Hierarchical porous carbon obtained from directly carbonizing carex meyeriana for high-performance supercapacitors

Hierarchical porous carbon materials with high surface area are facilely prepared by directly carbonizing carex meyeriana without any extra activation procedure. The as-prepared porous carbon samples possess high Brunauer–Emmett–Teller (BET) surface areas (in the?~?518–742 m² g^?1 range) and unique hierarchical porous structure containing macropore channels and mesopores and micropores developed in the wall of macropores. These intriguing characteristics make the as-prepared hierarchical porous carbon samples a promising electrode material for supercapacitors. The capacitive performance was measured in the three-electrode system with 6 M KOH electrolyte. The hierarchical porous carbon prepared at the carbonization temperature of 1000 °C presents a high specific capacitance of 178.6 F g^?1 at a current density of 0.5 A g^?1, a good rate performance ( about 65.2% retention ratio at the current density of 20 A g^?1), and an excellent cycling stability (no obvious performance fading after 10,000 cycles). In addition, the fabricated two-electrode device achieves an energy density of 4.33 Wh kg^?1 at a high power density of 5 kW kg^?1. These results provide a green and facile method to synthesize the electrode material from biomass for high-performance supercapacitors.

     

A facile preparation of pomegranate-like porous carbon by carbonization and activation of phenolic resin prepared via hydrothermal synthesis in KOH solution for high performance supercapacitor electrodes

High electrochemical performance pomegranate-like porous carbon was synthesized by the carbonization and activation of phenolic resin which was prepared by adding phenolic resin monomer mixture into KOH aqueous solution and hydrothermal treatment. In the process of hydrothermal, KOH solution could hinder the polymerization of phenolic resin monomer to form big phenolic resin particles. During the carbonization, phenolic resin plays the role of forming small particles and binder during carbonization, which can simultaneously achieve high specific surface area and form three dimensional structures to improve the conductivity. The results showed that pomegranate-like porous carbon composed of small nanometer-scale particles was observed. The obtained porous carbon electrode materials had a high content of micropores with specific surface area as high as 2199.9 m² g⁻¹. The porous carbon exhibited a high specific capacitance of 341.3 F g⁻¹ at 0.1 A g⁻¹, good rate capability with 71.0% retention from 0.1 to 5 A g⁻¹. Moreover, it showed high capacitance retention of 96.1% after 5000 cycles at a scan rate of 50 mV s⁻¹, indicating excellent cycling stability. The assembled symmetrical supercapacitor showed high energy densities of 17.0 Wh kg⁻¹ and 8.5 Wh kg⁻¹ with the corresponding power densities of 49.6 W kg⁻¹ and 1.8 kW kg⁻¹, respectively. The facile method could be a promising candidate for preparing porous carbon electrode materials with excellent electrochemical performance in the fields of supercapacitors.     

Nitrogen-doped hierarchical porous carbon materials derived from diethylenetriaminepentaacetic acid (DTPA) for supercapacitors

Nitrogen-doped porous carbon materials (NPCs) have been successfully fabricated by a simple one-step pyrolysis of diethylenetriaminepentaacetic acid (DTPA) in the presence of KOH. The as-synthesized NPCs displayed a high specific surface area (3214?m²?g^?1) and a well-defined porous structure when the annealing temperature reached 800?°C, which showed superior electrochemical performance as supercapacitor electrode materials. Electrochemical tests showed that the NPCs achieved an impressive specific capacitance of 323?F?g^?1 at a current density of 0.5?A?g^?1 in 6?M KOH aqueous solution and an outstanding cycle stability, negligible specific capacitance decay after 5000 cycles at 10?A?g^?1. This strategy offered a new insight into the preparation of novel carbon materials for the advanced energy storage devices, such as supercapacitors, fuel cells and lithium ion batteries.     

