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Toward high capacitance and rate capability supercapacitor: Three dimensional graphene network fabricated by electric field-assisted assembly method
Abstract
In this work, we report a facile method via electric field-assisted assembly of graphene oxide sheets to produce 3D graphene network. As expected, high specific capacitance (∼238 F g⁻¹ at 0.5 A g⁻¹) and well rate capability (the specific capacitance retained 60% at 10 A g⁻¹) have been achieved in 3D graphene network-based supercapacitor. The significantly improved performances are due to large electrolyte accessible surface (257 m² g⁻¹) and high electrical conductivity (12.58 S cm⁻¹). Furthermore, the electric field-assisted assembly method is a simple and promising way to fabricate 3D graphene network, compared to chemical vapor deposition, freeze drying, etc., which could efficiently reduce the production cost and promote its industrial production.
... Three-dimensional graphene networks (3DGNs) fabricated using an electric fieldassisted assembly method demonstrated a high specific capacitance of 238 F/g and maintained good rate capability [11]. Further advancements include the development of solidstate fractional-order electric double-layer capacitors (FO-EDLCs) that allow tuning of the low-frequency impedance phase angle. ...
The evolution of electric double-layer capacitors (EDLCs) has significantly benefited from advancements in graphene-based materials, particularly graphene oxide (GO) and reduced graphene oxide (rGO). This systematic review consolidates and analyzes existing research on the roles of GO and rGO in enhancing the performance of EDLCs, focusing on synthesis methods, electrode fabrication, electrolytes, and performance metrics such as capacitance, energy density, and cycling stability. Following the PICOS and PRISMA frameworks, a comprehensive literature search was conducted across Scopus, Web of Science, PubMed, and IEEE Xplore, covering the period from 2010 to 2023. A total of 128 articles were initially identified, with 27 studies meeting the inclusion criteria after rigorous screening and full-text analysis. Key findings reveal that the incorporation of GO and rGO in EDLCs leads to significant improvements in specific capacitance, energy density, and cycling stability. Notable advancements include novel synthesis techniques and composite materials such as nitrogen-doped graphene, graphene/polyaniline hybrids, and various metal oxide–graphene composites, which exhibit superior electrochemical performance. However, challenges such as material scalability, environmental sustainability, and consistency in synthesis methods remain. This review stresses the great potential of GO and rGO in the development of high-performance EDLCs and highlights the need for continued research to address existing challenges and further optimize material properties and fabrication techniques.
... They also create multidimensional channels to transport ions and electrons and facilitate access to electrolyte solutions [24]. Many researchers have reported applying 3D graphene structures in SCs [25,26]. Many efforts have been made to fabricate SCs through simple and low-cost processes. ...
Various graphene derivatives have been known as electrode-active materials for fabricating supercapacitors. Interconnected graphene networks with adjustable porous structures, i.e., 3D graphene aerogels (GAs), can control the restacking of graphene sheets very well and, thus, lead to the enhanced performance supercapacitors. In this study, carbohydrates (sucrose and fructose) were used to make two types of 3D porous carbohydrates–graphene aerogels, sucrose-graphene aerogel (SCR) and fructose-graphene aerogel (FRC). Carbohydrates operate as a cross-linking and reductant agent. Voltammograms of supercapacitor electrodes based on the FRC and SCR indicate a more rectangular shape with a larger area and a superior current than the GA (graphene aerogel without using carbohydrates) electrode. They have better capacitive performance, more electron transportation ability, and higher specific capacitance (CS) values than GA. The supercapacitor electrodes based on FRC, SCR, and GA demonstrate the CS values of 257.2 F g ⁻¹, 221.0 F g ⁻¹, and 95 F g ⁻¹ at ѵ = 10 mV.s⁻¹, respectively. Improvement in the performance of SCR and FRC supercapacitor electrodes, in comparison to GA, is attributed to the porous interconnected feature of their structures and their suitable available surface area, which facilitates electron and ion transportation throughout graphene networks. These supercapacitors also show excellent stability after recording 5000 consecutive voltammograms.
... Hence, they determine mainly the performance of LiBs and SCs [3,6,7]. Both these electrochemical energy storage devices can use various carbon materials as electrodes like graphite [8][9][10], graphene [5,[11][12][13], carbon nanotubes [2,5,[14][15][16], carbon nanoonions [17,18], activated carbons [19][20][21][22], etc. In the case of LiBs, the carbon electrodes are applied as anode materials [2,3,8,15], whereas these materials can act as anode or cathode in SCs [5,6,10]. ...
This work describes a use of a composite nanomaterial which consists of multiwall carbon nanotubes covered by iron oxide nanoparticles as a hybrid electrode in aqueous supercapacitor. The investigated nanomaterial was manufactured in a two-step simple chemical synthesis in which the first step was a functionalization of carbon nanotubes whereas the second one was the deposition of iron oxide. According the morphological and structural characterization, the carbon nanotubes with diameters of 10–40 nm were successfully covered by randomly-dispersed magnetite nanoparticles with average diameter of 10 nm. Moreover, the thermogravimetric analysis results indicated that the mass ratio between carbon nanotubes and iron oxide nanoparticles was about 65–35%. The electrochemical performance of studied hybrid electrode was tested in 1 M aqueous KCl electrolyte. The highest specific capacitance of 143 F g‒1 was recorded at a discharge current density of 1 A g‒1. The investigated nanomaterial also exhibited excellent cycling stability i.e. 81% retention of the initial capacitance after 3000 cycles.
