Electrochemical Capacitive Performance Research Articles

Environmentally Friendly Functionalization of Porous Carbon Electrodes for Aqueous-Based Electrochemical Capacitors

A green chemical method is reported for the synthesis and functionalization of high surface area carbon-based materials for applications as electrodes in short-term energy storage devices, such as supercapacitors. The proposed method is focused on sustainable chemistry and engineering. Our results evidenced an excellent performance of electrochemical capacitor devices with a high lifespan over a wide working voltage with low equivalent series resistance. Great enhancement of electrode wettability and charge transfer at the electrode/electrolyte interface using oxygenated surface functional groups was obtained using the present method. Actually, the present findings are quite promising thus encouraging further investigations of this green-functionalization method for all other carbon-based materials, such as graphene, carbon nanotubes, doped-diamond, and so on.

Zeolitic imidazolate framework-derived Co3S4@Co(OH)2 nanoarrays as self-supported electrodes for asymmetric supercapacitors

Core–shell Co3S4@Co(OH)2 nanosheet arrays with enhanced electrochemical capacitive performance were designed using a ZIF-engaged strategy.

Controllable synthesis and electrochemical capacitor performance of MOF-derived MnOx/N-doped carbon/MnO2composites

Different amount of carbon and nitrogen, for MOF-derived nitrogen-doped carbon/Mn3O4composites, can result in the discrepancies of synergistic effect which plays an important role in final electrochemical performance.

Insights into the electrochemical capacitor performance of transition metal-vertical graphene nanosheet hybrid electrodes.

Vertical graphene nanosheets (VGN) are envisioned as supercapacitor (SC) electrode materials due to their distinct geometry and remarkable properties. Of late, the hybrid structures of graphene-transition metal (TM) or oxides were found to exhibit enhanced charge storage capacity. Herein, we report the charge storage performance of VGN-transition metal nanoparticle (Au, Ag, Cu, and Ni) hybrid electrodes. Amongst them, Ni-decorated VGN exhibited the highest enhancement, up to 3.04 mF cm-2 (121.6 F g-1) compared to 0.16 mF cm-2 (6.4 F g-1) for as-grown VGN. Further, this was corroborated by the improved electrical as well as ionic conductivity of the metal-decorated VGN structures. Additionally, the presence of metal-oxygen-carbon bonding ensured a contribution of pseudocapacitance. Ab initio calculations elucidated the extent as well as the nature of charge (e-) transfer in TM nanoparticle-VGN hybrid structures. These findings are well corroborated with the charge storage performance. A combined effect from charge transfer and pseudocapacitance on the charge storage performance of TM nanoparticle-VGN hybrid electrodes is demonstrated. A symmetric coin-cell supercapacitor device using Ni/VGN electrodes was fabricated and the sustained performance tested over 10 000 charge-discharge cycles.

Mo-Based crystal POMOFs with a high electrochemical capacitor performance.

Mo-Based crystalline polyoxometalate-based metal-organic frameworks (POMOFs), namely, [CuIH2(C12H12N6)(PMo12O40)]·[(C6H15N)(H2O)2] (1) and [Cu(C12H12N6)4(PMoMoO39)] (2) (C12H12N6, 1,4-bis(triazol-1-ylmethyl) benzene, abbreviation btx) as promising capacitor electrode materials were synthesized by a hydrothermal reaction. Compound 1 consisted of two-dimensional (2D) lattice structures with free triethylamine (abbreviation, TEA) molecules and H2O molecules, and compound 2 showed a 3D host-guest structure, in which 1D polyoxometalate (POM) chains were encapsulated into a 3D Cu(ii)-btx metal-organic framework (MOF). The compound 1-based electrode showed much higher specific capacitance (249.0 F g-1 at 3 A g-1) than the 2-based one (154.5 F g-1 at 3 A g-1). Moreover, the specific capacitance of the 1-based electrode was not only higher than those of the majority of the reported POMOF materials as supercapacitors, but also higher than those of most state-of-the-art MOF-based and POM-based supercapacitor electrode materials. This superior capacitance performance of the 1-based electrode could be attributed to the high redox capacity and excellent electronic conductivity. More importantly, this work may open a new avenue for optimizing the performance of POMOF-based capacitor electrode materials.

