Compressible supercapacitors are novel energy-storage devices that can be used in elastic electronics; however, the performance of the supercapacitor depends mainly on its electrode materials and configuration. Herein, free-standing three-dimensional hierarchical porous polypyrrole (PPy) wrapped nitrogen-containing polyaniline based carbon nanospheres (NPACNS) are prepared and coated on the skeleton of sponge composite electrodes (PPy/NPACNS/sponge) via dipping and drying and chemical oxidation polymerization methods. Furthermore, an integrated highly compressible all-solid-state supercapacitor is fabricated using PPy/NPACNS/sponge as the electrode and polyvinyl alcohol (PVA)/LiClO4 gel as the electrolyte, which demonstrates an outstanding electrochemical performance of 95 F g−1 (2.8 F cm−3) specific capacitance, 3.3 W h kg−1 (0.1 mW h cm−3) energy density and 93% capacitance retention after 1000 cycles. Surprisingly, the electrochemical performance of the as-fabricated device remains nearly unchanged when it is compressed under 50% strain, and its specific capacitance and compressibility are well maintained after 400 repeated compressing-releasing cycles. More importantly, due to its solid-state and integrated configuration, several compressible supercapacitors can be conveniently interconnected together in series on one chip to power electronics. This device will pave the way for advanced supercapacitor applications in compressible energy storage devices that are compatible with compression-tolerant electronics.

Nitrogen-doped porous activated carbons have been fabricated through a simple and efficient carbonization method at 700 °C with the waste tea-leaves as carbon precursor and ZnCl2 as activating agent. The average pore size and specific surface area are in the ranges of 2.3–6.6 nm and 10.3 ~ 1143.9 m2 g−1, with the ZnCl2 to tea-leaves weight ratio from 0 to 3. As an electrode material for supercapacitors, the TPACs-2 (the ZnCl2 to tea-leaves weight ratio is 2) which has 3.0 wt% nitrogen content, possesses a large specific capacitance of 296 F g−1 at 0.5 A g−1 and excellent rate capability (74 % retention at 10 A g−1) in 2 mol L−1 KOH. Furthermore, the symmetric supercapacitor fabricated with TPACs-2 electrodes delivers a high energy density of 13.5 Wh kg−1 at a power density of 221 W kg−1 and superior cycle stability (only 9 % loss after 5000 cycles), operating in the wide voltage range of 0–1.8 V in 0.5 mol L−1 Na2SO4 aqueous electrolyte. The results demonstrate TPACs-2 is a promising candidate for the electrode material of supercapacitors.

A primary challenge of gel electrolytes in the development of flexible and wearable devices is their weak mechanical strength and poor electrochemical performances. Here, we prepare a novel PVA (polyvinyl alcohol)–H2SO4–BAAS (bromamine acid sodium) gel polymer with a porous network structure as both electrolyte and separator, which achieves excellent mechanical strength, maintains a high ionic conductivity of 21.4 mS cm−1 and provides a reversible redox reaction for enhanced supercapacitor performance. Surprisingly, the operating voltage of the present active electrolyte enhanced supercapacitor (AEESC) is up to 1.5 V, which is much larger than that of the previously reported active electrolyte based supercapacitors (about 1.0 V). Furthermore, the AEESC exhibits a maximum specific capacitance of 390 F g−1 at a current density of 0.8 A g−1, a remarkably high energy density of 30.5 W h kg−1 at a power density of 600 W kg−1 and good cycling stability. Additionally, such a device displays only a small capacitance loss when the gel polymer is under a large tensile strain of 100% or under a high pressure of 2000 kPa. Meanwhile, the capacitance of the device was maintained very well after 500 complete bending cycles, indicating that the robust gel polymer endows the fabricated AEESC with good flexibility and electrochemical stability.

