As-assembled Symmetric Supercapacitor Research Articles

Rational design of one-dimensional skin-core multilayer structure for electrospun carbon nanofibers with bicontinuous electron/ion transport toward high-performance supercapacitors

The fast transport of electrons and ions within electrodes is crucial to the final electrochemical properties. Herein, we have developed a unique ultra-long one-dimensional (1D) skin-core multilayer structure based on electrospun carbon nanofibers mainly through a facile Stöber method combined with resorcinol–formaldehyde resin, which not only achieves bicontinuous electron/ion transport during the charge/discharge process, but also provides large surface area for ion adsorption. Particularly, controlling the number of active layers as well as regulating the active sites in layer both can obviously improve capacitive properties. Benefiting from the synergistic effects of the desirable architecture, such the rational-designed skin-core structural carbon nanofibers as supercapacitor electrode can deliver a high specific capacitance up to 255 F g−1 at 0.5 A g−1, favorable rate capability with 89% capacitance retention of initial capacitance at 8 A g−1, and excellent cycling stability with nearly 93% capacity retention after 10,000 cycles at 2 A g−1. Furthermore, the as-assembled symmetric supercapacitor devices also present a maximum energy density of 8.77 Wh kg−1 at 0.25 kW kg−1 and a maximum power density of 3.70 kW kg−1 at 6.74 Wh kg−1. Such skin-core carbon nanofibers provide an effective strategy to design high-performance supercapacitor electrode for the next-generation energy storage devices.

Shrimp shell-derived N, O-doped honeycomb-carbon for high-performance supercapacitor

Electrochemical capacitors (ECs) have garnered gargantuan attention by virtue of their eminent features, such as admirable power density, infinite cycling stability, and fast charging/discharging rates. Herein, shrimp shell-derived honeycomb-carbons were scrupulously obtained via a molten-salt activation strategy, with the aim of developing advanced electrode materials for supercapacitors. The optimized sample exhibited a high specific surface area, expedient pore volume, and high nitrogen/oxygen content. Consequently, the as-assembled symmetric supercapacitor delivered a high specific capacitance of 218 F g−1 at 0.05 A g−1 and excellent cycling stability with 94.15 % capacitance retention over 10,000 cycles. More importantly, the as-constructed SS-0.7|2M ZnSO4|Zn foil zinc-ion hybrid supercapacitor (ZHS) displayed remarkable specific capacitance (109.6 mAh g−1) at 0.05 A g−1, superior energy density (87.56 Wh kg−1) at 36.87 W kg−1, along with unparalleled cycling performance (with only 4.19 % capacitance decay after 50,000 cycles). This work provides a new perspective on engineering honeycomb-like hierarchical porous carbon for application in supercapacitors.

High Performance of Functionalized Graphene Hydrogels Using Ethylenediamine for Supercapacitor Applications

High-performance supercapacitor (SC) electrodes typically require excellent rate capabilities, long cycle life, and high energy densities. In this work, ethylenediamine (EDA) functionalized graphene hydrogels (FGHs) with a high capacitor performance were prepared from graphene oxide (GO) dispersions using a two-step hydrothermal method. In addition, we used a very small amount of EDA to achieve the partial reduction and functional modification of GO, and the synthesized FGH-4 binder-free electrodes exhibited a high specific capacitance of −240 F/g at 1 A/g. We also successfully fabricated a symmetric SC device based on the FGH-4 electrode, with a wide voltage window of 3.0 V. More importantly, the as-assembled symmetric SC delivered a high specific energy of 39 Wh/kg at a specific power of 749 W/kg, while still maintaining its superior cycle life (retaining 88.09% of its initial capacitance after 10,000 cycles).

Preparation of Boron/Sulfur-Codoped Porous Carbon Derived from Biological Wastes and Its Application in a Supercapacitor.