Morphology-controllable synthesis of nanocarbons and their application in advanced symmetric supercapacitor in ionic liquid electrolyte

Controllable synthesis of nanocarbons with tunable morphologies from sustainable biomass through facile one-step route for ionic liquid based supercapacitors with high energy density and high power characteristics is of great interest but remains an ongoing challenge. Herein, we report the design and synthesis of nanocarbons with tunable morphologies (i.e., honeycomb-like porous carbons, carbon nanosheets and irregular-shaped carbon microparticles) from sustainable pine barks through reliable one-step chemical activation process. We found that the honeycomb-like porous carbons can be produced via direct KOH activation while the uniform carbon nanosheets were obtained by employing magnesium powder as the reactive self-sacrificing template. These three samples have different morphologies and textural properties render them totally disparate electrochemical performance in ionic liquid electrolyte. Benefiting from its distinct structural advantages, the as-obtained porous carbon nanosheets has excellent electrochemical capacitive performance including large specific capacitance (193 F/g at 1 A/g), superior rate capability (superior specific capacitance retention of 69.4% at 40 A/g), good cycling stability (good capacitance retention after 8000 cycles) and integrated high energy density& high power characteristics (excellent energy density of 55.8 Wh/kg even at an ultrahigh power density of 39.375 kW/kg). We believed that this work reported here not only provides a versatile strategy towards nanocarbons with tunable morphologies from sustainable biomass but also sheds some new light to efficiently regulate the morphologies of nanocarbons for electrochemical energy storage applications.

Facile synthesis of coral-like hierarchical polyaniline micro/nanostructures with enhanced supercapacitance and adsorption performance

We presented a newly facile approach to scalable synthesize three-dimensional (3D) coral-like polyaniline (CL-PANI) hierarchical micro/nanostructures. The CL-PANI composed of well-defined nanowires with ca.20 nm was self-assembled by in situ conventional chemical polymerization with a different charging sequence. Electron microscopy, UV-Vis spectroscopy, X-ray diffraction, and nitrogen adsorption-desorption studies showed that CL-PANI possessed unique mesoporous structure and highly crystallinity which could promote rapid ion diffusion and charge transfer. Electrochemical experimental results showed that the as-prepared CL-PANI electrode had a superior electrochemical capacitance performance with a relatively high specific capacitance of 817 F g−1 at a current density of 0.5 A g−1 and a great rate capability of 67% specific capacitance retaining from 0.5 to 20 A g−1. Meanwhile, CL-PANI exhibited an enhanced adsorption performance of azo dye Acid Red G (ARG) from aqueous solution with a Langmuir maximum adsorption of 310.2 mg g−1 at pH 2.0, 298 K. This study offers a simple and cost effective path for scalable synthesis of PANI materials for supercapacitor and adsorption application.

Electrode mass ratio impact on electrochemical capacitor performance

Smart adjustment of active mass loading on positive and negative electrodes, significant enhancement of energy density with long-term durability is achieved due to expand of operating potential window of the electrochemical capacitor. In the present contribution, two different carbon materials like indigenous activated carbon fibres and commercial Kuraray YP-50 carbon are utilised as electrodes and the equal/unequal mass configurations of electrochemical capacitor are systematically investigated by using 1 M tetraethylammonium tetrafluoroborate/AN as an organic electrolyte. The electrochemical performances of equal/unequal mass configurations are examined in terms of potential stability window and the durability of the electrochemical capacitor. The unequal mass configuration of carbon fibres electrodes shows 25% higher gravimetric energy density than unequal commercial YP-50 electrodes. Besides, unequal mass configuration of carbon fibres exhibit 41% higher gravimetric energy density as compared with commercial YP-50 carbon at 2.7 V as extensively reported in the literature. This result clearly explores the benefits of unequal mass configurations of electrochemical capacitor for extending the operation voltage window of organic electrolyte with long durability and this strategy enlightens the design of well-defined carbon-carbon based electrodes for commercial implementation.

Graphene oxide incorporated polypyrrole composite materials: optimizing the electropolymerization conditions for improved supercapacitive properties

For supercapacitor electrode materials, polypyrrole (PPy) usually shows compact microstructure due to its dense growth. To enhance its electrochemical capacitive properties by facilitating the dispersed distribution of PPy, we have incorporated graphene oxide (GO) nanosheets into PPy via facile electrochemical polymerization. And meanwhile, the effect of electropolymerization conditions (12 different conditions) on the electrochemical properties of the prepared PPy/GO composites is investigated detailedly. Three important results are obtained by electrochemical measurements. First, the electrochemical properties of PPy electrodes are remarkably boosted by the incorporation of GO. Second, galvanostatically polymerized PPy/GO composites exhibit better electrochemical performances than potentiostatically polymerized PPy/GO. Third, the galvanostatically polymerized PPy/GO composite with 1 mA cm−2 shows the best electrochemical capacitive performances, achieving high specific capacitance of 154.5 mF cm−2, good rate capability, and excellent cycle performance, showing 107.5% of initial capacitance after 5000 cycles. This study demonstrates that the electropolymerization conditions significantly affect the electrochemical properties of the prepared PPy/GO composites, and the electrodes prepared under the optimal condition are very promising for high-efficiency supercapacitor applications.

