Chemical adsorption of NiO nanostructures on nickel foam-graphene for supercapacitor applications

Few-layer graphene was synthesized on a nickel foam template by chemical vapor deposition. The resulting three-dimensional (3D) graphene was loaded with nickel oxide nanostructures using the successive ionic layer adsorption and reaction technique. The composites were characterized and investigated as electrode material for supercapacitors. Raman spectroscopy measurements on the sample revealed that the 3D graphene consisted of mostly few layers, while X-ray diffractometry and scanning electron microscopy revealed the presence of nickel oxide. The electrochemical properties were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and potentiostatic charge–discharge in aqueous KOH electrolyte. The novelty of this study is the use of the 3D porous cell structure of the nickel foam which allows for the growth of highly conductive graphene and subsequently provides support for uniform adsorption of the NiO onto the graphene. The NF-G/NiO electrode material showed excellent properties as a pseudocapacitive device with a high-specific capacitance value of 783 F g^?1 at a scan rate of 2 mV s^?1. The device also exhibited excellent cycle stability, with 84 % retention of the initial capacitance after 1000 cycles. The results demonstrate that composites made using 3D graphene are versatile and show considerable promise as electrode materials for supercapacitor applications.     

Hybrids of carbon nanotubes and graphene/graphene oxide

This paper reviews recent progress in hybrids based on carbon nanotubes (CNTs) and graphene (G) or graphene oxide (GO). The combination of CNTs, including single-walled (SW), double-walled (DW) and multi-walled (MW), and G or GO resulted in various hybrids. CNTs–G/GO hybrid thin films are usually prepared by using solution/suspension casting and layer-by-layer (LbL) deposition, free-standing sheets are fabricated by using vacuum filtration and 3D hierarchical structures are produced by using chemical vapor deposition (CVD). CNTs–G/GO hybrids have also been used as fillers to fabricate polymer composites with synergistic effects. The composites have significantly improved electrical, mechanical and thermal properties, which make them very useful for various potential applications, such as transparent electrodes replacing ITO, electrodes for supercapacitors, lithium-ion batteries and dye-sensitized solar cells.     

Synthesis and Self-Assembly of Ultrathin Holey Graphdiyne Nanosheets for Oxygen Reduction Reaction

Graphdiyne (GDY) is a fascinating graphene-like 2D carbon allotrope comprising sp and sp² hybridized carbon atoms. However, GDY materials synthesized by solution-phase methods normally come as thick and porous films or amorphous powders with severely disordered stacking modes that obstruct macroscopic applications. Here, a facile and scalable synthesis of ultrathin holey graphdiyne (HGDY) nanosheets is reported via palladium/copper co-catalyzed homocoupling of 1,3,5-triethynylbenzene. The resulting freestanding 2D HGDY self-assembles into 3D foam-like networks which can in situ anchor clusters of palladium atoms on their surfaces. The Pd/HGDY hybrids exhibit high electrocatalytic activity and stability for the oxygen reduction reaction which outperforms that of Pt/C benchmark. Based on the ultrathin graphene-like sheets and their unique 3D interconnected macrostructures, Pd/HGDY holds great promise for practical electrochemical catalysis and energy-related applications.     

High‐Performance Asymmetric Supercapacitors Based on Multilayer MnO2/Graphene Oxide Nanoflakes and Hierarchical Porous Carbon with Enhanced Cycling Stability

In this work, MnO₂/GO (graphene oxide) composites with novel multilayer nanoflake structure, and a carbon material derived from Artemia cyst shell with genetic 3D hierarchical porous structure (HPC), are prepared. An asymmetric supercapacitor has been fabricated using MnO₂/GO as positive electrode and HPC as negative electrode material. Because of their unique structures, both MnO₂/GO composites and HPC exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high voltage range of 0–2 V in aqueous electrolyte, which exhibits maximum energy density of 46.7 Wh kg^?1 at a power density of 100 W kg^?1 and remains 18.9 Wh kg^?1 at 2000 W kg^?1. Additionally, such device also shows superior long cycle life along with ～100% capacitance retention after 1000 cycles and ～93% after 4000 cycles.     

