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We designed high-volumetric-energy-density supercapacitors from monolithic composites composed of self-standing carbon foam (CF) as the conducting matrix and embedded hierarchically organized porous carbon (PICK) as the active material. Using multiprobe scanning tunneling microscopy at selected areas, we were able to disentangle morphology-dependent contributions of the heterogeneous composite to the overall conductivity. Adding PICK is found to enhance the conductivity of the monoliths by providing additional links for the CF network, enabling high and stable performance. The resulting all-carbon CF-PICK composites were used as self-standing electrodes for symmetric supercapacitors without the need for a binder, additional conducting additive, metals as a current collector, or casting/drying steps. Supercapacitors achieved a capacitance of 181 F g

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO

A novel and facile strategy is developed to tune parallel manganese dioxide (MnO2) to hollow parallel hydroxyl oxidize iron (FeOOH) replicas, which can exactly keep its original morphology. The key factors leading to the morphology-preserved transformation are the low-temperature and dropwise strategy via a serial of controlled experiments. Benefiting from the characteristics of parallel and hollow structures, the FeOOH replica delivers remarkable specific capacitance of 186.8F g−1 at 0.5 A g−1. The electrochemical performances delivered by the asymmetric supercapacitor (parallel MnO2//hollow parallel FeOOH) are much superior to those where conventional activated graphene or FeOOH nanoneedles are used as negative electrode materials. This can be attributed to the advantages of parallel nanostructure and high electrochemical matching effect of positive and negative electrode materials. The energy density is recorded up to 46.8 Wh kg−1 at the power density of 0.5 kW kg−1, while it still remains 20.7 Wh kg−1 with the maximum power density of 10 kW kg−1. Furthermore, this strategy shows great universality and can be broadened to almost all MnO2 related researches to synthesize ideal negative electrode materials with high structural and electrochemical matching effect, thus further enhances the electrochemical performances of as-prepared asymmetric supercapacitor devices.

High specific surface area carbons with a hierarchical porous structure and outstanding conductivity have gained tremendous attention for energy storage applications due to their stable electrochemical properties and high rate capability. However, high specific surface areas are always generated from a high content of micropores. Scalable syntheses of porous carbons with ultrahigh specific surface area as well as a high content of macropores and mesopores still remain a great challenge. Herein, N-doped hierarchical porous carbon with an ultrahigh specific surface area of 2315 m2 g−1 together with high contents of macropores and mesopores was synthesized from poly(acrylonitrile) (PAN) by using a rationally designed, stepwise pore-forming process. After mixing with a small amount of carbon nanotubes, excellent electrochemical properties, including a high specific capacitance (286.8 F g−1), outstanding rate capability and cycling stability (97.2% after 20 000 cycles), were obtained. An interdigitated symmetric micro-supercapacitor (MSC) prepared by a simple mask-painting method exhibits high areal capacitance up to 36.5 mF cm−2 at a current density of 0.25 mA cm−2 and a high energy density of 5.07 μW h cm−2 at a power density of 0.25 mW cm−2. Furthermore, symmetrical MSCs display excellent rate capability, outstanding cycling stability (98.2% after 10 000 cycles) and remarkable bending stability (81.3% after 500 bending cycles at a 180° bending angle). Additionally, the areal capacitance and output voltage of the symmetrical MSCs can be easily adjusted using tandem or shunt models representing practical applications.

In the past few years, intensive attention has been focused on birnessite based electrodes for supercapacitors. Much progress has been achieved in developing birnessite based nanostructures with high electrochemical performance. However, challenges still remain in taking full advantage of birnessite and building smart structures to overcome the gap between the obtained capacitance and its theoretical capacitance. In this review, the basic information on birnessite and its preparation strategies are summarized and the current challenges are put forward. Finally, some new strategies for preparing high electrochemical performance birnessite based nanostructures are highlighted.

In this work, a series of MnO2 nanostructures with different crystallographic structures, including δ-MnO2 nanotubes and α-MnO2 nanorods, were prepared using polycarbonate membrane as a template. The crystallographic structure and morphology were controlled by adjusting the pH of the KMnO4 solutions via a one-step hydrothermal method. The crystal form of the samples changed from birnessite to α-MnO2 with the decrease in the applied pH values and a precise pH value for the critical point was found. When used as positive electrode materials in the supercapacitor, the structure prepared in the higher pH value solutions (MnO2-12, pH = 12) with a δ-type crystallographic structure gave an ideal specific capacitance of 364.1 F g−1 at a current density of 0.5 A g−1, a good rate capability, and a favorable cycling stability. An asymmetric supercapacitor assembled with MnO2-12 as the positive electrode and activated graphene (AG) as the negative electrode produced an energy density of 29.4 W h kg−1 at a power density of 248.9 W kg−1. The excellent electrochemical properties were attributed to the novel tubular structure composed of poor crystalline δ-MnO2 nanosheets, resulting in a high ionic conductivity and two-sided reaction surfaces.

