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.     

Core–Shell Nitrogen‐Doped Carbon Hollow Spheres/Co3O4 Nanosheets as Advanced Electrode for High‐Performance Supercapacitor

Co₃O₄/nitrogen‐doped carbon hollow spheres (Co₃O₄/NHCSs) with hierarchical structures are synthesized by virtue of a hydrothermal method and subsequent calcination treatment. NHCSs, as a hard template, can aid the generation of Co₃O₄ nanosheets on its surface; while SiO₂ spheres, as a sacrificed‐template, can be dissolved in the process. The prepared Co₃O₄/NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co₃O₄ itself. A higher specific capacitance of 581 F g^?1 at 1 A g^?1 and a higher rate performance of 91.6% retention at 20 A g^?1 are achieved, better than Co₃O₄ nanorods (318 F g^?1 at 1 A g^?1 and 67.1% retention at 20 A g^?1). In addition, the composite is employed as a positive electrode to fabricate an asymmetric supercapacitor. The device can deliver a high energy density of 34.5 Wh kg^?1 at the power density of 753 W kg^?1 and display a desirable cycling stability. All of these attractive results make the unique hierarchical Co₃O₄/NHCS core–shell structure a promising electrode material for high‐performance supercapacitors.     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

Water-promoted zeolitic imidazolate framework-67 transformation to Ni–Co layered double hydroxide hollow microsphere for supercapacitor electrode material

Hollow Ni–Co layered double hydroxide (LDH) was synthesized with rhombic dodecahedral zeolitic imidazolate framework-67 (ZIF-67) as self-sacrificed template and cobalt precursor. Water was found to be very important role on the formation of Ni–Co LDH hollow microstructure. As a supercapacitor electrode material, the obtained hollow Ni–Co LDH delivered a high specific capacitance of 1530 F g^?1 at the current density of 1.0 A g^?1 and good cycle performance, which can be ascribed to its hollow mesoporous structure composed of the Ni–Co LDH nanosheets and high specific surface area. Combined with the AC negative electrodes, the assembled asymmetric supercapacitors performed an energy density of 27.5 Wh kg^?1 at the power density of 375 W kg^?1.     

MoS2/NiS Yolk–Shell Microsphere‐Based Electrodes for Overall Water Splitting and Asymmetric Supercapacitor

Rational designing of the composition and structure of electrode material is of great significance for achieving highly efficient energy storage and conversion in electrochemical energy devices. Herein, MoS₂/NiS yolk–shell microspheres are successfully synthesized via a facile ionic liquid‐assisted one‐step hydrothermal method. With the favorable interface effect and hollow structure, the electrodes assembled with MoS₂/NiS hybrid microspheres present remarkably enhanced electrochemical performance for both overall water splitting and asymmetric supercapacitors. In particular, to deliver a current density of 10 mA cm^?2, the MoS₂/NiS‐based electrolysis cell for overall water splitting only needs an output voltage of 1.64 V in the alkaline medium, lower than that of Pt/C–IrO₂‐based electrolysis cells (1.70 V). As an electrode for supercapacitors, the MoS₂/NiS hybrid microspheres exhibit a specific capacitance of 1493 F g^?1 at current density of 0.2 A g^?1, and remain 1165 F g^?1 even at a large current density of 2 A g^?1, implying outstanding charge storage capacity and excellent rate performance. The MoS₂/NiS‐ and active carbon‐based asymmetric supercapacitor manifests a maximum energy density of 31 Wh kg^?1 at a power density of 155.7 W kg^?1, and remarkable cycling stability with a capacitance retention of approximately 100% after 10 000 cycles.     