Nitrogen-doped porous activated carbons (N-PHACs) have been successfully synthesized using pomegranate husk as carbon precursor via ZnCl2-activation carbonization and subsequent urea-assisted hydrothermal nitrogen-doping method. The obtained N-PHACs possesses abundant mesoporous structure, high specific surface area (up to 1754.8 m2 g−1), pore volume (1.05 cm3 g−1), and nitrogen-doping content (4.51 wt%). Besides, the N-PHACs-based material showed a high specific capacitance of 254 F g−1 at a current density of 0.5 A g−1 and excellent rate performance (73% capacitance retention ratio even at 20 A g−1) in 2 M KOH aqueous electrolyte, which is attributed to the contribution of double-layer capacitance and pseudocapacitance. The assembled N-PHACs-based symmetric capacitor with a wide operating voltage range of 0–1.8 V exhibits a maximum energy density of 15.3 Wh kg−1 at a power density of 225 W kg−1 and superior cycle stability (only 6% loss after 5000 cycles) in 0.5 M Na2SO4 aqueous electrolyte. These exciting results suggest that the novel N-doping porous carbon material prepared by a green and low-cost design strategy has a potential application as high-performance electrode materials for supercapacitors.

A novel redox-mediated gel polymer (PVA–H2SO4–ARS) is prepared by introducing alizarin red S (ARS) into a polyvinyl alcohol–sulphuric acid (PVA–H2SO4) gel polymer system, and a symmetric supercapacitor using the gel polymer as electrolyte and activated carbon as electrode is also assembled. The PVA–H2SO4–ARS gel polymer has excellent bending, compressing and stretching mechanical properties. The introduction of ARS increases the ionic conductivity of the gel polymer, and improves the pseudocapacitance of the supercapacitor. As expected, the PVA–H2SO4–ARS gel polymer electrolyte has a high conductivity of 33.3 mS cm−1, and the supercapacitor with PVA–H2SO4–ARS electrolyte exhibits a larger electrode specific capacitance (441 F g−1) than the one with PVA–H2SO4 electrolyte (160 F g−1) at the same current density of 0.5 A g−1. Simultaneously, the supercapacitor with PVA–H2SO4–ARS electrolyte exhibits high energy density (39.4 W h kg−1) and good charge–discharge stability. Therefore, this novel electrolyte has good prospects for improving the electrochemical performance of an energy storage device.

In this work, the micromolecule l-glutamic acid (Glu) is employed as nitrogen-rich precursor to prepare a novel porous carbon, and ZnCl2 is used as activating agent to improve the surface area and electrochemical performance of the carbon. The nitrogen content of the carbon (Glu-2.5) prepared by Glu and ZnCl2 with a mass ratio of 1:2.5 retains as high as 7.1 % at an activation temperature of 700 °C. The surface area and pore volume of Glu-2.5 are 1007.4 m2 g−1 and 0.57 cm3 g−1, respectively. Glu-2.5 exhibits a high specific capacitance of 330.6 F g−1 in 2 M KOH electrolyte at the current density of 1 A g−1and good cycling stability (89 % retention of capacitance after 5000 charge/discharge cycles). More importantly, the assembled symmetric supercapacitor using Glu-2.5 as electrodes reveals a high energy density (16.7 Wh kg−1) under the power density of 404.7 W kg−1. Owing to its inherent advantages, Glu-2.5 could be a promising and scalable alternative applied to energy storage/conversion.

Correction for ‘Low-cost and high energy density asymmetric supercapacitors based on polyaniline nanotubes and MoO3 nanobelts’ by Hui Peng et al., J. Mater. Chem. A, 2014, 2, 10384–10388.

Highly crumpled nitrogen-doped graphene-like nanosheets (CN-GLSs) with a high specific surface area (1169 m2 g−1) and large pore volume (2.58 cm3 g−1) are prepared from a macroporous resin via simultaneous urea gasification expansion and CaCl2 activation methods. The CN-GLSs are tested as electrodes for supercapacitors and present excellent electrochemical performance.

A stable and effective redox-mediator gel electrolyte has been prepared by doping indigo carmine (IC) into a polyvinyl alcohol sulfuric acid polymer system (PVA–H2SO4), and a high performance solid state supercapacitor is fabricated by utilizing activated carbon as electrodes and the prepared gel polymer (PVA–H2SO4–IC) as an electrolyte and separator. The PVA–H2SO4–IC gel polymer has excellent bending, compressing and stretching mechanical properties. As expected, the ionic conductivity of the gel polymer electrolyte increased by 188% up to 20.27 mS cm−1 while introducing IC as the redox mediator in the PVA–H2SO4 gel electrolyte. Simultaneously, specific capacitance is increased by 112.2% (382 F g−1) and energy density (13.26 W h kg−1) is also increased. Furthermore, the fabricated device shows superior charge–discharge stability. After 3000 cycles, its capacitive retention ratio is still as high as 80.3%. This result may be due to the fact that the IC can act as a plasticizer and redox mediator, and the supercapacitor combines the double-layer characteristic of carbon-based supercapacitors and the faradaic reaction characteristic of batteries energy-storage processes.

