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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]

The design and preparation of electrode materials with unique nanostructure are regarded as a significant strategy to increase the capacitance and cycling stability of energy storage devices. Herein, a starfish-like core–shell Ni(OH)2@CoS material grown on Ni foam (Ni(OH)2@CoS/NF, denoted as NOCS-1/NF) was successfully fabricated via a stepwise hydrothermal method. Benefiting from the unique starfish-like core–shell nanostructure, obvious and abundant heterogeneous interfaces, and good synergy between every component, the specific capacitance of the as-prepared Ni(OH)2@CoS-1/NF electrode can reach up to 981 F g−1 at 1 A g−1 and maintained 73.2% of initial value at a high current density of 10 A g−1 in 2 M KOH aqueous solution. Moreover, a hybrid supercapacitor was prepared by using core–shell NOCS-1/NF as positive electrode and activated carbon coated on the NF (AC/NF) as negative electrode. The HSC delivered a high energy density of 17.9 Wh kg−1 at a power density of 749 W kg−1 and a satisfying cycling life with 90.1% capacitance retention after 4000 cycles. Eventually, two such devices in series successfully illuminated a red light-emitting diode. Meanwhile, this work probably provides a simple and convenient strategy to fabricate novel materials for the applicability of various energy-related fields. [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]

In this study, uniform nitrogen-doped hollow carbon spheres (NHCSs) have been synthesized using sphere-like SiO2 as a template and polydopamine as a carbon source. It is found that NHCSs have an ultrahigh specific surface area of 870.1 m2 g−1 and high porosity. 9,10-Phenanthrenequinone (PQ) molecules are selected to decorate NHCSs to obtain electrode materials (NHCSs/PQ) for supercapacitors, which show a clear capacitance increase in comparison with pure NHCSs when tested in 1 M H2SO4 aqueous solution. In a three-electrode system, the NHCSs/PQ (mass ratio 4 : 2) electrodes exhibit larger specific capacitance (as high as 252 F g−1 at 1 A g−1) and an ultrahigh rate capability (80.8% capacitance retention at 30 A g−1). Furthermore, the asymmetric supercapacitor is assembled using NHCSs/PQ as a positive electrode material and nitrogen-doped porous carbon (NPCs) that has adsorbed anthraquinone as a negative electrode material, respectively. The device exhibits a high energy density of 8.34 W h kg−1 along with a power density of 600 W kg−1. [ABSTRACT FROM AUTHOR]

A novel tetrahydroxy-anthraquinone zeolitic framework (TZM) with a Viburnum blossom-like structure is synthesized via a simple solvothermal method by using tetrahydroxy-anthraquinone to substitute imidazolate without carbonization at high temperature. Considering the excellent electrochemical performance of the TZM, including a high specific capacitance of 2030 F g−1 at a current density of 1 A g−1, and good cycling stability with a capacitance retention of 94% of the initial capacitance after 1000 cycling charge/discharge measurements, an aqueous TZM//AC asymmetric supercapacitor (ASC) in 1 M KOH electrolyte is successfully fabricated by using the resultant TZM as the positive electrode and activated carbon nanosheets (ACS) as the negative electrode, respectively. The as-assembled aqueous ASC delivers a high energy density of 47.7 W h kg−1 at a power density of 750 W kg−1 with a high potential window of 0–1.5 V. Moreover, for the purpose of exploring the practical application of the active materials, an all-solid-state ASC TZM//ACS device with PVA-KOH gel electrolyte and separator is assembled and connected, which can light up a red light-emitting diode (LED). Its good performance demonstrates that the TZM//ACS ASC is a promising energy-storage system. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have been turned out to be an excellently self-sacrificing template for preparing porous carbon. Herein, we synthesized a nitrogen-doped porous carbon materials (NPCs) by direct thermolysis of zinc-based MOFs (ZIF-8). Fortunately, the NPCs with high specific surface area and abundant pore structure was suitable for using as conductive substrate to anchor organic molecules. Anthraquinone (AQ), 1, 4-naphthoquinone (NQ) and tetrachlorobenzoquinone (TCBQ) were selected to functionalize NPCs via noncovalent interactions, respectively. As a consequence, the multielectron redox centers possessed by AQ, NQ and TCBQ were implanted in the NPCs. More interestingly, the electrochemical rate-determining step for the functionalized NPCs was surface process rather than diffusion, which is similar to capacitive behavior of the electrical double layer. The functionalized NPCs revealed an enhanced overall capacitance (about 1.4 times higher than NPCs) because the electrochemical capacitance was superposed on the electrical double layer capacitance. Furthermore, the as-assembled asymmetrical supercapacitor (ASC) exhibited excellent energy storage performance. The topological structure of MOFs skeleton and the potential self-matching behavior between the positive and negative electrodes were responsible for high energy density (23.5 Wh kg −1 at 0.7 kW kg −1 , which is 1.54 times higher than that of NPCs symmetrical supercapacitor) of the device. [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]