Vertically Oriented Graphene Nanoribbon Fibers for High‐Volumetric Energy Density All‐Solid‐State Asymmetric Supercapacitors

Graphene fiber based micro‐supercapacitors (GF micro‐SCs) have attracted great attention for their potential applications in portable and wearable electronics. However, due to strong π–π stacking of nanosheets for graphene fibers, the limited ion accessible surface area and slow ion diffusion rate leads to low specific capacitance and poor rate performance. Here, the authors report a strategy for the synthesis of a vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined‐hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process. As a result, the as‐obtained fiber shows high length specific capacitance of 3.2 mF cm^?1 and volumetric capacitance of 234.8 F cm^?3 at 2 mV s^?1, as well as excellent rate capability and outstanding cycling performance (96% capacitance retention after 10 000 cycles). Moreover, an all‐solid‐state asymmetric supercapacitor based on graphene nanoribbon fiber as negative electrode and MnO₂ coated graphene ribbon fiber as positive electrode, shows high volumetric capacitance and energy density of 12.8 F cm^?3 and 5.7 mWh cm^?3 (normalized to the device volume), respectively, much higher than those of previously reported GF micro‐SCs, as well as a long cycle life with 88% of capacitance retention after 10 000 cycles.     

Facile Synthesis of Vanadium Metal‐Organic Frameworks for High‐Performance Supercapacitors

Compared to traditional metal oxides, metal‐organic frameworks exhibit excellent properties, such as a high surface area, significant thermal stability, low density, and excellent electrochemical performance. Here, a simple process is proposed for the fabrication of rod‐like vanadium metal‐organic frameworks (V^IV(O)(bdc), bdc = 1,4‐benzenedicarboxylate, or MIL‐47), and the effect of the structure on the electrochemical performance is investigated via a series of electrochemical measurements. The V^IV(O)(bdc) electrode exhibits a maximum specific capacitance of 572.1 F g^?1 at current densities of 0.5 A g^?1. More significantly, aqueous and solid‐state asymmetric supercapacitors are successfully assembled. The solid‐state device shows an excellent energy density of 6.72 mWh cm^?3 at a power density of 70.35 mW cm^?3. This superior performance confirms that V^IV(O)(bdc) electrodes are promising materials for applications in supercapacitors.     

Graphene‐Based Linear Tandem Micro‐Supercapacitors with Metal‐Free Current Collectors and High‐Voltage Output

Printable supercapacitors are regarded as a promising class of microscale power source, but are facing challenges derived from conventional sandwich‐like geometry. Herein, the printable fabrication of new‐type planar graphene‐based linear tandem micro‐supercapacitors (LTMSs) on diverse substrates with symmetric and asymmetric configuration, high‐voltage output, tailored capacitance, and outstanding flexibility is demonstrated. The resulting graphene‐based LTMSs consisting of 10 micro‐supercapacitors (MSs) present efficient high‐voltage output of 8.0 V, suggestive of superior uniformity of the entire integrated device. Meanwhile, LTMSs possess remarkable flexibility without obvious capacitance degradation under different bending states. Moreover, areal capacitance of LTMSs can be sufficiently modulated by incorporating polyaniline‐based pseudocapacitive nanosheets into graphene electrodes, showing enhanced capacitance of 7.6 mF cm^?2. To further improve the voltage output and energy density, asymmetric LTMSs are fabricated through controlled printing of linear‐patterned graphene as negative electrodes and MnO₂ nanosheets as positive electrodes. Notably, the asymmetric LTMSs from three serially connected MSs are easily extended to 5.4 V, triple voltage output of the single cell (1.8 V), suggestive of the versatile applicability of this technique. Therefore, this work offers numerous opportunities of graphene and analogous nanosheets for one‐step scalable fabrication of flexible tandem energy storage devices integrating with printed electronics on same substrate.     