... These structural characteristics facilitate the transfer and adsorption of electrolyte ions during the chargedischarge process, leading to an improved energy storage performance. 3D graphene networks are usually prepared by the aerogel route [9], plasma-enhanced chemical vapor deposition (PECVD) [10], templating [11] and surfactant-directed assembly methods [12]. However, these methods also show some shortcomings. ...
Three-dimensional graphitic carbon materials with controllable composition and hierarchically porous structure are promising electrode materials for supercapacitors. In this work, a modified phase inversion method combined with a calcination process was developed to prepare three-dimensional graphene networks embedded with nitrogen-doped carbon nanoparticles. When used as electrode for supercapacitors, the as-prepared material delivered a high capacitance of 431.9 F g-1 at 0.1 A g-1 and 156.8 F g-1 at 20 A g-1, as well as a stable cyclic behavior with no capacitance decay after 5000 cycles. Such a remakable capacitive performance was attributed to its hierarchically porous structure and proper nitrogen doping content (9.68 ± 0.24 at%), which facilitated the migration of electrolyte ions and provided abundant redox active sites for the faradic reactions. The synthetic strategy may be exploited for the rational design and synthesis of new carbon materials with controlled doping level and three-dimensional porous structure.
As an efficient corrosion inhibitor in acidic medium, carboxymethyl chitosan (CMC) has a limited application in non-acidic medium, due to large consumption and high cost. In the study, magnetic reduced grapheme oxide (MRGO) is first introduced into CMC inhibitors to enhance the corrosion inhibition. By optimizing, the best corrosion inhibition efficiency of compound inhibitor is attained as high as 91.78% for carbon steel Q235 in 3.5 wt% NaCl solution, with the remarkably decreased amount of CMC from 800 mg L⁻¹ to 40 mg L⁻¹. Our work lays a good foundation for expanding the potential application of CMC and MRGO as non-acidic medium corrosion inhibitor.
Flexible supercapacitors have attracted widespread attention from many researchers as a type of portable energy storage device. As a unique carbon material, graphene has shown great potential in supercapacitor electrodes, mainly due to its large theoretical specific surface area, high conductivity and chemical stability. Therefore, reasonable design of graphene-based hydrogels with low cost, high specific surface area, and excellent mechanical properties is of great significance for flexible and wearable energy storage device applications. Oxygen-doped activated carbon/graphene composite hydrogels have been fabricated using a one-step hydrothermal method. In the hybrid hydrogel, the activated carbon derived from chitosan with high specific surface area and oxygen-containing groups which were introduced by using a facile room-temperature oxidation strategy with HNO3 are assembled into the framework of reduced graphene oxide (rGO) to effectively prevent the restacking of rGO nanosheets and result in high specific surface area and high conductivity of the composite hydrogels, thereby leading to an excellent energy storage performance. The optimal sample displayed a high specific capacitance of 375.7 F g-1 in 1 M H2SO4 electrolyte at a current density of 1 A g-1. Furthermore, the assembled flexible supercapacitor showed an ideal cycling stability of 83% after 5000 charge/discharge cycles at 10 A g-1. The facile strategy developed in this work is of significance for the performance improvement of supercapacitor electrode materials.
MXene, a new two-dimensional material, has attracted much attention in the field of energy storage. Assembling it into a three-dimensional structure is an effective way to solve the self-stacking problem. However, the assembly of MXene into a three-dimensional structure inevitably reduces the density of the electrode, resulting in a low volumetric capacitance. Here, three-dimensional MXene-holey reduced graphene oxide hydrogel with hierarchical porous structure was obtained by low-temperature hydrothermal treatment, which was used as superior performance binder-free supercapacitor electrode. In the MXene-holey reduced graphene oxide hydrogel electrode, holey reduced graphene oxide can accelerate ion transport, shorten ion and electron transport pathways, and improve the gravimetric capacitance as well as the volumetric capacitance of the electrode. When MX-HGH is applied to the electrode of supercapacitor, it can release gravimetric capacitance up to 415 F g⁻¹ and volumetric capacitance of 597 F cm⁻³. This work demonstrates a practical method to construct three-dimensional MXene structures with high gravimetric capacitance and relatively high volumetric capacitance, opening up a fresh idea for the application of MXene three-dimensional structures in supercapacitors.
High electrical conductivity and excellent pore affinity for electrolyte are the two necessary characteristics for high-rate performance supercapacitors based on activated carbon electrode. Nevertheless, it is fairly challenging to simultaneously improve them due to they are usually in the tug of war relationship in aqueous electrolyte. Herein, based on the different antioxidant abilities of graphitized carbon and amorphous carbon, a well-designed heterogeneous structure activated carbon (HGCAC) with graphitized carbon shell, amorphous carbon inner, and hydrophilic pores has been successfully prepared by a combined procedure of solid phase grinding, catalytic graphitization, and hydrothermal oxidation. Owing to the heterogeneous structure, HGCAC exhibits a joint improvement of electrical conductivity and the pore affinity for aqueous electrolyte, and thus leads to the remarkable enhancement of capacitance and rate capability, in comparison with the commercial coconut shell derived activated carbon (CAC) for supercapacitor. When the current density increases 100 times to 50 A g⁻¹, the specific capacitance of as-made HGCAC is 203.4 F g⁻¹, with the capacitance retention of 81.0%, being nearly 2.14 times of CAC’s capacitance (95.2 F g⁻¹) and 1.6 times of its capacitance retention (51.0%). Moreover, good rate capability is still maintained when HGCAC is assembled to a coin type supercapacitor, with the capacitance retention of 82.1% at 50 A g⁻¹.
