Outstanding Capacitive Performance Research Articles

In situ polymerization of pyrrole on CNT/cotton multifunctional composite yarn for supercapacitors

Yarn-shaped supercapacitors are favored due to their small size, high specific capacitance, and light weight. Herein, we reported a distinctive type of ply twist yarn supercapacitor by in situ polymerization of pyrrole on carbon nanotubes (CNTs)/cotton ring spun yarns. CNTs and polypyrrole (PPy) were successfully embedded into the cotton yarns with a ply twist structure. The as-developed electrode exhibited excellent electrical conductivity (20 Ω/cm), good mechanical properties (59.8 MPa, 24.6%), a high specific capacitance of 386.5 mF/cm2 with the current density of 1 mA/cm2, and ideal cycle stability with the retention of 87.8% after 5000 cycles. Meanwhile, the assembled supercapacitor showed a power density of 278.4 μW/cm2 and an energy density of 13.21 μWh/cm2. It also presented outstanding capacitive performance under different angles. This facile ply twist method provided new possibilities for one-dimensional (1D) supercapacitor and flexible wearable electronics applications.

Rapid and large-scale synthesis of polydopamine based N-doped carbon spheres@CoxNi1-x(OH)2 core-shell nanocomposites for high performance supercapacitors

The properties of electrode materials are greatly determined by their structures including surface area, pore size distribution and conductivity. Aiming for the advanced structure, we successfully design and develop a core-shell nanocomposite of polydopamine based N-doped carbon spheres (NCSs) and CoxNi1-x(OH)2 by a fast and simple two-step method. Firstly, regular NCSs are directly derived from carbonization of polydopamine, which offer conductive cores for fast electronic transport. Then, flower-like shells consisting of interlinked CoxNi1-x(OH)2 ultrathin nanosheets are vertically and evenly grafted on the surface of NCSs substrate by a chemical bath deposition method, which is faster and more suitable for large-scale production than hydrothermal synthesis. To get the homogeneous bimetal hydroxides CoxNi1-x(OH)2 through this rapid precipitation process, the influences of Co doping content on the morphologies, structure and capacitance properties of hybrids are further analyzed. Results show that the obtained NCSs@CoxNi1-x(OH)2 nanocomposite with small amount of Co doping exhibits impressively enhanced specific capacitance (2065 F g−1 at 1 A g−1) and rate capability (1429 F g−1 even at 45 A g−1) than NCSs@Ni(OH)2. The outstanding capacitive performance of this kind of nanocomposite is due to its large surface area, optimum porous size distribution and retained flower-like morphology, especially the high electrical conductivity originating from conductive skeleton of NCSs and Co ion doping. Furthermore, using the optimized NCSs@CoxNi1-x(OH)2 and activated carbon as a positive and negative electrode, the as-prepared energy storage device achieves higher energy (16–37 Wh kg−1) and power density (8−0.4 kW kg−1), along with satisfactory cycling stability.

Rambutan‐like hierarchically porous carbon microsphere as electrode material for high‐performance supercapacitors

AbstractUsed as high‐performance electrodes, both structural and compositional alterations of carbon materials play very important roles in energy conversion/storage devices. Especially in supercapacitors, hierarchical pores and heteroatom doping in carbon materials are indispensable. Here the rambutan‐like hierarchically porous carbon microspheres (PCMs) have been constructed via a hydrothermal treatment, followed by carbonization/activation. The hierarchically porous microstructure is composed of three‐dimensional porous carbon networks, which give rise to a large surface area. Moreover, N and O functional groups are introduced in the as‐prepared samples, which could generate the extra pseudocapacitance. Benefitting from the interconnected hierarchical and open structure, PCM exhibits outstanding capacitive performance, for example, superior specific capacitance and rate capability (397 and 288 F g−1 at 0.5 and 20 A g−1, respectively), as well as long cycling stability (about 95% capacitance retention after 10,000 cycles). These encouraging results may pave an efficient way to fabricate advanced supercapacitors in the future.

