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A nest-like N-doped hierarchical porous active carbon (N-HAC) with higher specific surface area is achieved successfully by melamine cyanurate (MCA) sacrifice template molding and assistant chemical activation of NH4Cl and CaCl2. The results testify that the nest-like hierarchical porous character of N-HAC can form an interconnecting structure and introduce plenty of supercapacitor reactive sites, which can facilitate the ion diffusion/migration among the material, while nitrogen doping in N-HAC can change the charge distribution of N-HAC and then promote the electron transfer. Attributing to the synergistic effect of the hierarchical porous structure and nitrogen doping, N-HAC800 displays the highest specific capacitance (284.6 F g−1 at 1 A g−1 and 183.1 F g−1 even at 20 A g−1) and superior cycle stability (80.4% after 5000 cycles at 100 mV s−1). This study results prove that the N-doped hierarchical porous active carbon is a promising material for energy storage application in the future.

NiCo2O4 has been proved to be a promising electrochemical material. In this work, a hollow NiCo2O4 material with an urchin-like structure is constructed by a self-template of Ni–Co complex compound based on the Ostwald ripening mechanism. During the thermal annealing in air, the residual carbon from the organic ligands of the Ni–Co complex compound leads to the generation of oxygen vacancies in urchin-like NiCo2O4. The as-obtained hollow NiCo2O4 (H-NiCo2O4-12) material manifests admirable specific capacitance of 886 F g−1 at 1 A g−1 and preserves 80% of capacitance retention after 5000 cycles. Moreover, the assembled asymmetric supercapacitor of H-NiCo2O4-12//AC delivers an energy density of 33.4 W h kg−1 at 747.7 W kg−1 and a high coulombic efficiency of about 95%. The improved supercapacitive performance of H-NiCo2O4-12 is attributed to its synergistic effect of hollow structure and oxygen vacancies. The hollow urchin-like structure of NiCo2O4 can buffer the volume expansion, expose abundant reaction active sites, and favor the transport of ions; while oxygen vacancies can adjust the electronic structure of NiCo2O4, which can favor the transfer of electrons. This work may throw some light on designing a virtue supercapacitor electrode material with hollow nanoporous morphology.

A 3D cross-network Co3O4–xNx nanostructure is obtained from the cobalt–alanine complex (Co(C3H5O2N)2) by amino acid self-assembly and subsequent pyrolysis. In this process, Co(C3H5O2N)2 forms a 2D ...

Single-atom Ag-decorated MnO2 hollow microspheres (Ag-MnO2 HMSs) with oxygen vacancies are successfully fabricated via a self-template strategy and redox etching method. The transmission electron m...

Three-dimensional N/S co-doped succulent-like hierarchical carbon (3D NS-SHC) is synthesized by carbonization of a supramolecular cluster. In this supramolecular process, potassium citrate can act as a reliable carbon source, while the thiourea as a N/S source and then, two molecules gradually tend to generate a giant “all-in-one” precursor via hydrogen bonding verified by Independent Gradient Model (IGM) calculation. TEM and SEM images show the N/S co-doped carbon holds a novel 3D succulent-like hierarchical structure. For NS-SHC-8:8 sample, element mapping images display the uniform N/S atoms distribution. These distinct features can be related to the supramolecular polymerization which promotes in-situ N/S co-doping homogenously and conduces to build 3D structure. Typically, NS-SHC-8:8 electrode exhibits prominent specific capacitance (258.5 F g−1 at 0.5 A g−1) and excellent cycle stability (94.4% after 20000 cycles) in three-electrode system. Furthermore, an assembled quasi-solid state symmetric supercapacitor delivers good energy density (10.2 Wh kg−1 at 250 W kg−1) and steady cycle endurance (85.1% after 10000 cycles). These eximious behaviors of NS-SHC-8:8 are mainly attributed to (1) the uniform N/S atoms distribution and their synergistic effect, which brings extra Faradaic reaction to higher specific capacitance, (2) the charming 3D succulent-like hierarchical structure, which serves as a multifunctional reservoir that can accommodate the ion/charge and facilitate their migration to further promote the electrochemical performance. Above mentions suggest that this uniformly heteroatom-modified carbon material produced by supramolecular technique is promising for high-performance energy storage devices.