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]

• The 3D bifunctional electrode was constructed via in-situ growth of MOF-74(Ni) and electrochemical deposition of NiCo LDH. • CC@MOF-74(NiO)@NiCo LDH demonstrates an ultra-high area specific capacitance, superior rate capability for supercapacitor. • The electrode also exhibits ultra-low detection limit, wide detection range for glucose detection. • The synergistic effect of unique structure and bimetal promote the diffusion of ions and reduce mass transfer resistance. The 3D self-supporting multistage structure CC@MOF-74(NiO)@NiCo LDH electrode was successfully synthesized, which demonstrated ultra-high specific capacitance, cyclic stability, excellent electrocatalytic performance and selectivity, providing a new reference for the research of bifunctional materials in the field of supercapacitors and non-enzymatic glucose sensors. [Display omitted] The bifunctional electrode materials for supercapacitors and non-enzymatic glucose sensors have attracted the researchers' great interest due to their excellent electrochemical performance. In this work, three-dimensional self-supporting multistage structure CC@MOF-74(NiO)@NiCo LDH electrode has been successfully prepared through a facile hydrothermal and electrochemical deposition method. Benefiting from the unique three-dimensional flower-like multistage structure, the optimized CC@MOF-74(NiO)@NiCo LDH electrode exhibits an excellent specific capacitance of 9.73 F cm−2 and a superior rate capability of 77.65% at a high current density of 50 mA cm−2. Besides, the material has a superior capacitance retention rate of 84.09% after 5000 cycles. Furthermore, the fabricated CC@MOF-74(NiO)@NiCo LDH//CC@NiCo 2 O 4 @NiFe LDH ASC device exhibits a high energy density of 22.85 Wh kg−1 and the power density of 1750 W kg−1 at the current density of 10 mA cm−2. Moreover, the as-prepared CC@MOF-74(NiO)@NiCo LDH shows an outstanding electrocatalytic performance in glucose detection, including a high sensitivity of 1699 μA mM−1 cm−2, a low detection limit of 278 nM (S/N = 3) and a wide linear range of 10 μM–1.1 mM and 1.5–9 mM. The electrode also has good long-term stability and remains 93.29% of the original current density after 35 days. The unique three-dimensional flower-like structure of MOF-74 and two-dimensional layered double hydroxides (LDHs) nanosheets structure provide a larger specific surface area and improve the conductivity of the MOF-74(NiO). Furthermore, the synergistic effect of the bimetal Ni-Co provides more active sites for electrochemical reactions and shortens the ion transport path. Accordingly, the fabricated CC@MOF-74(NiO)@NiCo LDH has great potential application prospects in the field of supercapacitors and non-enzymatic glucose sensors. [ABSTRACT FROM AUTHOR]