Intertwined Nanocarbon and Manganese Oxide Hybrid Foam for High‐Energy Supercapacitors

Rapid charging and discharging supercapacitors are promising alternative energy storage systems for applications such as portable electronics and electric vehicles. Integration of pseudocapacitive metal oxides with single‐structured materials has received a lot of attention recently due to their superior electrochemical performance. In order to realize high energy‐density supercapacitors, a simple and scalable method is developed to fabricate a graphene/MWNT/MnO₂ nanowire (GMM) hybrid nanostructured foam, via a two‐step process. The 3D few‐layer graphene/MWNT (GM) architecture is grown on foamed metal foils (nickel foam) via ambient pressure chemical vapor deposition. Hydrothermally synthesized α‐MnO₂ nanowires are conformally coated onto the GM foam by a simple bath deposition. The as‐prepared hierarchical GMM foam yields a monographical graphene foam conformally covered with an intertwined, densely packed CNT/MnO₂ nanowire nanocomposite network. Symmetrical electrochemical capacitors (ECs) based on GMM foam electrodes show an extended operational voltage window of 1.6 V in aqueous electrolyte. A superior energy density of 391.7 Wh kg^?1 is obtained for the supercapacitor based on the GMM foam, which is much higher than ECs based on GM foam only (39.72 Wh kg^?1). A high specific capacitance (1108.79 F g^?1) and power density (799.84 kW kg^?1) are also achieved. Moreover, the great capacitance retention (97.94%) after 13 000 charge–discharge cycles and high current handability demonstrate the high stability of the electrodes of the supercapacitor. These excellent performances enable the innovative 3D hierarchical GMM foam to serve as EC electrodes, resulting in energy‐storage devices with high stability and power density in neutral aqueous electrolyte.     

Self‐Assembled Nickel Pyrophosphate‐Decorated Amorphous Bimetal Hydroxides 2D‐on‐2D Nanostructure for High‐Energy Solid‐State Asymmetric Supercapacitor

To obtain a supercapacitor with a remarkable specific capacitance and rate performance, a cogent design and synthesis of the electrode material containing abundant active sites is necessary. In present work, a scalable strategy is developed for preparing 2D‐on‐2D nanostructures for high‐energy solid‐state asymmetric supercapacitors (ASCs). The self‐assembled vertically aligned microsheet‐structured 2D nickel pyrophosphate (Ni₂P₂O₇) is decorated with amorphous bimetallic nickel cobalt hydroxide (NiCo‐OH) to form a 2D‐on‐2D nanostructure arrays electrode. The resulting Ni₂P₂O₇/NiCo‐OH 2D‐on‐2D array electrode exhibits peak specific capacity of 281 mA hg^?1 (4.3 F cm^?2), excellent rate capacity, and cycling stability over 10 000 charge–discharge cycles in the positive potential range. The excellent electrochemical features can be attributed to the high electrical conductivity and 2D layered structure of Ni₂P₂O₇ along with the Faradic capacitance of the amorphous NiCo‐OH nanosheets. The constructed Ni₂P₂O₇/NiCo‐OH//activated carbon based solid‐state ASC cell operates in a high voltage window of 1.8 V with an energy density of 78 Wh kg^?1 (1.065 mWh cm^?3) and extraordinary cyclic stability over 10 000 charge–discharge cycles with excellent energy efficiency (75%–80%) over all current densities. The excellent electrochemical performance of the prepared electrode and solid‐state ASC device offers a favorable and scalable pathway for developing advanced electrodes.     

Ultrathin Hierarchical Porous Carbon Nanosheets for High‐Performance Supercapacitors and Redox Electrolyte Energy Storage

The design of advanced high‐energy‐density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape‐controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal–organic frameworks (MOFs) are developed. As a proof‐of‐concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon‐sheet‐based symmetric cell shows an ultrahigh Brunauer–Emmett–Teller (BET)‐area‐normalized capacitance of 21.4 µF cm^?2 (233 F g^?1), exceeding other carbon‐based supercapacitors. The addition of potassium iodide as redox‐active species in a sulfuric acid (supporting electrolyte) leads to the ground‐breaking enhancement in the energy density up to 90 Wh kg^?1, which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery‐level energy and capacitor‐level power density.     