Facile fabrication of comb-like porous NiCo2O4 nanoneedles on Ni foam as an advanced electrode for high-performance supercapacitor

It is very desirable to develop the high-performance supercapacitors to meet the rapidly growing demands for energy-autonomous operation and miniaturization of devices. Herein, comb-like porous NiCo2O4 nanoneedles on the three-dimension (3D) nickel foam (NF) have been successfully synthesized through a facile pulsed laser ablation (PLA) approach without any post-treatments and surfactant (denoted as NiCo2O4-PLA). The influence of working solution during the fabricated process on the properties of NiCo2O4-PLA has been demonstrated in detail in terms of the crystalline structure, specific surface area, morphology, and electrochemical performance. Benefiting from the large specific surface (261.4 m2 g−1), abundant pores, and highly conductive scaffold, the NiCo2O4-PLA binder-free electrode exhibits an outstanding specific capacitance (1650 F g−1 at a current density of 1 A g−1) and eminent cycling performance (91.78% retention after a 12,000-cycle test at a current density of 10 A g−1) compared with the control samples. The assembled asymmetric device (NiCo2O4-PLA//AC-ASCs) delivers the high specific capacitance of 126.9 F g−1 at the current density of 1 A g−1, the large energy density of 56.7 Wh kg−1 at a power density of 756 W kg−1, and the low internal resistance. The attractive results strongly prove that it is an ideal candidate for advanced supercapacitor application.

Microwave-assisted synthesis of MoS2/graphene composites for supercapacitors

Transition metal sulfides have been used in energy storage field recently, while single component can no longer meet increasing requirements of energy storage devices. Combining metal sulfides with carbon is proved to be feasible. Herein, microwave-assisted synthesis of MoS2/graphene composites is proposed. Uniform and small MoS2 nanoparticles can be rapidly grown on graphene by this method, which endows as-prepared composites with superior capacitive properties. The resulting MoS2/graphene composites exhibit a specific capacitance of 401.1 F g−1 at 1 A g−1 and 95.0% capacitance over 10000 cycles at 5 A g−1. Furthermore, they exhibit a high energy density of 26.4 Wh kg−1 at a power density of 1015.4 W kg−1, disclosing outstanding capacitive performances.

Synthesis of CoO-Decorated Graphene Hollow Nanoballs for High-Performance Flexible Supercapacitors

The formation of thin and uniform capacitive layers for fully interacting with an electrolyte in a supercapacitor is a key challenge to achieve optimal capacitance. Here, we demonstrate a binder-free and flexible supercapacitor with the electrode made of cobalt oxide nanoparticle (CoO NP)-wrapped graphene hollow nanoballs (GHBs). The growth process of Co(OH)2 NPs, which could subsequently be thermally annealed to CoO NPs, was monitored by in situ electrochemical liquid transmission electron microscopy (TEM). In the dynamic growth of Co(OH)2 NPs on a film of GHBs, the lateral formation of fan-shaped clusters of Co(OH)2 NPs spread over the surface of GHBs was observed by in situ TEM. This CoO-GHBs/CC electrode exhibits high specific capacitance (2238 F g-1 at 1 A g-1) and good rate capability (1170 F g-1 at 15 A g-1). The outstanding capacitive performance and good rate capability of the CoO-GHBs/CC electrode were achieved by the synergistic combination of highly pseudocapacitive CoO and electrically conductive GHBs with large surface areas. A solid-state symmetric supercapacitor (SSC), with CoO-GHBs/CCs used for both positive and negative electrodes, exhibits high power density (6000 W kg-1 at 8.2 Wh kg-1), high energy density (16 Wh kg-1 at 800 W kg-1), cycling stability (∼100% capacitance retention after 5000 cycles), and excellent mechanical flexibility at various bending positions. Finally, a serial connection of four SSC devices can efficiently power a red light-emitting diode after being charged for 20 s, demonstrating the practical application of this CoO-GHBs/CC-based SSC device for efficient energy storage.

