High Electric Double Layer Capacitance Research Articles

High-efficient water splitting over an in-situ growth novel electrocatalyst of metal-organic framework-based nanostructures

Metal-organic frameworks (MOFs) as emerging material have drawn much attention to apply to the field of water splitting. In this paper, layered NiFe-MIL-53 and nanoflower-like CoFe-MOF-74 were sequentially grown on nickel foam through two-step in-situ growth to construct a MOF-74/MIL-53 heterojunction. On this basis, we used the localized surface plasmon resonance (LSPR) effect of gold nanoparticles (Au NPs) to significantly improve the oxygen evolution reaction performance of MOF-74/MIL-53 heterojunction. Under illumation, the obtained Au-MOF-74/MIL-53 exhibits a lower overpotential of 218 mV, which is far superior to commercial catalyst. The reaction kinetics are significantly enhanced due to the lower charge transfer resistance and the higher electric double layer capacitance. We confirmed the existence of charge transfer between Au NPs and MOFs, and at the same time, the deposition of Au NPs significantly reduced the charge transfer resistance of MOF-74/MIL-53. On the basis of our work, we provide a novel MOF-based electrocatalytic nanocomposite structure for efficient water splitting.

Hierarchically Porous Carbon Rods Derived from Metal-Organic Frameworks for Aqueous Zinc-Ion Hybrid Capacitors.

Aqueous zinc-ion hybrid capacitors (ZIHCs), as ideal candidates for high energy-power supply systems, are restricted by unsatisfied energy density and poor cycling durability for further applications. The construction of a surface-functionalized carbon cathode is an effective strategy for improving the performance of ZIHCs. Herein, a high-performance ZIHC is achieved using oxygen-rich hierarchically porous carbon rods (MDPC-X) prepared by the pyrolysis of a metal-organic framework (MOF) assisted by KOH activation. The MDPC-X samples displayed high electric double-layer capacitance (EDLC) and pseudocapacitance owing to their oxygen-rich surfaces, abundant electroactive sites, and short ions/electron transfer lengths. The surface oxygen functional groups for the reversible chemical adsorption/desorption of Zn2+ are identified using ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Consequently, the as-assembled ZIHC exhibited a high capacity of 323.4 F g-1 (161.7mA h g-1) at 0.5 A g-1 and a retention of 147 F g-1 (73.5mA h g-1) at an ultrahigh current density of 50Ag-1, corresponding to high energy and power densities of 145.5W h kg-1 and 45kW kg-1, respectively. Furthermore, an excellent cycling life with 96.5% of capacity retention is also maintained after 10 000 cycles at 10 A g-1, demonstrating its promising potential for applications.

2D Materials-based Electrochemical Triboelectric Nanogenerators.

The integration of 2D materials in triboelectric nanogenerators (TENGs) is known to increase the mechanical-to-electrical power conversion efficiency. 2D materials are used in TENGs with multiple roles as triboelectric material, charge-trapping fillers, or as electrodes. Here, novel TENGs based on few-layers graphene (FLG) electrodes and stable gel electrolytes composed of liquid phase exfoliated 2D-transition metal dichalcogenides and polyvinyl alcohol are developed. TENGs embedding FLG and gel composites show competitive open-circuit voltage (≈ 300 V), instant peak power (530 mW m-2 ), and stability (> 11 months). These values correspond to a seven-fold higher electrical output compared to TENGs embedding bare FLG electrodes. It is demonstrated that such a significant improvement depends on the high electrical double-layer capacitance (EDLC) of FLG electrodes functionalized with the gel composites. The wet encapsulation of the TENGs is shown to be an effective strategy to increase their power output further highlighting the EDLC role. It is also shown that the EDLC is dependent upon the transition metal (W vs Mo) rather than the relative abundance of 1T or 2H phases. Overall, this work lays down the roots for novel sustainable electrochemical-(e)-TENGs developed exploiting strategies typically used in electrochemical capacitors.

