Search

Transition metal oxides with various valence states have high specific capacitance and have attracted much attention. However, the poor cycle stability caused by material agglomeration seriously limits the play of its high activity. Herein, we create a stress dispersion structure (CuxO composite porous carbon net) by in situ lyophilization and one-step carbonization, effectively anchoring highly reactive copper oxides and highly conductive carbon networks combined with high nitrogen doping of 10.7%, to investigate their electrochemical performance in supercapacitors. Specifically, the specific capacitance of CuxO@NPC can be as high as 392 F/g (0.5 A/g) in the three-electrode system with 6 mol/L KOH as electrolyte. When applied to the two-electrode system, the cycle stability of the whole device can reach 97% after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Abstract To solve the inevitable aggregation and the low cycling stability of NiCo 2 S 4 electrode materials, herein NiCo 2 S 4 nanoparticles anchoring onto polypyrrole nanotubes were synthesized by a hydrothermal method. The obtained NiCo 2 S 4 /polypyrrole nanotubes composites exhibit a high specific capacitance of 1705 F g−1 at 1 A g−1, and remarkable rate performance of 747.6 F g−1 at 20 A g−1. Furthermore, the assembled asymmetric supercapacitor using NiCo 2 S 4 /polypyrrole nanotubes as a positive electrode and activated carbons as a negative electrode delivers a high energy density of 52.5 Wh kg−1 at a power density of 562.5 W kg−1, and excellent cycling stability with 83.3% retention after 5000 cycles. The excellent electrochemical performance of NiCo 2 S 4 /polypyrrole nanotubes can be attributed to the high conductivity of polypyrrole nanotubes, and the key assistant effects of polypyrrole nanotubes which impede the aggregation of NiCo 2 S 4 and improve the exposed active sites for redox reaction. The results demonstrate that NiCo 2 S 4 /polypyrrole nanotubes are a promising electrode material for supercapacitors. Graphical abstract The NiCo 2 S 4 nanoparticles are in situ grown onto the surface of polypyrrole nanotubes via a hydrothermal method. The hierarchical NiCo 2 S 4 /polypyrrole nanotubes composites exhibit a high specific capacitance of 1705 F g−1 at 1 A g−1. The assembled asymmetric supercapacitors show high energy density of 52.5 Wh kg−1 at a power density of 562.5 W kg−1, and the capacitance retention remains 83.3% after 5000 cycles at 1 A g−1, indicating the excellent cycling stability. Unlabelled Image Highlights • NCS is in situ grown on PNTs via a hydrothermal method. • NCS/PNTs electrodes have a high capacitance of 1705 F g−1 at 1 A g−1. • The supercapacitors show high energy density of 52.5 Wh kg−1. • The capacity retention of supercapacitor device is 83.3% after 5000 cycles. [ABSTRACT FROM AUTHOR]

In this paper, willow leaves were used to prepare activated carbons (ACs) by one-step pyrolysis with ZnCl 2 activation. The as-prepared AC-1-800 exhibits porous structure with high specific surface area of 1031 m 2 g −1 and a large pore volume of 0.66 cm 3 g −1 . As a supercapacitor electrode, it shows a good capacitive performance in 6 M of KOH aqueous electrolyte, such as the specific capacitance reaches 216 F g −1 at a current density of 0.1 A g −1 and the retention of specific capacitance is 97% after 1000 cycles at 2 A g −1 . [ABSTRACT FROM AUTHOR]

