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The design and development of composite materials with novel structures is one of the effective ways to enhance the electrochemical properties of supercapacitors. In this paper, a one-step electrodeposition method is used to adjust the morphology and structure of CoMnS nanomaterials by changing the amount of CS2. CoMnS nanomaterials with unique flower-like structures are reasonably prepared, which promotes the flow of electron transfer and improves the electrochemical behavior. It is worth noting that when the amount of CS2 is 4 mmol, the specific capacitance of CoMnS-4 reaches 3469.5 F g−1 at 1 A g−1, and the specific capacitance is still 2830.5 F g−1 (maintaining 81.56%) until the high current density reaches 20 A g−1. After 10 000 cycles, it shows excellent cycle stability (maintaining 95.78% at 20 A g−1). The CoMnS-4//AC asymmetric supercapacitor device has an excellent energy density of 85.91 W h kg−1 when the power density is 800 W kg−1, which shows it's great application value. [ABSTRACT FROM AUTHOR]

Holey Fe-Anderson-type polyoxometalate/polyaniline/graphene (PPG) hybrid materials were first prepared by anchoring Anderson-type polyoxometalates [FeMo6O 2 4 H6] 3 − (FeMo 6) onto graphene modified with polyaniline via a facile hydrothermal treatment. The as-prepared materials exhibited an excellent electrochemical performance with a high specific capacitance of 1366 F g − 1 at 1 A g − 1 and outstanding cycling stability (97.6% capacitance retention after 5000 cycle times). The uptake of polyaniline/FeMo6 nanoparticles on graphene not only provided the pseudocapacitance but also weakened the aggregation between the graphene layers, resulting in a higher surface area compared with pure graphene. In addition, the AC//PPG-15 asymmetric supercapacitor device showed a high energy density of 24.65 W h kg − 1 at a low power density of 326.25 W kg − 1 and good cycling stability (94.82% capacitance retention after 5000 cycles). Hence, the as-prepared PPG hybrid materials in this work possess tremendous potential as electrodes for high-performance supercapacitors. Holey Fe-Anderson-type PPG hybrid materials were prepared via a facile hydrothermal treatment and subsequent freeze-drying process. Polyaniline/FeMo6 nanoparticles were well doped in graphene layers, which is favorable for improving ion and electron transport circumstances, resulting in high performance on the application of supercapacitor. [ABSTRACT FROM AUTHOR]

CoNi2S4/graphene nanocomposites were synthesized by a simple solvothermal method and used as supercapacitor electrodes. CoNi2S4 nanoparticles were doped in graphene layers, which is favorable for improving electrochemical performances of the as-prepared materials. The resulting electrochemical performance of CoNi2S4/graphene nanocomposite electrodes possessed pseudocapacitive behavior with high specific capacitance (1621 F g−1 at 0.5 A g-1), good rate capability (76.7% capacitance retention when reaching 10 A g-1) and outstanding cycling stability (no capacitance loss after 2500 charge-discharge cycles at 5 A g-1). In addition, as the positive electrode of an asymmetric supercapacitor, the material also shows a high specific capacitance of 126.6 F g-1 at 0.5 A g-1, good cycle stability with capacitance retention of 87.4% after 5000 cycles and the highest energy density of 39.56 W h kg-1 at the power density of 374.8 W kg-1. [ABSTRACT FROM AUTHOR]

A facile method for synthesising porous carbon materials with high nitrogen content is employed in this study using 1H-Benzotriazole (BTA) as carbon precursor and ZnCl as active agent at 600-800 °C for 2 h under N atmosphere. Pure BTA completely degrades even at low temperature (270 °C) under inert gas, but ZnCl can convert the more organics to carbon because of its dehydration. The obtained NC-2-700 sample possesses a high specific surface area (1228 m·g) and a nitrogen content up to 10.27 wt%. Moreover, the N-doped carbon exhibits a good electrochemical property (with a specific capacitance of 332 F·g at the current density of 0.5 A·g), as well as an outstanding cycle stability (96.5% of the initial specific capacitance is maintained after 5000 cycles at 1 A·g). In addition, this obtained symmetric ultra-capacitor prepared from the NC-2-700 sample exhibits a highest energy density of 12.94 Wh·kg with a power density of 375 W·kg at a current density of 1 A·g. And even this NC-2-700//NC-2-700 supercapacitor gives 5.43 Wh·kg with a power density of 3750 W·kg at a high current density of 10 A·g. Consequently, these experimental results confirm that the porous carbon materials with high nitrogen content can be a prospective electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