Boosted charge transfer in p-n heterojunctions LaMoO3/GQDs negative electrode for all-solid-state asymmetric supercapacitor

The low energy density of asymmetric supercapacitor (ASC) is limited by the negative electrodes; thus, to further increase the energy density of ASCs, it is necessary to optimize the design of the negative electrode and the device. Constructing p-n heterojunctions may be a viable approach for enhancing the performance of the negative electrode, as it enhances the driving force for the built-in charge transfer and thereby it is beneficial for the charge transfer dynamics. Herein, we attempted to configure graphene quantum dots (GQDs) and LaMoO3 as a p-n heterojunction via one-step hydrothermal method, which shows outstanding capacitance performance. The specific capacitance of the LaMoG-3 (1396 F g−1 at 1 A g−1) was higher than the theoretical value for molybdenum trioxide (1256 F g−1). Moreover, the ASC is successfully assembled all-solid-state ASC with GQDs/Mn3O4 as the positive electrode and LaMoG-3 as the negative electrode. The as-fabricated ASC exhibited an ultra-high density of 235.8 Wh kg−1 and a power density of ~1000 W kg−1. One device can light the LED indicator for more than 11 min after only charging for 5 min. The above-mentioned results will open up promising research pathways for achieving excellent energy density and high power density.

Microwave deposition synthesis of Ni(OH)2/sorghum stalk biomass carbon electrode materials for supercapacitors

Recycling of biomass wastes is an effective strategy to maximize resource utilization. Bio-waste derived carbon is a typical example of waste reuse, which has been used as supercapacitor electrode materials. Unfortunately, bare carbon usually possesses low specific capacitance and energy density. Combination of carbon and pseudocapacitive materials has been proved effective to achieve ideal capacitive performances. In this work, biomass carbon is firstly prepared using sorghum stalk as raw materials, and Ni(OH)2 is grown on sorghum stalk biomass carbon by a microwave deposition method. The resulting Ni(OH)2/sorghum stalk biomass carbon exhibits specific capacitances of 889.2 and 490.1 F g−1 at current densities of 2 and 20 A g−1, respectively. Moreover, 95.9% of capacitance is maintained over 30,000 cycles at 20 A g−1, unveiling exceptional cycling performances. Effective disposal of bio-wastes and preparation of electrode materials are both accomplished in this work. The microwave deposition allows fast growth of uniform Ni(OH)2 on sorghum stalk biomass carbon, ensuring outstanding capacitive performances.

Preparation of novel 3D hierarchical porous carbon membrane as flexible free-standing electrode for supercapacitors

A flexible 3D hierarchical porous carbon membrane was simply fabricated for supercapacitor electrode by using polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) as raw material and polyvinyl pyrrolidone (PVP) as additive via nonsolvent induced phase separation (NIPS) and carbonization. Experimental results show that the as-prepared carbon membranes display typical spongy skeleton structure and excellent flexibility. The specific surface area, micropore, mesopore, and total pore volume of the carbon membranes are increased with the increase of PVDF content. The prepared carbon membranes show large specific surface area (491 m2 g−1) and 3D hierarchical porous structure. As free-standing electrode for supercapacitors, the carbon membranes exhibit a high specific capacitance of 265 F g−1 in three-electrode system and 212 F g−1 in two-electrode system at 0.05 A g−1 in 6 M KOH aqueous electrolyte. Such outstanding capacitive performance is due to the hierarchical porous structure and ameliorated surface chemical functional groups, offering a favorable pathway for ion penetration, considerable surface for accumulation of electrolyte ions and improving the surface accessibility for electrolyte ions. It is believed that the simple and effective approach to hierarchical porous carbon membranes have good application prospect in production of freestanding electrode of supercapacitors.

Multi-shelled Ni6MnO8 hollow microspheres for high-performance supercapacitors

Binary transition metal oxides have attracted tremendous interest for their excellent redox activity and large natural abundance. They could achieve distinct electrochemical properties by engineering special hollow structures. In this work, we have synthesized triple-shelled Ni6MnO8 hollow microspheres constructed with nanosheets through step by step adsorption of the corresponding metal ions on carbon spheres followed by calcination in air. The as-prepared Ni6MnO8 hollow microspheres with nanosheet shells have an average diameter of ~900 nm, with a large surface area of 145.011 m2 g−1. They exhibit outstanding capacitive performance as electrode materials, including high specific capacitance (1380 F g−1 at 1 A g−1), distinguished rate capability (68% capacity retention at ultrahigh 100 A g−1) and stable cycling property (98% retention rate at 10 A g−1 after 5000 cycles), which are superior to those of the Ni6MnO8 hollow microspheres with nanoparticle shells. Furthermore, the assembled Ni6MnO8-NS//AC asymmetric supercapacitor demonstrates a high energy density (31.8 W h kg−1 at 750 W kg−1) with a high capacity retention of 93% even after 10,000 cycles. The distinguished performances can be attributed to the synergy of binary metals and the unique hollow structure with nanosheet shells.

