High Capacitive Properties Research Articles

Solving Gravimetric-Volumetric Capacitive Paradox of 2D Materials through Dual-Functional Chemical Bonding-Induced Self-Constructing Graphene-MXene Monoliths.

High electrical conductivity and all-open microstructure characteristics intrinsically endow both graphene and MXenes with superior electrochemical energy storage capability. However, the above two-dimensional (2D) thicker electrodes (>20 μm) severely dilute their unique rapid electronic-ionic transferring characteristic, posing a paradox of high gravimetric and high volumetric capacitive properties due to massively excessive macropores or an unduly restacked issue. Herein, we elaborately construct novel monolithic NH2-graphene and Ti3C2Tx MXene (NG@MX) composites through dual-functional induced self-assembly with the help of both covalent and hydrogen bonding interactions. Notably, much thicker monolithic NG@MX electrodes (>90 μm) fabricated by a conventional roll-coating method without any further compaction treatment can simultaneously deliver two times gravimetric (gra.) and volumetric (vol.) performance than those of pure graphene (in vol.) or MXene (in gra.) materials. Moreover, monolithic NG@MX-based supercapacitors can remarkably present two times energy density as that of graphene and four times as MXene, respectively. Such greatly enhanced electrochemical properties are closely related to the appropriate equilibrium of the volumetric density and the open structure, which can effectively guarantee the rapid transfer of both electrons and ions in the thick monolithic NG@MX electrodes. Undoubtedly, dual-functional chemical bonding-induced self-constructing NG@MX monoliths efficiently solve the long-existing gra. and vol. capacitive paradox of the thicker 2D materials used in supercapacitors, which will guide the design of high-performance capacitive materials and promote their practical application in electrochemical energy storage.

Геохимическая роль метеорных вод как фактор формирования пустотного пространства коллекторов нефти и газа

The features of the chemical composition of formation waters of the Upper Permian, Lower and Middle Triassic aquifers within individual structures of the Malozemelsk-Kolguev monocline of the Timan-Pechora oil and gas bearing basin are examined. It is shown that the aquifers that, despite their remoteness from the recharge areas, had experienced repeated processes of dipping and uplifting of the territory, preserved the infiltration waters, but significantly transformed ones. To identify their genetic profile and determine the relationship with the processes of catagenetic changes, hydrochemical coefficients and indices of water saturation of calcium carbonate and calcium sulfate are calculated. It is established that the examined infiltration waters are characterized by high aggressiveness, dissolution ability, leaching and removal of main minerals. It is pointed out that the consequence of these processes is the formation of secondary void space and the creation of high capacitive and filtration properties of rocks. The universality of geochemical interaction between water and rocks in thermodynamically open geological systems is emphasized and it is confirmed by individual geological examples that the heterogeneity of the hydrochemical field can act as a cause of screening zones of oil and gas accumulation, as well as provide appropriate conditions for localization of hydrocarbon fluids.

Biomass-Derived Nitrogen-Doped Porous Carbons Activated by Magnesium Chloride as Ultrahigh-Performance Supercapacitors

Porous carbons with high capacitive properties derived from biomass have been increasingly studied for supercapacitor applications. In this work, we prepared N-doped porous carbon through a one-pot...

A MXene-based EDA-Ti3C2Tx intercalation compound with expanded interlayer spacing as high performance supercapacitor electrode material

Expanding the interlayer spacing of the Ti3C2Tx MXene structure is realized by intercalation of ethylenediamine (EDA), which is anchored on the surface of Ti3C2Tx sheets by one side amino groups with N–Ti coordination bonds. The EDA-Ti3C2Tx intercalation compound has a high specific surface area of 59.2 m2 g−1 with mainly mesopores. The EDA-Ti3C2Tx possesses the low charge transfer resistances of ∼0.32/0.28 Ω in 1/3 M H2SO4 aqueous electrolytes, respectively. A large specific capacitance of 486.2 F g−1 (1312.7 F cm−3) is obtained for EDA-Ti3C2Tx at a scan rate of 2 mV s−1 in 1 M H2SO4 electrolyte, showing its high capacitance property. A good specific capacitance of 249.4 F g−1 (673.4 F cm−3) is retained at larger scan rate of 100 mV s−1, indicating its significantly high rate capability. Higher specific capacitances of 563.3 (1520.9), 522.1 (1409.7), 485.1 (1309.8), 436.2 (1177.7), 356.2 (961.7) and 290.6 F g−1 (784.6 F cm−3) are achieved for EDA-Ti3C2Tx at the scan rates of 2, 5, 10, 20, 50 and 100 mV s−1, respectively, in 3 M H2SO4 electrolyte. The cyclic retention of EDA-Ti3C2Tx after 10,000 cycles reaches 89.7% at 10 A g−1 in 3 M H2SO4 electrolyte, showing the excellent cyclic stability.