Superior capacitive behavior of porous activated carbon tubes derived from biomass waste-cotonier strobili fibers

As supercapacitor electrode materials, the sustainable biomass-derived activated carbons have attracted a great deal of attentions due to their low-cost, abundant, and unwanted natural wastes. In this work, a facile KOH activation method is adopted to prepare activated carbon tubes from the biomass waste-cotonier strobili fibers for the first time. The resultant PTAC-x materials possess highly accessible surface areas and abundant micro-mesopores, which benefit large ion storage and high-rate ion transfer. The optimized material denoted as PTAC-6 demonstrates a high specific capacity (346.1?F?g^?1 at 1?A?g^?1) and a superior rate performance (214.5?F?g^?1 at 50?A?g^?1) in the three-electrode supercapacitors. In addition, the symmetric supercapacitor exhibits excellent cycling stability with a capacitance retention of 84.21% and a columbic efficiency of nearly 100% after 10,000 cycles. Furthermore, the PTAC-6-based symmetric supercapacitor gives a remarkable specific energy of 33.04?Wh?kg^?1 at 160?W?kg^?1. Meanwhile, our proposed porous activated carbon tubes provide a green and low-cost electrode material for high-performance supercapacitors.     

Nitrogen-doping hierarchically porous carbon nanosheets for supercapacitor

Two-dimensional (2D) porous carbon nanosheets attract great attention because of their thin sheet-like morphology, abundant pores and high specific surface area, and their potential applicability in many fields including adsorption, oxygen reduction reaction, organic transistor and energy storage. Herein, a feasible method, named self-templating, to prepare 2D nitrogen-doping hierarchically porous carbon nanosheets (N-HPCNs) with prominent performances as supercapacitor electrode is reported. During the process of preparation, the inexpensive and easily available MgO rods are treated in water to form Mg(OH)₂ nanosheets further using as templates and then nitrogen contained resorcinol–formaldehyde resin oligomers as carbon and nitrogen precursor co-condense onto the templates by electrostatic interaction. The obtained N-HPCNs with large specific surface area, hierarchical pores and unique interconnected sheet-like structure are the potential candidates for high energy storage devices. As an active electrode material for electrochemical double-layer capacitors, N-HPCNs exhibit a capacitance of 201 F g^?1 at current density of 1 A g^?1 and high specific capacitance (78.1% retention of initial capacitance even at 10 A g^?1), with excellent cycling life stability (3.5% loss after 5000 cycles).     

Biomass-derived nitrogen-rich porous carbon composite for supercapacitor application

In this study, egg proteins are used as a nitrogen source for the synthesis of nitrogen-rich carbonaceous material through hydrothermal carbonization (HTC) for the electrochemical energy storage application. The composite of activated carbon with egg-derived protein (AC/EDP) is prepared by mixing untreated egg proteins in the aqueous dispersion of activated carbon, followed by HTC at 220 °C for 12 h in a Teflon-lined autoclave. The resultant composite is then directed to chemical activation with KOH and thermal activation at a temperature ranging from 500 to 700 °C. The nitrogen-doped activated carbon exhibited a microporous and mesoporous structure with a high specific surface area of 1660 m² g^?1, confirmed through BET analysis. The composite morphology was analyzed through scanning and high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy indicates the presence of a considerable amount of pyrrolic, pyridinic, and quaternary nitrogen in AC/EDP, which improved the electrochemical performance. The composite activated at 700 °C exhibited the highest capacitance of 263 F g^?1 at a current density of 0.2 A g^?1. The highest energy density and power density values are 32 Wh kg^?1 and 7920 W kg^?1, respectively. The AC/EDP exhibited high cyclic stability, and the capacitance retention observed after 10,000 cycles is 98%.

     

Biomass‐Derived Nitrogen‐Doped Carbon Nanofiber Network: A Facile Template for Decoration of Ultrathin Nickel‐Cobalt Layered Double Hydroxide Nanosheets as High‐Performance Asymmetric Supercapacitor Electrode