•Asymmetric supercapacitor is assembled based on novel Co0.85Se and N-PCNs electrodes.•Petal-like Co0.85Se nanosheets are synthesized via a simple solvothermal method.•N-PCNs are prepared by integrating polymerization and catalytic carbonization method.•Co0.85Se//N-PCNs aqueous ASC with an extended operating voltage window of 1.6 V.•The ASC exhibits a high energy density, high rate ability and good cycle stability.A novel asymmetric supercapacitor (ASC) is assembled based on petal-like cobalt selenide (Co0.85Se) nanosheets as positive electrode and nitrogen-doped porous carbon networks (N-PCNs) as negative electrode in a 2 M KOH aqueous electrolyte. The Co0.85Se nanosheets are synthesized via a simple low-temperature solvothermal method without any template and surfactant, and the N-PCNs are prepared by integrating in-situ oxidation polymerization and catalytic carbonization methods directly from the p-phenylenediamine monomers. Thanks to their unique structures and high capacitive performance, the as-assembled Co0.85Se//N-PCNs ASC device possesses an extended operating voltage window of 1.6 V, high energy density of 21.1 W h kg−1 at a power density of 400 W kg−1 and outstanding cycling stability (93.8% capacitance retention after 5000 cycles) in aqueous electrolyte.

•The eco-friendly polyaspartic acid is used as a precursor for nitrogen-doped porous carbon.•Redox-mediated Na2MoO4 is introduced in H2SO4 aqueous solution to form mixture electrolyte.•The supercapacitor exhibits high specific capacitance 841 F g−1 and energy density 378.5 Wh kg−1.Nitrogen-doped porous carbon derived from polyaspartic acid is utilized as activated carbon (AC) electrode for supercapacitor. The BET surface area and pore volume of the AC as high as 1071 m2 g−1 and 0.61 cm3 g−1. The AC electrode in 1 M H2SO4 electrolyte delivers high specific capacitance of 177 F g−1 at a high current density of 15 A g−1. Surprisingly, by introducing redox-mediated 0.6 g Na2MoO4 into 40 ml 1 M H2SO4 as a mixture electrolyte, the specific capacitance of the supercapacitor improved 841 F g−1, about 375.1% of specific capacitance in 1 M H2SO4 electrolyte. The high energy density 378.5 Wh kg−1 is also obtained. Furthermore, the AC electrode in the redox active Na2MoO4 electrolyte shows the excellent capacitance retention of 88.2% for over 1000 cycles. These improved performance are owed to the redox reaction between Mo(VI)/Mo(V) and Mo(VI)/Mo(IV) redox couples in the mixed H2SO4 and Na2MoO4 electrolyte at the electrode|electrolyte interface, and the concentration of the Na2MoO4 can also influence the electrochemical performance of the supercapacitor. Based on the overall performance, it is believed that the combination of polyaspartic acid derived nitrogen-doped porous carbon and redox active Na2MoO4 electrolyte is more attractive in the near future for high performance energy-storage devices.

We have employed the biomaterial white clover as a carbon precursor and ZnCl2 as an activating agent to prepare white clover carbons (WCCs). The WCC-2 (mass ratios of white clover and ZnCl2 is 1:2) possesses as high as 6.9 wt% nitrogen content and 857 m2 g−1 BET surface area. Furthermore, it exhibits 233.1 F g−1 specific capacitance at a current density of 1.0 A g−1, even 82.9% capacitance retention at 20 A g−1 in 2 mol L−1 KOH electrolyte. The specific capacitance could remain at almost about 100.0% when the cycle number is between the 200–5000 cycles. Because of the wide potential window (0–2.0 V) and high specific capacitance, the WCC-2//WCC-2 symmetric capacitor shows an energy density of 30–13.1 W h kg−1 under the power outputs of 503.5–9991.5 W kg−1 in 0.5 mol L−1 Na2SO4 electrolyte. The results demonstrate WCC-2 can be a promising candidate for the electrode material of high performance supercapacitors.