Carbon materials, with their diverse allotropes, have played significant roles in our daily life and the development of material science. Following 0D C60 and 1D carbon nanotube, 2D graphene materials, with their distinctively fascinating properties, have been receiving tremendous attention since 2004. To fulfill the efficient utilization of 2D graphene sheets in applications such as energy storage and conversion, electrochemical catalysis, and environmental remediation, 3D structures constructed by graphene sheets have been attempted over the past decade, giving birth to a new generation of graphene materials called 3D graphene materials. This review starts with the definition, classifications, brief history, and basic synthesis chemistries of 3D graphene materials. Then a critical discussion on the design considerations of 3D graphene materials for diverse applications is provided. Subsequently, after emphasizing the importance of normalized property characterization for the 3D structures, approaches for 3D graphene material synthesis from three major types of carbon sources (GO, hydrocarbons and inorganic carbon compounds) based on GO chemistry, hydrocarbon chemistry, and new alkali-metal chemistry, respectively, are comprehensively reviewed with a focus on their synthesis mechanisms, controllable aspects, and scalability. At last, current challenges and future perspectives for the development of 3D graphene materials are addressed.
Graphene films are promising electrode materials for flexible energy-storage device because of their excellent electrochemical stability, flexible and lightweight, etc. However, due to strong van der Waals (vdWs) interaction, graphene film based devices exhibit inadequate material utilization and low ion transport speed. Here we demonstrate a novel strategy of graphene oxide (GO) film swelling to prepare free-standing graphene hydrogel (GH) films with controlled structure for high-performance electrode. The regulation of GO film swelling is achieved by changing acting force (e.g., vdWs, hydrogen bonding and electrostatic repulsion) between GO nanosheets. After reaction, the resulting GH films with highly orientational hierarchical porous structure exhibit excellent electrochemical performance with impressive gravimetric capacitance of 237.6 F g⁻¹ at 1 A g⁻¹ and high areal capacitance of 608 mF cm⁻² at 1 mA cm⁻². Besides, assembled GH film based Zinc-ion hybrid supercapacitors (ZHSs) show a large capacity of 99.3 mAh g⁻¹ and a very high specific energy of 76.2 Wh kg⁻¹. Moreover, the ZHSs display excellent capacity retention rate of ~90% after 10,000 charge/discharge cycles. These results indicate that constructing unique structure GH films by utilizing swelling behavior of GO films is an innovative, simple and practical technology for preparation of electrode materials.
Manganese oxide nanoparticles decorated on 3D reduced graphene oxide aerogels (3D MnO x /rGOae) for neutral electrochemical capacitors were successfully produced by a rapid microwave reduction process within 20 s. The symmetric electrochemical capacitor of 3D MnO x /rGOae (Mn 3.0 at%) storing charges via both electric double layer capacitance (EDLC) and pseudocapacitance mechanisms exhibits a specific capacitance of 240 F g-1 as compared with 190 F g-1 of that using the bare 3D rGOae at 0.5 A g-1 in 1 M Na2SO4 (aq.) electrolyte. It retains 90% of the initial capacitance after 10 000 cycles, demonstrating high cycling stability. In addition, the charge storage mechanism of 3D MnO x /rGOae was investigated using an electrochemical quartz crystal microbalance. In situ gas analysis using differential electrochemical mass spectrometry (DEMS) shows the CO2 evolution at a cell potential over 1 V indicating that the positive electrode is possibly the voltage limiting electrode in the full cell. This finding may be useful for further development of practical high power and energy supercapacitors.
By using oxalic acid (OA) as template and reducer, a novel approach is developed to prepare reduced graphene oxide films with capsular pores (C‐rGOFs) under a hydrothermal condition. The effect of preparation conditions including concentrations of OA and reaction temperatures on the films' structure and capacitive performances has been systematically investigated. The optimal C‐rGOF shows uniform capsule‐like morphology and exhibits a density of 1.18 g cm−3. Tested by using a two‐electrode system, the optimal film shows gravimetric specific capacitance of about 234.9 F g−1 and volumetric specific capacitance of 277.2 F cm−3. Additionally, the optimal film which shows good rate capability can retain 63.9% of initial capacitance at high scan rate of 1.0 V s−1, which is much higher than that of the controlling reduced graphene oxide film (rGOF, 180.5 F g−1, 373.6 F cm−3 and retain only 45.0% of its initial capacitance at 1.0 V s−1). The cells assembled by the optimal C‐rGOF exhibit maximum energy density of 7.5 Wh kg−1, power density of 16.9 kW kg−1, and excellent cycling stability with 91.2% capacitance retention after 21 000 cycles. It is believed that this method can be developed as a useful strategy to prepare rGO‐based materials for energy storage applications. ●Oxalic acid crystal formed during the freezing process is used as shaping templates.●Reduced graphene oxide films with capsule‐like shapes (C‐rGOFs) have been prepared and the optimal C‐rGOF possesses a high specific surface area and density of 1.18g cm‐3.●Supercapacitor assembled by the optimal films shows excellent capacitive performances.