The fabrication of hierarchically porous carbon-coated nickel oxide nanomaterials with enhanced electrochemical properties

In our current work, hierarchically porous carbon-coated nickel oxide nanoplates were successfully synthesized through Ni(OH)2 cladding with resorcinol and formaldehyde resin after subsequent carbonization process. The as-prepared NiO-coated carbon nanomaterials were examined, using TEM, XRD, Raman, XPS, TG and BET measurements. The optimized electrode (NiO/Ni@C-450 nanoplates) has regular hexagonal core–shell structure, uniform diameter and thickness. Owing to its porous core–shell structure, high specific surface area (457.03 m2 g−1) and high contents of Ni (6.43 at.%) and O (19.35 at.%) elements, NiO/Ni@C-450 electrode possesses the specific capacitance of 276.1 F/g at 0.5 A/g and good coulombic efficiency. Because the coated carbon layer enables to protect NiO structure and extends the cyclic life of electrode materials, the capacitance retention of NiO/Ni@C-450 electrode is 88.7% after 1000 cycles, which is much higher than that of NiO electrode. All these measured results demonstrate that the as-prepared NiO/Ni@C-450 nanoplate is supposed to be a promising material with easy preparation, high specific capacitance and good cyclic stability properties for potential applications in energy storage devices.

High performance Bi2O2CO3/rGO electrode material for asymmetric solid-state supercapacitor application

Bi2O2CO3 and reduced graphene (rGO) are considered as promising electrode materials for the applications of supercapacitor due to their high specific capacitance and high cycle property, respectively. However, the poor conductivity of Bi2O2CO3 and low specific capacitance of rGO have restricted their practical application. In this research, we have prepared a novel Bi2O2CO3/rGO composite electrode with a unique flower-like microstructure by a facile hydrothermal synthesis. The as-prepared Bi2O2CO3/rGO composite electrode exhibits a high capacitance of 667 Fg-1 at 1 Ag-1, which is attributed to the short pathways for rapid ionic diffusion provided by the flower-like microstructure and the addition of high-conductive rGO. Furthermore, the asymmetric solid supercapacitor (ASSC) was assembled by using the Bi2O2CO3/rGO and the N/S co-doped rGO electrode, which shows excellent capacitive performance with the capacitance of 68 Fg-1 at 1 Ag-1 and high energy density of 19.85 Wh kg−1 at power density of 1051 W kg−1. In addition, the device exhibits remarkable cycle stability of about 92.6% after 4000 cycles at a current density of 3 Ag-1. The results have provided an effective way for significant improving the capacitance of Bi2O2CO3 electrode and realizing its practical application in ASSC.

Conductive copper-based metal-organic framework nanowire arrays grown on graphene fibers for flexible all-solid-state supercapacitors

Abstract Graphene fiber-based electrodes have the promising potential to develop flexible supercapacitors because of their outstanding advantages such as small volume, lightweight, high mechanical flexibility and large-scale production. However, the low electrochemical performance severely blocks their practical application. In this study, integrating the conductive Cu3(2,3,6,7,10,11-hexahydroxytriphenylene)2 (Cu-MOF) nanowire arrays into the reduced graphene oxide (rGO) fibers significantly boosts the electrochemical performance. Inside the electrode structure, the 3D conductive Cu-MOF nanowire array layers with an open porous structure and large surface area significantly enlarge the contact area between electrode materials and electrolytes, shorten the electrolyte diffusion path and offer high electrical conductivity. This composite fiber electrode shows high capacitance property of 44.6 mF cm−2 at a scan rate of 5 mV s−1, good cycling stability and excellent mechanical flexibility. The assembled all-solid-state symmetric fiber supercapacitor exhibits an energy density of 0.51 μW h cm−2 at a power density of 2.54 μW cm−2. The promising electrochemical performance makes the rGO/Cu-MOF fiber electrode have a great future in the flexible supercapacitor field.

