Ultra-high specific capacitance of self-doped 3D hierarchical porous turtle shell-derived activated carbon for high-performance supercapacitors

The turtle shell of biomass waste is used as raw material, and the natural inorganic salt contained in it is used as a salt template in combination with a chemical activation method to successfully prepare a high-performance activated carbon with hierarchical porous structure. The role of hydroxyapatite (HAP) and KOH in different stages of preparation was investigated. The prepared turtle shell-derived activated carbon (TSHC-5) has a well-developed honeycomb pore structure, which gives it a high specific surface area (SSA) of 2828 m² g^?1 with a pore volume of 1.91 cm³ g^?1. The excellent hierarchical porous structure and high heteroatom content (O 6.88%, N 5.64%) allow it to have an ultra-high specific capacitance of 727.9 F g^?1 at 0.5 A g^?1 with 92.27% of capacitance retention even after 10,000 cycles. Excitingly, the symmetric supercapacitor assembled from TSHC-5 activated carbon exhibits excellent energy density and cycling stability in a 1 M Na₂SO₄ aqueous solution. The energy density is 45.1 Wh·kg^?1 at a power density of 450 W kg^?1, with 92.05% capacitance retention after 10,000 cycles. Therefore, turtle shell-derived activated carbon is extremely competitive in sustainable new green supercapacitor electrode materials.     

Fabrication of the nitrogen doped ordered porous carbon derived from amino-maltose with excellent capacitance performance

In this paper, pristine and nitrogen doped ordered porous carbon materials were fabricated by using maltose and amino-maltose synthesized by hydrothermal reaction as precursors via template strategy. The fabricated pristine ordered porous carbon (OPC) and nitrogen doped ordered porous carbon (NOPC) exhibit excellent textural properties and good capacitance performance, which specific surface area (S_BET) reach 1107 and 726 m² g^?1 for the pristine OPC and NOPC materials while the specific capacitance reach up to 139 and 183 F g^?1 under a current density of 0.5 A g^?1, respectively. The capacitance retention rate for the pristine OPC and NOPC reaches ca. 81 and 92% as the current density increased from 0.5 to 20 A g^?1, and no apparent capacitance decrease was observed after 5000 cycles. Although a sharp decrease of specific surface area was observed after N doping, the specific capacitance of NOPC was improved about 31% than that of the pristine OPC, the enhanced wettability and surface availability after N doping were found to be responsible for the enhanced capacitance performance of NOPC.     

ZnS nanoparticles embedded in porous honeycomb-like carbon nanosheets as high performance anode material for lithium ion batteries

ZnS nanoparticles coated with honeycomb-like carbon nanosheets (ZnS@HPC) were synthesized via freeze drying and carbonization methods, using NaCl crystals as hard template. The ZnS@HPC composite possessed a novel three-dimensional network structure and high specific surface area of 128.9?m² g^?1. In this composite, ZnS nanoparticles with small diameter of 20–40?nm were embedded in carbon nanosheet matrix. Moreover, nitrogen-doped carbon formed successfully during the carbonization process. The porous carbon matrix provided a conductive network and also worked as a buffer to confine ZnS nanoparticle expansion during lithiation and delithiation process. So, the electrochemical performance of ZnS@HPC composite electrode was much better than that of ZnS and ZnS/C electrodes. As a novel anode material, ZnS@HPC composite exhibited the initial cycle discharge and charge capacities of 1359 and 889?mAh?g^?1 at 100?mA?g^?1; and showed excellent cycle performance, the discharge capacity achieved 408?mAh?g^?1 after cycling at 1?A?g^?1 for 200 cycles.     