The N-doped carbon nanotubes (CNTs) with different microstructures have been fabricated via the pyrolysis of melamine catalyzed by iron chloride. The morphologies of N-doped CNTs were tailored by the molar ratio of melamine and iron chloride and calcined temperature. The pure CNTs with bamboo-like structure are formed at 700 °C when the molar ratio of melamine and iron chloride is 4, and its BET surface and specific capacitance are higher than that of samples calcined at 600 °C or 800 °C. The BET surface and capacitance of samples increase with increasing the molar ratio of melamine and iron chloride, and the maximum BET surface area and specific capacitance are 298 m 2 g −1 and 67 F g −1 , respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cations serve as cross-linkers to induce MXene gelation and impede the restacking. • Melamine sponge as a support loads MXene aerogels with mechanical strength. • Mg-induced MXene@MS aerogel exhibits the maximum area capacity of 702.22 mF cm−2. The self-assembled aerogels are considered as an efficient strategy to address the aggregation and restacking of Ti 3 C 2 T x MXene nanosheets for high-performance supercapacitors. However, the low mechanical strength of the MXene aerogel results in the structural collapse of the self-standing supercapacitor electrode materials. Herein, a low-cost melamine sponge (MS) absorbed different cations (H+, K+, Mg2+, Fe2+, Co2+, Ni2+ and Al3+), serves as a carrier and crosslinker for loading MXene hydrogel induced by the absorbed cations on the skeleton surface and the pores of MS, resulting in the high loading mass MXene aerogels with high mechanical strength. The experimental results show that the Mg-Ti 3 C 2 T x @MS aerogel exhibits the maximum area capacitance of 702.22 mF cm−2 at 3 mA cm−2, and the area capacitance is still 603.12 mF cm−2 even at 100 mA cm−2, indicating the high rate capability with a capacitance retention of 85.89 %. It is worth noting that the constructed asymmetric supercapacitor with activated carbon achieves high energy densities of 104.53 μWh cm−2 and 93.87 μWh cm−2 at 800 μW cm−2 and 7999 μW cm−2, respectively. Furthermore, the asymmetric supercapacitor shows the high cycling stability with 90.2 % capacity retention after 10,000 cycles. This work provides a feasible strategy to prepare Ti 3 C 2 T x MXene aerogels with large layer spacing and high strength for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

• 3D flower-like NiCo-LDH/Ti 3 C 2 T x is prepared by ion-exchange reaction of ZIF-67/ Ti 3 C 2 T x. • NiCo-LDH/Ti 3 C 2 T x electrodes have a high capacitance of 635.7 C g−1 at 1 A g−1. • The asymmetrical supercapacitor show high energy density of 44.6 Wh kg−1. • The capacitance retention of device is 85.71% after 10,000 cycles. Nickel cobalt layer double hydroxides (NiCo-LDH) have high theoretical capacity for energy storage, but suffer from low electrical conductivity and sluggish charge transfer kinetics. Herein, three-dimensional (3D) porous flower-like NiCo-LDH/Ti 3 C 2 T x is facilely fabricated via the electrostatic self-assembly of metal-organic frameworks and Ti 3 C 2 T x followed by the ion-exchange reaction. The as-prepared NiCo-LDH/Ti 3 C 2 T x -5 delivers a high specific capacity of 635.7 C g−1 at 1 A g−1, and still remains 382.3 C g−1 at 20 A g−1. Furthermore, the corresponding asymmetric supercapacitor coupled with activated carbons achieves high energy density of 44.6 W h kg−1 under the power density of 852.5 W kg−1, and indicates remarkable cycling performance (85.71% of capacitance retention after 10,000 cycles). The outstanding electrochemical performance is assigned to 3D porous structure and high electrical conductivity, which not only increases the contract area between electrodes and electrolyte, but also enhances the ion diffusion and charge transfer kinetics. The as-prepared NiCo-LDH/Ti 3 C 2 T x -5 delivers a high specific capacity of 635.7 C g−1 at 1 A g−1, and still remains 382.3 C g−1 at 20 A g−1, indicating the excellent rate capability. [Display omitted] [ABSTRACT FROM AUTHOR]