Alteration in capacitive performance of Sn-decorated MnO2 with different crystal structure: An investigation towards the development of high-performance supercapacitor electrode materials

Hetero atom doped-MnO2 is considered as the promising supercapacitor electrode material due to its high capacitance properties. Depending on the way of MnO6 octahedra interlinking, it can form different types of crystal structure (α, β, γ, δ). The capacitance properties of MnO2 depend on the cation intercalation/de-intercalation and the type of crystallographic structures. This study emphasises the phase and interlayer spacing control synthesis of Sn-incorporated MnO2 (α, β, γ, δ crystal form) through a facile one-pot hydrothermal technique by using verities of starting materials. The specific capacitance of MnO2 depends on different crystal structure and the effect of hetero atom introduction. Sn-decorated β-MnO2 (β-SM) exhibits high specific capacitance of ~1957 F g−1 at 2 A g−1 in a three-electrode system. An asymmetric supercapacitor (ASC) is configured by intriguing high capacity β-SM as positive electrode and thermally reduced graphene oxide (TRGO) as negative electrode in the potential window of 1.4 V. The ASC delivers the maximum specific energy of ~29.79 W h kg−1 with a specific power of ~1625.31 W kg−1 at the current density of 2 A g−1. The ASC shows good cycle life of ~94% retention in specific capacitance after 10,000 charge-discharge cycles at 15 A g−1 current density.

Highly flexible and mechanically strong polyaniline nanostructure @ aramid nanofiber films for free-standing supercapacitor electrodes

A key challenge for the fabrication of flexible electrochemical capacitors is to prepare robust electrode materials with excellent integration of high specific capacitances and superior mechanical properties. Aramid nanofibers (ANFs) are emerging candidates for constructing flexible electrode materials due to their superior mechanical properties. However, the present ANF based electrode materials are generally designed by mixing ANFs with electrochemically active components, which results in an unfavorable trade-off in mechanical and electrochemical properties. In this work, we reported flexible, mechanically strong, and free-standing supercapacitor electrodes based on polyaniline (PANI) nanostructure functionalized ANF films for the first time. The flexible PANI@ANF film electrodes achieved an efficient combination of mechanical and electrochemical performance in a single platform with a specific capacitance of 441.0 F g-1 at a current density of 1 A g-1 and a tensile strength of 233.3 MPa, respectively. This kind of free-standing electrode material may have great potential in the development of flexible energy-storage devices. Furthermore, we anticipate that this study may provide insight into the functionalization of aramid nanofiber-based materials for structural energy and power systems with high mechanical performance.

From high-yield Ti3AlCN ceramics to high-quality Ti3CNTx MXenes through eliminating Al segregation

Ti3CNTx MXenes with unique electrical conductivity can be widely applied for supercapacitors and electromagnetic shielding. However, its relatively low-yield quaternary nitrogen-containing Ti3AlCN ceramics precursor (less than 50%), due to the inevitable Al segregation during the synthesizing process, significantly hindered its widely commercial applications. Herein, we employed the controllable AlN-oversaturation precursor strategy to precisely tune the phase transition point of quaternary Ti3AlCN ceramics to obtain high-yield Ti3AlCN precursor for the purpose of high conductivity Ti3CNTx MXenes. Combined energy dispersive X-ray spectrometer (XRD) with X-ray photoelectron spectroscopy (XPS) characterizations, the yield of the quaternary nitrogen-containing Ti3AlCN ceramics was evidently proved to be up to 70%, which is 1.4 times than that of previously reported works. Such relatively high-yield quaternary Ti3AlCN is mainly ascribed to the elimination of Al segregation. Based on it, we further developed accordion-like two-dimensional (2D) MXene via hydrofluoric acid etch and vacuum freeze-dry. This novel accordion-like 2D Ti3CNTx MXene possesses high electrochemical capacitive properties (209 F/g). Therefore, this controllable AlN-oversaturation precursor strategy will pave a way to exploit costly high-yield MAX ceramics precursor for high conductivity MXenes and also play a powerful role in promoting their practical applications including electrical and magnetic engineering fields.