At present, amino acids are often used as the source of heteroatom functional groups for the preparation of doped graphene materials. However, a large amount of amino acids will be used as reaction precursors in the preparation process, which will lead to increased cost, reduced efficiency and waste of resources. Herein, a very small amount of neutral l-alanine is employed to synthesize 3D carboxyl and hydroxyl co-enriched graphene hydrogels (CHGHs) by a one-pot hydrothermal method. The CHGHs contain copious carboxyl and hydroxyl groups, and a small amount of nitrogen-containing functional groups. In addition, the CHGHs also present large specific surface areas and 3D porous structures. Therefore, the CHGH-20 binder-free electrode displays a high specific capacitance of 262.8 F g⁻¹ at 0.3 A g⁻¹, and this value still maintains 84.3% (221.6 F g⁻¹) at 10 A g⁻¹ in a two-electrode system in 6 M KOH. Furthermore, the CHGH-20 electrode also displays outstanding cycle stability with 103.6% of its initial capacitance after 10,000 cycles at 10 Ag⁻¹. Therefore, the CHGHs samples prepared by a very small amount of neutral l-alanine have great significance for the practical application of supercapacitors.
A simple electrophoretic deposition method was developed to prepare graphene oxide (GO) films on the frameworks of nickel foam without any conductive agents and polymer binders. Then, GO was transformed into thermally-reduced graphene oxide (RGO) at an appropriate temperature. The effects of deposition voltage and thermal reduction temperature on the electrochemical properties of RGO were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge. The appropriate combination of deposition voltage and thermal reduction temperature was established. Moreover, scanning electron microscopy, thermal gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffractometry were applied to validate the results, which showed that the highest specific capacitance of RGO was obtained when the deposition voltage was 60 V and the thermal reduction temperature was 300 °C. The specific capacitance values calculated by CV and galvanostatic charge/discharge were 139 F·g(-1) (0.005 V·s(-1)) and 151 F·g(-1) (1 A·g(-1)), respectively. The specific capacitance of RGO maintained 55% and 66% of the initial value when the scan rate and the current density were increased up to 0.3 V·s(-1) and 10 A·g(-1), respectively. RGO also displayed an excellent cycling stability by maintaining 98% of the initial specific capacitance after 500 cycles.
A nanocomposite comprising of polypyrrole and reduced graphene oxide was electrodeposited onto a carbon bundle fibre (CBF) through a two-step approach (CBF/PPy-rGO-2). The CBF/PPy-rGO-2 had a highly porous structure compared to a nanocomposite of polypyrrole and reduced graphene oxide that was electrodeposited onto a CBF in a one-step approach (CBF/PPy-rGO), as observed through a field emission scanning electron microscope. An X-ray photoelectron spectroscopic analysis revealed the presence of hydrogen bond between the oxide functional groups of rGO and the amine groups of PPy in PPy-rGO-2 nanocomposite. The fabricated CBF/PPy-rGO-2 nanocomposite material was used as an electrode material in a symmetrical solid-state supercapacitor, and the device yielded a specific capacitance, energy density and power density of 96.16 F g− 1, 13.35 Wh kg− 1 and of 322.85 W kg− 1, respectively. Moreover, the CBF/PPy-rGO-2 showed the capacitance retention of 71% after 500 consecutive charge/discharge cycles at a current density of 1 A g− 1. The existence of a high degree of porosity in CBF/PPy-rGO-2 significantly improved the conductivity and facilitated the ionic penetration. The CBF/PPy-rGO-2-based symmetrical solid-state supercapacitor device demonstrated outstanding pliability because the cyclic voltammetric curves remained the same upon bending at various angles.
Graphical Abstract
Carbon bundle fibre modified with porous polypyrrole/reduced graphene oxide nanocomposite for flexible miniature solid-state supercapacitor.
Electronic supplementary material
The online version of this article (doi:10.1186/s11671-017-2010-3) contains supplementary material, which is available to authorized users.
Controlling the assembled structures of graphene has recently attracted enormous attention due to intriguing properties of the resultant structures. In this study, three-dimensional (3D) porous structures of reduced graphene oxide (RGO) with various ratios of RGO to cellulose have been fabricated by a scalable, but simple and efficient, approach that consists of ball milling assisted chemical reduction of GO, template shaping, coagulating, and lyophilization. The efficient mechanical shearing of ball milling and the hydrogen bond interactions between RGO and cellulose molecules contribute to the formation of a homogeneous RGO/cellulose hydrogel, improved thermal stability of the resultant composites, and enhanced crystallinity of the cellulose in the composites. The coagulation effect of cellulose maintains the RGO sheets in the 3D structures of cellulose; on the other hand, the RGO sheets facilitate the preservation of the 3D structures during freeze-drying, leading to the formation of 3D porous structures of RGO/cellulose composites. Benefiting from the continuous RGO network in the composites, the 3D porous structures of RGO(70)/cellulose(100) (GO:cellulose = 70:100 in weight) show an electrical conductivity of 15.28 S m(-1). Moreover, the 3D porous structures show potential application in supercapacitors due to the fact that they provide high specific surface area and fast charge propagation.