Abundant biomass resources are a good choice for preparing electrode materials for supercapacitors, but developing a versatile and simple synthetic method to convert them into electrode materials remains a challenge. In the present research, our team reports a promising strategy and cost-efficient method to fabricate boron/sulfur-codoped porous carbon from biomass sources, mainly utilizing four biomass materials. Detailed material characterization showed that the samples produced by this approach possess rich B and S doping. Additionally, the original biomass materials treated by activation produce abundant pores. Therefore, owing to the synergetic effect of abundant atomic doping and microporous/mesoporous distribution, the obtained carbon as electrode material manifested excellent specific capacitances of 290 F g−1 at a 0.5 A g−1 current density. Moreover, the specific energy of the prepared samples of the as-assembled symmetric supercapacitor is as high as 16.65 Wh kg−1 in 1 M Na2SO4, with a brilliant cyclical performance of only a 2.91% capacitance decay over 10,000 cycles. In addition, it has been verified universally that three other types of bio-wastes can also prepare electrode material using this method. This paper represents a significant attempt to turn waste biomass into treasure while also providing ideas for the design and preparation of supercapacitor electrode materials.

KMnO4-assisted synthesis of hierarchical porous carbon with ultrahigh capacitance for supercapacitor

Porous carbon obtained by the conventional method (KOH/ZnCl2 chemical activation after carbonization) is faced with long ion diffusion distance, large ion diffusion resistance, which resulting in unsatisfactory electrochemical properties. Herein, we report a facile method to synthesize oxygen rich hierarchical porous carbon (OHPC) using corn stalks as carbon precursor and KMnO4 act as activator. Due to the high specific surface area, hierarchical porous framework and abundant oxygen functional groups, the optimized OHPC-600 displays a large specific capacitance of 464.7 F g−1 at 0.5 A g−1 and still maintains a large specific capacitance of 253.3 F g−1 even at 50 A g−1, suggesting superior rate property. More interestingly, the as-assembled symmetric supercapacitor shows a large energy density of 21.0 W h kg−1 and good cycle stability (the retention rate is 89.8% after 10,000 cycles) in 1 M Na2SO4 aqueous electrolyte. This work provides an excellent renewable candidate and a practicable route design strategy for conversion of biowaste into excellent performance electrode material.

Kinetic enhanced bio-derived porous carbon tile laminate paper for ultrahigh-rate supercapacitors

Porous activated carbon is an attractive supercapacitor electrode material, but its problems, i.e., lengthened ion paths inside large particles, unsatisfactory conductivity caused by the use of insulating binder and rather low packing density, greatly limit their gravimetric/volumetric performance especially at ultrahigh charging rate. Herein, a novel, free-standing, compact carbon paper electrode (0.8 g cm−3) with ultrahigh conductivity (198 S cm−1) and porosity (1098 m2 g−1) is designed by layer-stacking the bio-derived porous carbon tile (CT) with ca. 0.7 μm in wall thickness together with a few of single-walled carbon nanotubes (SWNTs). Ascribed to its kinetically fast ion/charge transfer paths, i.e., ion access shortcuts in plane of quasi-2D layered CTs, interconnected interlayer channels and SWNT-bridged conductive network, this compact laminate electrode delivers remarkable rate performance without sacrificing volumetric capacitance (218 F g−1/174 F cm−3 at 20 A g−1). Significantly, such outstanding rate capability is till maintained in as-assembled symmetric supercapacitor in aqueous (60% capacitance retention at 3000 mV s−1) and organic (60% capacitance retention at 1000 mV s−1) electrolyte, suggesting great promising of our designed carbon electrode for ultrafast charging.

Fe2O3 Nanoparticles Anchored on the Ti3C2Tx MXene Paper for Flexible Supercapacitors with Ultrahigh Volumetric Capacitance.

Ti3C2Tx MXene, with high conductivity and flexibility, has drawn great attention in the wearable energy storage devices. However, the easy nanoflake-restacking phenomenon greatly restricts the achievable electrochemical performance of Ti3C2Tx-based supercapacitors, in particular volumetric capacitance. Herein, we report a flexible hybrid paper consisting of Fe2O3 nanoparticles (NPs) anchored on Ti3C2Tx (Fe2O3 NPs@MX) via electrostatic self-assembly and annealing treatments. The interlayer spacing of Ti3C2Tx nanoflakes is effectively enlarged through the incorporation of Fe2O3 NPs, allowing more electrochemical active sites to store charge. Meanwhile, Ti3C2Tx nanoflakes form a continuous metallic skeleton and inhibit the volume expansion of Fe2O3 NPs during the charging/discharging process, enhancing the cycling stability. The flexible, ultrathin (4.1 μm) Fe2O3 NPs@MX hybrid paper shows considerably improved electrochemical performances compared to those of pure Ti3C2Tx and Fe2O3, including a wide potential window of 1 V, an ultrahigh volumetric capacitance of ∼2607 F cm-3 (584 F g-1), and excellent capacitance retention after 13,000 cycles. Besides, the as-assembled symmetric solid-state supercapacitor exhibits an energy density of 29.7 Wh L-1 and excellent mechanical flexibility. We believe that the present nanostructure design, decorating NPs within a two-dimensional metallic network, has general applicability and could be used to fabricate highly efficient composites for advanced energy storage devices.