Highly Porous Carbon Aerogels for High-Performance Supercapacitor Electrodes

In recent years, porous carbon materials with high specific surface area and porosity have been developed to meet the commercial demands of supercapacitor applications. Carbon aerogels (CAs) with three-dimensional porous networks are promising materials for electrochemical energy storage applications. Physical activation using gaseous reagents provides controllable and eco-friendly processes due to homogeneous gas phase reaction and removal of unnecessary residue, whereas chemical activation produced wastes. In this work, we have prepared porous CAs activated by gaseous carbon dioxide, with efficient collisions between the carbon surface and the activating agent. Prepared CAs display botryoidal shapes resulting from aggregation of spherical carbon particles, whereas activated CAs (ACAs) display hollow space and irregular particles from activation reactions. ACAs have high specific surface areas (2503 m2 g-1) and large total pore volumes (1.604 cm3 g-1), which are key factors for achieving a high electrical double-layer capacitance. The present ACAs achieved a specific gravimetric capacitance of up to 89.1 F g-1 at a current density of 1 A g-1, along with a high capacitance retention of 93.2% after 3000 cycles.

Facile electrochemical synthesis of rGO/PANI/ZnO heterostructure for energy storage applications

The combination of carbon nanomaterials, conducting polymers, and metal oxides provides a superior combination of high-quality supercapacitor (SC) materials. The carbon based materials are best known for its high electric double layer capacitance (EDLC) and the polymers like polyaniline (PANI) for pseudocapacitance. Transition metal oxides (TMOs) exhibit a combination of pseudocapacitance and EDLC owing to their unique chemical and morphological behaviour. The presence of an electric double layer capacitance and pseudocapacitance in the hybrid by using these combinations helps to obtain a higher specific capacitance. In this study, reduced graphene oxide (rGO), polyaniline (PANI), zinc oxide (ZnO) were combined using the different electrodeposition methods on ITO substrate. RGO can electrophoretically deposited using GO and the simultaneous reduction occurs during deposition. The highly stable PANI in emeraldine salt oxidation state was obtained using anodic electrodeposition. ZnO nanopowders also can be electrophoretically deposited over rGO/PANI. This hybrid material is expected to exhibit superior electrochemical properties and be environmentally friendly. The morphologies and quality of the samples were analyzed using scanning electron microscopy, Raman spectroscopy and X-ray diffraction techniques and found to be morphologically suitable for energy storage devices like supercapacitors.

C/MoS2@Ti3C2Tx composite flexible films for high performance supercapacitors

Two-dimensional (2D) Ti3C2Tx MXene has important potential applications in supercapacitor due to its high electrical conductivity, good hydrophilicity and abundant surface functional groups. It can be prepared into films of flexible electrochemical capacitors without adhesives. However, the self-stacking of Ti3C2Tx nanosheets seriously reduces their capacitance. Here, we developed a novel structure of the flexible material C/MoS2@Ti3C2Tx through facile physical mixing, three-dimensional C/MoS2 nanoflowers were successfully inserted between two-dimensional Ti3C2Tx layers. The self-stacking of MoS2 and Ti3C2Tx attenuates simultaneously. And these two materials form a particle-layer structure. At a current density of 0.5 A/g, the freestanding C/MoS2@Ti3C2Tx film has an excellent specific capacitance of 410 F g−1, which is 2.6 times that of C/MoS2 and 1.9 times that of Ti3C2Tx, respectively. It remains in good condition after 5000 cycles at 10 A/g, demonstrating excellent long-life cycle stability. The improvement of electrochemical performance is attributed to the particle-layer structure, which effectively avoids the re-packing of Ti3C2Tx and greatly reduces the diffusion distance of electrolyte ions. Furthermore, the addition of C/MoS2 nanoflowers has no effect on the bending ability of MXene composite films. And The nano-flower-like structure of C/MoS2 provides high electric double layer capacitance performance. This study provides new ideas for Ti3C2Tx-based films in the field of energy storage and wearable devices.