Three-dimensional (3D) graphene materials (3DGMs) are of great importance due to their unique properties and practical applications. A number of 3DGMs with novel structures have been developed in recent years. This review presents the current progress of 3DGMs. After introducing the preparation strategies of 3DGMs, we summarize the reported 3DGMs based on their different structures, and then focus on the description of their preparation methods, properties and applications. Lastly, the applications of 3D graphene-based materials in supercapacitors are described.
Three-dimensional (3D) graphene-based composites have drawn increasing attention in energy applications due to their unique structures and properties. By combining the merits of 3D graphene (3DG), e.g., porous and interconnected network, high electrical conductivity, large accessible surface area, and excellent mechanical strength and thermal stability, with high chemical/electrochemical activities of active materials, 3DG-based composites show great promise as high-performance electrode materials in various energy devices. This article reviews some recent progress in 3DG-based composites and their applications in energy storage/conversion devices, i.e., supercapacitors, lithium-ion batteries, dye-sensitized solar cells, and fuel cells.
Abstract A novel porous graphene paper is prepared via freeze drying a wet graphene oxide gel, followed by thermal and chemical reduction. The macroscopic structure of the formed graphene paper can be tuned by the water content in the gel precursor. With 92% water content, an interconnected macroporous network can be formed. This porous graphene (PG) paper exhibits excellent electrochemical properties. It can deliver a high discharge capacity of 420 mAh g-1 at a current density of 2000 mA g-1 when used as binder-free lithium ion battery anode. PG paper exhibits a specific capacitance of 137 F g-1 at 1 A g-1 in a flexible all-solid-state supercapacitor with PVA/H2SO4 electrolyte. It can maintain 94% of its capacitance under bending. This electrochemical performance and mechanical flexibility makes it an excellent material for flexible energy storage devices.
Supercapacitors have attracted intense attention due to their great potential to meet the demand of both high energy density and power density in many advanced technologies. Various carbon-based nanocomposites are currently pursued as supercapacitor electrodes because of the synergistic effect between carbon (high power density) and pseudo-capacitive nanomaterials (high energy density). This feature article aims to review most recent progress on 3D (3D) carbon based nanostructures for advanced supercapacitor applications in view of their structural intertwinement which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The carbon nanostructures comprise of CNTs-based networks, graphene-based architectures, hierarchical porous carbon-based nanostructures and other even more complex carbon-based 3D configurations. Their advantages and disadvantages are compared and summarized based on the results published in the literature. In addition, we also discuss and view the ongoing trends in materials development for advanced supercapacitors.
Graphene is a promising electrode material for supercapacitors mainly because of its large specific surface area and high conductivity. In practice, however, several fabrication issues need refinement. The restacking of graphene flakes upon being packed into supercapacitor electrodes has become a critical challenge in the full utilization of graphene’s large specific surface area to further improve the device performance. In this review, a variety of recent techniques and strategies are overviewed for the prevention of graphene restacking. They have been classified into several categories to improve and facilitate the discussion on the underlying ideas. Based on the overview of the existing techniques, we discuss the trends of future research in the fields.
In order to develop energy storage devices with high power and energy densities, electrodes should hold well-defined pathways for efficient ionic and electronic transport. Herein, we demonstrate high-performance supercapacitors by building a three-dimensional (3D) macroporous structure that consists of chemically modified graphene (CMG). These 3D macroporous electrodes, namely, embossed-CMG (e-CMG) films, were fabricated by using polystyrene colloidal particles as a sacrificial template. Furthermore, for further capacitance boost, a thin layer of MnO(2) was additionally deposited onto e-CMG. The porous graphene structure with a large surface area facilitates fast ionic transport within the electrode while preserving decent electronic conductivity and thus endows MnO(2)/e-CMG composite electrodes with excellent electrochemical properties such as a specific capacitance of 389 F/g at 1 A/g and 97.7% capacitance retention upon a current increase to 35 A/g. Moreover, when the MnO(2)/e-CMG composite electrode was asymmetrically assembled with an e-CMG electrode, the assembled full cell shows remarkable cell performance: energy density of 44 Wh/kg, power density of 25 kW/kg, and excellent cycle life.
An N-superdoped 3D graphene network structure with an N-doping level up to 15.8 at% for high-performance supercapacitor is designed and synthesized, in which the graphene foam with high conductivity acts as skeleton and nested with N-superdoped reduced graphene oxide arogels. This material shows a highly conductive interconnected 3D porous structure (3.33 S cm−1), large surface area (583 m2 g−1), low internal resistance (0.4 Ω), good wettability, and a great number of active sites. Because of the multiple synergistic effects of these features, the supercapacitors based on this material show a remarkably excellent electrochemical behavior with a high specific capacitance (of up to 380, 332, and 245 F g−1 in alkaline, acidic, and neutral electrolytes measured in three-electrode configuration, respectively, 297 F g−1 in alkaline electrolytes measured in two-electrode configuration), good rate capability, excellent cycling stability (93.5% retention after 4600 cycles), and low internal resistance (0.4 Ω), resulting in high power density with proper high energy density.