Exceptional supercapacitive performance of bicontinuous carbon/MnO2 composite electrodes

A new type of porous carbon/MnO₂ composites, having bicontinuous structures, i.e., continuous channels and carbon skeletons, was prepared using a phase separation method, followed by a carbonization procedure and a subsequent redox reaction. In this work, such composite electrodes show a high specific capacitance of ca. 260?F?g^?1 at 0.5?A?g^?1 in 1?M Na₂SO₄ aqueous solution, a superior cycling stability (~80% retention after 2000 cycles) and a distinctive high-rate performance. Especially, unique bicontinuous structures endow such composites with a great specific capacitance of the constituent MnO₂ (~1100?F?g^?1), very close to the theoretical value. These excellent electrochemical behaviors may render this material a promising candidate as high-performance electrodes in supercapacitors. Therefore, our findings suggest that the strategy for constructing bicontinuous hybrid electrodes represents an exciting direction for designing next-generation supercapacitors.     

Synthesis of mesoporous hollow carbon microcages by combining hard and soft template method for high performance supercapacitors

Carbon materials have been widely used in electrochemistry filed such as supercapacitors because of the good conductivity, abundant sources and low prices. Further improving the electrochemical performance of carbon materials still attracts the interest of researchers. In this work, nitrogen-doped mesoporous hollow carbon microcages (N-MHCC) are successfully prepared by combining hard and soft template method. This hierarchically porous structure (meso- & micro-pore) of N-MHCC provides a large number of active centers, sufficient space and reaction interface, promoting the rapid diffusion of electron and electrolyte ions transport. By comparing the electrochemical performance of nitrogen-doped hollow carbon microcages (N-HCC) and N-MHCC, it can be calculated that N-MHCC shows high specific capacitance of 210.66 F g^?1 at 0.5 A g^?1 while N-HCC only shows 132.6 F g^?1. The cycle retention rate of N-MHCC is as high as 96.92 % at 5 A g^?1 after 4000 cycles. Furthermore, the simple preparation method and attractive performance make N-MHCC a promising candidate for high performance supercapacitors.     

A facile synthesis strategy of fungi-derived porous carbon-based iron oxides composite for asymmetric supercapacitors

Transition metal oxides (TMOs) have been considered as potential anode materials for asymmetric supercapacitors due to their high theoretical capacities. However, undesirable electric conductivity limits the further application in future energy storage. Here, a honeycomb-like architecture of FeOx embedded in the fungi-derived porous carbon-based material (FeOx/C) for asymmetric supercapacitor was reported. The facile synthesis strategy of fungi-derived porous carbon-based iron oxides was using the carbon derived from fungi and the process of carbothermal reduction to form the iron oxide compound. This carbon-encapsulated iron oxide compound provides highly specific surface area (The specific surface area of Fe–O–C-650 was largest (up to 219.0905 m²/g) compared with samples of Fe–O–C-550(144.0304 m²/g), Fe–O–C-750(201.7352 m²/g), Fe–O–C-850(163.2206 m²/g).), an abundance of redox sites, sufficient efficient channels for fast transportation of ions, excellent electrical conductivity, and stable skeleton. Under the three-electrode test system, the FeOx/C electrode delivers excellent specific capacitance of 565F/g at 1 mV/s and impressive cycling performance with capacitance retention of 100% after 3000 cycles. And the NiO electrode delivers a high specific capacitance of 425 F/g at a high current density of 5 mV/s. In addition, the FeOx/C//NiO asymmetric supercapacitor was assembled which exhibits remarkable specific capacitance of 111F/g at 10 mV/s and gravimetric energy density of 36 Wh/kg as well as gravimetric power density of 800W/kg with capacitance retention of 100% after 20,000 cycles, approaching those of ions capacitors.     