Electrode materials with excellent performance are urgently demanded for supercapacitors. Herein, heterogeneous nanostructure Co 9 S 8 /Ni 3 S 2 supported on conductive Ni foam (Co 9 S 8 /Ni 3 S 2 /NF) is fabricated using zeolite imidazole frameworks (ZIFs) as the sacrificial template. The Co 9 S 8 /Ni 3 S 2 /NF electrode shows an outstanding specific capacitance of 1356 F g−1 at a current density of 1 A g−1 and still remained 1145 F g−1 at 10 A g−1. The enhanced electrochemical performance should be attributed to the superior structural characteristics, the abundant active sites, the rich redox reactions, the strongly synergistic effect in heterogeneous sulfide composition and the good conductivity resulted from the NF and the Co 9 S 8 /Ni 3 S 2 /NF. Meanwhile, to further evaluate the practical application value of the Co 9 S 8 /Ni 3 S 2 /NF electrode, a hybrid supercapacitors (HSCs) device is constructed using Co 9 S 8 /Ni 3 S 2 /NF as positive electrode and activated carbon (AC) as negative electrode, and it displays a high energy density of 48.2 Wh kg−1 at a power density of 799.6 W kg−1 and a superior long-term cycling stability with 82% of initial capacitance after 8000 cycles. In addition, two as-assembled capacitors in series can light 7 LED bulbs. This strategy of obtaining multi-metal sulfides from Co/Ni-ZIF precursor provides a new perspective to design and develop electrode materials for high-performance hybrid supercapacitors. [Display omitted] [ABSTRACT FROM AUTHOR]

Rational designing and preparing of electrode materials with desirable electrochemical performance by a simple, efficient and safe method is of great significance for electrochemical energy storage devices, but it is also challenging. In this study, ultrafine CoNi 2 S 4 nanowire arrays directly grown on carbon cloth (CC) are synthesized by sulfuration of Co–Ni hydroxide precursor. Benefiting from the high conductivity, the synergistic effect between Co and Ni ions and open self-supporting three-dimensional (3D) nanoarchitectures constructed by 1D CoNi 2 S 4 ultrafine nanowires, the as-obtained CoNi 2 S 4 @CC electrode exhibits excellent electrochemical capacitance performances: high specific capacitance of 1872 F g −1 at 1 A g −1and 1565 F g −1 at 5 A g−1. Meanwhile, a battery-supercapacitor hybrid (BSH) device is fabricated using the as-obtained CoNi 2 S 4 @CC as the positive electrode and porous carbon nanosheets (PCNS) derived from wood fungus as the negative electrode. The constructed BSH exhibits a high energy density of 37.2 Wh kg −1 at a power density of 0.75 kW kg−1, as well as a robust long-term cycling stability (97.6% capacitance retention after 10 000 charge-discharge cycles at a constant current density of 1 A g−1). These outstanding results verify CoNi 2 S 4 material has potential application in the energy storage field and it has been explored and expected to be the promising electrode materials for the supercapacitor. Image 1 • CoNi 2 S 4 @CC with 3D porous structure is prepared by a facile hydrothermal method. • 3D structure is constructed by 1D ultrafine nanowires vertically to the surface of CC. • The as-fabricated CoNi 2 S 4 @CCexhibited ultrahigh specific capacitance of 1872F g -1 at 1 A g -1. • CoNi 2 S 4 @CC//PCNS BSH device was constructed. • The CoNi 2 S 4 @CC//PCNS BSH device showed high energyand excellent cycling stability. [ABSTRACT FROM AUTHOR]