In this work, we present a facile approach to prepare nitrogen-doped porous carbon materials via one-step carbonizing biowaste soybean curd residue (SCR) as the biomass carbon precursor. The morphology, structure and textural properties of the carbon materials are investigated by field emission scanning electron microscopy, transmission electron microscopy, N2 sorption isotherms, and X-ray photoelectron spectroscopy, respectively. The SCR carbonized at 700 °C exhibits a high charge storage capacity with a specific capacitance of 215 F g−1 at a current density of 0.5 A g−1 and good stability over 5000 cycles. Moreover, the assembled symmetric supercapacitor device possesses a energy density of 9.95 W h kg−1 at a power density of 236 W kg−1, which is higher than that of commercially available supercapacitors. The high supercapacitor performance of the porous carbon can be due to the high surface area and effective nitrogen-doping, indicating it has great potential for supercapacitors.

Cotton-based porous activated carbons (CACs) are prepared through a simple chemical activation method using cotton fiber as carbon source and ZnCl2 as activating agent. Powder X-ray diffraction, scanning electron microscopy, and N2 adsorption–desorption tests demonstrate that the carbons activated with different amounts of ZnCl2 have a large number of mesopores, notably, a maximum specific surface area of 2548.6 m2 g−1 and ultrahigh pore volume of 1.54 cm3 g−1 for CAC2 sample are obtained when the cotton/ZnCl2 mass ratio is 1:2. As an electrode material for supercapacitors, the CAC2 possesses a high specific capacitance of 239 F g−1 at 0.5 A g−1 and good rate capability (82% capacitance retention even at 8 A g−1) in 2 mol L−1 KOH aqueous electrolyte. Moreover, the as-assembled CAC2//CAC2 symmetric supercapacitor exhibits a high energy density of 13.75 Wh kg−1 at a power density of 225 W kg−1 operated at the voltage range of 0 to 1.8 V in 0.5 mol L−1 Na2SO4 aqueous electrolyte and an excellent cyclability retaining about 93% initial capacitance after 5000 cycles.

A novel superabsorbent composite with high swelling properties was synthesized by the grafted co-polymerization of partially neutralized acrylic acid (AA) onto a sodium alginate (NaAlg) backbone in the presence of organo-loess. The FTIR spectra, XRD patterns and SEM micrographs prove that the AA monomers were grafted onto the NaAlg backbone, and the organo-loess dispersed into the polymer matrix that improved the porous structure, which was verified by element mapping. TGA and DSC results indicate that the incorporation of loess enhances the thermal stability of the superabsorbent. Swelling results confirm that proper amount of organo-loess in the superabsorbent can enhance the swelling capability and salt-resistant performance. The maximum equilibrium water absorbency of the superabsorbent composite incorporated with 10 wt% organo-loess in distilled water and 0.9 wt% NaCl aqueous solution were 656 g g−1 and 69 g g−1, respectively. Furthermore, the superabsorbent composite exhibited good buffer ability to external pH in the range from 4 to 10 and water retention ability. According to the performance of the eco-friendly superabsorbent composite, it can be used as a promising candidate for applications in various fields.

A novel activated carbon material with a multi-level structure is prepared by KOH-activation of chestnut shells at 800 °C (CAC8). The specific surface area and pore volume of the activated carbon obtained are as high as 1568.0 m2 g−1 and 0.94 cm3 g−1. The electrochemical performance of the CAC8 is very promising; the specific capacitance is 207 F g−1 at a current density of 1 A g−1 in 1 M H2SO4 electrolyte. A CAC8/PANI composite, which was synthesized through an interfacial polymerization method, presents a good electrochemical performance, including an excellent specific capacitance of 597 F g−1 and 80% retention of capacitance after 1000 cycles at a current density of 1 A g−1 in 1 M H2SO4 electrolyte. The high electrochemical performance can be due to the use of the multi-level structured carbon, which improves the charge transfer performance of CAC8/PANI composite materials.