Hierarchically Fe-doped porous carbon derived from phenolic resin for high performance supercapacitor

Supercapacitors are promising for high power application in the recent years. In particular, the conversion of simple and available carbon materials into economic and high performance electrical devices receives excellent scientific and technological interest. This paper reports a one-step strategy for synthesizing hierarchical porous carbon derived from phenolic resin (PR), which is then used to configure electric double-layer capacitors (EDLCs). Here, a carbon material with a flexible porous structure, large specific surface area, and high graphitization degree is prepared using potassium ferrate (K₂FeO₄) to catalytically activate PR and to realize synchronous carbonization and graphitization. This method overcomes the disadvantage of time-consuming, high-cost, and environmentally unfriendly. In addition, the as-prepared carbon material has a high specific surface area (1086 m² g^?1) and a large pore size (3.07 nm), which can increase the transfer rate of electrolyte ions. The specific capacitance of the obtained electrode material is 315 F g^?1 at 1.0 A g^?1, and the optimized electrode material has an ultra-long cycle lifetime (capacitance retention rate is 96.3% after 10,000 cycles). Thus, the hierarchically Fe-doped porous carbon material derived from PR material is expected to realize high rate capacitance for supercapacitor applications.     

Nitrogen-doped porous carbons through KOH activation with superior performance in supercapacitors

A series of nitrogen-doped porous carbons are prepared through KOH activation of a nonporous nitrogen-enriched carbon which is synthesized by pyrolysis of the polymerized ethylenediamine and carbon tetrachloride. The porosity and nitrogen content of the nitrogen-doped porous carbons depend strongly on the weight ratio of KOH/carbon. As the weight ratio of KOH/carbon increases from 0.5 to 2, the specific surface area increases from 521 to 1913 m² g⁻¹, while the nitrogen content decreases from 10.8 to 1.1 wt.%. The nitrogen-doped porous carbon prepared with a moderate KOH/carbon weight ratio of 1, which possesses a balanced specific surface area (1463 m² g⁻¹) and nitrogen content (3.3 wt.%), exhibits the largest specific capacitance of 363 F g⁻¹ at a current density of 0.1 A g⁻¹ in 1 M H₂SO₄ aqueous electrolyte, attributed to the co-contribution of double-layer capacitance and pseudocapacitance. Moreover, it shows excellent rate capability (182 F g⁻¹ remained at 20 A g⁻¹) and good cycling stability (97% capacitance retention over 5000 cycles), making it a promising electrode material for supercapacitors.     

High-performance binder-free supercapacitor electrode by direct growth of cobalt-manganese composite oxide nansostructures on nickel foam

A facile approach composed of hydrothermal process and annealing treatment is proposed to directly grow cobalt-manganese composite oxide ((Co,Mn)₃O₄) nanostructures on three-dimensional (3D) conductive nickel (Ni) foam for a supercapacitor electrode. The as-fabricated porous electrode exhibits excellent rate capability and high specific capacitance of 840.2 F g^-1 at the current density of 10 A g^-1, and the electrode also shows excellent cycling performance, which retains 102% of its initial discharge capacitance after 7,000 cycles. The fabricated binder-free hierarchical composite electrode with superior electrochemical performance is a promising candidate for high-performance supercapacitors.     

Enhanced performance by polyaniline/tailored carbon nanotubes composite as supercapacitor electrode material

Polyaniline/tailored carbon nanotubes composite (PANI/TCN) synthesized via situ polymerization of aniline monomer in the presence of tailored carbon nanotubes (TCN) is reported as electrode material for supercapacitors. The morphology, structure, and thermostability of the composite were characterized by scanning electron microscope, Fourier transform infrared, and thermogravimetric analysis. The electrochemical property of the resulting material was systematically studied using cyclic voltammetry and galvanostatic charge–discharge. The results show that the short rod‐like PANI dispersed well in the TCN with three‐dimensional network structure. The as‐prepared composite shows high specific capacitance and good cycling stability. A specific capacitance of 373.5 F g^?1 at a current density of 0.5 A g^?1 was achieved, which is much higher than that of pure PANI (324 F g^?1). Meanwhile, the composite retains 61.7% capacity after 1000 cycles at a scan rate of 50 mV s^?1. The enhanced specific capacitance and capacity retention indicates the potential of composite as a promising supercapacitor electrode material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39971.     