Designed fabrication of hierarchical porous carbon nanotubes/graphene/carbon nanofibers composites with enhanced capacitive desalination properties

Carbonaceous materials, one of the most important electrode materials for sea water desalination, have attracted tremendous attention. Herein, we develop a facile and effective two-step strategy to fabricate hierarchical porous carbon nanotubes/graphene/carbon nanofibers (CNTs/G/CNFs) composites for capacitive desalination application. Graphite oxide (GO), Ni²⁺, and Co²⁺ are introduced into polyacrylonitrile (PAN) nanofibers by electrospinning method. During the annealing process, the PAN nanofibers are carbonized into CNFs felt, while the CNTs grow in situ on the surface of CNFs and graphite oxide are reduced into graphene simultaneously. Benefiting from the unique hierarchical porous structure, the as-prepared CNTs/G/CNFs composites have a large specific surface area of 223.9 m² g^?1 and excellent electrical conductivity. The maximum salt capacity of the composites can reach to 36.0 mg g^?1, and the adsorbing capability maintains a large retention of 96.9% after five cycles. Moreover, the effective deionization time of the CNTs/G/CNFs composites lasts more than 30 min, much better than the commercial carbon fibers (C-CFs) and graphene/carbon nanofibers (G/CNFs) composites. Results suggest that the designed hierarchical porous CNTs/G/CNFs architecture could enhance the capacitive desalination properties of electrode materials. And the possible adsorption mechanism of the novel electrode materials is proposed as well.     

Graphene in Photocatalysis: A Review

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets‐supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis‐related properties of graphene and its derivatives, and design rules and synthesis methods of graphene‐based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi‐junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H₂ production, and CO₂ reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene‐based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.     

石墨烯基复合材料的三维组装与应用研究进展

三维石墨烯结构体不仅继承了二维石墨烯片完美的碳晶体结构,还展现出超低的密度、极高的孔隙率和较大的比表面积等特点,具有导电、导热、吸附等优异性能,是近年来石墨烯功能材料中的一颗新星。目前,石墨烯与聚合物、无机纳米材料组装成三维结构复合材料的研究已经取得了实质性进展,研究者通过丰富的化学和物理路径实现了石墨烯与功能组分的三维有序组装,并赋予该材料奇特的结构特点和性能优势。这些特性使材料在能量储存、环境保护、传感器等研究领域表现出不错的应用前景。根据当前研究热点,综述了石墨烯基复合材料的三维组装与应用的研究进展,包括三维石墨烯/聚合物复合材料与三维石墨烯/无机纳米复合材料两种体系。重点总结了两种体系的三维组装方法,并分析了复合材料中石墨烯与功能组分的结构特点,简要概括了当前三维石墨烯基复合材料在环境保护、超级电容器等不同领域的应用进展,并对三维石墨烯基复合材料的三维结构设计与多样化应用进行了展望。     

Functional composite materials based on chemically converted graphene

Graphene, a one-atom layer of graphite, possesses a unique two-dimensional structure and excellent mechanical, thermal, and electrical properties. Thus, it has been regarded as an important component for making various functional composite materials. Graphene can be prepared through physical, chemical and electrochemical approaches. Among them, chemical methods were tested to be effective for producing chemically converted graphene (CCG) from various precursors (such as graphite, carbon nanotubes, and polymers) in large scale and at low costs. Therefore, CCG is more suitable for synthesizing high-performance graphene based composites. In this progress report, we review the recent advancements in the studies of the composites of CCG and small molecules, polymers, inorganic nanoparticles or other carbon nanomaterials. The methodology for preparing CCG and its composites has been summarized. The applications of CCG-based functional composite materials are also discussed.     