Inspired by supermolecular self-assembly strategy, the N, P co-doped reduced graphene oxide (NP-rGO) material is fabricated by heat treatment from the supermolecular system of GO/MP (melamine and p...

Inspired by the supramolcular chemistry assembly theory, carbon-coated MnO2 nanospheres (C@MnO2) were successfully synthesized by a two-step method. First, the supramolecular solution was prepared by β-cyclodextrin inclusion of manganese acetate, which was then treated by a hydrothermal reaction and the calcination in the following. The scan electron microscopy (SEM) and transmission electron microscopy (TEM) images present that the C@MnO2 composites have the nanosphere morphology, in which the carbon layer originated from the carbonization of β-cyclodextrin was uniformly coated on the MnO2 nanoparticles. The electrochemical characteristics were examined by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results demonstrated that C@MnO2 exhibited high specific capacitance (396.4 F g−1 at 2 A g−1) and good rate capability. In addition, 84.1% of the initial capacitance was maintained after 10000 cycles, indicating the excellent electrochemical stability. The superior electrochemical performance of the C@MnO2 was attributed to the outstanding uniform nanospheres structure that facilitates ion mobility and the synergistic effect between conductive carbon and pseudocapacitive MnO2. Hence, C@MnO2 can be a potential candidate material for the applications in supercapacitors.

A new type of sandwiched nanosheets 3D MoS2/C@RGO is synthesized by supramolecular self-assembly methods, as a novel and excellence electrode material. The surface characterization techniques show that the sandwiched 3D MoS2/C@RGO possesses rich porosity and large specific area, which is convenient for electrolyte ion transportation and beneficial for the improved electrical conductivity. An outstanding specific capacitance of the prepared MoS2/C@RGO of 340.0 F/g at 1 A g−1 is achieved with an excellent cycle stability of 90% after 1000 cycles at the scanning rate of 40 mV/s. The sandwiched 3D MoS2/C@RGO is suggested to be an ideal candidate for supercapacitors.

Supramolecular in-situ self-assembly is achieved to prepare carbon nanodots decorated graphene/polyaniline composites by adding β-cyclodextrin (β-CD) as the bonding agent in this work. With its unique structure, β-CD can form a supramolecular system with graphene oxide layers, generating the inclusion compound with aniline monomers, which makes the in-situ polymerization of polyaniline on the surface of graphene oxide. In the hydrothermal process, β-CD is carbonized to carbon nanodots anchored on the surface of reduced graphene oxide. The scanning electron microscopy (SEM) images show that the prepared reduced graphene oxide/carbon nanodots/polyaniline (RGO@CN/PANI) nanocomposites exhibit the micro morphology of a regular polyaniline particle array on the surface of graphene layers. The electrochemical tests demonstrate that the RGO@CN/PANI nanocomposites exhibit high specific capacitance (up to 871.8 F g−1 at 0.2A g−1), low charge transfer resistance (Rct), and presentable cycling performance (72% capacitance retention after 10000 cycles), indicating the satisfied performance for supercapacitors. The promising performance of RGO@CN/PANI can be attributed to the synergistic effect of RGO, carbon nanodots and PANI, as well as the regular microstructure in which the effective reaction area of polyaniline is increased and the rapid ion transport channel is provided.