Nitrogen-containing polyaniline-based carbon nanospheres (C-PANI) with diameters of about 200 nm are prepared through a direct carbonization method using polyaniline (PANI) nanospheres as carbon precursors at different temperatures. The PANI nanospheres are synthesized via in situ oxidation polymerization of aniline in the presence of sodium carboxymethyl cellulose as a polymerization template. The C-PANI with 6.69% nitrogen content obtained at 800 °C (C-PANI-800) can achieve a high capacitance of 359 F g−1 at the current density of 1 A g−1 in 6 M aqueous KOH electrolyte, meanwhile maintaining excellent rate capability (81% retention at 20 A g−1). Furthermore, a symmetric supercapacitor fabricated with C-PANI-800 electrodes exhibits an energy density of 17.5 W h kg−1 at a power density of 227 W kg−1 and superior cycle stability (only 4% loss after 5000 cycles), operating in the voltage range of 0–1.8 V in 0.5 mol L−1 Na2SO4 aqueous electrolyte.

A novel and eco-friendly xanthan gum-g-poly(acrylic acid)/laterite (XG-g-PAA/laterite) organic-inorganic composite polymer used as chemical sand-fixing agent (CSFA) was successfully prepared by grafted copolymerization of natural XG, partially neutralized acrylic acid (NaA), and laterite in solution. FTIR spectra confirmed that NaA had been grafted onto XG chains, and the –OH groups of laterite participated in polymerization reaction. The influence of the content of CSFA on sand-fixing effect was investigated, and the results of the aging test indicated that the CSFA had remarkable water resistance, heat resistance, anti-freeze-thaw, and anti-ultraviolet aging performances, which could meet the requirement of application in the harsh desert environment. Moreover, it also showed excellent water-retaining and anti-evaporation properties.

A facile one-step activation and nitrogen-doping combination method is developed for preparation of nitrogen-doped graphene-like carbon nanosheets (N-CNSs). The N-CNSs have abundant wrinkled structures and ultrahigh pore volume (3.19 cm3 g−1), and are used as high-performance electrode materials for supercapacitors.

Asymmetric supercapacitors (ASCs) with high energy density are assembled based on the pseudocapacitance of both electrodes, which use polyaniline (PANI) nanotubes as positive electrodes and MoO3 nanobelts as negative electrodes in a 1 M H2SO4 aqueous electrolyte. The assembled novel PANI//MoO3 ASC device with an extended operating voltage window of 2.0 V, in spite of the use of an aqueous electrolyte, exhibits excellent performance such as a high specific capacitance of 518 F g−1 at a current density of 0.5 A g−1, reaching an energy density as high as 71.9 W h kg−1 at a power density of 254 W kg−1 and good cycling stability.

We have developed a supercapacitor electrode composed of CuS microspheres with polypyrrole (PPy) uniformly inserted into the sheet-like subunit structure and coated onto the CuS surface to enhance the pseudocapacitive performance. Novel sphere-like CuS particles with intertwined sheet-like subunit structure are fabricated by a solvothermal approach without any surfactant or template. A CuS@PPy composite electrode is prepared by in situ oxidation polymerization of pyrrole in the presence of the CuS suspension. The CuS@PPy composite (CuS content is 16.7 wt%) exhibits a high specific capacitance of 427 F g−1 (at 1 A g−1) and its capacitance can still retain 88% after 1000 cycles.

Two-dimensional mesoporous carbon nanosheets (CNSs) have been prepared via simultaneous activation and catalytic carbonization route using macroporous anion-exchange resin (AER) as carbon precursor and ZnCl2 and FeCl3 as activating agent and catalyst, respectively. The iron catalyst in the skeleton of the AER may lead to carburization to form a sheetlike structure during the carbonization process. The obtained CNSs have a large number of mesopores, a maximum specific surface area of 1764.9 m2 g–1, and large pore volume of 1.38 cm3 g–1. As an electrode material for supercapacitors application, the CNSs electrode possesses a large specific capacitance of 283 F g–1 at 0.5 A g–1 and excellent rate capability (64% retention ratio even at 50 A g–1) in 6 mol L–1 KOH. Furthermore, CNSs symmetric supercapacitor exhibits specific energies of 17.2 W h kg–1 at a power density of 224 W kg–1 operated in the voltage range of 0–1.8 V in 0.5 mol L–1 Na2SO4 aqueous electrolyte, and outstanding cyclability (retains about 96% initial capacitance after 5000 cycles).Keywords: activation; anion-exchange resin; carbon nanosheets; catalytic carbonization; supercapacitors

