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An efficient approach to increase the energy density of supercapacitors is to prepare electrode materials with larger specific capacitance and increase the potential difference between the positive and negative electrodes in the device. Herein, an organic molecular electrode (OME) is prepared by anchoring 1,10‐phenanthroline‐5,6‐dione (PD), which possesses two pyridine rings and an electron‐deficient conjugated system, onto reduced graphene oxide (rGO). Because of the electron‐deficient conjugated structure of PD molecule, PD/rGOs exhibit a more positive redox peak potential along with the advantages of high capacitance‐controlled behaviour and fast reaction kinetics. Additionally, the small energy gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) leads to increased conductivity in PD/rGO. To assemble the asymmetric supercapacitor (ASC), a two‐dimensional metal carbide, as known as MXene, with a chemical composition of Ti3C2Tx is selected as the negative electrode due to its exceptional performance, and PD/rGO‐0.5 is employed as the positive electrode. Consequently, the working voltage is expanded up to 1.8 V. Through further electrochemical measurements, the assembled ASC (PD/rGO‐0.5//Ti3C2Tx) achieves a remarkable energy density of 36.8 Wh kg−1. Remarkably, connecting two ASCs in series can power 73 LEDs, showcasing its promising potential for energy storage applications. [ABSTRACT FROM AUTHOR]

A flexible self-supporting and binder-free supercapacitor electrode is fabricated by embedding a polypyrrole (PPy) nanostructured network into only one side of a graphene thin film via a spin coating method and a subsequent hydrothermal process. Based on the amphiphilic nature of the graphene oxide (GO) thin film, the well-defined PPy nanoparticles are well dispersed and form a reticular structure on the thin film surface. After reduction treatment at a temperature of 180 °C, the reduced graphene oxide (rGO) thin film not only provides a large accessible surface area for the dispersion of PPy nanoparticles but also acts as a binder-free conductive current collector. The polypyrrole/graphene film (PGF) electrode material exhibits an excellent electrochemical performance in the three-electrode configuration, including a high specific capacitance of up to 455 F g−1 at 1 A g−1 and outstanding cycling stability (97% capacitance retention after 1000 cycles). In addition, the symmetric PGF supercapacitor shows a specific capacitance of up to 49.3 F g−1 at a cell voltage of 1.4 V and exhibits a maximum energy density of 13.4 W h kg−1 at a power density of 700 W kg−1, with 96% capacitance retention after 1000 cycles. This work shows impressive potential in fabricating high-performance flexible electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

2,6-Diaminoanthraquinone (DQ) molecules were covalently modified onto the surface of graphene (GO) via a nucleophilic displacement reaction between the epoxy groups on the surface of GO and the –NH2 groups of DQ molecules in the presence of ammonia to form a composite material (labeled as DQ–RGO). The rapid reversible faradaic reactions of DQ molecules are realized by means of the good conductivity of graphene. Therefore, the DQ–RGO composite material can combine the Faraday pseudocapacitance of DQ with the double-layer capacitance of graphene, thus displaying outstanding electrochemical performance in acidic electrolyte solution, including a high specific capacitance (332 F g−1 at 1 A g−1), excellent rate capability (the capacitance retention rate is 72.9% at 50 A g−1) and good cycling stability (maintaining 81.8% of the initial capacitance after 5000 cycles). Meanwhile, a thionine-functionalized graphene hydrogel (Th–GH) was also prepared via a non-covalent strategy. Finally, the DQ–RGO composite acted as the negative electrode and Th–GH acted as the positive electrode to construct an asymmetric supercapacitor (ASC). The ASC exhibited an energy density of 14.2 W h kg−1 along with a power density of 0.763 kW kg−1 and long cycling durability (maintaining 80% of the initial capacitance after 8000 cycles at 5 A g−1). More importantly, two such devices in series successfully illuminated 16 red light-emitting diodes (LEDs), demonstrating its outstanding energy storage performance. This work can provide ideas for the construction of green, all-carbon and excellent electrochemical performance devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new electrode material (CHY/RGO) is prepared. • Chrysin (CHY) are grafted onto the surface of Reduced graphene oxide (RGO) by π-π electrostatic force. • The specific capacitance of CHY/RGO can reach up to 707F g−1 at 1 A g−1. • Density functional theory (DFT) calculation shows CHY are parallel adsorbed on RGO. • CHY/RGO//CHY/RGO device can deliver the energy density of 38 Wh kg−1. In this study, chrysin (CHY) molecules are immobilized on the surfaces of graphene oxide (GO) via π-π interactions to obtain organic molecular-modified reduced graphene oxide (RGO) composite electrode material (CHY/RGO) by one-step hydrothermal. On one hand, CHY molecules can contribute to capacitance through faradic reactions. On the other hand, they act as spacers that impede the accumulation of graphene nanosheets and promote electrolyte ion migration. As a result, CHY/RGO exhibits excellent capacitance performance. The specific capacitance is up to 707F g−1 (1 A g−1), and the capacitance remains 100% after 10 000 circles. In addition, the symmetrical supercapacitor (CHY/RGO//CHY/RGO) displays excellent energy storage performance, achieving an energy density of 38 Wh kg−1 at a power density of 800 W kg−1. Two CHY/RGO//CHY/RGO devices in series is capable of lighting 50 LEDs. Density functional theory (DFT) calculations show that CHY molecules are adsorbed parallel to the RGO by the π-π stacking. The DFT calculations also indicate that the modification of CHY molecules alters the charge distribution on the surface of RGO. Therefore, CHY/RGO composites offer a higher capacitance and superior cycle stability, making them a promising choice for future energy storage electrode materials. [ABSTRACT FROM AUTHOR]