High-performance ternary cobalt-based metal oxides, especially ZnCo 2 O 4 , have attracted increasing attention as promising electrode materials for supercapacitors. However, there are still great challenges for the as-reported ZnCo 2 O 4 materials, such as self-aggregation during repeated discharging-charging process and low packing density. To tackle the above issues, it is envisaged as an efficient strategy to combine the advantages of both hierarchical porous micro/nanostructures and self-supporting electrode to fabricate a free-standing hierarchical micro/nanostructured ZnCo 2 O 4 electrode. Herein we propose an efficient and simple synthetic strategy for the controllable synthesis of self-supporting hierarchical porous cactus-like ZnCo 2 O 4 material directly grown on Ni-foam using a facile hydrothermal method with post-calcination treatment. Furthermore, a growth mechanism is also proposed. The as-prepared cactus-like ZnCo 2 O 4 material possesses unique structural merits, such as hierarchical porous structures, large specific surface area, robust structural stability, and strong connections between the substrate and the ZnCo 2 O 4 active material. The unique cactus-like ZnCo 2 O 4 film electrode displayed excellent electrochemical performance, including a high specific capacity of 1115.7 F g−1 at 1 A g−1 and remarkable long cycle stability with 80.8% capacity retention after 30,000 cycles. A practical asymmetric supercapacitor (ASC) device was assembled using cactus-like ZnCo 2 O 4 and active carbon, which showed an excellent energy density of 35.4 Wh kg−1 at high power density of 160.1 W kg−1 and superior cycle stability (62.5% capacity retention after 30,000 cycles at 1 A g−1). All these results show that such hierarchical porous ZnCo 2 O 4 micro/nanostructured films are a promising candidate for high-performance supercapacitors for energy storage application. [Display omitted] • 3D hierarchical porous cactus-like ZnCo 2 O 4 film is grown on Ni foam. • A growth mechanism of the 3D cactus-like ZnCo 2 O 4 film is proposed. • The cactus-like ZnCo 2 O 4 electrode shows 80.8% capacitance retention after 30,000 cycles at 5 A g−1. • The ZnCo 2 O 4 @NF//AC asymmetric supercapacitor exhibits an excellent energy density and power density. [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]

Graphical abstract Abstract This paper is the first study of the application of non-metallic element modified metal-organic frameworks in supercapacitors. Three-dimensional metal-organic frameworks modified by non-metallic element have a novel flower cluster structure, which effectively improve the structural stability and the electrochemical performance of the supercapacitors. The electrochemical performances of the materials modified by the vulcanizing agent are particularly significant with a high specific capacitance of 1453.5F g−1 at a current density of 1 A g−1 and excellent cycle stability (retention rate of 89.23% after 5000 cycles). In addition, the assembled asymmetric supercapacitor S@Ni-MOF//AC also shows a high energy density of 56.85 Wh kg−1 at power density of 480 W kg−1 and good cycle stability with a capacitance retention of 86.67% after 20,000 cycles at current density 5 A g−1. As a result, metal-organic frameworks materials modified by the non-metallic element make up for the crystal defects, which can be used as promising electrode materials for practical applications. [ABSTRACT FROM AUTHOR]

Provide more active sites and concise preparation is an effective technology in renewable energy storage sets. A soluble graphitic carbon nitride (SCN) nanosheets promoted two-dimensional nano electrochemical activity flake NiFe-LDH is successfully fabricated through electrostatic self-assembly, as a layer by layer high performance electrode (NiFe-LDH@SCN) for supercapacitor. The g-C 3 N 4 guarantees the effectiveness of the combination through the ζ-potential of g-C 3 N 4 flake (−19.5 mV) and NiFe-LDH flake (+15.6 mV), moreover, ensures the exposure of more active sites of NiFe-LDH. The optimized electrode shows an impressive specific capacitance of 1060.4 F g-1 at 1 A g-1 and remains 770.8 F g-1 at 10 A g-1. The fabricated hybrid supercapacitor (HSC) exhibits a magnificent energy density (up to 68.7 Wh kg-1) along with the power density of 827.5 W kg-1 in the wide voltage window of 1.7 V and a prominent long-term stability (83.3 % of capacitance retention even after 8000 cycles). Finally, two HSCs in series can light 40 LEDs. Hence, this work demonstrates the great potential of g-C 3 N 4 in developing high-performance LDH-based energy storage devices. [Display omitted] • The high performance electrode (NiFe-LDH@SCN) is fabricated through electrostatic self-assembly. • NiFe-LDH@SCN-32 electrode shows an impressive specific capacitance of 1060.4 F g-1 at 1 A g-1. • The NiFe-LDH@SCN-32//AC displays a high energy density of 68.7 Wh kg-1. • The capacitance retention is high up to 83.3 % after 8000 cycles. [ABSTRACT FROM AUTHOR]