(Invited) Multifunctional Mxene-Based Fibres

Yarn-shaped supercapacitors (YSCs) once integrated into fabrics provide promising energy storage solutions to the increasing demand of wearable and portable electronics. In such device format, however, it is a challenge to achieve outstanding electrochemical performance without compromising flexibility. Metal carbides or carbonitrides called “MXene” has presented a distinct combination of very high conductivity (~10,000 S cm-1), volumetric capacitance (~1,500 F cm-3), and hydrophilic properties. To date, however, MXene-based fibers or yarns that can be used for wearable applications have been relatively unexplored. Their small sheet size (<2 µm) and weak inter-sheet interactions have made it challenging to fabricate MXene-based fibers or yarns. Here, we present strategies to achieve fibers or yarns from Ti3C2 MXene. Our works include high-performance yarn supercapacitors fabricated by coating MXene on conductive carbon fiber bundles. This device showed length capacitance of ~132 mF cm-1 higher than the literature reports (typically lower than 100 mF cm-1) even at low mass loading of 2 mg cm-1. We also used wet-spinning technique by taking advantage of the templating role of liquid crystalline (LC) graphene oxide (GO) to produce fibres with high MXene content of ~88 wt. %. These fibres demonstrate excellent flexibility and a high volumetric capacitance of ~341 F cm-3. We also employed biscrolling technique to scroll MXene nanosheets within carbon nanotube helical corridors. Here, the yarns are predominantly MXene containing up to ~98 wt.% MXene yielding an areal capacitance as high as ~3,188 mF cm−2, which exceeds the previously recorded performance for any fiber or yarn supercapacitor electrode. The supercapacitor prototype in asymmetric configuration reached a maximum energy and power densities of ~61.6 mWh cm–3 and ~5428 mW cm–3 respectively. We show that the MXene-based fibers and yarns are useful for powering small electronic devices when knitted or woven into a textile. Our works have introduced a new class of fibers that can be excellent candidates for integration within textile-based electronics and wearable devices.

Few-layered mesoporous graphitic carbon nitride: a graphene analogue with high capacitance properties

Exfoliation of multi-layered MGCN into few-layered MGCN results in 50% enhancement in the specific capacitance value.

Wet-spun poly(ionic liquid)-graphene hybrid fibers for high performance all-solid-state flexible supercapacitors

Abstract It is crucial to develop flexible and wearable electronic devices that have attracted tremendous interest due to their merits on compactness, flexibility and high capacitive properties. Herein we report the continuously ordered macroscopic poly(ionic liquid)-graphene fibers by wet spinning method via liquid crystal assembly for supercapacitor application. The fabricated all-solid-state supercapacitors exhibited a high areal capacitance (268.2 mF cm−2) and volumetric capacitance (204.6 F cm−3) with an outstanding areal energy density (9.31 µWh cm−2) and volumetric energy density (8.28 mWh cm−3). The fiber supercapacitors demonstrated exceptional cycle life for straight electrodes of about 10,000 cycles (94.2% capacitance retention) and flexibility at different angles (0°, 45°, 90°, 180°) along with a good flexible cycling stability after 6000 cycles (92.7% capacitance retention). To date, such a novel poly (ionic liquid)-graphene fiber supercapacitors would be a new platform in real-time flexible electronics.