Graphene-polymer nanocomposites electrode with ionic nanofibrous membrane for highly sensitive supercapacitive pressure sensor

Wearable pressure sensors have obtained significant interests owing to their diverse applications in electronic skins and smart health informatics. Ultrahigh sensitivity, wide linearity, and better pressure resolution are highly desirable attributes of the pressure sensors for versatile applications. Here, a flexible supercapacitive pressure sensor (SPS) based on a novel reversible ion pumping mechanism is reported that remarkably increases the pressure sensitivity over a broad linear range exceeding the limits of the existing iontronic pressure sensors. The SPS is composed of lower concentration ionic nanofibrous membrane between two graphene-polymer nanocomposite electrolyte films, which engages in ion pumping, triggering a high electrical double layer capacitance under external stimuli. The fabricated SPS exhibited an ultra-high sensitivity of 9029 kPa−1 over wide linear range (0–100 kPa) with outstanding pressure resolution of 0.446%. Additionally, a wireless fitness tracker system is successfully demonstrated by integrating the SPS, which can monitor the food consumption and posture of users to improve their lifestyle.

Highly mesoporous carbon nanofiber electrodes with ultrahigh specific surface area for efficient capacitive deionization

Porous carbon with high specific surface area (SSA) has attracted considerable attention in capacitive deionization (CDI) owing to the abundant active adsorption sites. However, porous carbon dominated by the micropores tends to increase the ion transfer resistance and overlap the electrical double layers (EDLs), greatly limiting the ion adsorption rate and amount. In this work, a highly mesoporous carbon nanofiber electrode with an ultrahigh specific surface area (SSA) was prepared via electrospinning ZIF-8/benzoxazine/polyacrylonitrile (ZIF-8/BA-a/PAN) composite solution as carbon precursor. Benefiting from the cooperation of the simultaneous evaporation of Zn in ZIF-8 and activation treatment, the resultant carbon nanofibers show an ultrahigh SSA of 3066.29 m2/g, a pore volume of 2.23 cm3/g and a mesopore ratio of 72.53%, which has a high salt adsorption capacity (SAC) of 47.22 and 63.83 mg/g in 500 mg/L NaCl (50 mL) solution at 1.2 and 1.6 V, respectively. Furthermore, electrochemical measurement revealed that the high electrical double-layer capacitance facilitates ion storage in the mesoporous carbon nanofibers due to the increased nanopore size and reduced EDLs overlapping. This work provides new insight into designing novel highly mesoporous carbon with ultrahigh SSA for the next-generation electrode materials for energy and environmental applications.

Micro-electricity utilization performance and microbial mechanism in microbial fuel cell powered electro-Fenton system for azo dye treatment

A microbial fuel cell powered electro-Fenton system (MFCⓅEFs) with low consumption of power source and high efficiency of degrading refractory pollutants was constructed to treat textile wastewater. The bioelectricity generated from the degradation of sewage sludge and was used by the microbial fuel cell to generate H2O2 in situ to stimulate methylene blue (MB) degradation. On pH 3, external resistance 100 Ω and air flow rate 400 mL/min, Coulombic efficiency, Faraday efficiency, H2O2 production, and the degradation rates of total chemical oxygen demand (TCOD) and MB were 1.26 %, 74.25 %, 20.18 mg/L, 31.58 % and 93.50 %, respectively. For the MFCⓅEFs, open circuit voltage and power density have been improved to 0.96 V and 1.99 W/m3 (0.81 V and 1.31 W/m3 of control group) respectively, higher electric double layer capacitance indicating faster electron transfer performance. The system’s degradation of MB mainly relied on the oxidation of hydroxyl radical (·OH). After the·OH in the system was quenched, the degradation rate of MB decreased by 45.19 %. CAZy, KEGG, and COG were characterized to annotate the functional genes of the MFCⓅEFs, which has a great significance to explore the mechanism of advanced treatment of dying wastewater by microbial electrochemical system.