Dual-templated 3D nitrogen-enriched hierarchical porous carbon aerogels with interconnected carbon nanosheets from self-assembly natural biopolymer gel for supercapacitors

This work reports the design and fabrication of nitrogen-enriched hierarchical porous carbon aerogel (NPCA) with high supercapacitance performance derived from self-assembly natural biopolymer gel using a novel dual-template method. The as-obtained NPCA exhibited a honeycomb-like 3D network architecture composed of interconnected carbon nanosheets with hierarchical porous structure, large specific surface area (SSA, large to ∼1438 cm3 g−1) and high content of N element (large to ∼6%). The 3D hierarchical porous structure was designed and tailored to enhance the electron/ion transport ability. NaCl was in favor of the enhancement of SSA/graphitization degree and the support of 3D architecture, while NaOH played an important role in the formation of micropores. The N dopants were introduced to provide the extra pseudocapacitance, which could improve the performance of energy storage. It was also found that the SSA, graphitization degree and N dopants were highly affected by pyrolysis temperature. Among the resultant samples, NPCA-650 displayed the highest specific capacitance (264.3 F g−1 at 0.5 A g−1) attributed to not only the developed pore structure but also the abundant active N dopants. The as-assembled symmetric supercapacitor exhibited a high energy density of 12.4 Wh kg−1 with excellent cycling stability. Overall, this work provides a novel approach for the fabrication of low-cost biomass-based energy storage materials and could be also helpful for the design and tailoring of the hierarchical porous carbon aerogel architecture.

N, S, O Self-Doped Porous Carbon Nanoarchitectonics Derived from Pinecone with Outstanding Supercapacitance Performances.

Biomass-derived porous carbons are considered as one of the most promising electrode materials for supercapacitors due to their low-cost and natural abundance. In this work, pinecone is used to fabricate biomass N, S, O-doped porous carbon via one-step carbonization process with KOH activation. By optimizing the additive amount of KOH and calcination temperature, the asprepared product shows a high specific surface area and pore volume up to 1593.8 m² g-1 and 0.8582 cm³ g-1, respectively. As an electric double-layer capacitor (EDLC) electrode, the N, S, O-doped porous carbon exhibits a high specific capacitance of 285 F g-1 at 0.5 A g-1 and good rate performance with a capacitance retention of 78.6% from 0.5 to 20 A g-1. Furthermore, the as-assembled symmetric supercapacitor with 6 mol L-1 KOH as electrolyte possesses a promising energy density of 6.34 Wh kg-1 and a power density of 250 W kg-1. Outstanding cycling stability was also demonstrated with 94.4% capacitance retention after 10,000 charge/discharge cycles at 1 A g-1.

Ti3C2Tx MXene-Reduced Graphene Oxide Composite Electrodes for Stretchable Supercapacitors.

The development of stretchable electronics requires the invention of compatible high-performance power sources, such as stretchable supercapacitors and batteries. In this work, two-dimensional (2D) titanium carbide (Ti3C2Tx) MXene is being explored for flexible and printed energy storage devices by fabrication of a robust, stretchable high-performance supercapacitor with reduced graphene oxide (RGO) to create a composite electrode. The Ti3C2Tx/RGO composite electrode combines the superior electrochemical and mechanical properties of Ti3C2Tx and the mechanical robustness of RGO resulting from strong nanosheet interactions, larger nanoflake size, and mechanical flexibility. It is found that the Ti3C2Tx/RGO composite electrodes with 50 wt % RGO incorporated prove to mitigate cracks generated under large strains. The composite electrodes exhibit a large capacitance of 49 mF/cm2 (∼490 F/cm3 and ∼140 F/g) and good electrochemical and mechanical stability when subjected to cyclic uniaxial (300%) or biaxial (200% × 200%) strains. The as-assembled symmetric supercapacitor demonstrates a specific capacitance of 18.6 mF/cm2 (∼90 F/cm3 and ∼29 F/g) and a stretchability of up to 300%. The developed approach offers an alternative strategy to fabricate stretchable MXene-based energy storage devices and can be extended to other members of the large MXene family.