The development of biomass‐based energy storage devices is an emerging trend to reduce the ever‐increasing consumption of non‐renewable resources. Here, nitrogen‐doped carbonized bacterial cellulose (CBC‐N) nanofibers are obtained by one‐step carbonization of polyaniline coated bacterial cellulose (BC) nanofibers, which not only display excellent capacitive performance as the supercapacitor electrode, but also act as 3D bio‐template for further deposition of ultrathin nickel‐cobalt layered double hydroxide (Ni‐Co LDH) nanosheets. The as‐obtained CBC‐N@LDH composite electrodes exhibit significantly enhanced specific capacitance (1949.5 F g^?1 at a discharge current density of 1 A g^?1, based on active materials), high capacitance retention of 54.7% even at a high discharge current density of 10 A g^?1 and excellent cycling stability of 74.4% retention after 5000 cycles. Furthermore, asymmetric supercapacitors (ASCs) are constructed using CBC‐N@LDH composites as positive electrode materials and CBC‐N nanofibers as negative electrode materials. By virtue of the intrinsic pseudocapacitive characteristics of CBC‐N@LDH composites and 3D nitrogen‐doped carbon nanofiber networks, the developed ASC exhibits high energy density of 36.3 Wh kg^?1 at the power density of 800.2 W kg^?1. Therefore, this work presents a novel protocol for the large‐scale production of biomass‐derived high‐performance electrode materials in practical supercapacitor applications.     

Flower-like hierarchical porous nitrogen-doped carbon spheres from a facile one-step carbonization method for supercapacitors

A facile one-step carbonization method was developed to fabricate flower-like hierarchical porous nitrogen-doped carbon sphere (FHPNCS) from polyimide using polyurethane foam as macroporous scaffold. The FHPNCS possessed flower-like spherical morphology, well-developed hierarchical porous structure, high specific surface area and nitrogen-containing functional groups. These advantages led to excellent electrochemical performance. The FHPNCS electrode exhibited a high specific capacitance of 251.6 F g^?1 at 1 A g^?1, a high rate capability of 76% capacitance retention at 5 A g^?1, and an outstanding cycling stability of only 4.4% loss in specific capacitance after 2000 cycles. Compared with previously reported multi-step templating methods, the present method only involves a facile thermal treatment procedure and avoids the use of hard templates and toxic raw materials, thus exhibiting great potential for large scale production of nitrogen-doped carbon materials for practical applications in supercapacitors.     

A novel hierarchically carbon foam templated carbon nanotubes/polyaniline electrode for efficient electrochemical supercapacitor

In this work, a high-performance electrode material has been fabricated by the incorporation of carbon nanotubes (CNTs) and polyaniline (PANI) on a carbon foams (CF) to improve its electrochemical performance. The microstructure and performance of as-prepared material was characterized in detail. Results showed that the resultant material exhibited a high gravimetric capacitance up to 467.1?F g^?1, higher energy density of 104. 2?Wh kg^?1 and power density of 3000?W kg^?1 at a current density 3?A g^?1 when the electrochemical doping time of PANI equals to 20?min. Furthermore, it appeared a good cycling stability with capacitance retention of 94.5% after 10000 cycles. The enhanced electrochemical performance can be attributed to the unique carbon nanostructure and synergistic effects of active materials CNTs and PANI. It indicates that this novel CF/CNTs/PANI-20 composite is a promising candidate for electrochemical capacitors.     

The application of biomass-based carbon materials in flexible all-solid supercapacitors

Four different kinds of carbon materials were synthesized successfully from saussurea involucrata, cotton stalk and cellulose by two activation methods (KOH-chemical activation method and mixed molten-salt synthesis). Carbon structures, electrochemical and flexible properties are studied. The saussurea involucrata-based flexible symmetric all-solid states supercapacitor exhibited high electrochemical performances, including high specific capacitance (129 F g^?1 at 2 mV s^?1) and excellent cycle stability (～ 85% capacitance retention even after 10,000 cycles). More importantly, it also displays excellent bending endurance, the specific capacitance is almost unchanged after 100 bends. This study shows promising materials in symmetric all-solid state supercapacitor applications.