Multifunctional CuO Nanosheets for High-Performance Supercapacitor Electrodes with Enhanced Photocatalytic Activity

This paper reports the facile hydrothermal approach to synthesize porous CuO nanosheets. Their crystalline phase, metallic vibrations, topography, morphology, pore size distribution and magnetic behavior has been studied in detail. Magnetic properties of nanosheets were studied at 300 K using vibrating sample magnetometer which indicates the superparamagnetic behavior with saturation magnetization of 2.46 emu g−1 for as prepared 2D nanostructures. The electrochemical spectroscopy of these sheets reveals that as prepared sheets have a specific capacitance of 1057 F g−1 at a current density of 2 A g−1 which is retained up to 93% even after 4000 cycles. Furthermore, photocatalytic activity along with electrochemical properties of the as-obtained nanostructures were studied for various organic dyes. The high value of saturation magnetization, high specific capacitance and better dye degradation properties of the developed CuO nanosheets make the developed materials good for application in energy storage devices, astonishing electrode material and photocatalyst for degradation of organic dyes in visible light.

Biowaste-Derived Hierarchical Porous Carbon Nanosheets for Ultrahigh Power Density Supercapacitors.

Low-cost activated carbons with high capacitive properties remain desirable for supercapacitor applications. Herein, a three-dimensional scaffolding framework of porous carbon nanosheets (PCNSs) has been produced from a typical biowaste, namely, ground cherry calyces, the specific composition and natural structures of which have contributed to the PCNSs having a very large specific surface area of 1612 m2 g-1 , a hierarchical pore size distribution, a turbostratic carbon structure with a high degree graphitization, and about 10 % oxygen and nitrogen heteroatoms. A high specific capacitance of 350 F g-1 at 0.1 A g-1 has been achieved in a two-electrode system with 6 m KOH; this value is among the highest specific capacitance of biomass-derived carbon materials. More inspiringly, a high energy density of 22.8 Wh kg-1 at a power density of 198.8 W kg-1 can be obtained with 1 m aqueous solution of Li2 SO4 , and an ultrahigh energy density of 81.4 Wh kg-1 at a power density of 446.3 W kg-1 is realized with 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte.

Yolk Type Asymmetric Ag–Cu2O Hybrid Nanoparticles on Graphene Substrate as Efficient Electrode Material for Hybrid Supercapacitors

Abstract Yolk type asymmetric Ag–Cu2O hybrid nanostructures are in situ synthesized on reduced graphene oxide (RGO) sheets for the first time under one pot hydrothermal mild reaction condition. The co-reduction method provides a facile and straight forward approach to metal/metal oxide hybrid NPs growth on graphene nanosheets and the nano heterostructures are found to be homogeneously distributed over graphene sheets with unique yolk type morphology forming Ag–Cu2O/RGO nanocomposite (NC). The supercapacitor performances of the NCs are evaluated in aqueous 6.0 M KOH by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD) in two electrode cell assembly using Ag-Cu2O/RGO as electrode material. The ternary NCs exhibit excellent hybrid capacitance behavior having ~812 Fg−1 specific capacitance value with high energy density 27.2 Wh kg−1 and power density 285 W kg−1, respectively, at current density of 0.5 Ag−1 that suits for potential applications in hybrid capacitor. The high capacitance property of ternary NCs without use of binder can be attributed to excellent electronic/ionic conductivity due to presence of highly conductive graphene sheets in addition of noble Ag metal and unique yolk type morphology which causes faster electronic conduction among different components of the electrode material.

Synthesis of the cobalt sulfide hydrangea macrophylla for the energy storage electrode

Cobalt sulfide is one of the attractive materials for the energy storage electrodes due to its high specific capacitance (C F) and cost-effective properties. Well-defined nanostructures with promising features are intensively designed to achieve highly effective energy storage electrodes. In this study, a three-dimensional (3D) cobalt sulfide hydrangea macrophylla is successfully synthesized using a simple one-pot method by adding 1-dodecanethiol with long carbon chains as the sulfur and carbon layer sources. The morphology and the corresponding electrochemical performance of cobalt sulfide are examined in views of the vulcanization temperature and duration, as well as the annealing temperature and the loading mass. A C F value of 324.17 F g− 1 is obtained for the cobalt sulfide hydrangea macrophylla-based energy storage electrode at a scan rate of 10 mV s− 1 with the optimized loading mass on flexible nickel foam, owing to the large surface area and improved conductivity benefitted from the hydrangea macrophylla nanostructure and the carbon layer surrounded the cobalt sulfide, respectively. The utilization of this promising hydrangea macrophylla nanostructure of cobalt sulfide on energy storage electrodes opens a window for establishing structure-controlling techniques to improve the electrochemical performances.