Laser‐Assisted Lattice Recovery of Graphene by Carbon Nanodot Incorporation

Producing highly oriented graphene is a major challenge that constrains graphene from fulfilling its full potential in technological applications. The exciting properties of graphene are impeded in practical bulk materials due to lattice imperfections that hinder charge mobility. A simple method to improve the structural integrity of graphene by utilizing laser irradiation on a composite of carbon nanodots (CNDs) and 3D graphene is presented. The CNDs attach themselves to defect sites in the graphene sheets and, upon laser‐assisted reduction, patch defects in the carbon lattice. Spectroscopic experiments reveal graphitic structural recovery of up to 43% and electrical conductivity four times larger than the original graphene. The composites are tested as electrodes in electrochemical capacitors and demonstrate extremely fast RC time constant as low as 0.57 ms. Due to their low defect concentrations, the reduced graphene oxide‐carbon nanodot (rGO‐CND) composites frequency response is sufficiently fast to operate as AC line filters, potentially replacing today's electrolytic capacitors. Using this methodology, demonstrated is a novel line filter with one of the fastest capacitive responses ever reported, and an aerial capacitance of 68.8 mF cm^?2. This result emphasizes the decisive role of structural integrity for optimizing graphene in electronic applications.     

Extrusion‐Based 3D Printing of Hierarchically Porous Advanced Battery Electrodes

A highly porous 2D nanomaterial, holey graphene oxide (hGO), is synthesized directly from holey graphene powder and employed to create an aqueous 3D printable ink without the use of additives or binders. Stable dispersions of hydrophilic hGO sheets in water (≈100 mg mL^?1) can be readily achieved. The shear‐thinning behavior of the aqueous hGO ink enables extrusion‐based printing of fine filaments into complex 3D architectures, such as stacked mesh structures, on arbitrary substrates. The freestanding 3D printed hGO meshes exhibit trimodal porosity: nanoscale (4–25 nm through‐holes on hGO sheets), microscale (tens of micrometer‐sized pores introduced by lyophilization), and macroscale (<500 µm square pores of the mesh design), which are advantageous for high‐performance energy storage devices that rely on interfacial reactions to promote full active‐site utilization. To elucidate the benefit of (nano)porosity and structurally conscious designs, the additive‐free architectures are demonstrated as the first 3D printed lithium–oxygen (Li–O₂) cathodes and characterized alongside 3D printed GO‐based materials without nanoporosity as well as nanoporous 2D vacuum filtrated films. The results indicate the synergistic effect between 2D nanomaterials, hierarchical porosity, and overall structural design, as well as the promise of a freeform generation of high‐energy‐density battery systems.     

Laser‐Induced Molybdenum Carbide–Graphene Composites for 3D Foldable Paper Electronics

Versatile and low‐cost manufacturing processes/materials are essential for the development of paper electronics. Here, a direct‐write laser patterning process is developed to make conductive molybdenum carbide–graphene (MCG) composites directly on paper substrates. The hierarchically porous MCG structures are converted from fibrous paper soaked with the gelatin‐mediated inks containing molybdenum ions. The resulting Mo₃C₂ and graphene composites are mechanically stable and electrochemically active for various potential applications, such as electrochemical ion detectors and gas sensors, energy harvesters, and supercapacitors. Experimentally, the electrical conductivity of the composite is resilient to mechanical deformation with less than 5% degradation after 750 cycles of 180° repeated folding tests. As such, the direct laser conversion of MCGs on papers can be applicable for paper‐based electronics, including the 3D origami folding structures.     

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.     

An Electrosynthesized 3D Porous Molybdenum Sulfide/Graphene Film with Enhanced Electrochemical Performance for Lithium Storage

Molybdenum sulfide/graphene composites are promising anode materials for lithium‐ion batteries (LIBs). In this work, MoS_x/graphene composite film with an ideal 3D porous structure is developed via a facile and straightforward electrochemical route. The MoS_x nanoparticles are uniformly anchored on the graphene nanosheets that are randomly arranged, resulting in MoS_x/graphene composites with well‐developed porous structure. Benefiting from such structure and the synergistic effect from two components, this material shows a high specific capacity over 1200 mA h g^?1, an excellent rate performance, and superior cycling stability. The dominating pseudocapacitive behavior in Li storage contributes to the outstanding rate capacity. Importantly, this kind of novel material can be easily produced as 3D microelectrodes for microscaled LIBs that are highly demanded for autonomous microelectronic systems.     