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.     

Efficient Supercapacitor Energy Storage Using Conjugated Microporous Polymer Networks Synthesized from Buchwald–Hartwig Coupling

Supercapacitors have received increasing interest as energy storage devices due to their rapid charge–discharge rates, high power densities, and high durability. In this work, novel conjugated microporous polymer (CMP) networks are presented for supercapacitor energy storage, namely 3D polyaminoanthraquinone (PAQ) networks synthesized via Buchwald–Hartwig coupling between 2,6‐diaminoanthraquinone and aryl bromides. PAQs exhibit surface areas up to 600 m² g^?1, good dispersibility in polar solvents, and can be processed to flexible electrodes. The PAQs exhibit a three‐electrode specific capacitance of 576 F g^?1 in 0.5 m H₂SO₄ at a current of 1 A g^?1 retaining 80–85% capacitances and nearly 100% Coulombic efficiencies (95–98%) upon 6000 cycles at a current density of 2 A g^?1. Asymmetric two‐electrode supercapacitors assembled by PAQs show a capacitance of 168 F g^?1 of total electrode materials, an energy density of 60 Wh kg^?1 at a power density of 1300 W kg^?1, and a wide working potential window (0–1.6 V). The asymmetric supercapacitors show Coulombic efficiencies up to 97% and can retain 95.5% of initial capacitance undergo 2000 cycles. This work thus presents novel promising CMP networks for charge 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.     

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.     

One‐Step Synthesis of Monodispersed Mesoporous Carbon Nanospheres for High‐Performance Flexible Quasi‐Solid‐State Micro‐Supercapacitors

Cost‐effective synthesis of carbon nanospheres with a desirable mesoporous network for diversified energy storage applications remains a challenge. Herein, a direct templating strategy is developed to fabricate monodispersed N‐doped mesoporous carbon nanospheres (NMCSs) with an average particle size of 100 nm, a pore diameter of 4 nm, and a specific area of 1093 m² g^?1. Hexadecyl trimethyl ammonium bromide and tetraethyl orthosilicate not only play key roles in the evolution of mesopores but also guide the assembly of phenolic resins to generate carbon nanospheres. Benefiting from the high surface area and optimum mesopore structure, NMCSs deliver a large specific capacitance up to 433 F g^?1 in 1 m H₂SO₄. The NMCS electrodes–based symmetric sandwich supercapacitor has an output voltage of 1.4 V in polyvinyl alcohol/H₂SO₄ gel electrolyte and delivers an energy density of 10.9 Wh kg^?1 at a power density of 14014.5 W kg^?1. Notably, NMCSs can be directly applied through the mask‐assisted casting technique by a doctor blade to fabricate micro‐supercapacitors. The micro‐supercapacitors exhibit excellent mechanical flexibility, long‐term stability, and reliable power output.     

Controlled microstructure in two dimensional Ni-Co LDH nanosheets-crosslinked network for high performance supercapacitors

Based on the electrochemical mechanism of Faraday supercapacitors (FSs), we design a microstructure configuration of electrode materials (EMs) in this work, aiming to promote the electrochemical performance of FSs. This configuration of EMs has two dimensional sheets-crosslinked network with narrow mesopore size distribution. It is reasonable to believe that the configuration is in favor of the electrochemical performance of EMs to the greatest extent. We try to build this structure configure using Ni-Co layered double hydroxide (LDH) nanosheets as building blocks by a facile sol-gel approach. Due to the Co²⁺ ions, we realize this structure configuration consisting of Ni-Co LDH nanosheets. Benefiting from the advantages of this configuration, the Ni-Co LDH presents high electrochemical performance. It has high specific capacity of 1170 C g^?1 at low current density of 2.0 A g^?1, and 500 C g^?1 at high current density of 39.6 A g^?1. The asymmetric supercapacitors of Ni-Co LDH exhibit high energy density of 74.37 Wh kg^?1 at low power density of 492 Wh kg^?1 and keep relatively high energy density of 15.99 Wh kg^?1 at high power density of 6395 Wh kg^?1. These results suggest that the designed structure configuration of EMs is rational for application in FSs.     