•Alkali and potassium ferricyanide doped polyvinyl alcohol gel electrolyte is prepared.•The PVA–KOH–K3[Fe(CN)6] gel electrolyte can also be used as separator.•The introduction of K3[Fe(CN)6] increases the ionic conductivity of electrolyte.•The supercapacitor exhibits flexible and wide potential window properties.A gel polymer PVA–KOH–K3[Fe(CN)6] is prepared by potassium hydroxide and potassium ferricyanide doped polyvinyl alcohol, and a solid-state supercapacitor is assembled using the gel polymer as electrolyte and separator, activated carbons as electrode. The gel polymer exhibits flexible, high ionic conductivity and wide potential properties. The electrochemical properties of the supercapacitor are investigated using cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy techniques. The electrode specific capacitance of the supercapacitor can be as high as 430.95 F g−1, and after 1000 cycles at a current density of 1 A g−1 it still remains higher than 380 F g−1. The energy density and power density of the supercapacitor reach 57.94 Wh kg−1 and 59.84 kW kg−1, respectively. These novel flexible gel polymers are desirable for applications in supercapacitor devices.

The demand for high-performance energy storage devices such as supercapacitors and lithium-ion batteries has been increasing to meet the application requirements of renewable energy systems. Here, high energy density aqueous asymmetric supercapacitor (ASC) is assembled based on carbon nanofibers (CNF) network positive electrode and tungsten trioxide (WO3) nanorod bundles negative electrode. Polyaniline-based CNF are prepared by direct carbonization of polyaniline nanofibers. WO3 nanorod bundles are synthesized via a simple sodium chloride assisted hydrothermal process. The CNF//WO3 ASC device operates with a voltage of 1.6 V and achieved a high energy density of 35.3 Wh kg−1 at a power density of 314 W kg−1. Furthermore, the device shows an excellent cycling performance with capacitance retention of 88% after 1000 cycles.

•Alkali and P-phenylenediamine doped polyvinyl alcohol gel electrolyte is prepared.•The PVA-KOH-PPD gel electrolyte can also be used as separator.•The introduction of PPD increases the ionic conductivity of electrolyte.•The supercapacitor exhibits flexible and high energy density.A supercapacitor utilize a novel redox-mediated gel polymer (PVA-KOH-PPD) as electrolyte and separator, and activated carbon as electrodes is assembled. The PVA-KOH-PPD gel polymer as potential electrolyte for supercapacitor is investigated by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. It is found that the supercapacitor exhibits high ionic conductivity (25 mS cm−1), large electrode specific capacitance (611 F g−1) and high energy density (82.56 Wh kg−1). The high performance is attributed to the addition of quick redox reactions at the electrolyte|electrode interface as PPD undergoes a two-proton/two-electron reduction and oxidation during cycling. Furthermore, the supercapacitor with PVA-KOH-PPD gel polymer shows excellent charge-discharge stability, after 1000 charge-discharge cycles, the supercapacitor still retains a high electrode specific capacitance of 470 F g−1. It is believed that the idea using redox mediator has a good prospect for improving the performances of supercapacitors.

•Novel organic–inorganic composite superabsorbent was successfully synthesized.•Low-cost, abundant reserves and eco-friendly loess is used as raw material.•The composite superabsorbent exhibits excellent swelling ratio and pH stability.•These excellent properties are attributed to organic–inorganic crosslinking polymerization.A new, low-cost, and eco-friendly organic–inorganic composite superabsorbent was successfully synthesized in aqueous solution by polymerization xanthan gum (XG), neutralized acrylic acid (AA) and loess using ammonium persulfate (APS) as initiator and N,N-methylenebisacrylamide (MBA) as crosslinker. Structure and morphological characterizations of the composite superabsorbent were investigated by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The loess content, pH values, surfactants, salts and temperature which could affect the swelling and water-retention capabilities of the composite superabsorbent were investigated. The composite superabsorbent exhibits excellent water absorbency (610 g/g in distilled water), pH-stability (pH 5–10), and higher swelling capacity in anionic surfactant solution; on the other hand, the composite superabsorbent can be used for removing multivalent metal ions.