Superior environmentally friendly stretchable supercapacitor based on nitrogen-doped graphene/hydrogel and single-walled carbon nanotubes

Abstract Lightweight and flexible supercapacitors with high volumetric capacitance are vitally required for wearable and portable energy storage devices. We propose an eco-friendly, simple-to-fabricate high performance supercapacitor, which consists of a solid state material based on nitrogen-doped graphene flake electrodes distributed in the NaCl-containing hydrogel electrolyte, achieving a large surface area interface. Stretchability is achieved by sandwiching this structure between two single-walled carbon nanotube film current collectors. The as-prepared quasi-solid material exhibits outstanding volumetric capacitive performance, high energy density and power density values, attaining corresponding values of 806 F cm−3, 112 mW h cm−3 and 294 W cm−3 at 0.3 A g−1. This superior capacitive behavior is due to the excellent network comprising NaCl-containing hydrogel, N-Graphene powder and carbon nanotube film, offering new strategy for developing of sustainable high-performance supercapacitors.

Boron and nitrogen co-doped double-layered mesopore-rich hollow carbon microspheres as high-performance electrodes for supercapacitors

In this paper, double-layered mesopore-rich hollow carbon microspheres (DHCM) were prepared by a Stöber method using tetraethyl orthosilicate, resorcinol and formaldehyde as precursor materials, and further utilized as carbon sources to prepare the boron and nitrogen co-doped double-layered mesopore-rich hollow carbon microspheres (B, N-DHCM) by hydrothermal approach utilizing ammonium tetraborate tetrahydrate (NH4B5O8·4H2O) as boron and nitrogen sources. Compared with the undoped DHCM, the as-obtained B, N-DHCM displays improved capacitive properties with a high specific capacitance (221.5 F g−1 at 1 A g−1), good rate performance (104.1 F g−1 at 20 A g−1) and superior cycle life (91% of capacitance retention at 3 A g−1 after 10,000 cycles). The outstanding capacitive performances result from the synergistic effect of the unique double-layered mesopore-rich hollow structure contributing to the rate property and cycle stability and the modification of B and N co-doping providing pseudocapacitance for the enhancement of specific capacitance. Therefore, the excellent capacitive behaviors render the B, N-DHCM promising electrode materials for application in supercapacitors and other energy storage systems.

Microstructure design of porous nanocarbons for ultrahigh-energy and power density supercapacitors in ionic liquid electrolyte

Exploiting various nanocarbons for supercapacitors with excellent energy retention under ultrahigh power output in high-voltage ionic liquid electrolytes possesses enormous potential for next-generation supercapacitor applications. To address the poor rate capability of the carbon electrodes in ionic liquid electrolytes, we develop an efficient strategy toward porous nanocarbons with controllable microstructure that fully solves this bottleneck to gain an outstanding capacitive performance. We found the introduction of laser-induced graphene and Mg as the additives can serve multiple roles not only as the morphology modifier agents but also as the template for the developing rich mesopores. In particular, a curved nanosheet network-like porous carbons constructed by nanocages with ultrahigh specific surface area and considerable amount of mesopores can be rationally obtained. When served as an electrode for ionic liquid-based supercapacitor, it can display an impressive specific capacitance of 201.1 F/g at 1 A/g, superb rate performance (71% capacitance retained at 100 A/g) and encouraging energy density up to 60.76 Wh/kg at a recording power density of 87.5 kW/kg, which is comparable with the best results reported for carbon-based supercapacitors in ionic liquid electrolyte reported so far.