Novel dense graphene foams were fabricated by directly growing graphene on nickel templates by chemical vapor deposition. The as-grown graphene foam showed a hierarchical structure consisting of graphene microspheres with nano pores as flower-like morphology. The high quality of the graphene foam was confirmed by Raman spectrum and conductivity measurement as high as 5100 S m⁻¹. To test its potential application in lithium ion battery, the monolithic graphene foam hybridized with TiO2 nanoparticles as anode material was synthesized via atomic layer deposition. The electrode exhibited high specific capacity (204 mAh g⁻¹, 91 mAh g⁻¹) even at high current (20 C, 60 C, respectively, 1 C = 335 mA g⁻¹) with good stability and reversibility. The outstanding electrical performance could be attributed to the flower-like dense porous nanostructure in the graphene foam, which would work not only as a highly conductive host matrix for ion and electron transportation, but also effectively buffer the volume expansion during the lithiation and delithiation process.
In this work, a dissolution-recrystallization method (DRM) with chlorobenzene and dimethylsulfoxide treating the perovskite films during the spin-coating process is reported. This is the first time that DRM is used to control perovskite crystallization and improve the device performance. Furthermore, the DRM is good for reducing defects and grain boundaries, improving perovskite crystallization and even improving TiO2/perovskite interface. By optimizing, the DRM2-treated perovskite solar cell (PSC) obtains the best photoelectric conversion efficiency (PCE) of 16.76% under AM 1.5 G illumination (100 mW cm⁻²) with enhanced Jsc and Voc compared to CB-treated PSC.
Highly porous carbon film (PCF) coated on nickel foam was prepared successfully by microwave plasma-assisted chemical vapor deposition (MPCVD) with C2H2 as carbon source and Ar as discharge gas. The PCF is uniform and dense with 3D-crosslinked nanoscale network structure possessing high degree of graphitization. When used as the electrode material in an electrochemical supercapacitor, the PCF samples verify their advantageous electrical conductivity, ion contact and electrochemical stability. The test results show that the sample prepared under 1000 W microwave power has good electrochemical performance. It displays the specific capacitance of 62.75 F/g at the current density of 2.0 A/g and retains 95% of its capacitance after 10,000 cycles at the current density of 2.0 A/g. Besides, its near-rectangular shape of the cyclic voltammograms (CV) curves exhibits typical character of an electric double-layer capacitor, which owns an enhanced ionic diffusion that can fit the requirements for energy storage applications.
Desirable porous structure and huge ion-accessible surface area are crucial for rapid electronic and ionic pathway electrodes in high-performance graphene-based electrochemical capacitors. However, graphene nanosheets tend to aggregate and restack because of van der Waals interaction among graphene sheets, resulting in the loss of ion-accessible surface area and unsatisfactory electrochemical performance. To resolve this daunting challenge, a novel approach is developed for the self-assembly of holey graphene sheets intercalated with carbon spheres (H-GCS) to obtain freestanding electrodes by using a simple vacuum filtration approach and a subsequent KOH activation process. Through the introduction of carbon spheres as spacers, the restacking of reduced graphene oxide (rGO) sheets during the filtration process is mitigated efficiently. Pores on rGO sheets produced by subsequent KOH activation also provide rapid ionic diffusion kinetics and high ion-accessible electrochemical surface area, both of which favor the formation of electric double-layer capacitance. Furthermore, a higher degree of graphitization of CSs in H-GCS thin film improves the electrical conductivity of the H-GCS electrode. The H-GCS electrode exhibits 207.1 F g⁻¹ of specific capacitance at a current density of 1 A g⁻¹ in 6 M KOH aqueous electrolyte. Moreover, the symmetric electrochemical capacitor assembled with H-GCS electrodes and organic electrolyte is capable of delivering a maximum energy density of 29.5 Wh kg⁻¹ and a power density of 22.6 kW kg⁻¹.
Graphene paper has attracted considerable attention because of its impressive electrical and mechanical properties, which endow it with the great potential for applications in future flexible electronics. Therefore, developing a high-efficiency route to fabricate large-area and foldable graphene paper with good electrical and mechanical properties is quite necessary. In this work, a facile in-situ chemical reduction method for the preparation of graphene paper was successfully developed. The in-situ chemical reduction process involves simultaneous film formation and reduction, and the produced graphene paper has high integrity and good foldability. The thickness and area of graphene paper can also be readily regulated by adjusting the experimental parameters. Furthermore, the dissipation of reductant air stream (HI/CH3COOH air stream) can “push up” the graphene nanosheets to form a loose layered structure. This inside-out reduction process gives the produced graphene paper a sheet resistance as low as 17.8 Ω sq⁻¹, verifying the advantages of this in-situ chemical reduction method. For the application of the obtained graphene paper, a flexible solid-state supercapacitor based on the graphene paper was fabricated, which had a device areal capacitance of 44 mF cm⁻² (device volumetric capacitance of 858 mF cm⁻³) and excellent electrochemical stability.