• A fluorenone molecule electrode was reported, in which DHFO was anchored on GO to form hierarchical porous hydrogel. • The redox peak position of DHFO/rGO is located near 0.75 V, which is suitable for positive electrode in EES. • An ASC was assembled and delivered high energy density (28.57 Wh Kg−1), finally lighted 45 LED bulbs. Here, we report an organic molecule electrode for more efficient energy storage, in which 2,7-Dihydroxy-9-fluorenone (DHFO) molecules are anchored on interconnected and highly conductive graphene sheets by non-covalent π–π interactions. The optimal DHFO/rGO composite can reach a high specific capacitance of 412.3 F g−1 at scan rate of 5 mV s−1 in 1 mol L−1 H 2 SO 4 aqueous electrolyte with a satisfactory capacitive retention of 91% after 10,000 consecutive constant galvanostatic charge-discharge at current density of 5 A g−1. And it is worth noting that the Faraday current response peaks occurs within the positive potential range around 0.75 V, which is more suitable for positive electrode materials of supercapacitors with high performances. Additionally, charge storage mechanism and binding interactions of DHFO on graphene was evaluated based on the density functional theory (DFT) calculations. To match with the consequent positive electrode, AQ functionalized graphene (AQ/rGO) was prepared as negative electrode. Benefiting from the companionable match of two electrodes in structure, charge quantity and kinetics, the as-assembled asymmetrical supercapacitor (DHFO/rGO//AQ/rGO) delivers a maximum energy density of 28.57 Wh kg−1 along with 0.62 kW kg−1, and excellent cycle stability (82.3% specific capacitance retention after 10,000 cycling at 5 A g−1). Two tandem DHFO/rGO//AQ/rGO devices could light 45 LEDs. [Display omitted] [ABSTRACT FROM AUTHOR]

• BAQ and DHBQ are anchored on graphene to form organic molecules electrodes. • The BAQ (DHBQ)/rGO electrodes achieve capacitance all in excess of 400 F g−1 at 1 A g−1. • DFT calculations are employed to understand the experimental mechanism. • The two ASCs device in series easily lights 47 red light-emitting diodes compounding in parallel. Organic molecules electrodes with high electrochemical reversibility has enormous potential in energy storage. Here, benz[a]anthracene-7, 12-quinone (BAQ) and 2, 5-dihydroxy-p-benzoquinone (DHBQ) are anchored on reduced graphene oxide (rGO) [BAQ (DHBQ)/rGO] by non-convent method to form the porous 3D dry aerogels. The optimal BAQ (DHBQ)/rGO electrode materials display capacitance all in excess of 400 F g−1 at current density of 1 A g−1 and an excellent rate capability in 1 M H 2 SO 4 electrolyte. And BAQ/rGO and DHBQ/rGO are used respectively as the negative and positive electrode to fabricate the asymmetric supercapacitor (ASC), which achieves high energy density of 30.33 Wh kg−1 with power density of 802.9 W kg−1. Finally, 47 light-emitting diode (LED) bulbs aligned in a 'NWNU' shape are lit by two ASCs device in series, demonstrating its outstanding energy storage performance. Moreover, density functional theory (DFT) calculations are employed to understand the adsorption orientations, binding interactions and charge storage mechanism of BAQ on rGO surface, elucidating the superior electrochemical performance of the tested organic molecule electrode. In short, quinones non-covalently modified graphene is a promising and effective strategy for energy storage devices in future. [ABSTRACT FROM AUTHOR]