Molten salt and air induced nitrogen-containing graphitic hierarchical porous biocarbon nanosheets derived from kitchen waste hydrolysis residue for energy storage

Herein, the feasibility to fabricate nitrogen-containing biocarbon material from kitchen waste hydrolysis residue by a molten salt-air -assisted synthetic strategy is investigated. Hierarchical porosity and graphitic carbon nanosheet structure are found for the developed biocarbon. The porosity is mainly induced by O2 and the specific surface area of biocarbon (fabricated in air) reaches 818.65 m2 g−1, much higher than that of O2-free sample (11.84 m2 g−1). Meanwhile, the heteroatom (e.g. N) is also retained and introduced into carbon structure even in air atmosphere. It is also suggested that O2 may accelerate a destructive effect on the order of graphitic structure, while the molten salts of NaCl and KCl play the roles of graphitization catalyst and sealing agent, promoting the graphitization of biocarbon. When the developed biocarbon is applied as electrode material, the as-assembled symmetric supercapacitor exhibits a high energy density of 11.7 Wh kg−1 in 1 M Na2SO4. Forthermore, the applicability of current strategy for industrial biocarbon fabrication is verified by salt recycling test and ten times scale-up trail experiment, which shows great potential for green and large-scale production of advanced carbon materials from biomass precursors, for exmple, kitchen waste hydrolysis residue.

Extraordinary Thickness-Independent Electrochemical Energy Storage Enabled by Cross-Linked Microporous Carbon Nanosheets.

Two-dimensional carbon-based nanomaterials have demonstrated great promise as electrode materials for electrochemical energy storage. However, there is a trade-off relationship between energy storage and rate capability for carbon-based energy storage devices because of the incrementing ion diffusion limitations, especially for thick electrodes with high mass loading. Herein, we report the cross-linked microporous carbon nanosheets enabling high-energy and high-rate supercapacitors. The as-fabricated microporous carbon nanosheets exhibit an extraordinary thickness-independent electrochemical performance. With the thickness of 15 μm, the as-fabricated carbon nanosheet electrode possesses areal/volumetric/gravimetric capacitance of 895 mF cm-2/596 F cm-3/358 F g-1. Even at a high electrode thickness of 125 μm, the as-fabricated thick electrode presents an ultrahigh areal/volumetric/gravimetric capacitance of 4102 mF cm-2/328 F cm-3/328 F g-1. Furthermore, the as-assembled symmetric supercapacitor delivers an outstanding energy density of 19.2 W h kg-1 at a power density of 135 W kg-1 and ultralong cycling stability (capacitance retention of 95% after 180 000 charge/discharge cycles) in an alkaline electrolyte. This work not only provides a facile method for low-cost preparation of carbon nanostructures and high-value utilization of biomass wastes but also offers new insights into rational design and fabrication of advanced electrode materials for high-performance electrochemical energy storage.

Phenolic hydroxyl functionalized partially reduced graphene oxides for symmetric supercapacitors with significantly enhanced electrochemical performance

In this paper, three-dimensional phenolic hydroxyl functionalized partially reduced graphene oxides with high hydroxyl content and significantly enhanced electrochemical performance have been successfully prepared by a one-pot hydrothermal method from graphene oxide dispersions. A very small amount of 4-aminophenol is employed as reducing and N-doping agent, structure modifier and the phenolic hydroxyl source, at the same time. The electrochemical test results show that as binder-free electrode, the as-synthesized sample with high hydroxyl content (6.15 at%) exhibits an ultrahigh specific capacitance of 284.1 F g−1 at current density of 0.3 A g−1 in 6 M KOH electrolyte, and retains for 80.4% even at a current density of 10 A g−1. Above all, the as-assembled symmetric supercapacitor shows superior energy density of 9.9 Wh kg−1 at a power density of 75.0 W kg−1. The significantly enhanced electrochemical performance can be ascribed to the high hydroxyl content and other oxygen functional groups, N-doping, modified porous framework and the high specific surface area of the graphene. Those special characteristics suggest that the as-synthesized graphene materials may have potential applications in high performance supercapacitors.