1D/2D Co3O4/Graphene Composite Electrodes for High-Performance Supercapacitor Applications

Nanostructured Co3O4/reduced graphene oxide (rGO) composite material has been synthesized by a hydrothermal method. Urea was used as a structure-directing and assembling agent for Co3O4 nanorods. The structure and morphology of the as-synthesized Co3O4/rGO composite were investigated by x-ray diffraction analysis, scanning electron microscopy, and high-resolution transmission electron microscopy. Fourier-transform infrared spectroscopy analysis confirmed successful reduction of rGO and formation of the composite. Qualitative Raman spectral analysis of GO and the Co3O4/rGO composite revealed the reestablishment of an sp2-conjugated network of carbon atoms after reduction of graphene. Electrochemical analysis disclosed the pseudocapacitive behavior of the composite electrode material. The specific capacitance of the composite electrode was calculated to reach a higher value of 916.6 F g−1 at 0.5 A g−1 in 1 M KOH electrolyte, with excellent rate capability and long-term stability including 98% capacitance retention after 1000 cycles. This outstanding capacitive performance makes the Co3O4/rGO hybrid nanocomposite a promising candidate for use in supercapacitors.

A facile Zn involved self-sacrificing template-assisted strategy towards porous carbon frameworks for aqueous supercapacitors with high ions diffusion coefficient

Controllable synthesis of various nanostructured carbons with different textural parameters to achieve excellent electrochemical performance has attracted tremendous attention in recent years. Herein, a facile one-step Zn involved self-sacrificing template combined with KOH activation strategy has been developed for the producing porous carbon frameworks (PCFs) from sustainable biomass. The resulting PCFs display an interconnected 3D structure with large specific surface area and abundant mesoporous, which is beneficial to capacitive energy storage. Specifically, PCF-1 prepared with 1 g of Zn power presents a large specific capacitance of 285 F/g at 1 A/g and still remain a large value of 220 F/g at 50 A/g in 6 M KOH aqueous electrolyte. Moreover, it also displays an outstanding capacitive performance in 1 M Li2SO4 electrolyte within 0–1.6 V. The basic principle behind this good performance are closely associated with the interconnected 3D structure architecture and abundant mesoporous resulting from Zn involved self-sacrificing template and KOH activation, which is in favour of rapid ionic mass transport. Concerning the facile and efficient process, this Zn involved self-sacrificing template combined with KOH activation strategy is a promising strategy towards functional carbons for electrochemical capacitive storage.

Hydrothermal activated carbon cloth as electrode materials for symmetric supercapacitors

Activated commercial carbon cloth (ACC) was prepared by a facile hydrothermal process using a low concentration of hydrogen peroxide as the solvent. Microcracks, mesopores, and oxygen-containing functional groups were formed on the surface of ACC, which significantly enhanced the electrochemical properties for ACC. The ACC showed the high areal-specific capacitance, good rate capability, and excellent cycling stability in the three-electrode system. And the ACC exhibited satisfactory charging–discharging. Furthermore, the symmetric supercapacitor based on the ACC exhibited an areal-specific capacitance of 549.3 mF/cm2 and achieved an energy density of 1.29 mWh/cm3 at a power density of 533.02 mW/cm3 and a high power density of 618.16 mW/cm3 at an energy density of 0.61 mWh/cm3, respectively. Moreover, the outstanding capacitive performance reveals that ACC could be considered as a competitive potential candidate as an electrode for supercapacitor.

Areca nut–derived porous carbons for supercapacitor and CO2 capture applications

The preparation and application of biomass-derived carbons in supercapacitor and CO2 absorption have inspired increasing attention due to the ease of fabrication, cost-effectiveness, and sustainability of the meso-/microporous carbon produced from various biological precursors. With this respect, areca nut (AN) was used to derive porous carbons, through carbonization and KOH activation, at various temperatures without or in the presence of N-doping agent of adenine. KOH-activation temperature and the N-doping agent are parameters influencing the surface area, porosity, and the micro-/mesoporous structure of the porous carbons. Appropriate adjustment of the preparation parameters resulted in porous carbons with extremely high Brunauer–Emmett–Teller surface area (SBET, up to 3723 m2/g), excellent CO2 absorption capacity (up to 4.8 mmol/g) at 25 °C, and outstanding capacitive performance with high specific capacitance (up to 419 F/g) and retention (> 91%) over 1000 cycles. Effect of preparation parameters on the micro-/mesoporous structures and the resolved SBET values, CO2 absorption capacity, and the capacitive performances of the porous carbons are the main focuses of this research.