Anode electrodeposition of 3D mesoporous Fe2O3 nanosheets on carbon fabric for flexible solid-state asymmetric supercapacitor

Novel nanostructured Fe₂O₃ with a network of 3D mesoporous nanosheets was synthesized by depositing on carbon fabric (Fe₂O₃@CF) for use as an anode using a potentially low-cost electrodeposition technique. The electrode with freestanding binder-free Fe₂O₃@CF of high surface area displayed an exceptional specific capacitance of 394.2?F?g^?1. Moreover, a flexible solid-state asymmetric supercapacitor (ASC) was fabricated with a negative electrode based on Fe₂O₃@CF and a positive electrode based on MnO₂@CF in the presence of PVA-LiCl as gel electrolyte. The above ASC exhibited a high operating potential up to 1.8?V, a favorable specific capacitance of 93.5?F?g^?1 (2.92?F?cm^?3), long-term stability (91.3% retention of initial value over 5000 cycles), and remarkable mechanical stability and flexibility, suggesting its potential application for wearable electronics.     

CoO/rGO composite prepared by a facile direct-flame approach for high-power supercapacitors

In this study, CoO nanoparticles (NPs) measuring approximately 20?nm in size are successfully grown on reduced graphene oxide (rGO) layers through a facile direct-flame approach. The obtained CoO/rGO nanocomposites are applied as electrode materials and show a high specific capacitance, reaching 1615.0?F?g^?1 at a current of 1?A?g^?1 (737.5?F?g^?1 at 50?A?g^?1), and good cycling stability (88.12% retention after more than 15,000 cycles at 5?A?g^?1), which are outstanding characteristics compared with those of recently reported pseudosupercapacitors. Furthermore, an asymmetric supercapacitor (ASC) produced using CoO/rGO as a positive electrode material and activated graphene (AG) as a negative electrode achieves a high cell voltage of 1.6?V and delivers a maximum energy density of 62.46?Wh?kg^?1 at a power density of 1600?W?kg^?1. The fabrication technique is facile and represents a promising means of obtaining metal oxide/graphene composites for high-performance supercapacitors.     

Preparation and molten salt-assisted KOH activation of porous carbon nanofibers for use as supercapacitor electrodes

Carbon nanofiber paper was prepared by electrospinning from thermosetting phenolic resin, followed by activation via KOH-containing molten salt at high temperature. By adding a small dosage of KOH in the molten salt the porous volume and specific surface area could be greatly improved. The obtained porous carbon nanofibers had a specific surface area of 1007 m² g^?1, total pore volume of 0.363 cm³ g^?1, micropore volume of 0.247 cm³ g^?1. The electrochemical measurements in 6 M KOH aqueous solution showed that the porous carbon nanofibers possessed high specific capacitance and considerable rate performance. The maximal specific capacitance of 288 F g^?1 was achieved at 0.2 A g^?1 and the specific capacitance could still remain 204 F g^??1 at 20 A g^?1 with the retention of 71%. In the molten salt system, the reaction between activating agent and carbon could be more efficient, hence, such molten salt-assisted activation method was considered as a general activation method for the high-specific-surface-areaed carbons.     

One-pot facile synthesis and electrochemical evaluation of selenium enriched cobalt selenide nanotube for supercapacitor application