Dipping fabrication of rHGO@NiO@NF flexible supercapacitor electrode and its potential in bendable electronic devices

A flexible nickel foam (NF) based reduced Holey Graphene Oxide (rHGO) wrapping on NiO@NF hybrid supercapacitor electrode is fabricated using facile hydrothermal reaction followed by HGO dispersion dipping to achieve an efficient, bendable and scalable supercapacitor with high capacitance for wearable smart device usage. The sample electrode reveals a typical wrapping morphology of porous rHGO spreading on uniform nickel oxide crystal layer while exposing crystals through recurrent rHGO slits. Benefiting from this morphology and optimization of fabrication parameters, the sample electrode gains better electrochemical performance from higher electric double layer capacitance incorporation and more efficient electrolyte ion transportation, with less than 0.1 Ω equivalent series resistance (ESR), 752.9 F/g of capacitance, and 90% capacitance retention under 10 A/g current density. The sample electrode is then made into an all-solid-state supercapacitor device possessing 0.267 Wh/m2 energy density at a power density of 8.14 W/m2, and the bendable fact of the device endows it 97% capacitance retention after 500 times of curving, making it especially suitable as flexible energy provider. This simple fabrication method should shed light on flexible hybrid supercapacitor development.

Hand-drawn electrode based disposable paper chip for artificial sweat analysis using impedance spectroscopy.

Low cost, disposable paper based electrical sensor to examine the analyte concentration in an extremely small volume of sample solution is essential for environmental and healthcare applications. For the development of paper based devices, sophisticated instruments are essential to pattern electrode on the top surface of the paper. In most cases, such fabricated device results in direct contact with the analyte solution on the surface of the electrode during electrical detection and leads to high electrical double layer capacitance. In this work, we have focused to reduce the double layer capacitance by fabricating hand drawn electrode paper sensor utilising the reverse side of the paper. This design acts as a sample storage and facilitate impedimetric sensing of ionic concentration of analyte solution using a few microlitre. Droplet formation at the bottom of the paper in the confined area is visually monitored to reduce sample wastage. The interaction between two different electrode materials (graphite and silver) on the paper substrate with the different volume and concentration of the electrolyte is analysed to improve the robustness and sensitivity of the measurement. Simultaneously, we observed a reduction in the electrical double layer effect on the low sample volumes. The proposed paper based sensor shows the enhanced impedance stability on silver electrode patterned paper chip than graphite electrode paper chip to detect the different ionic concentration of artificial sweat sample. Finally, it demonstrates that paper chip has great potential as a disposable diagnostics sensor in healthcare applications.

Egg albumen-based biopolymer electrolyte lateral capacitive coupling thin-film transistors on logical operation

Recently, green electronic products are receiving increasing attention from scientists. Here, biodegradable lateral capacitively coupled electric-double-layer (EDL) oxide-based thin-film transistors (TFTs) were fabricated on a flexible paper substrate. The TFTs exhibit good performance due to the extremely high EDL capacitance of the egg albumen based electrolyte. Good transistor performances against mechanical stress were observed. In the coplanar double-gate structure, the high-low level of the different periods is input to the two gates to realize the logical function ‘AND’ operation. Resistor loaded inverters were built, exhibiting full-swing amplitude and high-voltage gain at low operating voltages, and implementing ‘NOT’ logic function. And the inverters were used to realize the conversion of the noise signal to the two-bit output. Therefore, the proposed lateral capacitively coupled TFTs may have potential applications in low-cost green portable logic computing devices. Laterally capacitively coupled TFTs were fabricated on a paper substrate by using egg albumen solid electrolyte film as a gate dielectric. The TFTs exhibit good performance due to the extremely high EDL capacitance of the egg albumen based electrolyte. AND logic operations and NOT logic functions are implemented on TFTs based on this lateral planar coupling structure. • Thin-film transistors (TFTs) with lateral capacitive coupling are fabricated on a paper substrate using natural egg albumen as gate dielectric. •These egg albumen-based flexible TFTs can implement logic operation functions under low voltage conditions and have excellent noise immunity. •The proton movement mechanism of lateral capacitive coupling in an external electric field is explained in our coplanar-gate structure of TFTs.