This study proposes a novel strategy to modulate the morphology and electronic structure of MOFs through ligand exchange for high-performance energy storage and conversion devices. The prepared CoNi-TDA/0.2Fc had an oxygen generation reaction (OER) overpotential of 236 mV at 10 mA cm−2 and a significant specific capacitance of 1409 F−1 at 1 A/g, maintaining a capacitance retention of 96.54% after 20,000 cycles. [Display omitted] Rationally designing metal organic frameworks (MOFs) as an ideal dual-function material for water electrolysis and supercapacitors is of great significance for energy storage and conversion. Herein, we successfully synthesized the nanoneedle-like structure CoNi-MOF by partially replacing 2, 5-thiophenedicarboxylic acid (TDA) with 1, 1′-Ferrocenedicarboxylate (Fc). The exchange of Fc ligand can modulate the morphology and electronic structure of CoNi-TDA, thus exposing the abundant active sites and improving the electrical conductivity. The as-prepared CoNi-TDA/0.2Fc exhibited a low overpotential of 236 mV at 10 mA cm−2 for oxygen evolution reaction (OER) and a low Tafel slope of 40.44 mV dec−1. Additionally, CoNi-TDA/0.2Fc demonstrated a notable specific capacitance of 1409 F g−1 at 1 A/g and excellent stability, maintaining a capacitance retention of 96.54 % after 20,000 cycles. The study proposes a new strategy to modulate the morphology and electronic structure of MOFs via the ligand exchange for high-performance energy storage and conversion device. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal-organic frameworks (MOFs) have attracted considerable attention in the field of energy storage and conversion due to their large specific surface area, regulatable pore structure and composition. However, the poor electrical conductivity and few active sites of MOFs impede their application. Herein, highly conductive MXene nanosheets are introduced to modulate the electronic conductivity and structure of rod-like Co-pyridinedicarboxylic acid (Co-PDC), and thus enhancing the electrochemical performance of MOFs. The heterostructural Co-PDC/MXene (CPM) was facily synthesized at room temperature. The as-prepared CPM-30 with 30 % MXene only requires the overpotential of 75.1 mV to achieve a current density of 10 mA cm−2 for hydrogen evolution reaction (HER), and the assembled electrolytic cell with CPM-30 and RuO 2 as cathode and anode electrodes can achieve a current density of 10 mA cm−2 at a voltage of 1.65 V. In addition, CPM-10 exhibits a high specific capacitance of 583.1 F g−1 at 0.5 A g−1 and an excellent rate performance of 41.6 % at 50 A g−1. Furthermore, the assembled asymmetric supercapacitor CPM-10//AC exhibited an energy density of 15.55 Wh kg−1 at a power density of 750 W kg−1 and excellent stability with a capacitance retention rate of 95 % after 10,000 cycles. The excellent electrochemical properties of Co-PDC / MXene are attributed to the unique structure and synergistic effect of Co-PDC and MXene. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D porous MXene microgels were induced by 2-MeIM. • The intercalated 2-MeIM can improve the layer spacing of MXene nanoshets. • M-MXene film exhibits a high capacitance of 223.4 F g−1 at 1000 mV s−1. • MXene//AC supercapacitor displays a 16.88 Wh kg−1 at 799 W kg−1. Ti 3 C 2 T x MXene has been considered a potential supercapacitor electrode material on account of its fast electron transfer performance, large volume pseudocapacitance, excellent hydrophilicity and mechanical properties. However, the serious stacking of MXene nanosheets reduced the exposed active sites and hindered diffusion of ions, leading to bad electrochemical property. Here, we report a strategy to transform MXene nanosheets into 3D MXene microgels induced by 2-methylimidazole. Benefitting from the existence of microgels, it facilitates the rapid vacuum filtration to prepare the porous MXene film, thus enhancing the ion transfer efficiency. Furthermore, 2-methylimidazole can also act as an intercalated agent to increase the layer spacing of MXene nanosheets. Therefore, the as-prepared porous MXene film demonstrates a superior rate capacity, and its capacitance reaches 223.4 F g−1 at the scan rates of 1000 mV s−1. Moreover, the assembled MXene//AC asymmetrical supercapacitor displays a 16.88 Wh kg−1 at a power density of 799 W kg−1, and maintains 13.11 Wh kg−1 at a power density of 8 kW kg−1. This work develops a simple way to prepare the porous MXene film for supercapacitors with excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