Graphene hydrogels (GH), as a derivative of graphene have become a research hotspot in the field of energy storage due to their three-dimensional network structure which can prevent the agglomeration of graphene. The specific capacitance and energy storage ability can be further increased by non-covalent functional graphene hydrogels with organic small molecules. In this work, 4-methylumbelliferone (DTBF) molecules interacted on the surfaces of GH via π-π interactions to get a carbon electrode material (DTBF/GH) by one-step hydrothermal. On the one hand, the DTBF molecules can contribute capacitance by faradic reactions, on the other hand, they can act as spacers to hinder the accumulation of graphene nanosheets, thus enhancing the specific surface area of graphene and promoting the migration of electrolyte ions. As a result, DTBF/GH displays an ultrahigh-specific capacitance. The specific capacitance can reach up to 578 F g−1 (1 A g−1). To verify the influence of electrode material matching on capacitor performance, an asymmetric supercapacitor and a symmetrical capacitor are assembled respectively. Although the specific capacitance of the DTBF/GH material is higher than that of activated carbon (AC), the energy density (E d = 19 Wh kg−1) of the DTBF/GH//AC capacitors is higher than that of the DTBF/GH//DTBF/GH capacitors. It shows that the matching of electrode materials has a great influence on the E d and the power density (P d) of the capacitor. In addition, two DTBF/GH//AC devices in series can light 47 LEDs. [Display omitted] • A new carbon electrode material (DTBF/GH) is prepared. • GH with 3D network structure is conducive to the migration of electrolyte ions. • The specific capacitance of DTBF/GH can reach up to 578 g−1 at 1 A g−1. • The DTBF/GH //AC displays energy density of the 19 Wh kg−1. [ABSTRACT FROM AUTHOR]

The naphthoquinone and RuO2 hybrid graphene hydrogel (NQ–RuO2/SGH) composite, which can be a suitable positive electrode material of an asymmetric supercapacitor, is prepared via a two-step process. The RuO2/graphene hydrogel composite (RuO2/SGH) is first synthesized through a simple hydrothermal method by using oxidized graphite (GO) and RuCl3 as raw materials, and then, 1,4-naphthoquinone (NQ) molecules are adsorbed on the exposed graphene hydrogel surface of the RuO2/SGH composite via a π–π stacking interaction. The electrochemical tests show that the NQ–RuO2/SGH composite delivers a high specific capacitance (450.8 F g−1) even at a low RuO2 loading mass (14.6%), meanwhile, an asymmetric supercapacitor (ASC) is constructed by using NQ–RuO2/SGH as the positive electrode and a nitrogen-doped porous carbon material (MNC) as the negative electrode. The electrochemical measurements prove that the energy density of the ASC can reach up to 16.3 W h kg−1 in a 1 M H2SO4 electrolyte. [ABSTRACT FROM AUTHOR]