Hybrid supercapacitor based on graphene and Ni/Ni(OH)2 nanoparticles formed by a modified electrochemical exfoliation method

Hybrid supercapacitor combined with the merits of both the electric double layer capacitance and redox pseudocapacitance and thus have great potential. Here, hybrid materials of graphene and Ni/Ni(OH)2 nanoparticles were prepared through a modified electrochemical exfoliation method for using for supercapacitor. Large quantities of Ni/Ni(OH)2 nanoparticles with high redox pseudocapacitance were found to disperse either on the outer surface of the graphene or enclosed by the graphene with high electric double layer capacitance. The hybrid materials as-prepared show a capacitance as ultrahigh as 5715 mF/cm2 (1905 F/g) at 10 mA/cm2 and it remains 94.8% after 1000 cycles in 6 M KOH.

Heterostructure of 3D sea-grape-like MoS2/graphene on carbon cloth for enhanced water splitting

MoS2 has been widely used as a hydrogen evolution reaction (HER) electrocatalyst because of its unique characteristics, such as a tunable band gap, near-zero Gibbs free energy, and earth abundance. However, its low electrical conductivity and the electrochemically inert basal plane of MoS2 decrease the HER performance. Herein, we used graphene and carbon cloth (CC) to boost the electrocatalytic activity of MoS2. Using nickel electrodeposition and chemical vapor deposition (CVD) at high temperature, graphene was grown on carbon cloth (Gr/CC) and a sea-grape-like morphology was formed simultaneously. Finally, Gr/CC was covered up with MoS2 using two-zone CVD (MoS2/Gr/CC), resulting in a three-dimensional (3D) sea-grape-like heterostructure. The MoS2/Gr/CC exhibits outstanding HER performance, with a suitable onset potential (50 mV), low ŋ10 (91 mV, overpotential at 10 mA cm−2), high electrical double layer capacitance (Cdl; 239 mF cm−2), low Tafel slope value (48 mV dec−1), and high stability in 0.5 M H2SO4 for two days at various overpotentials. The 3D sea-grape-like morphology and the synergistic effect of MoS2 and graphene led to the enhanced electrocatalytic activity of MoS2/Gr/CC, indicating much better HER performance than most electrocatalysts based on graphene and MoS2.

Amorphous titanium-oxide supercapacitors with high capacitance

An amorphous titanium-oxide film oxidized anodically on amorphous Ti–10at%V–15at%Si alloy ribbons demonstrated excellent electric properties. Specifically, it showed a remarkable increase in parallel capacitance Cp, series capacitance Cs, time constant RCs, and decrease in the dielectric loss with decreasing frequency. The oblate semicircle after a semicircle with a Warburg region in the Nyquist diagram and rapid increases in the real impedance in the low-frequency region in the Bode diagram demonstrated a parallel circuit comprising an electric transport resistance Re (0.64 MΩ), and a high electric double-layer capacitance Cdl (604.0 μF/cm 2) at a nanometer-sized ( in convex size) uneven surface between an upper (Ti0.84V0.11Si0.05)O1.655 layer approximately 45-nm deep and air. The superior capacitances could be elucidated by electrostatic induction of a large positive charge to the uneven oxide surface based on the electronic conduction state derived from TiO2/VO2 nanostructural interfaces in the upper oxide layer.

Fluctuation of electrode potential based on molecular regulation induced diversity of electrogenesis behavior in multiple equilibrium microbial fuel cell

In this study, the electrogenesis behaviors and mechanisms in multiple equilibrium microbial fuel cells (MEMFCs) which volatile fatty acids as multiple electron donors are investigated. The electrochemical property and energy recovery can be enhanced in propionic acid dominant systems (HPr-D-MEMFCs) which compares to butyric acid dominant systems (HBu-D-MEMFCs), increase power density from 0.04 to 0.43 W/m2 and energy recovery efficiency from 2.07 to 5.44%, respectively. With isotope experiment analysis, the fluctuation of electrode potentials induce diverse electrogenesis pathways that high utilization efficiencies and bioconversion efficiency of hybrid acids observed in HPr-D-MEMFCs which different with HAc-D-MEMFCs and HBu-D-MEMFCs. In addition, the electrochemical and microbial community variation of MEMFCs reveal that the direct interspecies electron transfer stimulated with higher electric double layer capacitance, and activities of exoelectrogens enhanced with high relative abundance in HPr-D-MEMFCs. The findings present an intensive study in electrogenesis, providing a promising way to promote energy recovery and further extend its application value.