•Polyaspartic acid was used to prepare nitrogen-doped porous carbon.•The morphologies and structures of carbon deeply depend on carbonization temperature.•Carbon exhibits high specific capacitance and excellent cycling stability.•The approach may be used in all amino acids to prepare nitrogen-doped carbon.Nitrogen-doped porous carbon is prepared by carbonizing polyaspartic acid under inertia atmosphere without template and activation. The powder X-ray diffraction, element analysis, scanning electron microscopy, and N2 adsorption–desorption tests show that the morphologies and structures of the nitrogen-doped carbon samples deeply depend on carbonization temperature. Electrochemical measurements show that the specific capacitance of the PASP700 sample obtained at 700 °C is 166.1 F g−1 at a current density of 1 A g−1, and after 5000 charge/discharge cycles it still remains 97% which exhibits an excellent cycling stability.

•CuS with different morphologies are prepared via solvothermal methods in different solvents.•CuS electrode materials have a wide electrochemical window (1.5 V) in an aqueous electrolyte.•The flower-like CuS exhibit high specific capacitance and excellent cycling stability.•These excellent electrochemical properties of CuS are attributed to the special architecture.CuS with different morphologies (plate-like, nanoparticle-like, sphere-like, and flower-like) are successfully synthesized via a simple low-temperature solvothermal approach without any surfactant or template. CuS are used as supercapacitor electrode materials, which provide a large voltage window as high as 1.5 V and excellent capacitive performance in an aqueous electrolyte. The specific capacitance of the flower-like CuS synthesized in glycerol can reach up to 597 F g−1 (at 1 A g−1). Meanwhile, the flower-like CuS exhibits a good cycling stability.

We introduce a facile integrated oxidation polymerization and catalytic carbonization method to prepare three-dimensional porous nitrogen-doped carbon networks (3D N-CNWs) with high nitrogen content (about 8.4 wt %) directly from poly(p-phenylenediamine). In the synthesis process, the FeCl3 serves not only as an oxidant for oxidative polymerization of p-phenylenediamine monomers but also as the carbonization catalyst to promote porous carbon network formation. The 3D N-CNWs prepared at 700 °C exhibit an interconnected porous framework with high specific surface area and show remarkable performance as an electrode material for supercapacitors. The maximum specific capacitance of 304 F g–1 at a current density of 0.5 A g–1, which retains the high values of 226 F g–1 even at a high current density of 20 A g–1, is obtained for the N-CNW electrode in 6 M KOH aqueous solution. Moreover, the as-assembled N-CNW symmetric supercapacitor exhibits a considerably high energy density of 15.8 Wh kg–1 at a power density of 450 W kg–1 operated in the voltage range 0–1.8 V in 0.5 M Na2SO4 aqueous solution, and exhibits an excellent cycling performance with 97% specific capacitance retention after 5000 cycles.

We report a facile strategy to synthesize of polypyrrole/molybdenum disulfide (PPy/MoS2) nanocomposite as an advanced electrode material for high-performance supercapacitors applications. Flowerlike MoS2 with graphene-like subunits structure is prepared using a hydrothermal method, and the nanocomposite PPy are embedded in MoS2 nanosheets is prepared by in situ oxidation polymerization of pyrrole in the presence of MoS2 suspension. Structural and morphological characterizations of the nanocomposite are investigated by XRD, FE-SEM and TEM measurements. Their electrochemical properties are also investigated using cyclic voltammetry, and galvanostatic charge/discharge. The PPy/MoS2 nanocomposite exhibit high specific capacitance of 553.7 F g−1 and its capacitance can still remain 90% after 500 cycles at a current density of 1 A g−1.Graphical abstractHighlights► Flowerlike MoS2 with graphene-like structure is prepared by hydrothermal method. ► The PPy/MoS2 nanocomposite is prepared by in situ oxidation polymerization. ► The MoS2 provides a path for insertion and extraction of ions within PPy. ► This PPy/MoS2 nanocomposite exhibit high capacity and excellent cycling stability.