Three-dimensional nitrogen-doped carbon nanosheets framework (N-CNF) has been obtained starting with cellulose acetate. The product is prepared through a so-called one-step method that carbonization, activation and nitrogen-doping occur simultaneously. The resultant N-CNF shows an architecture like graphene hydrogel with interconnected hierarchical porous structure, N-doping with high nitrogen content (8.7 wt%) and high specific surface area (1003.6 m 2 g −1 ). The N-CNF electrode displays excellent electrochemical performances due to the unique architecture and pseudocapacitance contribution from heteroatoms. In the three-electrode configuration, the N-GNF achieves a high specific capacitance of 242 F g −1 at 1 A g −1 and displays ultrahigh rate capability (83.4% capacitance retention at 100 A g −1 ) in 6 mol L −1 KOH electrolyte. The symmetric supercapacitor (SSC) based N-CNF exhibits energy density as high as 60.4 Wh kg −1 (at a power density of 1750 W kg −1 ) and 17.9 Wh kg −1 (at 850 W kg −1 ) in ionic liquid and aqueous electrolytes, respectively. It is surprised that the single device filled by ionic liquid electrolyte is able to light easily 60 red light-emitting diodes (LEDs, 2.2 V) in parallel after charging for only 10 s, showing an excellent energy storage/release performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new all-carbon electrode material (2-DCTQ/RGO) is prepared. • 2-DCTQ are non-covalent grafted onto the surface of RGO. • The specific capacitance of 2-DCTQ/RGO can reach up to 660F g−1 at 1 A g−1. • For comparision, one asymmetric and symmetric supercapacitors are constructed. • The symmetric supercapacitor shows higher energy density than the asymmetric supercapacitor. To effectively solve the problem of the low energy density of graphene-based supercapacitors, an effective strategy is to couple graphene with organic molecules with redox reactions, multiple active sites, and good stability. Quinones have been used as electrode materials because they are widely available, cheap, and environmentally friendly. In this study, 2,3-dichloro-1,4-naphthoquinone (2-DCTQ) was non-covalently interacted on reduced graphene oxide (RGO) to get an all-carbon material (2-DCTQ/RGO). 2-DCTQ/RGO composites possess both the advantages of 2-DCTQ molecules (reversible Faraday reactions with multiple electron transfer) and graphene (good conductivity and large specific surface area). As a result, the specific capacitance of the single electrode can achieve 660F g−1 at 1 A/g, which is higher than most organic small molecules reported previously. In addition, an asymmetric supercapacitor (2-DCTQ/RGO//BZTQ/RGO 1) and a symmetric supercapacitor (2-DCTQ/RGO//2-DCTQ/RGO) are assembled at the same time. The energy density of the 2-DCTQ/RGO//BZTQ/RGO 1 supercapacitor can be as high as 45 Wh kg−1 at 0.91 kW kg−1, which is considerably greater than the 2-DCTQ/RGO//2-DCTQ/RGO (25 Wh kg−1). 50 LEDs can be lit by connecting two such devices in series. This work provides a good idea for the construction of green and all-carbon electrode materials. [ABSTRACT FROM AUTHOR]

Chemical oxidation is used to cut and unzip multi-walled carbon nanotubes in the transverse direction and the axial direction to form graphene oxide nanoribbon (GONR). Ruthenium oxide/reduced graphene oxide nanoribbon composite (RuO2/rGONR) with a 72.5 wt% RuO2 loading is synthesized through an aqueous-phase reaction, in which GONR is served as starting material, followed by mild thermal treatment in ambient air. The resulting RuO2/rGONR composite achieves specific capacitance up to 677 F·g−1 at the current density of 1 A·g−1 in three-electrode system using 1 mol·L−1 H2SO4 as electrolyte. The resultant electrode exhibits an excellent rate capability (91.8% retention rate at 20 A·g−1). Especially, the symmetric supercapacitor assembled on the basis of RuO2/rGONR electrode delivers high energy density (16.2 Wh·kg−1) even at the power density of 9885 W·kg−1, which is very essential for supercapacitors. [ABSTRACT FROM AUTHOR]