In this work, carbon nanoparticle-anchored MoS2 nanosheets are synthesized by a supramolecular self-assembly method, through which β-cyclodextrins (β-CDs) are combined with l -cysteine by the hydrogen bond and the electrostatic interaction in the aqueous solution, which are then carbonized to carbon nanoparticles and anchored on the surface of MoS2 nanosheets during the hydrothermal process. The carbon nanoparticles anchored on MoS2 nanosheets effectively inhibit the aggregation and restacking of MoS2, and then enhance the electrical conductivity of the composite. The superior electrochemical performance is exhibited through cyclic voltammetry and galvanostatic charge-discharge, including a high specific capacitance of 394.2 F g−1 at the scan rate of 5 mV s−1 and a high rate retention ratio of 63.3% when the scan rate increases from 5 to 200 mV s−1. The remarkable performance is mainly attributed to the better electrical conductivity and the higher rates of electron migration and ion transport, making the carbon nanoparticle-anchored MoS2 nanosheets a potential candidate material for advanced energy storage systems.

NiCo2O4 has been proved to have promising electrochemical performance. In this work, a new type of hollow urchin-like NiCo2O4 material is constructed by a self-template of Ni-Co complex compound based on the Ostwald ripening mechanism. During the thermal annealing in air, the residual carbon from the organic ligands of Ni-Co complex compound leads to the generation of oxygen vacancies in urchin-like NiCo2O4. The as-obtained hollow NiCo2O4 (H-NiCo2O4-12) material manifests admirable specific capacitance of 886 Fg-1 at 1Ag-1, and preserves 80% of capacitance retention after 5000 cycles. Meanwhile, the assembled asymmetric supercapacitor of H-NiCo2O4-12//AC delivers an energy density of 33.4 Wh g-1 at 747.7 W kg-1. The improved supercapacitive performance of H-NiCo2O4-12 should attribute to its synergistic effect of hollow structure and oxygen vacancies. The hollow urchin-like structure of NiCo2O4 can buffer the volume expansion, expose abundant reaction active sites and favor the transport of ions; while oxygen vacancies can adjust the electronic structure of NiCo2O4 which can favor the transfer of electrons. This work may throw some light on designing a virtue supercapacitor electrode material with hollow nanoporous morphology.

Transition metal phosphides (TMPs) have attracted great interest owing to the metallic properties and high specific capacities. Here, we designed hollow NiCoP nanocubes with increased specific surface area using a Ni-Co Prussian blue analogue as a self-template and NH3·H2O as an etching agent. During the synthesis, both carbonization and phosphorization are completed in one step. The obtained hollow structure alleviates the volume variation of electrode material during reversible electrochemical reaction. Meanwhile, the residual carbon distributed uniformly in NiCoP at the molecular level, resulting in a high conductivity. DFT calculations further reveal that the electrical conductivity of NiCoP is superior to those of monometallic phosphide and metal oxide. Therefore, the optimized NiCoP-4–500 displays a high specific capacity (1590 F g−1 at 1 A g−1) and outstanding cycling stability (78.2% retention after 12,000 cycles). Moreover, a prepared hybrid supercapacitor device delivers an energy density of 38.4 W h kg−1 with a power density of 799.9 W kg−1 at 1 A g−1. The results indicate that the obtained high-performance TMPs with hollow structures have an application potential for energy storage devices.

We report a supramolecular strategy to fabricate high-doping-leveled (10.5 at.%) porous nitrogen-doped reduced graphene oxide (P-NrGO) with outstanding electrochemical properties as electrode material for supercapacitors. The introduced supramolecular polymers melamine cyanurate (MC) acts a barrier to prevent the graphene sheets from restacking, and meanwhile functions as a soft template to create porous structure as well as nitrogen source for in-situ N-doping. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images show that the P-NrGO exhibits wrinkled and loose-packed thin layer structure with a large number of pores. X-ray photoelectron spectrometer (XPS) spectra demonstrate that pyridine and pyrrole-N was the main nitrogen bonding states, which were favorable for the improvements of supercapacitive performance. Attributed to the synergistic effects of the porous structure and the N-doping, the P-NrGO1 exhibits an increase of 56.5% in the specific capacitance (335 F g−1) when compared with the rGO (214 F g−1). In addition, the capacitance retention ratio reaches 94.3% after 10000 cycles, indicating the excellent electrochemical stability. The present work benefits the large-scale production of N-doped graphene oxide for high-performance supercapacitors.