• The 3D MXene@rGO hydrogel was fabricated by Al-induced self-assembly and reduction. • The MXene@rGO hydrogel exhibits a maximum area capacitance of 4.33 F cm−2 at 10 mA cm−2. • Constructed asymmetric supercapacitor shows a high cyclic stability with a mere 8.37% decrease after 100,000 cycles. MXene nanosheets are one of the most promising supercapacitor electrode materials due to their excellent conductivity and redox activity. However, the balance of high capacity and rate performance of MXene nanosheets are still a big challenge due to their easy re-stacking, especially with a high mass loading. Here, the 3D MXene@graphene (MXene@rGO) hydrogel with high ion accessibility is engineered by Al-induced self-assembly of MXene and GO nanosheets. Trace acid solution is used as the initiator to etch the blunted aluminum oxide layer and release the Al3+ ions, which acts as the linker to assemble nanosheets into 3D structure. At the same time, the mechanical strength of the hydrogel is further enhanced via the reduction of GO induced by Al. The MXene@rGO hydrogel exhibits a maximum area capacitance of 4.33 F cm−2 at 10 mA cm−2 and maintains a high area capacitance of 1.76 F cm−2 at 1000 mA cm−2, indicating the high capacitance retention of 40.6%. Remarkably, the constructed asymmetric supercapacitor shows a high cyclic stability with a mere 8.37% decrease after 100,000 cycles, indicating the excellent application prospect. [Display omitted] [ABSTRACT FROM AUTHOR]

Developing highly porous and conductive carbon electrodes are crucial for high-performance electrochemical double-layer capacitors. Herein, we provide a supercapacitor electrode material consisting of N-doped porous carbon tightly anchored on carbon nanotubes. This nanocomposite with high specific surface area of 659.5 m 2 g −1 is fabricated by pyrolyzing the ZIF-8/polypyrrole nanotubes. When the nanocompiste is used as supercapacitor electrodes, it deliveres high specific capacitance of 248 F g −1 and 97.3% of capacitance retention after 3000 cycles. The superior capacitive performance is attributed to the conductive network for electron transport constributed by CNTs and the abundant reservoir for the charge storage derived from ZIF-derived porous carbon. Benefiting from the unique structural features and high N doping, the PC-CNTs obtained by our route could be a promising candidate of electrode mateials for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

The porous carbon microtubes/flakes composites are prepared via a facile hydrothermal treatment with bamboo chopsticks as a carbon precursor and KOH as an activating agent. The as-prepared samples possess the large specific surface area up to 2337 m 2 g −1 . They exhibit the high specific capacitance of 212 F g −1 at a current density of 0.1 A g −1 , and the capacitance retention remains 96% after 1000 cycles in 6 M KOH. The results indicate that the natural resource of bamboo chopsticks could be an essential raw material for the energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • The N -doped MXene film was fabricated by vacuum filtration and carbonization. • The interlayer spacing of N -doped MXene film were optimized by introducing HMT molecules. • N -MXene-300 film exhibits a remarkable capacitance of 193 F g−1 at 2000 mV s−1. • The asymmetric capacitor exhibits high energy density of 16.04 W h k g−1 at 90 kW k g−1. Two-dimensional titanium carbide (MXene) has attracted a wide attention for its fast charging and discharging ability as an electrode for supercapacitors. Tremendous efforts have been dedicated to further optimize the electrochemical performance of MXene by adjusting the interlayer spacing and surface functional groups. Here, hexamethylenetetramine (HMT) molecules are used as an intercalation agent to enlarge the layer spacing of MXene nanosheets and regulate their electronic structure by the partial replacement of the surface functional groups (F, O and OH) with N elements via the carbonization temperature at 300 °C. The as-prepared N -doped MXene film exhibits the excellent flexibility, appropriate layer spacing and high electrical conductivity, which can be used directly as supercapacitor electrode materials. It delivers the excellent rate performance with a specific capacitance of 193 F g−1 at 2000 mV s−1. In addition, the assembled asymmetric supercapacitor with N -doped graphene aerogel, delivers a high energy density of 26.22 W h kg−1 at a power density of 899 W kg−1, and the capacitance retention of 92.1 % after 25,000 discharging/charging cycles, indicating the excellent application prospect. [ABSTRACT FROM AUTHOR]