Improved manganese oxide electrochemical capacitor performance arising from a systematic study of film storage/drying effects on electrochemical properties

This work is the first to systematically relate manganese oxide film storage/drying to a full gamut of electrochemical capacitor (EC) properties, with the aim of enhancing these properties and addressing this oxide's well-known stability issues. Cyclic voltammetry and galvanostatic charging-discharging show that increased film-drying temperatures result in lower resistance and higher power but at the expense of capacitance and energy. Film drying reduces physical stability and cycle life, while undried, electrolyte-stored films exhibit poor long-term aging. Novel electrolyte-stored films show a ∼102% capacitance increase, ∼75% energy increase and 32% improved film usage compared to 200 °C-dried films, while 200 °C drying results in a ∼69% power increase and ∼75% decrease in resistance compared to non-heat-treated films.Using the knowledge acquired from this systematic study, we then strategically design an innovative double-deposition in which an initial manganese oxide layer is oven-dried and subsequently recoated with a second manganese oxide layer before storing the entire electrode in electrolyte. Films made with this novel double-deposition demonstrate the optimal properties achieved from both electrolyte-stored films (high energy, capacitance, coulombic efficiency, and physical stability) and heat-treated films (low resistance, higher power and rate capability, good aging, and stability in a large potential window); they also demonstrate the smallest degree of self-discharge. This novel synthesis produces films suitable for a wider range of EC applications.

A facile approach to improve the electrochemical properties of polyaniline-carbon nanotube composite electrodes for highly flexible solid-state supercapacitors

We seek to improve the electrochemical properties of supercapacitor via engineering the interface of electroactive material/current collector. A facile electrochemical method is put forward to fabricate expanded graphite (ExGP), and polyaniline-carbon nanotube (PANI-CNT) composite electrodes using ExGP as substrate are prepared by one-step co-electrodeposition. Compared with PANI-CNT/GP electrodes, PANI-CNT/ExGP electrodes show significantly improved electrochemical capacitive performances due to reduced constriction/spreading resistance. This effect is ascribed to the increased area of contact points at the interface of electroactive material/current collector for the latter. The PANI-CNT/ExGP electrodes deliver a specific capacitance of 826.7 F g−1, higher than previous reports based on PANI-CNT composites. A highly flexible solid-state supercapacitor is assembled using PANI-CNT/ExGP electrodes. The device shows high rate capability, superior energy/power characteristics (7.1 kW kg−1 at an energy density of 12.0 Wh kg−1), and good cycling stability. This study demonstrates that optimizing electroactive material/current collector interface can implement faster electron transport and represents an effective strategy to promote electrochemical capacitive properties of supercapacitors.

The shape effect of manganese(II,III) oxide nanoparticles on the performance of electrochemical capacitors

Manganese(II,III) oxide (Mn3O4) with various shapes including square prisms, polyhedra and tetragonal bipyramids are selectively synthesized with the mediation of fatty acids at nanoscale (<20 nm). Among all nanostructures, Mn3O4 tetragonal bipyramids show the largest gravimetric capacitance of 304 F g−1 with excellent rate capability and long-term cycling stability. In contrast, Mn3O4 polyhedra show relatively large intercalation capacity and poor stability, which could be related to the abundant low-coordination sites (edges, corners and defects) exposed on the surface. Transmission electron microscopy analysis reveals that the capacitance loss is caused by the dissolution of Mn3O4. Electrochemical analysis shows that the iR drop increases during cycling, probably due to the deterioration of the electric contact between Mn3O4 nanoparticles and the conductive matrix in the electrode.

Solid State Electrochemical Capacitors

Solid-state electrochemical capacitors were prepared by combining composite electrodes based on a carbon paper/carbon nanotubes assembly coated with a layer of a pseudocapacitive electrode materials such as manganese dioxide or ruthenium dioxide separated by a solid state membrane to support the electrolyte. The composite electrodes were prepared by using a simple slow filtration technique. The electrolytes consist of ion-exchange membranes (such as Nafion or CMX from Neosepta) that are impregnated with an appropriate electrolyte. Acidic and neutral electrolytes were investigated in this work. Symmetrical electrochemical capacitors were prepared with two similar electrodes. Different combinations of electrode and membrane were assembled and characterized electrochemically by cyclic voltammetry and constant current charge/discharge cycling. The effect of cycling rate and temperature (from – 60 to + 60 °C) on the electrochemical performance of the solid-state electrochemical capacitors was evaluated.