A manganese dioxide (MnO2) film is electrodeposited onto a gold-coated quartz crystal electrode by a galvanostatic method. The scanning electron microscopy (SEM) image shows that the electrodeposited MnO2 film consists of nanorods with diameters of 15–20 nm. The cyclic voltammetric (CV) and electrochemical quartz crystal microbalance (EQCM) results demonstrate that the MnO2 electrodes exhibit similar specific capacitance (SC) and mass-to-charge ratios (MCR) in those electrolytes that contain the same cation but different anions. However, the SC and MCR are different in those electrolytes that contain the same anion but different cations. The SC of MnO2 electrodes increases with a decrease of the cationic radius and an increase of the cationic charge. The smaller the cationic radius, the smaller the deviation of the MCR from the equivalent weight (EW) of the cation. The results illustrate that the pseudocapacitive charge storage mechanism of MnO2 involves the cation in the electrolyte and its intercalation/deintercalation, which are affected by the charge number and the cationic radius. This work offers a theoretical basis for selecting suitable electrolytes to couple MnO2-based electrodes in supercapacitors.

Delicately engineering nano-architecture and electronic structure can assist in constructing the high-performance electrode materials for high-energy supercapacitor. Herein, a hollow nanocage is in-situ introduced into bimetallic phosphide-based materials via a green self-template strategy at room temperature. The homogeneous hollow configuration that N-doped carbon confined NiCoP nanoparticles hybrid nanocages (NiCoP/NC) is harvested via elaborately manipulating the physicochemical properties at the molecular level. This well-defined hollow geometry ensures the convenient electrolyte access for electroactive sites, thus facilitating the electrochemical activities. X-ray photoelectron spectroscopy reveals the electronic interaction among Ni, Co and P elements, which can induce an appropriate electric-field environment favors for the charge-carriers immigration. Density-functional-theory simulations indicate the increased electronic states of d-orbital around the Fermi level, which benefit for lower OH– adsorption energies (-3.80 eV), therefore resulting the faster electrochemical dynamics. Accordingly, as-prepared NiCoP/NC electrode achieves superb rate-capability (1127 and 873F g−1 at 1 and 16 A g−1, respectively) and long-term durability (75.5% retention after 8000 cycles). Furthermore, a hybrid supercapacitor based on NiCoP/NC cathode demonstrates an ultra-high energy density (52.5 Wh kg−1), outperforming similar hybrid devices. Our studies successfully give an insight into the relationship between nano-morphology, electronic modulation and electrochemical performance, which can provide some guidance for garnering a desirable electrode material.

Transition metal sulfides (TMS) are of great interest as promising battery-type electrode materials, however, the poor conductivity and sluggish reaction kinetics seriously limit their application. Here, we designed a hollow structured precursor of Ni-based metal-organic frameworks (Ni-MOFs) via Ostwald ripening mechanism. Based on this unique precursor, a hollow carbon-coated nickel sulfide nanocrystal (H-NiS1-X/C) with sulfur vacancies was further synthesized through an ion exchange strategy and thermal annealing. By optimizing the content of sulfur source, the sample with appropriate S-vacancies (H-NiS1-X/C-50) was developed. Benefiting from its hollow structure and S-vacancies, this H-NiS1-X/C-50 displayed a high reversible specific capacity (1728 F g−1, 1 A g−1), stable cycling (72% capacity retention over 8000 cycles) and superior rate capability. After assembling the asymmetric supercapacitor, a high energy density of 36.88 Wh kg−1 was achieved. Experimental results and DFT calculations demonstrate that introducing S-vacancies builds an embedded electric field and produces lattice distortions in H-NiS1-X/C, thus enhancing the conductivity of the material. Our strategy also provides a facile way to construct high-performance TMS with unique hollow structure and S-vacancies for developing advanced energy storage devices.