A review on three‐dimensional graphene: Synthesis,electronic and biotechnology applications‐The Unknown Riddles

In the last decade, carbon‐based nanostructures such as buckyball (C₆₀), carbon nanotube (CNT), graphene and three‐dimensional (3D) graphene have been identified as promising materials for electronic, electrochemical energy storage (batteries and supercapacitors), optical and sensing applications. Since the discovery of graphene in 2004, scientists have devised mass production techniques and explored graphene as a promising material for a wide range of applications. Most of the electronic and solar cell applications require materials with good electronic conductivity, mobility and finite bandgap. Graphene is a zero bandgap material which prevents it from the mainstream applications. On the other hand, 3D graphene has good electronic conductivity, mobility, bandgap and electrochemical properties. This review article will focus on the synthesis of the 3D graphene, its structure‐property relationships, biotechnology and electronic applications and the hidden properties that are yet to be explored fully.     

Promoted Glycerol Oxidation Reaction in an Interface‐Confined Hierarchically Structured Catalyst

Confined catalysis in a 2D system is of particular interest owing to the facet control of the catalysts and the anisotropic kinetics of reactants, which suppress side reactions and improve selectivity. Here, a 2D‐confined system consisting of intercalated Pt nanosheets within few‐layered graphene is demonstrated. The strong metal–substrate interaction between the Pt nanosheets and the graphene leads to the quasi‐2D growth of Pt with a unique (100)/(111)/(100) faceted structure, thus providing excellent catalytic activity and selectivity toward one‐carbon (C1) products for the glycerol oxidation reaction. A hierarchically porous graphene architecture, grown on carbon cloth, is used to fabricate the confined catalyst bed in order to enhance the mass‐diffusion limitation in interface‐confined reactions. Owing to its unique 3D porous structure, this graphene‐confined Pt catalyst exhibits an extraordinary mass activity of 2910 mA mg_Pt ^?1 together with a formate selectivity of 79% at 60 °C. This paves the way toward rational designs of heterogeneous catalysts for energy‐related applications.     

3D Graphene Frameworks/Co3O4 Composites Electrode for High‐Performance Supercapacitor and Enzymeless Glucose Detection

3D graphene frameworks/Co₃O₄ composites are produced by the thermal explosion method, in which the generation of Co₃O₄ nanoparticles, reduction of graphene oxide, and creation of 3D frameworks are simultaneously completed. The process prevents the agglomeration of Co₃O₄ particles effectively, resulting in monodispersed Co₃O₄ nanoparticles scattered on the 3D graphene frameworks evenly. The prepared 3D graphene frameworks/Co₃O₄ composites used as electrodes for supercapacitor display a definite improvement on electrochemical performance with high specific capacitance (≈1765 F g^?1 at a current density of 1 A g^?1), good rate performance (≈1266 F g^?1 at a current density of 20 A g^?1), and excellent stability (≈93% maintenance of specific capacitance at a constant current density of 10 A g^?1 after 5000 cycles). In addition, the composites are also employed as nonenzymatic sensors for the electrochemical detection of glucose, which exhibit high sensitivity (122.16 µA mM ^?1 cm^?2) and noteworthy lower detection limit (157 × 10^?9 M , S/N = 3). Therefore, the authors expect that the 3D graphene frameworks/Co₃O₄ composites described here would possess potential applications as the electrode materials in supercapacitors and nonenzymatic detection of glucose.     

Freestanding 3D Graphene–Nickel Encapsulated Nitrogen‐Rich Aligned Bamboo Like Carbon Nanotubes for High‐Performance Supercapacitors with Robust Cycle Stability