• The morphology and electronic properties of NiMOF are regulated by the Carbon quantum dots (CQDs). • CQD@MOF-0.5 exhibits a high capacitance of 1081.5 C g−1 at 1 A g−1. • The capacitance retention of CQD@MOF-0.5 electrode is 85.4% after 5000 cycles. • The hybrid supercapacitor showed a high energy density of 56.3 Wh kg−1 at the power density of 4.3 kW kg−1. Rational design of metal-organic framework (MOF) materials with rich active sites and high conductivity is very important for their applications in the energy storage devices, but it is still a great challenge. Herein, carbon quantum dot (CQD)/NiMOF composites are synthesized via a one-pot hydrothermal method. The experimental results show that CQDs can effectively enhance the electrical conductivity of NiMOF and regulate its morphology to expose abundant active sites, which are beneficial for electrochemical performance. The as-prepared CQD@MOF composite delivers a specific capacitance of 2457.9 F g−1 at 1 A g−1, and the outstanding cycling stability with the capacitance retention of 84.5% after 5000 charge/discharge cycles. Moreover, the hybrid supercapacitors with activated carbon (AC) as the negative electrode and CQD@MOF as the positive electrode exhibits a wide voltage window of 1.7 V and a high energy density of 67.1 Wh kg−1 at a power density of 5.1 kW kg−1. The results can effectively boost the electrochemical performance of MOF and promote its application in supercapacitor electrode materials. Carbon quantum dot (CQD)/NiMOF composites are synthesized via a one-pot hydrothermal method, in which CQDs can effectively enhance the electrical conductivity of NiMOF and regulate its morphology to expose abundant active sites. [Display omitted] [ABSTRACT FROM AUTHOR]

• The morphology and electronic structure of NiMOF are regulated by the replacement of terephthalic acid with benzoic acid. • Benzoic acid-modified 2D Ni-MOF electrodes have a high capacitance of 2.38 c cm−2 at 1 mA cm−2. • The hybrid supercapacitor showed a high energy density of 50.1 Wh kg−1 at the power density of 2550 W kg−1. • The capacitance retention of benzoic acid-modified 2D Ni-MOF electrode is 88% after 10,000 cycles. Designing metal-organic frameworks (MOFs) with large specific surface area, high conductivity and abundant active sites are highly desirable for high-performance supercapacitors. Herein, the microstructure and electronic structure of NiMOF nanosheets were regulated by the partial substitution of dicarboxylic terephthalic acid (PTA) with monocarboxylic benzoic acid (BA), leading to high electronic conductivity and abundant electroactive sites of MOFs. The prepared NiMOF-10 nanosheets with 10 mol% BA substituting PTA exhibit the excellent electrochemical performance with a high specific capacity of 2.38 C cm−2 at 1 mA cm−2, and outstanding cycling stability (88% after 10,000 cycles). The fabricated hybrid supercapacitor (HSCs) demonstrated the maximum energy density of 50.1 Wh kg−1 at a power density of up to 2550 W kg−1. The exceptional electrochemical performance of NiMOF nanosheets is assigned to the improved electronic conductivity and abundant active sites induced by ligand exchange. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Fishbone-like Ni 3 S 2 /Co 3 S 4 integrated with nickel MOF nanosheets was prepared. • NiMOF@Ni 3 S 2 /Co 3 S 4 /NF electrodes have a high capacitance of 8.7C cm−2 at 1 mA cm−2. • The hybrid supercapacitor showed a high energy density of 58.8 Wh kg−1 at a power density of 781.31 W kg−1. • The capacitance retention of HSC is 96.19% % after 10,000 cycles. It is still a challenge to improve the electronic conductivity and expose more active sites of metal-organic frameworks (MOFs). Herein, the fishbone-like Ni 3 S 2 /Co 3 S 4 grown on nickel foam (NCS/NF) was employed as a conductive support for in-situ growing nickel MOF (NiMOF) nanosheets to enhance their electrochemical properties. The as-prepared NiMOF@Ni 3 S 2 /Co 3 S 4 /NF (NiMOF@NCS/NF) exhibited a high areal specific capacity of 8.7C cm−2 at 1 mA cm−2, and the capacity retention remains 65% at 50 mA cm−2. Furthermore, the assembled NiMOF@NCS/NF//AC hybrid supercapacitor achieves an intriguing energy density of 58.8 Wh kg−1 at the power density of 781.3 W kg−1, and the capacity retention remains 96.2% after 10,000 charge/discharge cycles. The prominent electrochemical performance of NiMOF@NCS/NF can be ascribed to the remarkable electronic conductivity and specific capacity of Ni 3 S 2 /Co 3 S 4 composites coupled with their three-dimensional porous structure. [ABSTRACT FROM AUTHOR]

