidity and poor liquid-phase processing capability of graphene sheets, it is challenging to fabricate 3D graphene monolith with high mechanical performance, including strength, toughness and resiliency. Graphene oxide (GO) shows an improved dispersibility and reduction-restorable conductivity, which enables it to effectively balance the processing and comprehensive performances of graphene monolith. Here, we demonstrate a strategy to fabricate high-performance, shape-designable 3D graphene monolith through a 3D printing method based on large-sized graphene oxide (LGO) fluid ink. The concentration of the LGO ink for printing is as low as 20 mg/mL. The resulting monolith exhibits low density (12.8 mg/cm3), high electrical conductivity (41.1 S/m), high specific strength (10.7 × 103 N·m/Kg) and compressibility (up to 80% compressive strain). Such a 3D printing technique enables plenty of complicated monolith structures and broadens the application range of graphene.

Polymeric Graphene Bulk Materials with a 3D Cross‐Linked Monolithic Graphene Network

Although many great potential applications are proposed for graphene, till now none are yet realized as a stellar application. The most challenging issue for such practical applications is to figure out how to prepare graphene bulk materials while maintaining the unique two-dimensional (2D) structure and the many excellent properties of graphene sheets. Herein, such polymeric graphene bulk materials containing three-dimensional (3D) cross-linked networks with graphene sheets as the building unit are reviewed. The theoretical research on various proposed structures of graphene bulk materials is summarized first. Then, the synthesis or fabrication of these graphene materials is described, which comprises mainly two approaches: chemical vapor deposition and cross-linking using graphene oxide directly. Finally, some exotic and exciting potential applications of these graphene bulk materials are presented.

Hierarchical Porous N-doped Graphene Monoliths for Flexible Solid-State Supercapacitors with Excellent Cycle Stability

N-doped-graphene-assembled (NG-assembled) monoliths with hierarchical porous structure and outstanding electrochemical properties are desired for making high-performance flexible supercapacitors. H...

Free-standing, layered graphene monoliths for long-life supercapacitor

Fabricating free-standing film/paper or 3D material without additive binder is of great importance to maintain its original architectures and properties. Here, we for the first time introduce a simple, facile approach to fabricate a free-standing, layered N-doping reduced graphene oxide (NRGO) monolith for supercapacitor, firstly mixing graphene oxide (GO) with urea, and lastly taking a short-term flame bath. It is found that urea is a key sacrificial grasper, which can effectively prevent reduced GO (RGO) sheets from being peeled off in flame bath. Moreover, 3.5–7.0 at.% of N elements are successfully introduced into RGO skeleton. These structural characteristics are translated into high specific capacitance (323.7 F g−1 at 1 A g−1, higher than RGO powder (252.1 F g−1)), ultra-high coulombic efficiency (125% at 1 A g−1) and superior cycle performance with a 9.2% improvement in specific capacitance after 50,000 cycles at 30 A g−1. Relatively, only 69.3% of the specific capacitance for RGO powder remains after 10,000 cycles at 30 A g−1. Compared with RGO powder, NRGO shows obviously improvement in coulombic efficiency, energy efficiency, and especially in cycle stability. Thus, this layered NRGO not only shows a high energy storage capacity, but also successfully solves the stability problem in the long-term charge/discharge cycle. This provides a novel clue for designing long-life graphene-based electrode materials for supercapacitor.

Gaoquan Shi (1963‐2018): A Pioneer in the Chemistry of Graphene and Electrochemistry of Conjugated Polymers.

Gaoquan Shi (1963‐2018): A Pioneer in the Chemistry of Graphene and Electrochemistry of Conjugated Polymers.

Dense Graphene Monolith for High Volumetric Energy Density Li–S Batteries

AbstractDespite the outstanding gravimetric performance of lithium–sulfur (Li–S) batteries, their practical volumetric energy density is normally lower than that of lithium‐ion batteries, mainly due to the low density of nanostructured sulfur as well as the porous carbon hosts. Here, a novel approach is developed to fabricate high‐density graphene bulk materials with “ink‐bottle‐like” mesopores by phosphoric acid (H3PO4) activation. These pores can effectively confine the polysulfides due to their unique structure with a wide body and narrow neck, which shows only a 0.05% capacity fade per cycle for 500 cycles (75% capacity retention) for accommodating polysulfides. With a density of 1.16 g cm−3, a hybrid cathode containing 54 wt% sulfur delivers a high volumetric capacity of 653 mA h cm−3. As a result, a device‐level volumetric energy density as high as 408 W h L−1 is achieved with a cathode thickness of 100 µm. This is a periodic yet practical advance to improve the volumetric performance of Li–S batteries from a device perspective. This work suggests a design principle for the real use Li–S batteries although there is a long way ahead to bridge the gap between Li–S batteries and Li–ion batteries in volumetric performance.

Vapor–Liquid Deposition Strategy To Prepare Superhydrophobic and Superoleophilic Graphene Aerogel for Oil–Water Separation

The problems of high temperature and volume shrinkage are frequently encountered in the process of fabricating superhydrophobic graphene aerogels. We present ultralight graphene aerogels with superhydrophobicity and superoleophilicity by a vapor–liquid deposition process. The graphene aerogels are prepared by graphene oxide assembled into monolithic graphene hydrogel in dopamine-mediated aqueous solution at mild temperature and a sealed reaction, then by directional freezing and freeze-drying. Subsequent fluorinated alkyl silane is introduced to produce ultralight graphene aerogel by vapor–liquid deposition treatments; the surface of the aerogel has outstanding superhydrophobicity and superoleophilicity with water and oil contact angles of 160.2° and 0°, respectively. In addition, the resulting graphene aerogels showed super low density, large specific surface area, excellent adsorption capacities, and superior adsorption recyclability. Its adsorption capacity was higher than 109 g/g for the used common o...