3D hierarchical structures are reported based on graphene–nickel encapsulated nitrogen‐rich aligned bamboo like carbon nanotubes, which show not only high‐performance supercapacitance behavior but also a great robust cyclic stability. A facile synthesis route is developed of 2D nickel oxide decorated functionalized graphene nanosheets (2D‐NiO‐f:GNSs) hybrids and 3D nitrogen doped bamboo‐shaped carbon nanotubes (NCNTs) vertically standing on the functionalized graphene nanosheets (3D‐NCNT@f:GNSs) by using a thermal decomposition method. The chemical reduction and morphology‐dependent electrochemical response are investigated. The enhanced specific capacitance of 3D‐NCNT@f:GNSs as compared to that of 2D‐NiO‐f:GNSs suggests the synergistic effects and indicates the importance of energy storage and superior long‐term cycling performance that are achieved. This 3D‐NCNT@f:GNSs hybrid shows a remarkable cycling stability with a maximum power density of 12.32 kW kg⁻¹ and maximum energy density of 109.13 Wh kg⁻¹ due to the good connection of NCNT and f:GNSs. This unique 3D nano network architecture enables the availability of large surface areas of NCNT, thus endowing the nanohybrids with high specific capacitance and excellent reusability.     

Colloids of Holey Gd2O3 Nanosheets Converted from Exfoliated Gadolinium Hydroxide Layers

This paper proposes a confined solid‐state conversion approach using layered metal‐hydroxides for the production of a colloidal suspension of porous 2D crystalline metal oxide layers with superior electrochemical H₂O₂ sensing performance. This study investigates the conversion chemistry of delaminated layers of gadolinium hydroxide (LGdH), [Gd₂(OH)₅]⁺, encapsulated in a silica nanoshell that provides an antistacking and antisintering environment during the phase‐transition at high temperature. Thermal treatment of the LGdH layers within the protected environment results in a dimensionally confined phase‐transition into crystalline Gd₂O₃ nanosheets with an isomorphic 2D structure. Furthermore, annealing at higher temperatures leads to the evolution of in‐plane mesoporous structure on the Gd₂O₃ nanosheet. Based on insight acquired from in‐depth investigation, the evolution of in‐plane porosity proceeds through the in‐plane dominant silicate‐formation reaction at the interface with the surrounding silica shell. Their 2D‐anisotropic and mesoporous morphological features are preserved, producing a colloidal suspension of holey nanosheets that can be used to fabricate a thin and porous film through wet‐coating deposition. This study also demonstrates the superior electrochemical H₂O₂ sensing ability of the resultant porous Gd₂O₃ film, which represents a ≈1000‐ and 10‐fold enhancement of the detection limit and sensitivity, respectively, in comparison to previously reported Gd₂O₃ films.     

A Simple Route to Porous Graphene from Carbon Nanodots for Supercapacitor Applications

A facile method to convert biomolecule‐based carbon nanodots (CNDs) into high‐surface‐area 3D‐graphene networks with excellent electrochemical properties is presented. Initially, CNDs are synthesized by microwave‐assisted thermolysis of citric acid and urea according to previously published protocols. Next, the CNDs are annealed up to 400 °C in a tube furnace in an oxygen‐free environment. Finally, films of the thermolyzed CNDs are converted into open porous 3D turbostratic graphene (3D‐ts‐graphene) networks by irradiation with an infrared laser. Based upon characterizations using scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and Raman spectroscopy, a feasible reaction mechanism for both the thermolysis of the CNDs and the subsequent laser conversion into 3D‐ts‐graphene is presented. The 3D‐ts‐graphene networks show excellent morphological properties, such as a hierarchical porous structure and a high surface area, as well as promising electrochemical properties. For example, nearly ideal capacitive behavior with a volumetric capacitance of 27.5 mF L ^{? 1} is achieved at a current density of 560 A L ^{? 1}, which corresponds to an energy density of 24.1 mWh L ^{? 1} at a power density of 711 W L ^{? 1}. Remarkable is the extremely fast charge–discharge cycling rate with a time constant of 3.44 ms.     

石墨烯基有序介孔金属氧化物复合材料的制备及研究进展

综述了以石墨烯作为载体,利用有序介孔金属氧化物特殊的3D结构,以及两者共存产生的协同效应,开发系列新型石墨烯基有序介孔金属氧化物复合材料的最新研究进展。介绍了本课题组在有序介孔金属氧化物的可控合成、与石墨烯的有效复合以及复合材料的光电性能等方面的探索性研究。着重对石墨烯基有序介孔金属氧化物复合材料的制备方法、形成机理及其在催化、电化学、传感和能量储存等领域的最新应用进行概述,并展望了其未来的发展趋势。