Effect of Electrolyte Cation on the Electrochemical Performance of AC Electrochemical Capacitor

The aim of this study is to observe the effects of electrolyte cation on the electrochemical performance of anodic electrode in electrochemical capacitor. In an ideal electrochemical capacitor, the symmetrical anodic and cathodic electrodes have the same contribution to overall cell performances. However, the performance of anodic and cathodic electrodes is dependent on the size of electrolyte cations and anions which are adsorbed at the surface of electrodes. Hence, there would be a deviation in anodic and cathodic potential due to diffusion of ions with different characteristics into the electrode materials. In this study, each electrochemical cell has been made of two symmetrical activated carbon (AC) electrodes with the same mass of active material on each electrode. The AC electrochemical cells have been tested in organic electrolytes with the same anion and different cations, using cycling voltammetry (CV) at 25 mV/s sweep rate. This was followed by the step potential electrochemical spectroscopy (SPECS) experiment with a 10 mV potential step and 300 s equilibration time. SPECS method is based on applying a series of equal magnitude potential steps on a working electrode, with sufficient rest time to allow for equilibrium to be established for each step throughout an applied potential window [1]. At the same time, the open circuit potential (OCP) of both electrodes have been measured with respect to Ag/AgNO3 reference electrode during the CV and SPECS experiments. This technique allows us to see how an individual electrode behaves in overall cell performances. The outcome of this work indicates the shift between the anodic and cathodic potential in all different electrolytes. It was found that, the cathodic potential is more shifted towards the anodic electrode which means that during charging process more anions are adsorbed at the surface of the cathodic electrode so it covers a larger potential window than the anodic electrode. Additionally, the specific capacitance obtained by the SPECS method was used to obtain the performance of the AC electrochemical cell in non-aqueous electrolytes with different cations in the form of a Ragone diagram. [1]. Marveh Forghani and Scott W. Donne, Journal of the Electrochemical Society 2018 165: A664-A673.

Hierarchical nanocarbon-MnO2 electrodes for enhanced electrochemical capacitor performance

High-capacity energy storage in electrochemical capacitors may benefit from the combination of electric double-layer capacitance (EDLC) and pseudocapacitance to lead to high specific energy and power beyond the current capacity of rechargeable batteries. However, commonly pursued combinations of non-conductive pseudocapacitive and conductive EDLC materials rarely achieve synergistic effects. This work addresses the issue by demonstrating unique hierarchical microstructured electrodes comprising uniformly dispersed MnO2 nanoparticles on intentionally converted “pseudocapacitive” edges of plasma-grown Vertically Oriented Graphenes (VGs), with side-walls fully open to EDLC effects, and bonded at the base to the supporting highly conducting carbon nanofibers (CNFs), without any binder. The hierarchical structure combines the benefits of good conductivity of VGs and CNFs, the unique edge nucleation behavior and small size of MnO2 nanoparticles, and the large surface areas of the exposed graphene walls. Moderate oxidation of VGs helps refine MnO2 nanostructures and improve the cycle stability. The hybrid electrode delivers a specific capacitance of 612 F g-1 (32.7 F cm-3) at scan rate of 2 mV s-1 and exhibits good stability 109% after 5000 CV cycles at the scan rate of 100 mV s-1 in three-electrode system. The asymmetric electrode configuration based on it reveals a specific energy of 30.4 Wh kg-1 (0.90 mWh cm-3) and a specific power of 27.8 kW kg-1 (824 mW cm-3) at 15 A g-1. This work suggests new ways to produce hybrid MnO2-carbon hierarchical composite materials for the improved electrochemical capacitor performance.

Development of Novel and Ultra-High-Performance Supercapacitor Based on a Four Layered Unique Structure

This paper presents an electrode with a core/shell geometry and a unique four-layered porous wrinkled surface for pseudocapacitive supercapacitor applications. To design the electrode, Ni foam was used as a substrate, where the harmonious features of four constituents, ZnO (Z), NiS (N), PEDOT:PSS (P), and MnO2 (M) improved the supercapacitor electrochemical performance by mitigating the drawbacks of each other component. Cyclic voltammetry and galvanostatic charge discharge measurements confirmed that the ZNPM hybrid electrode exhibited excellent capacitive properties in 2 M KOH compared to the ZNP, ZN, and solely Z electrodes. The ZNPM electrode showed superior electrochemical capacitive performance and improved electrical conductivity with a high specific capacitance of 2072.52 F g−1 at 5 mA, and a high energy density of 31 Wh kg−1 at a power density of 107 W kg−1. Overall, ZNPM is a promising combination electrode material that can be used in supercapacitors and other electrochemical energy conversion/storage devices.