Polyaniline/sodium carboxymethyl cellulose (PANI/CMC) nanorods have been synthesized via in-situ oxidation polymerization of aniline in the presence of sodium carboxymethyl cellulose as a polymerization template. The structure and morphology of the nanorods are characterized by TEM, FE-SEM and XRD. The size and shape of the composite nanorods are uniform with a diameter of 100 nm. Their electrochemical properties are also investigated using cyclic voltammetry and galvanostatic charge/discharge measurement. The specific capacitance of PANI/CMC nanorods prepared with 20 wt% CMC can be as high as 451.25 F g−1. Its capacitance remains higher than 300 F g−1 after 1000 cycles at a current density of 1 A g−1. These novel nanorods are desirable for applications in supercapacitor devides.Graphical abstractHighlights► Sodium carboxymethyl cellulose is employed as a polymerization oriented agent. ► Uniform diameters about 100 nm polyaniline/sodium carboxymethyl cellulose nanorods are obtained by a facile method. ► This novel nanorods for supercapacitors showed enhanced specific capacitance and cycling stability than pure polyaniline.

We have developed a supercapacitor electrode composed of CuS microspheres with polypyrrole (PPy) uniformly inserted into the sheet-like subunit structure and coated onto the CuS surface to enhance the pseudocapacitive performance. Novel sphere-like CuS particles with intertwined sheet-like subunit structure are fabricated by a solvothermal approach without any surfactant or template. A CuS@PPy composite electrode is prepared by in situ oxidation polymerization of pyrrole in the presence of the CuS suspension. The CuS@PPy composite (CuS content is 16.7 wt%) exhibits a high specific capacitance of 427 F g−1 (at 1 A g−1) and its capacitance can still retain 88% after 1000 cycles.

A facile one-step activation and nitrogen-doping combination method is developed for preparation of nitrogen-doped graphene-like carbon nanosheets (N-CNSs). The N-CNSs have abundant wrinkled structures and ultrahigh pore volume (3.19 cm3 g−1), and are used as high-performance electrode materials for supercapacitors.

Asymmetric supercapacitors (ASCs) with high energy density are assembled based on the pseudocapacitance of both electrodes, which use polyaniline (PANI) nanotubes as positive electrodes and MoO3 nanobelts as negative electrodes in a 1 M H2SO4 aqueous electrolyte. The assembled novel PANI//MoO3 ASC device with an extended operating voltage window of 2.0 V, in spite of the use of an aqueous electrolyte, exhibits excellent performance such as a high specific capacitance of 518 F g−1 at a current density of 0.5 A g−1, reaching an energy density as high as 71.9 W h kg−1 at a power density of 254 W kg−1 and good cycling stability.

Highly crumpled nitrogen-doped graphene-like nanosheets (CN-GLSs) with a high specific surface area (1169 m2 g−1) and large pore volume (2.58 cm3 g−1) are prepared from a macroporous resin via simultaneous urea gasification expansion and CaCl2 activation methods. The CN-GLSs are tested as electrodes for supercapacitors and present excellent electrochemical performance.

Correction for ‘Low-cost and high energy density asymmetric supercapacitors based on polyaniline nanotubes and MoO3 nanobelts’ by Hui Peng et al., J. Mater. Chem. A, 2014, 2, 10384–10388.

A stable and effective redox-mediator gel electrolyte has been prepared by doping indigo carmine (IC) into a polyvinyl alcohol sulfuric acid polymer system (PVA–H2SO4), and a high performance solid state supercapacitor is fabricated by utilizing activated carbon as electrodes and the prepared gel polymer (PVA–H2SO4–IC) as an electrolyte and separator. The PVA–H2SO4–IC gel polymer has excellent bending, compressing and stretching mechanical properties. As expected, the ionic conductivity of the gel polymer electrolyte increased by 188% up to 20.27 mS cm−1 while introducing IC as the redox mediator in the PVA–H2SO4 gel electrolyte. Simultaneously, specific capacitance is increased by 112.2% (382 F g−1) and energy density (13.26 W h kg−1) is also increased. Furthermore, the fabricated device shows superior charge–discharge stability. After 3000 cycles, its capacitive retention ratio is still as high as 80.3%. This result may be due to the fact that the IC can act as a plasticizer and redox mediator, and the supercapacitor combines the double-layer characteristic of carbon-based supercapacitors and the faradaic reaction characteristic of batteries energy-storage processes.