Nanotunnels inserted hierarchical-porous carbon (NTHPC) have been synthesized successfully via a MnO2-introduced-tunnels strategy using MnO2 nanorods as template, with agar and β-cyclodextrin serving as hybrid carbon precursors. The as-prepared NTHPC possesses a higher specific surface area of 1441 m2 g−1, a moderate pore volume of 1.23 cm3 g−1, and the hierarchical-porous structure with inserted nanotunnels. Transmission electron microscopy has demonstrated that the width of the nanotunnels is between 20 and 100 nm, and the length ranges from 0.2 to 2.0 μm. Tests in a three-electrode system showed that the NTHPC has high specific capacitance (253.1 F g−1, 5 mV s−1), as well as good rate capability (203.3 F g−1, 100 mV s−1) and excellent cycling stability. More importantly, an assembled symmetric supercapacitor with NTHPC electrodes delivered an outstanding energy density of up to 34.9 Wh kg−1 with power density of 755.2 W kg−1. The remarkable electrochemical performance of the NTHPC is ascribed to the nanotunnels, which act as ion reservoirs and liquid transfer channels that can increase the ion transport rate and shorten the ion transfer distance. This study provides a novel method for the preparation of high-performance hierarchical-porous carbon and guidance for its potential applications in supercapacitors.

Graphene oxide/CoAl-layered double hydroxide (GO/CoAl-LDHs) composites were successfully prepared by a face-to-face electrostatic self-assembly method. Positively charged colloidal CoAl-LDHs nanosheets (CoAl-LDH-NS) and negatively charged colloidal GO nanosheets were uniformly mixed; then CoAl-LDH-NS were assembled on GO nanosheets via electrostatic attraction to prepare GO/CoAl-LDHs composites. The GO/CoAl-LDHs composites were then transformed to the reduced graphene oxide/CoAl-layered double hydroxide (RGO/CoAl-LDHs) composites with a hydrothermal method. The results showed that the content of RGO has a remarkable influence on the capacitive properties of composites. Among the composites with different RGO content, the RGO/CoAl-LDHs composite containing 12.0 wt% RGO displayed a maximum specific capacitance of 825 F g −1 at low current density of 1 A g −1 , while that of pure CoAl-LDHs was 552 F g −1 . The capacitance retention of the RGO/CoAl-LDHs composite from 1 A g −1 to 8 A g −1 is found to be 62.3%, whereas that of pure CoAl-LDHs is only 31.9%. Face-to-face self-assembling between positively charged CoAl-LDH-NS and negatively charged GO nanosheets can effectively reduce the self-agglomeration of GO nanosheets and avoid CoAl-LDH-NS stacking together, which lead to improvement of the capacitive performance.

A porous graphene layers with a three-dimensional structure (3DG) was prepared via a gas foaming method based on a polymeric predecessor. This intimately interconnected 3DG structure not only significantly increases the specific surface area but also provides more channels to facilitate electron transport. In addition, 3D N-doped (3DNG) layers materials were synthesized using melamine as a nitrogen source. The nitrogen content in the 3DNG layers significantly influenced the electrochemical performance. The sample denoted as 3DNG-2 exhibited a specific capacitance of 335.2 F g −1 at a current density of 1 A g −1 in a three-electrode system. Additionally, 3DNG-2 exhibited excellent electrochemical performance in aqueous and organic electrolytes using a two-electrode symmetric cell. An energy density of 58.1 Wh kg −1 at a power density of 2500 W kg −1 was achieved, which is approximately 3 times that (19.6 Wh kg −1 ) in an aqueous electrolyte in a two-electrode system. After 1000 cycles, the capacity retention in aqueous electrolyte was more than 99.0%, and this retention in organic electrolytes was more than 89.4%, which demonstrated its excellent cycle stability. This performance makes 3DNG-2 a promising candidate as an electrode material in high-power and high-energy supercapacitor applications.