Direct Synthesis of MnO2 Nanorods on Carbon Cloth as Flexible Supercapacitor Electrode

MnO2 nanorod/carbon cloth (MnO2/CC) composites were prepared through in situ redox deposition as freestanding electrodes for flexible supercapacitors. The CC substrates possessing porous and interconnecting structures enable the uniform decoration of MnO2 nanorods on each fiber, thus forming conformal coaxial micro/nanocomposites. Three-dimensional CC can provide considerable specific surface area for high mass loading of MnO2, and the direct deposition process without using polymeric binders enables reliable electrical connection of MnO2 with CC. The effect of MnO2 decoration on the electrochemical performances was further investigated, indicating that the electrode prepared with 40 min deposition time shows high specific capacitance (220 F/g at a scan rate of 5 mV/s) and good cycling property (90% of the initial specific capacitance was maintained after 2500 cycles) in 1 M Na2SO4 aqueous solution. This enhanced electrochemical performance is ascribed to the synergistic effect of good conductivity of carbon substrates as well as outstanding pseudocapacitance of MnO2 nanorods. The obtained MnO2/CC compositing electrode with the advantages of low cost and easy fabrication is promising in applications of flexible supercapacitors.

Novel Hybrid Nanoparticles of Vanadium Nitride/Porous Carbon as an Anode Material for Symmetrical Supercapacitor

Hybrid materials of vanadium nitride and porous carbon nanoparticles (VN/PCNPs) were fabricated by a facile pyrolysis process of vanadium pentoxide (V2O5) xerogel and melamine at relatively low temperature of 800 °C for supercapacitor application. The effects of the feed ratio of V2O5 to melamine (r), and nitrogen flow rate on the microstructure and electrochemical performance were also investigated. It was found that the size of the as-synthesized nanoparticles is about 20 nm. Both r value and N2 flow rate have enormous impacts on morphology and microstructure of the nanoparticle, which correspondingly determined the electrochemical performance of the material. The VN/C hybrid nanoparticles exhibited high capacitive properties, and a maximum specific capacitance of 255.0 F g−1 was achieved at a current density of 1.0 A g−1 in 2 M KOH aqueous electrolyte and the potential range from 0 to −1.15 V. In addition, symmetrical supercapacitor fabricated with the as-synthesized VN/PCNPs presents a high specific capacitance of 43.5 F g−1 at 0.5 A g−1 based on the entire cell, and an energy density of 8.0 Wh kg−1 when the power density was 575 W kg−1. Even when the power density increased to 2831.5 W kg−1, the energy density still remained 6.1 Wh kg−1.Graphical

Facile synthesis of porous SnO2 film grown on Ni foam applied for high-performance supercapacitors

Here, a novel three dimensional Ni foam-supported porous SnO2 film (SnO2/Ni composite foam) was successfully synthesized by the simple hydrothermal method. The porous SnO2 film had closely coated on the backbones of Ni foam without assistant of surfactant at mild conditions. At the same time, the pore size of SnO2/Ni composite foam was easily controlled by the reaction temperature. Furthermore, it was found that the capacitive properties of SnO2/Ni composite foam were related to the pore size of SnO2 film. The SnO2 film with smaller pore size showed higher capacitive properties, in which the porous SnO2/Ni composite foam with pore size of ca.60.0 nm showed high rate capability of 541.0 F g−1 at 10.0 A g−1 and good cycle stability with capacitance retention of 98.1% after 1000 cycles. The high capacitive properties was due to the SnO2 active materials grown on the backbone of Ni foam and porous structure of SnO2 materials, resulting in the reduce of resistance and enhancement of active surface area. Our work not only demonstrates the controlled synthesis of high-quality porous SnO2/Ni composite foam at mild conditions on a large scale, but also provides a universal route for the rational design of supercapacitors with high performance.