     

Controlled Air‐Etching Synthesis of Porous‐Carbon Nanotube Aerogels with Ultrafast Charging at 1000 A g−1

Supercapacitors are energy storage systems capable of fast charging and discharging, thus generating superior power density. Porous carbon with high surface area and tunable pore size represents a promising candidate to construct ultrafast supercapacitors; so far, most porous carbon–based electrodes can only be charged to a moderate current density (100–200 A g^?1), also with significant capacitance loss at increasing rate. Here, it is shown that a 3D aerogel consisting of interconnected 1D porous‐carbon nanotubes (PCNs) can serve as a freestanding supercapacitor electrode with excellent rate performance. As a result, the PCN aerogel electrodes achieve 1) ultrafast charging at current densities up to 1000 A g^?1 (corresponding to a charge period of 16 ms), which is the highest value among other porous carbon–based supercapacitors, 2) superior cycling stability at high charging rates (88% capacitance retention after 10⁵ cycles at 1000 A g^?1). Mechanism study reveals favorable kinetics including a centralized pore size distribution at 0.8 nm which is a dominant factor to allow high‐rate charging, a low and linear IR drop, and a metallic feature of 1D PCNs by theoretical calculation. The results indicate that 1D PCNs with controlled porous structures have potential applications in ultrafast energy conversion and storage.     

Enhanced electrochemical performances of heteroatom-enriched carbon with hierarchical pores prepared by trehalose as a pore-forming agent and a simple one-step carbonization/activation process for supercapacitors

It is highly desired to simultaneously introduce active heteroatoms and abundant hierarchical pore structures for enhanced electrochemical performances on carbon materials. Herein, trehalose as a pore-forming agent was added into polyvinylpyrrolidone/melamine formaldedyde resin mixture with high concentrations of nitrogen and oxygen. Then a simple one-step carbonization/activation process was adopted and heteroatom-enriched carbon with hierarchical pores (HPC) was fabricated successfully. HPC/HPC symmetric supercapacitors were assembled using KOH electrolyte. It is clearly demonstrated that due to the pore-forming action of trehalose HPC shows the porous honeycomb, interconnected and worm-like pore structure, which is favorable to enhance the double-layer capacitance. It is confirmed that in our system the three active species of pyridinic nitrogen (N-6), pyrrolic nitrogen (N-5) and quinone type oxygen (O-I) are responsible for the pseudocapacitive behavior. Based on XPS, nitrogen adsorption/desorption isotherms and electrochemical impedance spectroscopy, it is deduced that the ratio-optimized HPC-T30 exhibits high concentration of three active species (8.17 at.%), increased specific area (351.26 m² g^?1) and tuned hierarchical pore structures with substantial micropores (micropore area of 321.68 m² g^?1) and a small amount of mesopores and macropores, which lead to decrease of charge transfer resistance, increase of transfer rate of electrolyte ions in the pores and excellent electrochemical performances. In cyclic voltammetry tests of three-electrode system and galvanostatic charge/discharge tests of two-electrode system, HPC-T30 displays high specific capacitance, 46% and 1.2-time enhancement compared to untreated HPC-T0, respectively. The optimized HPC-T30/HPC-T30 supercapacitor delivers the energy density of 6.69 W h kg^?1 in 6 M KOH electrolyte. Furthermore, the supercapacitor shows a capacitance retention of 91.16% up to 6000 cycles and the coulombic efficiency reaches nearly 100% for each charged/discharge cycle, demonstrating its good cyclic stability.     

Condiment‐Derived 3D Architecture Porous Carbon for Electrochemical Supercapacitors

The one‐step synthesis of porous carbon nanoflakes possessing a 3D texture is achieved by cooking (carbonization) a mixture containing two condiments, sodium glutamate (SG) and sodium chloride, which are commonly used in kitchens. The prepared 3D porous carbons are composed of interconnected carbon nanoflakes and possess instinct heteroatom doping such as nitrogen and oxygen, which furnishes the electrochemical activity. The combination of micropores and mesopores with 3D configurations facilitates persistent and fast ion transport and shorten diffusion pathways for high‐performance supercapacitor applications. Sodium glutamate carbonized at 800 °C exhibits high charge storage capacity with a specific capacitance of 320 F g^?1 in 6 m KOH at a current density of 1 A g^?1 and good stability over 10 000 cycles.     