Nitrogen-containing porous carbons with numerous micropores were fabricated by pyrolysing polyvinylidene fluoride (PVDF) membrane following potassium hydroxide (KOH) activation at 600-900 °C for 2 h under N atmosphere. The fabricated nitrogen-containing porous carbons have a large specific surface area of approximately 2289 m g, a certain nitrogen content of 1.35 at.% and a favourable hierarchical porous structure possessing a great number of micropores and a part of mesopores. The carbon materials exhibit high specific capacitance of 338 F g at 0.5 A g in a 6 M KOH and outstanding cycling property of 91.6% maintenance at 2 A g after 10000 cycles. An all-solid-state symmetrical supercapacitor with these as-prepared materials as electrodes can deliver energy densities of 21.9 to 10.4 W h kg at power densities from 700.8 to 12910.3 W kg. To sum up, the as-obtained porous carbon is a type of potential electrode material for electrical double-layer capacitor. [ABSTRACT FROM AUTHOR]

In this work, hemicellulose-derived porous activated carbon materials are synthesized by a new method. The nanoporous carbon is prepared for the first time by one-step chemical activation of hemicellulose. The hemicellulose extracted from pomelo peel is used as precursor, and zinc chloride is used as the activator. The porous activated carbon material with large specific surface area of up to 1361 m2 g−1 is fabricated by a one-step chemical activation at a low temperature of 500 °C. The roles of the activator/carbon material ratio and activation temperature are studied in detail. Benefiting from the porous structure and favorable activation temperature, the as-prepared carbon material possesses ideal electrochemical capacity. The porous activated carbon material performs an excellent specific capacitance of 302.4 F g−1 at the current density of 0.5 A g−1 in 6 M KOH and cycling stability of 98.6% capacitance retention after 10000 cycles. For all-solid symmetric supercapacitor, the energy density is 11.7 W h kg−1 at the power density of 349.9 W kg−1. The hemicellulose-derived porous activated carbon material shows unique properties, making it an ideal advanced electrode material for high-performance supercapacitors. Fig. 1. The graphical abstract of HPAC-x-y materials. Image 1 • The carbon source of the material is hemicellulose. • Porous carbon is synthesized by a one step ZnCl 2 activation. • Porous carbon is prepared at low temperature of 500 °C. • The raw material of the activated carbon is pomelo peel. • The HPAC-1-500 sample exhibits large surface area of 1361 m2 g−1 and 98.6% capacitance retention. [ABSTRACT FROM AUTHOR]

Although water-soluble redox based supercapacitors (SCs) had attractive supercapacitor characteristics, they still suffered from problems of low operating voltages and unsatisfactory energy density. Herein, it was reported that the oxygen defect modulated copper oxide on flexible carbon fiber (denoted as CuO x /CF) achieved a broad potential range of up to 3.0 V in 1 M Na 2 SO 4 contained 0.05 M K 4 [Fe (CN) 6 ]/K 3 [Fe (CN) 6 ] electrolyte. Oxygen defects in CuO x /CF improved charge transfer efficiency, adjust [Fe (CN) 6 ]3−/4− ions diffusion and stimulated more pseudocapacitive behavior, which demonstrated by electrochemical characterization and theoretical calculation results. It is noteworthy that the 3.0 V high voltage water-soluble CuO x /CF based symmetric supercapacitor yielded a maximum energy density of 53.1 Wh kg−1 at a power density of 1950 W kg−1 and exceptionally remarkable cycling durability of 98.9%. This work presented a viable strategy for constructing wide-voltage flexible supercapacitor devices. [Display omitted] • Introduced defect engineering successfully increased specific capacitance of CuO x /CF symmetric supercapacitor. • The water-soluble redox electrolytes broaden the voltage window and improved ionic conductivity. • DFT theoretical calculation analysis was performed for the contribution of oxygen vacancies modulated copper oxide for the energy storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Directly grown Cu/Co-MOF on the surface of NF as a template. • Hierarchical CuCo 2 O 4 @CoS-Cu/Co-MOF core-shell nanoflower are synthesized. • The material exhibits high electrochemical performance with brilliant cyclic performance. • The device delivers a large energy density of 73.29 Wh kg−1 at 849.94 W kg−1. Rational design of composite materials with unique core-shell nanoflower structures is an important strategy for improving the electrochemical properties of supercapacitors such as capacitance and cycle stability. Herein, a two-step electrodeposition technique is used to orderly synthesize CuCo 2 O 4 and CoS on Ni foam coated with Cu/Co bimetal metal organic framework (Cu/Co-MOF) to fabricate a hierarchical core-shell nanoflower material (CuCo 2 O 4 @CoS-Cu/Co-MOF). This unique structure can increase the electrochemically active site of the composite, promoting the Faradaic redox reaction and enhancing its electrochemical properties. CuCo 2 O 4 @CoS-Cu/Co-MOF shows a prominent specific capacitance of 3150 F g−1 at 1 A g−1, marvelous rate performance of 81.82% (2577.3 F g−1 at 30 A g−1) and long cycle life (maintaining 96.74% after 10,000 cycles). What is more, the assembled CuCo 2 O 4 @CoS-Cu/Co-MOF//CNTs device has an energy density of 73.19 Wh kg−1 when the power density is 849.94 W kg−1. It has unexpected application prospects. [ABSTRACT FROM AUTHOR]