High-Performance Ni-Co Sulfide Nanosheet-Nanotubes Grown on Ni Foam as a Binder Free Electrode for Supercapacitors

The novel hierarchical Ni-Co sulfide nanosheet-nanotubes arrays were directly grown on Ni foam, as binder-free electrodes, have been successfully synthesized following a one-step facile hydrothermal method combined with a sulfide treatment. The initial value of the area capacitance achieved 2.28 F cm−2 at a current density of 1 mA cm−2. A high areal capacitance retention of 95.2% compared to activation-induced peak value is achieved after 3000 charge-discharge cycles, which is much better than counter Ni-Co oxide electrode (1.75 F cm−2 at 1 mA cm−2, 93.2% retention compared to activation induced peak value). The outstanding and excellent super capacitive performance is ascribed to ion-exchange reaction, which induces a flexible hollow nanotube feature and show higher conductivity, compared with Ni-Co oxide NWs. Cyclic voltammetry (CV) and Electrochemical impedance spectra (EIS) results confirmed that the synthesized electrode contains the lowest resistance at high, and at lower frequency, leading to easy penetration of electrolytes and fast transportation of electrons inside the electrode. In this proposed work, a one-step hydrothermal method has been followed, and provided for the sulfide-induced, with a noticeable electrochemical performance of nickel cobaltite compounds and supplying a promising route for high-performance supercapacitor electrodes.

Electrodes derived from carbon fiber-reinforced cellulose nanofiber/multiwalled carbon nanotube hybrid aerogels for high-energy flexible asymmetric supercapacitors

Developing electrodes with excellent electrochemical and mechanical properties is the key to achieve state-of-the-art flexible asymmetric supercapacitors (ASCs). This work proposes a facile and scalable strategy to prepare high-performance flexible electrodes based on carbon fiber-reinforced cellulose nanofiber/multiwalled carbon nanotube-hybrid aerogels (CF-CNF/MWCNT-HAs). The three-dimensional (3-D) porous structure, excellent conductivity, binder-free nature, and high strength of the CF-CNF/MWCNT-HAs enable it to serve as a powerful platform for constructing flexible electrodes with outstanding capacitive performance. The as-prepared CF-CNF/MWCNT/MnO2 positive electrode and CF-CNF/MWCNT/active carbon (AC) negative electrode display remarkably high areal-specific capacitances (1745 and 1273 mF/cm2 at a current density of 1 mA/cm2, respectively). In addition, the carbon fiber-reinforced electrode also presented an excellent mechanical property with a maximum stress up to 27.9 MPa. The as-fabricated CF-CNF/MWCNT/MnO2//CF-CNF/MWCNT/AC flexible ASC device exhibits significant capacitance and energy density of 19.4 F/cm3 and 8.93 mWh/cm3, respectively. Additionally, this flexible ASC device can retain more than 96.7% of its capacitance after 3000 charge-discharge cycles. These results will enable us to fabricate flexible solid-state ASC devices from CF-CNF/MWCNT-HAs, and to expand its applications in the fields of portable and wearable electronics.

Nitrogen-doped microporous carbon derived from a biomass waste-metasequoia cone for electrochemical capacitors

Naturally nitrogen-doped porous carbon is acquired from the fruit of Metasequoia (dawn redwood cone) by two facile steps of pre-carbonization and chemical activation. Current collectors coated with the porous carbon as electrodes are evaluated in 6.0 M basic electrolyte for the application of electrochemical capacitors. Results show that the porous carbon obtained with an activated temperature of 700 °C keeps the highest specific surface area (1,831 m2 g−1) and the largest pore volume (0.92 cm3 g−1). In three-electrode test, the carbon based electrode not only possesses an outstanding capacitive performance up to 326 F g−1 and 236 F g−1 at current densities of 0.5 A g−1 and 10 A g−1, respectively, but also shows a stable cycling characteristic. The two-electrode symmetric device also harvests a specific capacitance of 197 F g−1 at a current density of 1.0 A g−1 and an excellent energy density as high as 7.6 W h kg−1. Our study suggests that the cone can be applied as a promising and almost zero-cost precursor in fabricating porous carbon samples for supercapacitor, thanks to the abundance of resources.