Layer-by-layer assembly of iron oxide-decorated few-layer graphene/PANI:PSS composite films for high performance supercapacitors operating in neutral aqueous electrolytes

The layer-by-layer assembly of polyaniline-PSS (PANI:PSS) complexes and iron oxide nanoparticles-decorated few-layer graphene (Fe-FLG) from aqueous dispersions, yielding an electrode material with excellent electrochemical capacitive performance in simple neutral aqueous electrolyte is presented. The simple dip-coating procedure allows the effective incorporation of both materials and the control of the film nanoarchitectonics. The resulting composite coating was characterized by XPS and Raman spectroscopies. A linear dependence of the capacitance on the film mass indicates that both building blocks are efficiently (and electrochemically) connected within the films. The electrochemical performance of the film-coated electrodes was tested in both acidic (0.1 M HCl) and neutral (0.1 M KCl) aqueous electrolytes. Electrodes constituted of 15 self-assembled bilayers showed the best performance with a high capacitance of 768.6 F g−1 and 659.2 F g−1 in 0.1 M HCl and 0.1 M KCl, respectively, at the current density of 1 A g−1. Moreover, a high stability to continuous cycling was observed, even in aqueous neutral solution (86% capacitance retention after 1600 cycles at 3 A g−1). This ternary material then constitutes a promising candidate for the construction of environmentally friendly supercapacitors.

Electrochemical Performance of Lithium-Ion Capacitor Using Reduced Graphene Oxide–Carbon Nanotube Pre-Lithiated by Direct Contact Method

Graphene-based electrodes have continued to gain attention for application in lithium-ion capacitors (LICs). This work demonstrates the promising electrochemical performance of LICs with reduced graphene oxide-carbon nanotubes (rGO-CNT) electrodes prepared by electrostatic spray deposition (ESD). The rGO-CNT anode was pre-lithiated by direct contact method prior to the LIC assembly. The resulting rGO-CNT // lithiated rGO-CNT LIC system operated within 0.01 V to 4 V delivered a specific capacity up to 94.5 mAhg-1 at 0.1 Ag-1. The LIC also displayed 76.7 % capacity retention after 2000 cycles at 0.5 Ag-1. A maximum energy density of 170 WhKg-1 and maximum power density of 1385 Wkg−1 were obtained.

Capillarity-driven assembly of single-walled carbon nanotubes onto nickel wires for flexible wire-shaped supercapacitors

The carbon nanomaterials have been incorporated into composite electrode for wire-shaped supercapacitors (WSSs) to promote development of wearable electronics. Coating of carbon nanomaterials directly onto functional fiber is a facile strategy to prepare wire-shaped electrodes. However, it is still a critical challenge to maximize the adhesion of the nanomaterials onto aimed substrate fiber, while still maintaining the high specific area of the nanomaterials. Herein, both carbon nanotubes (CNTs) and graphene were coated onto the surface of nickel wires via capillary effect driven process. It was discovered that the one dimensional morphology of the CNTs not only benefited the adhesion of CNTs on the relatively smooth surface of the nickel metal wire, but also strengthened the infiltration of the electrolyte among the CNTs. On the contrast, the restacking of graphene oxide (GO) sheets retarded the infiltration of the electrolyte, resulting in inferior capacitive performance. The prepared Ni-CNT electrodes showed excellent electrochemical double layer capacitive performance along with the mechanical robustness and high flexibility. The constructed all-solid flexible wire-shaped supercapacitors maintained a high specific capacitance of approximately 30 F/g after 3000 cycles when bent by 45 degree.

Synthesis and Electrochemical Performance of Molybdenum Disulfide-Reduced Graphene Oxide-Polyaniline Ternary Composites for Supercapacitors.

Molybdenum disulfide/reduced graphene oxide/polyaniline ternary composites (MoS2/rGO/PANI) were designed and synthesized by a facile two-step approach including hydrothermal and in situ polymerization process. The MoS2/rGO/PANI composites presented an interconnected 3D network architecture, in which PANI uniformly coated the outer surface of the MoS2/rGO binary composite. The MoS2/rGO/PANI composites with a weight percent of 80% (MGP-80) exhibits the best specific capacitance (570 F g−1 at 1 A g−1) and cycling stabilities (78.6% retained capacitance after 500 cycles at 1 A g−1). The excellent electrochemical capacitive performance is attributed to its 3D network structure and the synergistic effects among the three components that make the composites obtain both pseudocapacitance and double-layer capacitance.