Two-dimensional metal-organic frameworks have been considered as promising electrodes for high-performance supercapacitors because of their large accessible surface area, abundant active sites, and fast ion and electron transfer rates, but their relatively low conductivities hinder their application. Herein, 2D/2D NiCo-MOF/GO (NCMG) hybrid nanosheets are prepared by a simply ultrasonic method. GO nanosheets are evenly dispersed onto the surface of NiCo-MOF, constructing a conductive network, which not only enhances the electronic conductivity of NiCo-MOF nanosheets, but also efficiently prevents their aggregation. Benefiting from the unique structure of NCMG, its specific capacity is up to 413.61 C g−1 at 0.5 A g−1. An asymmetric supercapacitor (ASC) constructed by NCMG and activated carbon presents a maximum energy density of 36.83 Wh kg−1 at a power density of 374.99 W kg−1. The results demonstrate that NCMG hybrid nanosheets have the promising potential application for efficient energy storage devices. [Display omitted] • Ultrathin NiCo-MOF@GO hybrid nanosheets were synthesized via an ultrasonic method. • NiCo-MOF@GO electrodes have a high capacity of 413.61C g−1 at 0.5 A g−1. • Asymmetric supercapacitor shows high energy density of 36.83 Wh kg−1 at a power density of 374.99 W kg−1. [ABSTRACT FROM AUTHOR]

• Ni-MOF/MXene hybrid nanosheets were facilely prepared by an ultrasonic method. • Hybrid nanosheets exhibit high electronic conductivity. • The specific capacitance of Ni-MOF/MXene reaches up to 867.3 F g−1. Nickel-organic framework (Ni-MOF)/Ti 3 C 2 T x (MXene) hybrid nanosheets as supercapacitor electrode materials are fabricated via a facile ultrasonic method. Ti 3 C 2 T x nansheets are uniformly dispersed on the surface of Ni-MOF, thus enhancing the electronic conductivity and preventing the aggregation of Ni-MOF nanosheets. The as-prepared Ni-MOF/MXene hybrid nanosheets exhibit high specific capacitance of 867.3 F g−1 at 1 A g−1, and excellent rate capacity. [ABSTRACT FROM AUTHOR]

The self-supported monolithic carbon materials are attractive supercapacitor electrode materials owing to their three-dimensional interconnected hierarchical porous network, suitable surface area and relatively high conductivity. Here, zeolitic imidazolate framework-8 (ZIF-8) crystals were in situ synthesized on the skeletons of melamine foam (MF). After the pyrolysis at high temperature, ZIF-8/MF precursors were carbonized into three-dimensional (3D) hierarchically porous N doped carbon/carbon foam (PNC/CF) with large surface area, good electrical conductivity and mechanical property. Thus, PNC/CF achieves high specific capacitance of 250.6 F g−1 at 0.5 A g−1 and excellent rate performance. Furthermore, the constructed symmetrical supercapacitor based on PNC/CF delivers a maximum energy density of 14.2 Wh kg−1 at the power density of 375 W kg−1 and superior cycling stability of 98.4%. The superior capacitive performance can be assigned to 3D hierarchically porous structure with a suitable surface area, good wettability of between electrodes and aqueous electrolyte, and relatively high electronic conductivity of PNC/CF. Unlabelled Image • Self-standing porous N doped carbon/carbon foam for high-performance supercarpacitor • 3D porous N doped carbon/carbon foam (PNC/CF) derived from the pyrolysis of ZIF-8/melamine foam. • PNC/CF electrodes have a high capacitance of 250.6 F g−1 at 0.5 A g−1. • The supercapacitor shows high energy density of 14.2 Wh kg−1 at 375 W kg−1. [ABSTRACT FROM AUTHOR]