Carbon nanotube (CNT) aerogels and sponges are macroscopic porous materials with a unique isotropic structure. CNTs make an interconnected 3D scaffold, therefore the resulting aerogels are robust, highly conductive, and flexible, enabling a much broader range of applications than aligned arrays and thin films, especially in energy and environmental areas. A comprehensive overview of the recent progress in isotropic CNT-based macroscopic structures is provided, including their synthesis methods, structural characteristics, mechanical properties, and deformation mechanism, as well as potential applications in energy and environmental fields. In particular, this study focuses on the CNT sponges developed, which are high-performance porous materials with many distinct properties such as their versatile deformations and shape recovery. Importantly, the CNT sponges provide a universal platform for designing and manufacturing a variety of hierarchical functional composites by introducing polymers or inorganic guests, thus greatly extend application areas from highly compressible electrodes for supercapacitors and batteries, catalysis, to environmental cleanup. Future research directions and associated challenges in this field are proposed.
Stacking of Graphene usually results in a close packing of graphene nanosheeets corresponding to a low specific surface area and pore volume. A new simple method to prepare reduce graphene oxide (rGO) film has been developed using an in situ electrochemical reduction of the as-formed GO hydrogel film in an aqueous solution electrolyte. The as-obtained rGO hydrogel film has a highly specific surface area and was directly used as the electrodes for a supercapacitor, in which the ion channels remained with excellent capacitance, even at a high current density. The as-obtained rGO hydrogel film has also been used to prepare a flexible belt-like supercapacitor, which may light up a LED lamp for more than two minutes. Electrochemical in situ reduction provides a simple method to prepare novel graphene based supercapacitors for a wide variety of applications in the near future.
In order to obtain excellent desalination behavior during the capacitive deionization (CDI) process, electrodes should provide efficient pathways for ion and electron transport. Here we open up a new opportunity to prepare high performance capacitive deionization (CDI) electrodes based on three-dimensional macroporous graphene architectures (3DMGA). The 3DMGA were fabricated by a simple template-directed method using polystyrene microspheres as sacrificial templates. The resulting 3DMGA exhibited a 3D interconnected structure with large specific surface area and high electric conductivity. The electrochemical behavior of the 3DMGA electrodes was analyzed by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. It was found that the 3DMGA showed superiority in electrosorption capacitance, low inner resistance, high reversibility and excellent stability. The power and energy density analysis further demonstrated that the 3DMGA electrode had a higher power output and lower energy consumption. According to the electrochemical measurements, the 3DMGA is quite desirable for high performance and low energy consumption capacitive deionization. The desalination capacity was evaluated by a batch mode electrosorptive experiment in a NaCl aqueous solution. An excellent desalination behavior of the 3DMGA was obtained due to the large accessible surface area, high electric conductivity and unique 3D interconnected macroporous structure. The 3DMGA was confirmed to be a promising material for CDI application.
Reduced graphene oxide (r-GO) paper is easily synthesized by a flame-induced reduction of graphene oxide (GO) paper under ambient conditions. The X-ray diffraction and X-ray photoelectron spectroscope results confirm the effectivity of the flame-induced reduction. The resulting r-GO paper has a high surface area of 274.9 m2 g−1 and contains a certain amount of oxygen-containing groups. Electrochemical behaviors of the electrode built with the r-GO paper are investigated in two kinds of electrolytes, 2 M KOH aqueous solution and 1 M Et4NBF4-acetonitrile solution, respectively. The results show that the high values of the specific capacitance for the r-GO can be obtained in both electrolytes, which reach 212 and 160 F g−1 at the same current density of 1 A g−1 respectively. Also, the r-GO-based electrode and supercapacitor exhibits stable cycling performance. The good capacitive performances in KOH aqueous electrolyte are due to the high surface area and the remaining oxygen containing groups of the r-GO paper.
Flexible solid-state supercapacitors are of considerable interest as mobile power supply for future flexible electronics. Graphene or carbon nanotubes based thin films have been used to fabricate flexible solid-state supercapacitors with high specific gravimetric capacitances (80-200 F/g), but usually with a rather low overall or area specific capacitance (3-50 mF/cm2) due to the ultra-small electrode thickness (typically a few microns) and ultralow mass loading, which is not desirable for practical applications. Here we report the exploration of three-dimensional (3D) graphene hydrogel for the fabrication of high-performance solid-state flexible supercapacitors. With a highly interconnected 3D network structure, graphene hydrogel exhibits exceptional electrical conductivity and mechanical robustness to make it an excellent material for flexible energy storage devices. Our studies demonstrate the flexible supercapacitors with a 120-μm thick graphene hydrogel thin film can exhibit excellent capacitive characteristics, including a high gravimetric specific capacitance of 186 F/g (up to 196 F/g for 42-μm thick electrode), an unprecedented area-specific capacitance of 372 mF/cm2 (up to 402 mF/cm2 for 185 μm thick electrode), along with low leakage current (10.6 μA), excellent cycling stability and extraordinary mechanical flexibility. This study demonstrates exciting potential of 3D graphene macrostructures for high performance flexible energy storage devices.