High Performance of N‐Doped Graphene with Bubble‐like Textures for Supercapacitors

Nitrogen‐doped graphene (NG) with wrinkled and bubble‐like texture is fabricated by a thermal treatment. Especially, a novel sonication‐assisted pretreatment with nitric acid is used to further oxidize graphene oxide and its binding with melamine molecules. There are many bubble‐like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets. The bubble‐like texture provides more active sites for effective ion transport and reversible capacitive behavior. The specific surface area of NG (5.03 at% N) can reach up to 438.7 m² g^?1, and the NG electrode demonstrates high specific capacitance (481 F g^?1 at 1 A g^?1, four times higher than reduced graphene oxide electrode (127.5 F g^?1)), superior cycle stability (the capacitance retention of 98.9% in 2 m KOH and 99.2% in 1 m H₂SO₄ after 8000 cycles), and excellent energy density (42.8 Wh kg^?1 at power density of 500 W kg^?1 in 2 m KOH aqueous electrolyte). The results indicate the potential use of NG as graphene‐based electrode material for energy storage devices.     

Nitrogen‐Superdoped 3D Graphene Networks for High‐Performance Supercapacitors

An N‐superdoped 3D graphene network structure with an N‐doping level up to 15.8 at% for high‐performance supercapacitor is designed and synthesized, in which the graphene foam with high conductivity acts as skeleton and nested with N‐superdoped reduced graphene oxide arogels. This material shows a highly conductive interconnected 3D porous structure (3.33 S cm^?1), large surface area (583 m² g^?1), low internal resistance (0.4 Ω), good wettability, and a great number of active sites. Because of the multiple synergistic effects of these features, the supercapacitors based on this material show a remarkably excellent electrochemical behavior with a high specific capacitance (of up to 380, 332, and 245 F g^?1 in alkaline, acidic, and neutral electrolytes measured in three‐electrode configuration, respectively, 297 F g^?1 in alkaline electrolytes measured in two‐electrode configuration), good rate capability, excellent cycling stability (93.5% retention after 4600 cycles), and low internal resistance (0.4 Ω), resulting in high power density with proper high energy density.     

Activated carbons derived from sugarcane bagasse for high-capacitance electrical double layer capacitors

Activated carbon (AC) from sugarcane bagasse was prepared using a simple two-step method of carbonization and chemical activation with four different activating agents (HNO₃, H₂SO₄, NaOH, and KOH). Amorphous carbon structure as identified by X-ray diffraction was observed in all samples. Scanning electron microscopy revealed that the AC had more porosity than the non-activated carbon (non-AC). Specific capacitance of the non-AC electrode was 32.58 F g^?1 at the current density of 0.5 A g^?1, whereas the AC supercapacitor provided superior specific capacitances of 50.25, 69.59, 109.99, and 138.61 F g^?1 for the HNO₃ (AC-HNO₃), H₂SO₄ (AC-H₂SO₄), NaOH (AC-NaOH), and KOH (AC-KOH) activated carbon electrodes, respectively. The AC-KOH electrode delivered the highest specific capacitance (about 4 times of the non-AC electrode) because of its good surface wettability, the largest specific surface area (1058.53 m² g^?1), and the highest total specific pore volume (0.474 cm³ g^?1). The AC-KOH electrode also had a great capacitance retention of almost 100% after 1000 GCD cycles. These results demonstrate that our AC developed from sugarcane bagasse has a strong potential to be used as high stability supercapacitor electrode material.

     

Unveiling Superior Capacitive Behaviors of One-Pot Molten Salt-Engineered B,N Co-Doped Porous Carbon Sheets

Heteroatom-doped porous carbon materials with distinctive surface properties and capacitive behavior have been accepted as promising candidates for supercapacitor electrodes. Currently, the researches mainly focus on developing facile synthetic method and unveiling the structure-activity relationship to further elevate their capacitive performance. Here, the B, N co-doped porous carbon sheet (BN-PCS) is constructed by one-pot pyrolysis of agar in KCl/KHCO₃ molten salt system. In this process, the urea acts as directing agent to guide the formation of 2D sheet morphology, and the decomposition of KHCO₃ and boric acid creates rich micro- and mesopores in the carbon framework. The specific capacitance of optimized BN-PCS reaches 361.1 F g⁻¹ at a current density of 0.5 A g⁻¹ in an aqueous KOH electrolyte. Impressively, the fabricated symmetrical supercapacitor affords a maximum energy density of 43.5 Wh kg⁻¹ at the power density of 375.0 W kg⁻¹ in 1.0 mol L⁻¹ TEABF₄/AN electrolyte. It also achieves excellent long-term stability with capacitance retention of 91.1% and Columbic efficiency of 100% over 10 000 cycles. This study indicates one-pot molten salt method is effective in engineering advanced carbon materials for high-performance energy storage devices.     