The excessive concern over the energy density of supercapacitors is changing their applied direction while the power density is always overlooked. Supercapacitors should be considered as a high-power energy device rather than a neither fish nor fowl energy device. Herein, an ultrafine α-MnO2 needle was formed on β-MnO2 networks, not distributed randomly, but standing on the surface of β-MnO2 vertically forming an array structure with low-charge-carrier scattering. These novel structures possess a rational arrangement of the needles resulting in high capacitance (278.2 F g–1 for α-MnO2/β-MnO2 networks) and excellent rate capability (41.0% remaining with the specific current increased from 0.25 to 64.0 A g–1). Asymmetrical supercapacitors fabricated by reduced graphene oxide (RGO) as the anode and as-prepared structures as the cathode deliver excellent electrochemical performance. Specifically, the devices give a favorable specific energy (29.8 W h kg–1) considering the weight of α-MnO2/β-MnO2 and reduced g...

Two-dimensional birnessite has attracted attention for electrochemical energy storage because of the presence of redox active Mn4+/Mn3+ ions and spacious interlayer channels available for ions diffusion. However, current strategies are largely limited to enhancing the electrical conductivity of birnessite. One key limitation affecting the electrochemical properties of birnessite is the poor utilization of the MnO6 unit. Here, we assemble β-MnO2/birnessite core–shell structure that exploits the exposed crystal face of β-MnO2 as the core and ultrathin birnessite sheets that have the structure advantage to enhance the utilization efficiency of the Mn from the bulk. Our birnessite that has sheets parallel to each other is found to have unusual crystal structure with interlayer spacing, Mn(III)/Mn(IV) ratio and the content of the balancing cations differing from that of the common birnessite. The substrate directed growth mechanism is carefully investigated. The as-prepared core–shell nanostructures enhance th...

Ni-doped Bi2O3 (Ni–Bi2O3) microspheres have been synthesized by a one-pot solvothermal route. The morphology and structure of Ni–Bi2O3 microspheres can be well controlled by tailoring the preparative parameters (e.g., the content of Ni and reaction time). The resulted Ni–Bi2O3 microspheres are formed via a dissolution-recrystallization process resulting in mesoporous structure. Furthermore, when using as photocatalyst for removal of NO in air, it exhibits an enhanced performance in comparison with bare Bi2O3 under simulated solar light. First-principles calculations reveal that the enhanced activity of the catalyst could be attributed to the modification of geometric and electronic structure resulting from the dopant Ni. The present work could provide a new approach for synthesizing doped mesoporous Bi2O3 nanostructures with controlled morphology.

Herein, we firstly prepared Co-doped birnessite and Mn-FeOOH nanotubes by a simple hydrothermal process using a sacrificed template method. The doping ratio was adjusted by setting the molar ratios of Co and Mn in the preparing process. Both the Co-doped birnessite and Mn-FeOOH nanotubes exhibit ideal electrochemical properties, especially their excellent rate capability.

Mesoporous Au@MnO2 was fabricated via a facile self-decomposition process and is used as the electrode material for supercapacitors. Au@MnO2 electrode gave a high capacitance of 906.4 F g−1 with outstanding rate capability and excellent stability (97.2% of the original capacitance was retained after 5000 cycles). A two-electrode cell assembled by Au@MnO2 network and activated graphene oxide/Au mixture delivers an energy density of 62.8 Wh kg−1 at the power density of 1000 W kg−1.

A facile two-step hydrothermal method is modified to synthesize NiCo 2 S 4 nanosheets on activated multiporous carbon (AMC) for application in supercapacitors. The structure and performance of both NiCo 2 S 4 and the intermediate product, i.e. NiCo 2 O 4 on AMC are investigated in detail to clarify the effect of the sulfidation treatment. Owing to the high electronic conductivity of NiCo 2 S 4 , the unique designed nanostructure exhibits a high specific capacitance (651.1 F g −1 at 0.6 A g −1 ), good rate performance (88.1% retention for current increases around 17 times) and excellent cycling stability (87.4% retention after 2000 cycles). These results suggest this hybrid composite to be a promising electrode material for high-performance supercapacitors and the rational fabrication provides an approach to improve the electrochemical energy storage for other transition metal sulfides and oxides.