In the present work, a three-dimensional (3D) porous framework of RuO2/reduced graphene oxide hydrogels (RuO2/RGOH) was prepared by a facile one-step hydrothermal method. In this hybrid hydrogel, RuO2 nanoparticles were homogeneously dispersed on the exfoliated RGO sheets. The as-prepared RuO2/RGOH electrode shows excellent supercapacitive performances with high specific capacitance (345 F g−1 for 15% RuO2 loading), good rate capability and a long electrochemical cycling life (without decaying after 2000 cycles). Furthermore, RuO2 in the hybrid can contribute a capacitance as high as 1365 F g−1, which is comparable to its theoretical value. These excellent results originate from the factors that the 3D porous network structure provides a more accessible surface area and facilitates an electron and proton injecting/expelling process in the electrochemical reaction. This work provides a facile method for preparing graphene-based composite materials with remarkable capacitive performances. [ABSTRACT FROM AUTHOR]

Further increasing the energy density of supercapacitors without reducing their high power density and stability remains a challenge. Organic quinone molecules have demonstrated potential in electrochemical energy storage on account of their excellent electrochemical activity and reversibility. Herein, 2-amino-3-chloro-1,4-naphthoquinone (2-NTQ) is covalently connected to the reduced graphene oxide (RGO) to obtain a new all‑carbon electrode material (2-NTQ-RGO). The 2-NTQ-RGO composite exhibits excellent capacitance performance by incorporating the merits of the 2-NTQ molecules and RGO. The optimized 2-NTQ-RGO possesses a high specific capacitance of 453 F g−1 at 1 A g−1 and displays good cycle stability (83% of the initial after 8000 cycles) in 1 M H 2 SO 4 electrolyte. Moreover, two asymmetric supercapacitors are assembled for the purpose of investigating the influence of the electrode materials matching on the performance of the capacitor. With the same positive material, the 2-NTQ-RGO//DQ-RGO can achieve an energy density of 23.4 Wh kg−1 and a power density of 900 W kg−1. Two ASC devices in series can light up in the shape of a "butterfly" consisting of 71 light-emitting diodes (LEDs). In contrast, the energy density of the 2-NTQ-RGO//AC is only 16.7 Wh kg−1 (812 W kg−1). The covalent grafting offers a new promising and effective method for the preparation of green all‑carbon energy storage materials. [Display omitted] • A new all‑carbon electrode material (2-NTQ-RGO) is prepared. • 2-NTQ is covatently grafted onto the surface of RGO. • The specific capacitance of 2-NTQ-RGO can reach up to 453 g−1 at 1 A g−1. • For comparison, two asymmetric supercapacitors are constructed. • The 2-NTQ-RGO//DQ-RGO displays a high energy density of the 23.4 Wh kg−1. [ABSTRACT FROM AUTHOR]

A redox-active organic molecular electrode is prepared for supercapacitors. Benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BDTD), planar molecule with fused heteroaromatic structure, has been adsorbed on conductive reduced graphene oxide (rGO) by π–π interactions to form a 3D interconnected and functionalized xerogel (BDTD-rGO). Because the five-membered aromatic heterocycle is more electron-rich than the six-membered aromatic ring, which enlarges the electronic interaction between the BDTD molecule and the conjugated graphene network and accordingly reduce the solubility of BDTD molecule in electrolyte. As a result, the optimized BDTD-rGO electrodes achieve specific capacitance of 360 F g−1 at 1 A g−1, with ultra-long cycle life of 96.4% after 10,000 cycles, and even 80% after 50,000 cycles at 5 A g−1 in 1 M H 2 SO 4. Furthermore, the asymmetric supercapacitor (ASC), which is assembled by using the BDTD-rGO as the negative electrode and lamellar holey graphene hydrogel (LGH) as the positive electrode respectively, exhibits better energy storage performance. Image 1 • Reduced graphene oxide was non-covalently functionalized by organic molecules. • The BDTD-rGO exhibits an ultra-long cycle life (96.4% for 10,000 cycle). • The BDTD-rGO possesses an excellent specific capacitance of 360 F g−1 at 1 A g−1. • Negative and positive electrodes can generate potential self-matching behavior. • As-fabricated the asymmetric supercapacitor delivers a superior cyclic stability. [ABSTRACT FROM AUTHOR]