A lightweight, flexible, and highly efficient energy management strategy is needed for flexible energy-storage devices to meet a rapidly growing demand. Graphene-based flexible supercapacitors are one of the most promising candidates because of their intriguing features. In this report, we describe the use of free-standing, lightweight (0.75 mg/cm(2)), ultrathin (<200 μm), highly conductive (55 S/cm) and flexible three-dimensional (3D) graphene networks, loaded with MnO(2) by electrodeposition, as the electrodes of a flexible supercapacitor. It was found that the 3D graphene networks showed an ideal supporter for active materials and permitted a large MnO(2) mass loading of 9.8 mg/cm(2) (~92.9% of the mass of the entire electrode), leading to a high area capacitance of 1.42 F/cm(2) at a scan rate of 2 mV/s. With a view to practical applications, we have further optimized the MnO(2) content with respect to the entire electrode and achieved a maximum specific capacitance of 130 F/g. In addition, we have also explored the excellent electrochemical performance of a symmetrical supercapacitor (of weight less than 10 mg and thickness ~0.8 mm) consisting of a sandwich structure of two pieces of 3D graphene/MnO(2) composite network separated by a membrane and encapsulated in polyethylene terephthalate (PET) membranes. This research might provide a method for flexible, lightweight, high-performance, low cost and environmentally-friendly materials used in energy conversion and storage systems for the effective use of renewable energy.
This paper presents a review of the research progress in the carbon-metal oxide composites for supercapacitor electrodes. In the past decade, various carbon-metal oxide composite electrodes have been developed by integrating metal oxides into different carbon nanostructures including zero-dimensional carbon nanoparticles, one-dimensional nanostructures (carbon nanotubes and carbon nanofibers), two-dimensional nanosheets (graphene and reduced graphene oxides) as well as three-dimensional porous carbon nano-architectures. This paper has described the constituent, the structure and the properties of the carbon-metal oxide composites. An emphasis is placed on the synergistic effects of the composite on the performance of supercapacitors in terms of specific capacitance, energy density, power density, rate capability and cyclic stability. This paper has also discussed the physico-chemical processes such as charge transport, ion diffusion and redox reactions involved in supercapacitors.
Three-dimensional graphene-based frameworks (3D-GFs) with hierarchical macro- and meso-porous structures are presented. The interconnected macropores are derived from hydrothermally assembled 3D graphene aerogels (GAs) while the mesopores are generated by the silica networks uniformly grown on the surface of graphene. The resulting 3D-GFs exhibit narrow mesopore size distribution (2~3.5 nm), high surface area, and low mass density. These intriguing features render 3D-GFs a promising template for creating various 3D porous materials. Specifically, 3D GA based mesoporous carbons (GA-MC) and metal oxide hybrids (GA-Co3O4, GA-RuO2) can be successfully constructed via a nanocasting technology. Benefiting from the integration of meso- and macro-porous structures, 3D GA-MC manifests outstanding specific capacitance (226 F g-1), high rate capability and excellent cycling stability (no capacitance loss after 5000 cycles) when it is applied in electrochemical capacitors.
We have successfully fabricated an asymmetric supercapacitor with high energy and power densities using graphene hydrogel (GH) with 3D interconnected pores as the negative electrode and vertically aligned MnO(2) nanoplates on nickel foam (MnO(2)-NF) as the positive electrode in a neutral aqueous Na(2)SO(4) electrolyte. Because of the desirable porous structure, high specific capacitance and rate capability of GH and MnO(2)-NF, complementary potential window of the two electrodes, and the elimination of polymer binders and conducting additives, the asymmetric supercapacitor can be cycled reversibly in a wide potential window of 0-2.0 V and exhibits an energy density of 23.2 Wh kg(-1) with a power density of 1.0 kW kg(-1). Energy density of the asymmetric supercapacitor is significantly improved in comparison with those of symmetric supercapacitors based on GH (5.5 Wh kg(-1)) and MnO(2)-NF (6.7 Wh kg(-1)). Even at a high power density of 10.0 kW kg(-1), the asymmetric supercapacitor can deliver a high energy density of 14.9 Wh kg(-1). The asymmetric supercapacitor also presents stable cycling performance with 83.4% capacitance retention after 5000 cycles.
Chemical vapor deposition is used to prepare novel 3D graphene networks, with ethanol as the carbon source. These networks are used as templates for the construction of graphene/metal oxide composite-based supercapacitor electrodes. As a proof of concept, NiO is deposited on 3D graphene networks. The product exhibits a high specific capacitance of about 816 F g -1 at a scan rate of 5 mV s -1 and good cycling performance.
We report a high-performance supercapacitor incorporating a poly(ionic liquid)-modified reduced graphene oxide (PIL:RG-O) electrode and an ionic liquid (IL) electrolyte (specifically, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide or EMIM-NTf(2)). PIL:RG-O provides enhanced compatibility with the IL electrolyte, thereby increasing the effective electrode surface area accessible to electrolyte ions. The supercapacitor assembled with PIL:RG-O electrode and EMIM-NTf(2) electrolyte showed a stable electrochemical response up to 3.5 V operating voltage and was capable of yielding a maximum energy density of 6.5 W·h/kg with a power density of 2.4 kW/kg. These results demonstrate the potential of the PIL:RG-O material as an electrode in high-performance supercapacitors.
- Li