Amorphous Red Phosphorus Embedded in Sandwiched Porous Carbon Enabling Superior Sodium Storage Performances

The red P anode for sodium ion batteries has attracted great attention recently due to the high theoretical capacity, but the poor intrinsic electronic conductivity and large volume expansion restrain its widespread applications. Herein, the red P is successfully encapsulated into the cube shaped sandwich‐like interconnected porous carbon building (denoted as P@C‐GO/MOF‐5) via the vaporization–condensation method. Superior cycling stability (high capacity retention of about 93% at 2 A g^?1 after 100 cycles) and excellent rate performance (502 mAh g^?1 at 10 A g^?1) can be obtained for the P@C‐GO/MOF‐5 electrode. The superior electrochemical performance can be ascribed to the successful incorporation of red P into the unique carbon matrix with large surface area and pore volume, interconnected porous structure, excellent electronic conductivity and superior structural stability.     

Coupling PEDOT on Mesoporous Vanadium Nitride Arrays for Advanced Flexible All‐Solid‐State Supercapacitors

Tailored construction of advanced flexible supercapacitors (SCs) is of great importance to the development of high‐performance wearable modern electronics. Herein, a facile combined wet chemical method to fabricate novel mesoporous vanadium nitride (VN) composite arrays coupled with poly(3,4‐ethylenedioxythiophene) (PEDOT) as flexible electrodes for all‐solid‐state SCs is reported. The mesoporous VN nanosheets arrays prepared by the hydrothermal–nitridation method are composed of cross‐linked nanoparticles of 10–50 nm. To enhance electrochemical stability, the VN is further coupled with electrodeposited PEDOT shell to form high‐quality VN/PEDOT flexible arrays. Benefiting from high intrinsic reactivity and enhanced structural stability, the designed VN/PEDOT flexible arrays exhibit a high specific capacitance of 226.2 F g^?1 at 1 A g^?1 and an excellent cycle stability with 91.5% capacity retention after 5000 cycles at 10 A g^?1. In addition, high energy/power density (48.36 Wh kg^?1 at 2 A g^?1 and 4 kW kg^?1 at 5 A g^?1) and notable cycling life (91.6% retention over 10 000 cycles) are also achieved in the assembled asymmetric flexible supercapacitor cell with commercial nickel–cobalt–aluminum ternary oxides cathode and VN/PEDOT anode. This research opens up a way for construction of advanced hybrid organic–inorganic electrodes for flexible energy storage.     

MOF‐Derived Hollow Cage NixCo3−xO4 and Their Synergy with Graphene for Outstanding Supercapacitors

Highly optimized nickel cobalt mixed oxide has been derived from zeolite imidazole frameworks. While the pure cobalt oxide gives only 178.7 F g^?1 as the specific capacitance at a current density of 1 A g^?1, the optimized Ni:Co 1:1 has given an extremely high and unprecedented specific capacitance of 1931 F g^?1 at a current density of 1 A g^?1, with a capacitance retention of 69.5% after 5000 cycles in a three electrode test. This optimized Ni:Co 1:1 mixed oxide is further used to make a composite of nickel cobalt mixed oxide/graphene 3D hydrogel for enhancing the electrochemical performance by virtue of a continuous and porous graphene conductive network. The electrode made from GNi:Co 1:1 successfully achieves an even higher specific capacitance of 2870.8 F g^?1 at 1 A g^?1 and also shows a significant improvement in the cyclic stability with 81% capacitance retention after 5000 cycles. An asymmetric supercapacitor is also assembled using a pure graphene 3D hydrogel as the negative electrode and the GNi:Co 1:1 as the positive electrode. With a potential window of 1.5 V and binder free electrodes, the capacitor gives a high specific energy density of 50.2 Wh kg^?1 at a high power density of 750 W kg^?1.