Controllable Synthesis of Atomically Thin Type‐II Weyl Semimetal WTe2 Nanosheets: An Advanced Electrode Material for All‐Solid‐State Flexible Supercapacitors

Compared with 2D S‐based and Se‐based transition metal dichalcogenides (TMDs), Te‐based TMDs display much better electrical conductivities, which will be beneficial to enhance the capacitances in supercapacitors. However, to date, the reports about the applications of Te‐based TMDs in supercapacitors are quite rare. Herein, the first supercapacitor example of the Te‐based TMD is reported: the type‐II Weyl semimetal 1Td WTe₂. It is demonstrated that single crystals of 1Td WTe₂ can be exfoliated into the nanosheets with 2–7 layers by liquid‐phase exfoliation, which are assembled into air‐stable films and further all‐solid‐state flexible supercapacitors. The resulting supercapacitors deliver a mass capacitance of 221 F g^?1 and a stack capacitance of 74 F cm^?3. Furthermore, they also show excellent volumetric energy and power densities of 0.01 Wh cm^?3 and 83.6 W cm^?3, respectively, superior to the commercial 4V/500 µAh Li thin‐film battery and the commercial 3V/300 µAh Al electrolytic capacitor, in association with outstanding mechanical flexibility and superior cycling stability (capacitance retention of ≈91% after 5500 cycles). These results indicate that the 1Td WTe₂ nanosheet is a promising flexible electrode material for high‐performance energy storage devices.     

Rational Construction of Hollow Core‐Branch CoSe2 Nanoarrays for High‐Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core‐branch CoSe₂ nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe₂ in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core‐branch CoSe₂ has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe₂ delivers a high specific capacitance of 759.5 F g^?1 at 1 mA cm^?2, which is much larger than that of CoO nanocones (319.5 F g^?1). In addition, the CoSe₂ electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge–discharge cycles at 5 mA cm^?2. An asymmetric supercapacitor using the CoSe₂ as cathode and an N‐doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg^?1 at a power density of 1914.7 W kg^?1, and maintains 24.9 Wh kg^?1 when power density increased to 7354.8 W kg^?1. Moreover, the CoSe₂ electrode also exhibits better oxygen evolution reaction activity than that of CoO.     

Tailoring Hierarchically Porous Nitrogen‐, Sulfur‐Codoped Carbon for High‐Performance Supercapacitors and Oxygen Reduction

Heteroatom‐doped carbon materials are intensively studied in supercapacitors and fuel cells, because of their great potential for sustainably bearing on the energy crisis and environmental pollution. Although enormous efforts are put in material perfection with a hierarchically porous microstructure, the simultaneous optimization of both porous structures and surface functionalities is hard to achieve due to inevitable concurrent dopant leaching effect and structural collapse under required high pyrolysis temperature. In this study, an in situ dehalogenation polymerization and activation protocol is introduced to synthesize nitrogen‐ and sulfur‐codoped carbon materials (NS‐PCMs) with hierarchical pore distribution and abundant surface doping, which endows them with good conductivity, abundant accessible active sites, and efficient mass transport. As a result, the as‐prepared carbon materials (NS‐a‐PCM‐1000) show an excellent mass specific capacitance of 461.5 F g^?1 at a current density of 0.1 A g^?1, long cycle life (>23 k, 10 A g^?1), and high device energy and power density (17.3 Wh kg^?1, 250 W kg^?1). Significantly, NS‐a‐PCM‐1000 also exhibits one of the highest oxygen reduction reaction activities (onset potential of 1.0 V vs reversible hydrogen electrode) in alkaline media among all reported metal‐free catalysts.