Well-aligned hierarchical NiMn-layered double hydroxide (NiMn-LDH) nanosheets are successfully grown on Ni foam by a facile one-step wet-method, wherein urea hydrolysis supplies alkali and carbonate ion. As-obtained NiMn-LDH@Ni foam presents highly oriented layered structure with ultrathin nanosheets. By fine tuning Ni/Mn mole ratio, the optimized Ni 3 Mn 1 -LDH@Ni foam displays maximum specific capacitance (1511 F g −1 at 2.5 A g −1 ), excellent rate capability (80.1% retention at 48 A g −1 ), high coulombic efficiency and long-term cycling life. In principle, this work provides a rapid and tunable strategy approach for synthesis of NiMn-LDH with largely enhanced supercapacitor behavior.

The development of portable and wearable electronics has promoted the increasing demand for high-performance power sources with high energy/power density, low cost, lightweight, as well as ultrathin and flexible features. Herein, a low-cost high-performance flexible asymmetric supercapacitor (ASC) with Co2AlO4@MnO2 nanosheets and Fe3O4 nanoflakes grown on nickel foam is designed and fabricated. The as-designed ASC device with an extended operating voltage window of 1.6 V achieves a specific capacitance of 99.1 F g−1 at a current density of 2 A g−1 with a maximum energy density of 35.3 W h kg−1 and very long-term cycling stability (92.4% capacitance after 5000 cycles).

Manganese dioxide (MnO 2 )-decorated flower-like bismuth subcarbonate ((BiO) 2 CO 3 ) and calcined product (Bi 2 O 3 ) have been uniformly fabricated via a hydrothermal approach, and further investigated as the electrodes for supercapacitor. Both of the core-shell nanostructures displayed moderate capacities (196 F g −1 or 54.5 mAh g −1 for (BiO) 2 CO 3 @MnO 2 and 139.4 F g −1 or 38.7 mAh g −1 for Bi 2 O 3 @MnO 2 ) with superb cycling stability (125% for (BiO) 2 CO 3 @MnO 2 and 112% for Bi 2 O 3 @MnO 2 after 1000 cycles). The electrochemical properties of the electrode are strongly related to their high surface area, porous structure and good conductivity, which cannot only provide rich active sites but also shorten the ion transport pathways.

Birnessite MnO2-decorated hollow dandelion-like CuO architectures are synthesized by a simple hydrothermal method in which tetraoctylammonium bromide is used as surfactant. X-ray diffraction spectroscopy and field emission scanning electron microscopy are applied to investigate the structure and morphology of the as-synthesized dandelion-like CuO hollow sphere and CuO/MnO2 core-shell nanostructures. Furthermore, the electrochemical properties of CuO/MnO2 core-shell structures electrodes are elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 1 M Na2SO4 electrolyte. The result shows specific capacitance of 228 F g(-1) and a long-term cycling stability which retains 82.2 % of its initial capacitance even after 5000 cycles. Such a facile strategy to fabricate the hierarchical CuO/MnO2 core-shell structures with significantly improved functionalities opens up a novel avenue to design electrode materials on demand for high-performance supercapacitor applications.

Flower-like MnO2 decorated activated multihole carbon (AMC) was fabricated by a simple but effective strategy. Such unique MnO2@AMC nanocomposite exhibited the optimized pseudocapacitance performance, revealing a specific capacitance (297.8 F g−1) with excellent rate ability. An asymmetric supercapacitor with nanocomposite as the positive electrode and activated graphene (AG) as the negative electrode yielded an energy density of 18.04 W h kg−1 and a maximum power density of 8.97 kW kg−1. And thus, this facile synthetic strategy could be useful to design high-performance electrode for supercapacitors.

Colloidal mesoporous carbon (MC) supported MnO 2 nanocomposites have been synthesized via a facile and cost-effective strategy at room temperature. The structure and morphology of as-prepared nanocomposites are characterized by X-ray diffraction (XRD), Thermogravimetric analyzer (TGA), nitrogen adsorption, focused ion beam scanning electron microscopy (FIB/SEM) and high-resolution transmission electron microscopy (HRTEM). The as-obtained three-dimensional architecture can be well controlled by tailoring preparative parameters (e.g., the ratio of KMnO 4 and MC) and applied as supercapacitor electrodes. Cycle voltammetric (CV) and galvanostatic charge–discharge (GC) measurements present MC–MnO 2 composites exhibit the optimized pseudocapacitance performance (270.5 F g −1 ) with newfangled cycling stability, and ideal rate capability owning to rational design of the novel nanostructures. In principle, these findings exhibit potential in developing long cycling and quick-charge/slow-discharge supercapacitors for practical applications.