The present study emulates a one-pot facile synthesis of selenium-enriched CoSe nanotube using a chemical bath deposition (CBD) procedure. Schematic incorporation of 3D Ni foam current collectors as substrates for the growth of CoSe–Se nanotubes helped us achieve a binder-less thin film coating. The controlled synthesis of CoSe–Se nanotube was carried out by optimizing the temperature and time of the deposition. CoSe–Se nanotubes were grown on a porous Ni foam substrate using lithium chloride as a shape directing agent. The study found that the one dimensional structure of the nanotubes with porous nature results in an uninterrupted network of electroactive sites. Due to the superior conductivity, the as-fabricated material exhibited excellent rate capability and a higher degree of electrolyte ion diffusion across the CoSe–Se crystal structure. The CoSe–Se@Ni foam electrodes exhibited a specific capacitance of 1750.81 F g^?1 at 1 A g^?1. The electrode exhibited excellent cycling stability and showed a capacitance retention of 95% after 4000 charge-discharge cycles. Finally, an asymmetric supercapacitor (ASC) device was fabricated with the as-synthesized CoSe–Se@Ni foam electrode as the cathode, activated carbon@Ni foam electrode as the anode, and a thin filter paper separator soaked in 1 M aqueous KOH electrolyte solution. The ASC device showed a specific capacitance value of 106.73 F g^?1 at 0.5 A g^?1, and achieved an energy density of 37.94 Wh kg^?1 at a power density of 475.30 W kg^?1. The ASC device was utilized in an extended potential window of 1.6 V. The fabricated device displayed exceptional cycling stability with a capacitance retention of 93% after 5000 charge-discharge cycles.     

Hexagonal boron nitride nanosheet/carbon nanocomposite as a high-performance cathode material towards aqueous asymmetric supercapacitors

The two-dimensional hexagonal boron nitride (h-BN) has garnered tremendous interest due to its unique mechanical, thermal and electronic properties. However, the application of h-BN has been restricted as electrode materials for supercapacitors because of its wide band gap and rather low conductivity. Herein, a carbon-modified hexagonal boron nitride nanosheet (h-BN/C) nanocomposite is prepared through a facile and scalable solid-state reaction. Interestingly, the h-BN/C nanocomposite as cathode material exhibits a pair of distinct and reversible redox peaks in 2?M KOH aqueous electrolyte. Because of the enhanced electrical conductivity derived from the modified carbon and the increased specific surface area, the h-BN/C nanocomposite presents a high specific capacitance of 250?F?g^?1 at the current density of 0.5?A?g^?1. More importantly, the fabricated aqueous asymmetric supercapacitor with the h-BN/C as cathode and activated carbon as anode displays an operating voltage of 1.45?V, an energy density of 17?Wh?kg^?1 at a power density of 245?W?kg^?1, and high stability up to 1000 cycles. Therefore, h-BN/C nanocomposite would promisingly be a cathode material for aqueous asymmetric supercapacitors.     

Macroporous defective tungsten oxide nanostructure electrodes deliver ultrahigh capacitance and remarkable long cyclic durability in LiCl electrolyte

Tungsten oxide (WO₃) has been considered as an fascinating candidate for supercapacitors (SCs) material because of its desirable physico-chemical properties and electrochemical behaviors. Nevertheless, it is still a significant challenge to enhance its electrochemical properties and stability. Herein, we report an electroreduction strategy to fabricate the macroporous defective tungsten oxide nanostructure (ER-WO₃) as a negative electrode material with outstanding electrochemical behavior and remarkable cycling durability in 5?M LiCl aqueous electrolyte, which attributes to the introduction of oxygen deficiencies. The ER-WO₃ electrode exhibits a large areal capacitance of 244.7?mF?cm^?2 and an ultrahigh gravimetric specific capacitance of 266.6?F?g^?1 at scan rate of 50?mV?s^?1. More importantly, the ER-WO₃ product also delivers an ultralong cyclic stability with 97.4% capacitance retention after 5000 cycles. Such these optimized properties of the ER-WO₃ nanostructure electrode will promote its applications in the field of science and technology.     