High-throughput fabrication of porous carbon by chemical foaming strategy for high performance supercapacitor

Inspired by people to make flour food, a one-pot, low-cost, green and environmental friendly gas foaming strategy is adopted here to prepare the three-dimensional hierarchical porous carbon (HPC) by introducing NaHCO3 as foaming and activation agent. During the pyrolysis process, the CO2 gas produced during the transforms from NaHCO3 into Na2CO3 will resulted in the producers of the macro-pores and meso-pores, meanwhile, the as-produced Na2CO3 further reactor with the carbon intermediate at a high temperature, and finally result in forming a micro-pores porous structure. Such intimate structural interconnectivities provide three-dimensional continuous pathway for electron rapid transfer and the interconnected pores allow for the ion to penetrate and evenly contact the electrode material quickly. The electrochemical performance of HPC exhibits a high specific capacitance of 350 F g−1 at 1 A g−1 and outstanding electrochemical stability with capacitance retention up to 97% after 10,000 cycles. Moreover, the as-assembled symmetric supercapacitor exhibits an ultrahigh energy density of 27.4 Wh kg−1, much higher than most of carbon-based supercapacitors. These results demonstrate a straightforward environment friendly method to mass-produce economical, robust carbon materials as promising candidates for supercapacitor application.

Polyurethane foam derived nitrogen-enriched porous carbon/reduced graphene oxide composite with sandwich-like nanoarchitectures for supercapacitors

A new type of polyurethane (PU) foam derived nitrogen-enriched porous carbon/reduced graphene oxide (PU/rGO) composite was synthesized and studied for the first time. By taking advantages of PU foam as carbon skeleton precursor, GO nanosheets wrapped onto the skeleton’s surface through hydrothermal process, then the stable porous sandwich-like nanoarchitectures built after carbonization process. Moreover, the wrapped GO can be transformed into rGO due to thermal reduction during the carbonization process. When being applied as supercapacitor electrodes, the prepared PU/rGO composite could achieve an extremely high specific capacitance of 490 and 341.7 F g−1 at a current density of 1 and 20 A g−1, respectively. After 5000 cycles, the specific retention yielded to 97.3% at 1 A g−1. Resulting from these merits, the as-assembled symmetric supercapacitor device with a wide operating voltage window of 1.5 V exhibit an excellent energy density of 21.66 Wh kg−1 at a power density of 825 W kg−1 and remain 7.5 Wh kg−1 even at a high power density of 2250 W kg−1. Most importantly, this work may offer a strategy for converting the PU foam wastes into carbon material with excellent electrochemical performance applied on energy storage.

Three-dimensional porous activated carbon derived from loofah sponge biomass for supercapacitor applications

Biomass carbon source is generally cheap, environmentally friendly and readily available in high quality and quantity. In this work, a series of loofah sponge-derived activated carbon (SAC-x) with hierarchical porous structures are prepared by KOH chemical activation and used as electrode materials for supercapacitors. The pore size can be easily controllable by changing the dosage of KOH. The optimized material (SAC-4) exhibits a high specific capacitance of 309.6Fg−1 at 1Ag−1 in the three-electrode system using 6M KOH electrolyte. More importantly, the as-assembled symmetric supercapacitor based on SAC-4 exhibits a high energy density of 16.1Whkg−1 at a power density of 160.0Wkg−1 using 1M Na2SO4 electrolyte. These remarkable results demonstrate the exciting commercial potential of SAC-x for high-performance supercapacitor applications due to their high specific surface area, appropriately porous structure, and the trace heteroatom (O and N) functionalities.

Black aspergillus-derived highly porous carbon fibers for capacitive applications

The increasing demand for high-performance supercapacitors has aroused great interest in fabricating materials with excellent specific capacitance and cycling stability. Here we report a porous activated carbon (PAC) derived from the pyrolysis of the renewable filamentous fungi in an inert atmosphere. PAC exhibits a high specific surface area of 1800 m2 g−1 with hierarchical structures. The N doped PAC electrode shows a remarkable gravimetric capacitance of 298 F g−1, and excellent cycling stability with 100% capacitance retention after 10,000 cycles. In addition, the rate capability of this material is pretty good and better than that of previously reported graphene and activated carbon-based materials. Furthermore, the as-assembled symmetric supercapacitor device exhibits good gravimetric energy density of 10.32 W h Kg−1. This work provides a new sustainable source of filamentous fungi for fabricating high performance porous carbon materials for supercapacitors.