MnO 2 @colloid carbon spheres nanocomposites with tunable interior architecture have been synthesized by a facile and cost-effective strategy at room temperature. The structure and morphology of as-prepared nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption, focused ion beam scanning electron microscopy (FIB/SEM) and high-resolution transmission electron microscopy (HRTEM). The as-obtained composites exhibited a three-dimensional architecture with core–shell, yolk–shell and hollow interior structure. Furthermore, the electrochemical properties of composites were evaluated by cycle voltammetric (CV) and galvanostatic charge–discharge measurements. The yolk–shell structure exhibited the optimized pseudocapacitance performance, revealing a specific capacitance (273 F g −1 ) with a good rate and cycling stability, owing to its unique structure and the poor crystallinity of MnO 2 nanofilms. Therefore, this facile synthetic strategy could be useful to design and synthesis of tunable nanostructures with enhanced supercapacitor behavior.

In this work, we report a novel self-assembly of zero-dimensional (0D) MnO 2 nanoparticles into three-dimensional (3D) dendrite MnOOH nanostructures via the hydrothermal method without any template or surfactant. Through characterization techniques including field emission scanning electron microscopy (FESEM) and high-resolution-transmission electron microscopy (HRTEM), we found that the morphologies of obtained 3D dendrite MnOOH nanostructures could be controlled via fine tuning process temperature, amount of MnO 2 nanoparticles and solution media. The results also demonstrated that the weak acid hydrothermal solution and high temperature favored the hydrothermal growth of uniform 3D dendrite MnOOH nanostructures. Further evidence of time-dependent experiments revealed that oriented attachment and structure defects played an important role in the formation of such dendrite MnOOH nanorod. In principles, these findings could be useful for other metal oxides to fabricate their novel nanostructures for electrochemical electrodes.

Two kinds of novel CeO2@MnO2 nanostructures have been synthesized via a self-assembly strategy. The as-prepared CeO2 nanowire@MnO2 nanostructures exhibited unprecedented pseudocapacitance performance (255 F g(-1)) with outstanding rate capability. A new mechanism based on the synergistic effect between CeO2 and MnO2 was proposed to interpret this phenomenon. When assembled as an asymmetric supercapacitor, an energy density of 27.5 W h kg(-1) with a maximum power density of 1.6 kW kg(-1) was achieved for CeO2 nanowire@MnO2 nanostructures.

Because of the great breakthroughs of self-healing materials in the past decade, endowing devices with self-healing ability has emerged as a particularly promising route to effectively enhance the device durability and functionality. This article summarizes recent advances in self-healing materials developed for energy harvesting and storage devices (e.g., nanogenerators, solar cells, supercapacitors, and lithium-ion batteries) over the past decade. This review first introduces the main self-healing mechanisms among different materials including insulators, electrical conductors, semiconductors, and ionic conductors. Then, the basic concepts, fabrication techniques, and healing performances of the newly developed self-healing energy harvesting (nanogenerators and solar cells) and storage (supercapacitors and lithium-ion batteries) devices are described in detail. Finally, the existing challenges and promising solutions of self-healing materials and devices are discussed.

Herein, Ni(OH)2 on carbon sphere nanostructure together with its derivatives, including NiO on carbon sphere, yolk–shell structure of NiO on carbon sphere and hollow NiO, were prepared with precise control and then applied as supercapacitors. Among them, NiO on carbon sphere exhibits a high specific capacitance (270.4[Formula: see text]F g[Formula: see text] at 0.5[Formula: see text]A g[Formula: see text]), excellent rate performance (77.6% retention with 20-time current density increase) and good cycling stability (75.9% retention after 2000 cycles). The results indicate that carbon sphere plays a significant role in enhancing the electrical conductivity and electronic transportation process, ensuring the synergistic effects between carbon sphere and NiO shell.

In this work, an ultrafast and facile method is developed to synthesize Au(I)-dodecanethiolate nanotubes (Au(I)NTs) with the assistance of glycyl-glycyl-glycine (G-G-G). Transmission electron microscopy (TEM) images reveal that the as-prepared Au(I)NTs can be obtained in a 2-h reaction instead of a previous 24-h reaction and are uniform with a hollow structure and smooth surface by virtue of the G-G-G peptide tubular template. According to structural analysis, a possible preparative mechanism is proposed that the G-G-G peptide could help to curl into tube-like morphology in alkaline situation spontaneously to accelerate the formation of Au(I)NTs. Meanwhile, PVDF-stabilized Au(I)NT-modified glassy carbon electrodes present their promising potential for Hg(2+) detection.