Hierarchical porous NiCo2O4 nanomaterials with excellent cycling behavior for electrochemical capacitors via a hard-templating route

Hierarchical porous nickel cobaltite (NiCo₂O₄) nanomaterials were synthesized via a hard-templating route. The obtained materials consist of nanostructured cubic NiCo₂O₄ spinels and a spot of cubic NiO nanoparticles, and the materials display a typical hierarchical porous structure. The NiCo₂O₄ electrode displays quasireversible dynamics characteristics, mainly Faradaic capacitance behavior and capacitance relaxation feature. The NiCo₂O₄ electrode exhibits an excellent long cycling behavior with no capacitance decays during 5,000 cycles at a current density of 2?A?g^?1 in 1?M KOH electrolytes, and the NiCo₂O₄ electrode exhibits both high power and energy performances even after 5,000 cycles with respective value of 1,758?W?kg^?1 and 8.3?W?h?kg^?1 in 1?M KOH electrolytes, indicating that the NiCo₂O₄ nanomaterials are promising candidates for electrochemical capacitors.     

A new strategy for porous carbon synthesis: Starch hydrogel as a carbon source for Co3O4@C supercapacitor electrodes

A novel Co₃O₄@C composite with a three-dimensional (3D) interconnected network morphology was successfully fabricated by anchoring cobalt oxide nanocrystals onto porous carbon originating from starch hydrogels via freeze drying, precarbonization and thermal treatment in an aqueous system. Benefiting from unique structural features, the optimized electrode delivers an excellent capacitance of 1314.0 F g^?1 (1 A g^?1) and outstanding durability in terms of capacity preservation (93.5% over 10,000 cycles). In addition, an asymmetric supercapacitor consisting of DF-2 and active carbon exhibits an energy density of 149.1 Wh?kg^?1 at 800 W kg^?1 while maintaining great stability. The observed excellent performance is attributed to the unique 3D network, good conductivity and high surface-to-volumetric ratio of the carbon skeleton derived from the starch gel, which has wide scope for applications.     

Fluidized‐bed CVD of unstacked double‐layer templated graphene and its application in supercapacitors

Graphene is inclined to stack with each other that greatly hinders the full utilization of its intrinsic extraordinary properties. Introducing protuberant spacers is a straightforward strategy to avoid the stacking of graphene nanosheets, resulting in a novel unstacked double‐layer templated graphene (DTG) structure. Herein, a family of layered double hydroxides were used for the bulk chemical vapor deposition (CVD) of DTG in a fluidized‐bed reactor. A high specific surface area of 1554.2 m² g^?1 and a large pore volume of 1.70 cm³ g^?1 were achieved. When used as the electrode material for supercapacitors, the DTG afforded a specific capacitance of 65.5 F g^?1 at a sweep rate of 5.0 mV s^?1 and a capacitance retention of 77% when the sweep rate was increased to 500 mV s^?1. Therefore, the DTG obtained via fluidized bed CVD is a promising electrode material for supercapacitor applications. © 2014 American Institute of Chemical Engineers AIChE J, 61: 747–755, 2015     

Facile preparation of Ni-doped MnCO3 materials with controlled morphology for high-performance supercapacitor electrodes

Doping homogeneous elements and conducting morphological adjustment as commonly-used modification methods are both effective to promote the electrochemical properties of electrode materials. In this work, nickel-doped manganese carbonate with 3D flower-like structure was synthesized by a one-step hydrothermal method, and the corresponding growth mechanism was investigated. The electrochemical characteristics of as-fabricated electrode materials were measured, among which 3D self-assembled Ni_0.2Mn_0.8CO₃ nanoflower with large surface area exhibited superior areal capacitance of 583.5?F?g^?1 at 1?A?g^?1 (fourfold more than MnCO₃ microcubes), excellent electrical conductivity as well as satisfactory cycling stability (84.78% capacitance retention after 2000 cycles at 2?A?g^?1). In addition, the asymmetric supercapacitor assembled with Ni_0.2Mn_0.8CO₃ as cathode and commercial activated carbon as anode displayed a high energy density of 24.1?Wh?kg^?1 at the power density of 0.74?kW?kg^?1 and showed a desirable cycle life. In summary, the unique 3D flower-like Ni_0.2Mn_0.8CO₃ nanomaterial could be regarded as a promising electrode material for high-performance supercapacitors.