Delicate design of nanostructured electrode materials with built-in electric field effect can make them have satisfactory electrochemical performance through the synergistic effects. Here, we prepare an advanced electrode material, a hollow N-doped carbon@O-vacancies NiCo2O4 nanocage (HNC@NiCo2O4), in which NiCo2O4 nanosheets are homogeneously grown on the N-doped carbon frame. This unique hollow nanocage can increase the contact-area between the material and electrolyte, further improving the electrochemical activities. Density functional theory simulations reveal that O-vacancies in NiCo2O4 can narrow the bandgap, which may contribute to the charge transfer dynamic of HNC@NiCo2O4 series. Meanwhile, N-doping can change the carbon-skeleton states density, thereby improving the electron-accepting capabilities for nearby NiCo2O4, and thus elevating the capacitive behaviors. Accordingly, a built-in electric field is in-situ constructed via the O-vacancies and N-doping. Due to the synergistic effect of a hollow structure and built-in electric field, as-fabricated HNC@NiCo2O4-0.45 electrode delivers noticeable specific-capacitance (966.2 F g−1@1 A g−1) and long-term endurance. Impressively, the HNC@NiCo2O4-0.45 electrode is employed to assemble a hybrid supercapacitor with the active carbon anode, which behaves a high energy-density (41.9 Wh kg−1 at 750.4 W kg−1). Above results validate that the electric field modulation and nanostructure construction are important tactics to design a high-performance supercapacitor electrode.

Adding redox-active species into the electrolyte can supply extra capacitance to the carbon-based supercapacitors. However, the devices may suffer from serious self-discharge caused by the shuttling and intermixing of charged active species between the electrodes. Confining these active species in a solid-state electrode material is an effective strategy to avoid this. Inspired by this, we fabricate a three-dimensional reduced graphene oxide confined methylene blue composite via a supramolecular strategy, combined with a hydrothermal reduction and a freeze-drying process. Benefited from the porous and conductive structure of the product, the fast-reversible electrochemical reaction of methylene blue, and the spatial confinement effect of the methylene blue confined in reduced graphene oxide, the as-prepared product exhibits a high-rate capability (311 and 262 F g−1 at 1 and 20 A g−1, respectively) and an excellent cycle stability (96% capacitance retention after 10000 cycles) in a three-electrode system. Moreover, a solid-state symmetric supercapacitor device based on the as-prepared product delivers the maximum energy density of 8.2 Wh kg−1 and outstanding cycle stability. This supramolecular-induced confining active species in reduced graphene oxide strategy provides insight into the fabrication of other high-performance graphene-based pseudocapacitors.

Co3O4-based materials are regarded as superior electrode candidates in various energy storage devices due to their high theoretical capacity. Unfortunately, the poor electronic conductivity and huge volume expansion hamper their widespread applications. Therefore, nano-processing and introducing conductive matrix can view as the necessary methods to make Co3O4-based materials better for an advanced supercapacitor electrode. Herein, a dual-template nanocasting technique is proposed to design the ultrafine Co3O4 grains highly-dispersed on the reduced oxide graphene nanosheets (Co3O4/rGO-C), in which cetyltrimethyl ammonium bromide and silicate species are hired as the ideal soft and hard template, respectively. Co3O4 grains with size

The remarkable electrochemical performance of graphene-based materials has drawn a tremendous amount of attention for their application in supercapacitors. Inspired by supramolecular chemistry, the supramolecular hydrogel is prepared by linking β-cyclodextrin to graphene oxide (GO). The carbon nanoparticles-anchored graphene nanosheets are then assembled after the hydrothermal reduction and carbonization of the supramolecular hydrogels; here, the β-cyclodextrin is carbonized to carbon nanoparticles that are uniformly anchored on the graphene nanosheets. Transmission electron microscopy reveals that carbon nanoparticles with several nanometers are uniformly anchored on both sides of graphene nanosheets, and X-ray diffraction spectra demonstrate that the interlayer spacing of graphene is enlarged due to the anchored nanoparticles among the graphene nanosheets. The as-prepared carbon nanoparticles-anchored graphene nanosheets material (C/r-GO-1:3) possesses a high specific capacitance (310.8 F g–1, 0.5 A g–1...