Improving biomass-derived carbon by activation with nitrogen and cobalt for supercapacitors and oxygen reduction reaction

Biomass-derived carbon by activation with nitrogen and cobalt (denoted as NPACCo) was prepared by one-pot pyrolysis of pomelo peel with melamine, cobalt nitrate and potassium hydroxide, followed by acid leaching. NPACCo possesses high content of quaternary-N (2.5%) and pyridinic-N (1.7%), co-existences of amorphous and short-range ordered carbon, high specific surface area and pore structure with majority of micropores and small mesopores. As electrode material of supercapacitors, NPACCo exhibits high specific capacitance and good rate capability. At ultrahigh rate of 50Ag−1 (135mAcm−2), the capacitance of NPACCo remains 246Fg−1, which is 6.3, 1.9 and 3.2 times as high as that of other three materials (PC, PAC and NPAC). The as-assembled symmetric supercapacitor of NPACCo delivers high energy density, high power density and excellent cycling stability. With respect to oxygen reduction reaction (ORR), NPACCo exhibits high onset potential (0.87V), high half-wave potential (0.78V), excellent methanol tolerance and low yield of H2O2. The ORR properties of NPACCo are comparable or superior to those of commercial Pt/C. This investigation of pomelo peel-based NPACCo would be valuable for development of both supercapacitor and ORR.

Ultrathin MnO2 nanoflakes deposited on carbon nanotube networks for symmetrical supercapacitors with enhanced performance

Abstract Manganese dioxide is a promising electrode material for electrochemical supercapacitors, but its poor electronic conductivity (10 −5 ∼10 −6 S cm −1 ) limits the fast charge/discharge rate for practical applications. In the present work, we use the chemical vapor deposition (CVD) method to grow highly conductive carbon nanotube (CNT) networks on flexible Ni mesh, on which MnO 2 nanoflake layers are deposited by a simple solution method, forming a hierarchical core-shell structure. Under the optimized mass loading, the as-fabricated MnO 2 nanoflake@CNTs/Ni mesh electrode exhibits a high specific capacitance of 1072 F g −1 at 1 A g −1 in three-electrode configuration. Due to advantageous features of these core-shell electrodes (e.g., high conductivity, direct current path, structure stability), the as-assembled symmetric supercapacitor (SSC) based on MnO 2 @CNTs/Ni mesh has a wide working voltage (2.0 V) in 1 M Na 2 SO 4 aqueous electrolyte. Finally an impressive energy density of 94.4 Wh kg −1 at 1000 W kg −1 and a high power density of 30.2 kW kg −1 at 33.6 Wh kg −1 have been achieved for the as-assembled SSC, which exhibits a great potential as a low-cost, high energy density and attractive wearable energy storage device.

Soybean Root-Derived Hierarchical Porous Carbon as Electrode Material for High-Performance Supercapacitors in Ionic Liquids.

Soybeans are extensively cultivated worldwide as human food. However, large quantities of soybean roots (SRs), which possess an abundant three-dimensional (3D) structure, remain unused and produce enormous pressure on the environment. Here, 3D hierarchical porous carbon was prepared by the facile carbonization of SRs followed by chemical activation. The as-prepared material, possessing large specific surface area (2143 m2 g-1), good electrical conductivity, and unique 3D hierarchical porosity, shows outstanding electrochemical performance as an electrode material for supercapacitors, such as a high capacitance (276 F g-1 at 0.5 A g-1), superior cycle stability (98% capacitance retention after 10,000 cycles at 5 A g-1), and good rate capability in a symmetric two-electrode supercapacitor in 6 M KOH. Furthermore, the maximum energy density of as-assembled symmetric supercapacitor can reach 100.5 Wh kg-1 in neat EMIM BF4. Moreover, a value of 40.7 Wh kg-1 is maintained at ultrahigh power density (63000 W kg-1). These results show that the as-assembled supercapacitor can simultaneously deliver superior energy and power density.