TiO 2 nanotube arrays (NTAs) are excellent energy storage materials due to their chemical stability, high specific surface area and wide voltage window. However, poor electrochemical activity and electrical conductivity limit the application in supercapacitors. Herein, we develop a promising modification strategy for improving electrochemical performance of TiO 2 , through bulk-phase Nb-doping by in-situ anodization of Ti-Nb alloy and surface self-doping of Ti3+/oxygen vacancy (V o) with one-step electrochemical reduction. Material characterizations indicate the successful formation of Nb5+ in the lattice, as well as Ti3+/V o and hydroxyl are also introduced. Electrochemical measurements demonstrate that reduced co-doping system (denoted as R-Ti-Nb-O) yields a superior areal capacitance (19.56 mF cm−2 at 0.1 mA cm−2), which enhances by 3 orders of magnitude compared with pristine TiO 2. Furthermore, R-Ti-Nb-O exhibits high energy density (1.33 mWh cm−2), superior power density (35 mW cm−2), outstanding rate capability (81.70%) and remarkable cycling stability (76.76% capacitance retention after 1000 cycles). Density functional theory (DFT) calculations further reveal that reduced co-doping system indeed significantly increases the carrier density, electrical conductivity and hydrophilicity. This work involving bulk-phase Nb-doping and surface oxygen defective engineering may help provide a feasible and effective strategy to improve areal capacitance of Ti-based nanostructures for enhanced electrochemical energy storage. [ABSTRACT FROM AUTHOR]

In this paper, we synthesize honeycomb structure titanium dioxide (TiO 2) grafted with carbon fiber (CF) composites (CF/TiO 2) for flexible supercapacitors (SCs), which evidently boosts specific surface areas (SSA) of CF. In addition, we put forward an effective strategy for enhancing conductivity of TiO 2 relying on construction of oxygen defects in NaBH 4 solution. Amazingly, the reduced-TiO 2 supporting on CF electrode (CF /R–TiO 2) obtains from optimum conditions (2 M 4h) and exhibits the highest specific capacitance of 115.2 F g−1 at 1200 mA g−1, suggesting ultra-utilization of R–TiO 2 for SC. Interestingly, its capacitance retention still remains 98.37% after 10000 cycles, which declares prominent cycling stability. Furthermore, we conduct density functional theory (DFT) analysis to reveal the enhancement mechanism of R–TiO 2. With the reduction process, Fermi energy (E F) can obviously move conduction band (CB), which indicates increments of electronic conductivity of TiO 2. Moreover, the aqueous symmetric SC based on CF/R–TiO 2 (CF/R–TiO 2 -SC) expresses a high energy density of 49.6 Wh kg−1 at a power density of 1440 W kg−1. Meanwhile, the all-solid-state flexible supercapacitor (CF/R–TiO 2 -AFSC) further presents favorable flexibility in tested bending angles. Our results demonstrate that CF/R–TiO 2 is provided with introduction of oxygen defects and honeycomb structure, which might have tremendous potential for SC. [Display omitted] • Honeycomb structure TiO 2 with oxygen defects was designed for supercapacitors. • Oxygen defects were introduced into TiO 2 by one-step NaBH 4 reduction. • Flexible CF/R–TiO 2 -SC exhibited the remarkable energy density of 48.4 Wh kg−1. • The CF/R–TiO 2 -AFSC could show favorable flexibility. [ABSTRACT FROM AUTHOR]

Pomelo peel is a popular biomass material that is eco-friendly and widely distributed worldwide. However, a large amount of pomelo peel is directly discarded instead of being utilized. This study synthesizes nitrogen/sulfur dual-doped porous carbon materials using pomelo peel and ammonium persulfate, followed by potassium hydroxide (KOH) activation at 600 °C, which is lower than most average activation temperature. The as-obtained products are electrode materials applied in supercapacitors. Results indicate that the as-prepared nitrogen/sulfur dual-doped porous carbon material (NSC-600) has high nitrogen (5.89%) and sulfur (0.46%) contents, and a large surface area (1193 m2 g−1). As the current density is 0.5 A g−1, the specific capacitance of the NSC-600 material up to 310 F g−1. After 10,000 cycles, the capacity retention is approximately 98.8% at a current density of 2 A g−1 in 6 M KOH, which indicates outstanding cycling performance. Moreover, the assembled symmetric electrochemical capacitor exhibits a high energy density of 21.4 Wh kg−1 at a power density of 259.9 W kg−1. Therefore, the nitrogen/sulfur dual-doped porous carbon materials synthesized at comparatively low temperatures exhibit promising applications in superior-performance supercapacitors. • Porous carbon materials are synthesized at 600 °C, which is lower than most average activation temperatures. • Porous carbon materials have high nitrogen (5.89%) and sulfur (0.46%) contents. • The carbon source of the materials is pomelo peel. • Outstanding cycling performance of 98.8% is retained after 10,000 cycles at a current density of 2 A g−1. • The NSC-600 material achieves a large surface area of 1193 m2 g−1 at 600 °C. [ABSTRACT FROM AUTHOR]