Catalytic Carbonization of Acenaphthene for the Preparation of Ordered Mesoporous Carbon CMK-1 toward Application as Electrochemical Double-layer Capacitor Electrode with Ionic Liquid Electrolyte

Ordered mesoporous carbon CMK-1 with partially graphitized domains was prepared from acenaphthene in Ni-loaded MCM-48, which showed an extremely high electric double-layer capacitance of 13.6 µF cm...

Wearable supercapacitors based on graphene nanoplatelets/carbon nanotubes/polypyrrole composites on cotton yarns electrodes

The development of highly conductive, flexible, mechanical reinforced and chemically modified cotton yarns for electrodes of supercapacitors represents an important advance in the energy storage devices applied in wearable electronics. The production of carbon-based conductive layers as supports for chemical polymerization of active polymeric materials (such as polypyrrole) is an important strategy that associates the high electrical double-layer capacitance of the carbon derivatives (carbon nanotubes and graphene nanoplatelets) and the pseudocapacitance of the polypyrrole in truly flexible devices with improved electrochemical response—high capacitance. These properties are affected by relative concentration of graphene nanoplatelets in carbon complexes due to the variation in overall conductivity of electrodes (in consequence of low aggregation degree and available surface area) and the electrochemical properties of the resulting devices that reaches capacitance in order of 45.5 F g−1 with a capacitive retention of 70% after 2000 cycles of use. These promising results open possibilities for new systems in wearable electronics.

Ditungsten carbide nanoparticles embedded in electrospun carbon nanofiber membranes as flexible and high-performance supercapacitor electrodes

Abstract Ditungsten carbide (W 2 C) nanoparticles embedded in graphene nanoribbon/carbon nanotube-carbon nanofiber (GC-CNF) composite membrane has been prepared by one-pot electrospinning with subsequent carbonization. The homogeneous distribution of small-sized W 2 C nanoparticles in-situ formed during carbonization within the carbon nanofibers, provides abundant electroactive sites for high electric double layer capacitance. The carbon nanotube bridged graphene nanoribbon hybrid could enhance the conductivity of carbon nanofibers, while the fibrous web structure favors rapid ion diffusion, thus offering fast electron/ion transport pathways during the electrochemical process. Moreover, the W 2C nanoparticles embedded in nanofiber structure could prevent their oxidation during the electrochemical process, contributing to enhanced cyclic stability. Consequently, the GC-CNF@W2C composite membrane exhibits high specific capacitance of 256 F g-1 at 1 A g-1 and good cycling stability of 95.6% retention after 2500 cycles. Therefore, the GC-CNF@W2C composite membrane shows great potential as electrode material for high-performance supercapacitors.

Exceptionally High Electric Double Layer Capacitances of Oligomeric Ionic Liquids.

Electric double layer (EDL) capacitors are promising as next-generation energy accumulators if their capacitances and operation voltages are both high. However, only few electrolytes can simultaneously fulfill these two requisites. Here we report that an oligomeric ionic liquid such as IL4TFSI with four imidazolium ion units in its structure provides a wide electrochemical window of ∼5.0 V, similar to monomeric ionic liquids. Furthermore, electrochemical impedance measurements using Au working electrodes demonstrated that IL4TFSI exhibits an exceptionally high EDL capacitance of ∼66 μF/cm2, which is ∼6 times as high as those of monomeric ionic liquids so far reported. We also found that an EDL-based field effect transistor (FET) using IL4TFSI as a gate dielectric material and SrTiO3 as a channel material displays a very sharp transfer curve with an enhanced carrier accumulation capability of ∼64 μF/cm2, as determined by Hall-effect measurements.