Electrode Material For Asymmetric Supercapacitors Research Articles

Electrochemical Deposition of γ-MnO2 on Ag/rGO Hybrid Films as Flexible Electrode Materials for Asymmetric Supercapacitor

The flexible electrodes are the essential components for fabricating modern flexible supercapacitors. In this study, a composite hybrid film integrated with silver nanoparticles (Ag NPs), reduced graphene oxide (rGO) and γ-MnO2 nanorods as a flexible electrode has been developed by the electrochemical deposition method. The substrate (rGO) of the electrode not only provides mechanical stability but also ensures fast electron transfer during charge–discharge. The Ag NPs distributed in electrode provide the electronic channel to enhance the electric conductivity. The γ-MnO2 electroplated on the surface of hybrid films further improved the electrochemical performance of them. The resultant γ-MnO2/Ag/rGO hybrid films exhibit a high specific capacitance of 1090.3 F g−1 at current density of 0.3 A g−1. The asymmetric supercapacitor (ASC) devices were further fabricated by γ-MnO2/Ag/rGO films as anode and AC/rGO films as cathode electrodes within a wide operating voltage of 0–1.7 V. The energy density of obtained ASC devices was 71.8 Wh kg−1 at a power density of 279.4 W kg−1.

Synthesis of mesoporous defective graphene-nanosheets in a space-confined self-assembled nanoreactor: Highly efficient capacitive energy storage

Two-dimensional graphene-based materials are of great interest in electrochemical energy storage devices owing to their high theoretical specific capacitance; however, it is a big challenge to approach the theoretical limit. Here, we report a facile strategy for the selective production of N-doped graphene nanosheets (NGNS) in quasi-closed montmorillonite (MMT), which act as a nanoreactor and open only along the perimeter to enable the entrance of aniline (AN) monomer. As a proof of concept applications, as-synthesized NGNS are used as the electrode material for a symmetric supercapacitor (SSC). The NGNS supported on carbon paper (NGNS@CP) exhibits excellent capacitive performance in an aqueous neutral electrolyte (LiCl) by achieving a high capacitance of 480 and 472 F g−1 at 1 A g−1 for negative and positive electrodes, respectively. The NGNS@CP electrode also shown outstanding rate capabilities and cycling stabilities in positive and negative voltage windows by retaining the 98.07, and 99.44 % of the original value, respectively. Moreover, the assembled flexible symmetric supercapacitor (NGNS@CP//NGNS@CP) using LiCl/PVA hydro-gel electrolyte can operate at high voltage window of 0.0–2.0 V and achieved an ultra-high energy density of 82.72 Wh kg−1 at a moderate power density of 425.68 W kg−1 with remarkable cycling stability of 96.91 % over 10000 charge/discharge cycles. Furthermore, the NGNS@CP//NGNS@CP demonstrates excellent flexibility and one device can power the two light-emitting diodes brightly. The achieved energy density of the NGNS@CP//NGNS@CP is much superior to the previous graphene-based SSCs and suggests a new generation of ultra-fast symmetric supercapacitor as novel high-performance energy storage devices.

Template synthesis of NiCo2S4/Co9S8 hollow spheres for high-performance asymmetric supercapacitors

Nickel cobalt sulfides have been widely used as the battery-type electrode materials for asymmetric supercapacitors. However, it is still a challenge that obtains a unique structure to improve their electrochemical characteristics and practical applications. Hollow porous structures with hetero-interfaces are currently promising to endow electroactive materials with excellent properties, such as well-defined interior voids, low density, high pore volume, and surface permeability. Herein, hetero-structure NiCo2S4/Co9S8 hollow spheres were synthesized by using the carbon spheres as the sacrificial template via the solvothermal method and anion exchange process. When evaluated as a promising electrode for supercapacitors, the NiCo2S4/Co9S8 electrode exhibited an excellent specific capacitance of 2180 F g−1 at the current density of 1 A g−1, a high capacity retention that the specific capacitance retained 1400 F g−1 even at 20 A g−1, and a long stable cycling performance of retaining ∼85% after 10,000 cycles. In addition, the asymmetric supercapacitors based on these hollow hetero-spheres exhibited a high energy density of 96.5 W h kg−1 at a power density of 0.8 kW kg−1. The energy density can achieve 51.7 W h kg−1 even at a higher power density of 20 kW kg−1, indicating that the NiCo2S4/Co9S8 hollow spheres have superior practical applications for energy storage.

ACF/NiCo2S4 honeycomb-like heterostructure material: Room-temperature sulfurization and its performance in asymmetric supercapacitors

Transition metal sulfide, especially NiCo2S4, is of great interest as the promising battery-type electrode material for asymmetric supercapacitor (ASC). However, such material has its own disadvantages of energy waste of preparation and poor electrical conductivity. In this work, we adopted a green and environmentally friendly room-temperature sulfurization method to successfully prepare the electrode material (ACF/NCS-HL) with activated carbon fiber (ACF) as the core and honeycomb-like NiCo2S4 as the shell (NCS-HL). This material has porous structure with heterogeneous redox electron pairs and shows excellent electrochemical performance. The optimized ACF/NCS-HL exhibits remarkable specific capacitance of 1682 F g−1 at 1 A g−1 in 2 M KOH aqueous electrolyte in the three-electrode system. The asymmetric supercapacitor device with ACF/NCS-HL as positive electrode and ACF as negative electrode shows the high energy density of 49.38 W h kg−1 at the power density of 800 W kg−1 and the preeminent cycle stability up to 82.88% after 5000 cycles, indicating its promising potential application in the future as high-performance supercapacitors.

Fabrication of porous MgCo2O4 nanoneedle arrays/Ni foam as an advanced electrode material for asymmetric supercapacitors

The porous MgCo2O4 nanoneedle arrays/Ni foam (MCNA@NF) fabricated using the two-step method. Porous MgCo2O4 nanoneedle arrays have a regular diameter of 40–70 nm, and the nanoneedle is composed of numerous nanoparticles. Nitrogen adsorption-desorption surface area of the porous MgCo2O4 is about 25.6 m2 g−1, the volume of pores is 0.164 cm3 g−1. The MCNA@NF as the electrode material display 804 F g−1 (at 1 A g−1). After 2000 cycles, the pours MgCo2O4 maintains 87% of initial capacitance (725 F g−1, 6 A g−1). The electrochemical performances of the MCNA@NF are further investigated in an asymmetric supercapacitor (ASC). This asymmetric supercapacitor (MgCo2O4//rGO) device up to 81 Wh kg−1 at 1350 W kg−1. At 6750 W kg−1, the MgCo2O4//rGO ASC device still kept 59 Wh kg−1 (0–1.5 V). These good ASC device performances can be attributed to the spinel structure and its high surface areas, which is beneficial for the rich redox reaction sites growth. The MCNA@NF have a good potential application in ASC devices.

Ternary core-shell structured transition metal chalcogenide for hybrid electrochemical capacitor

Hybrid structured semiconductor nanomaterials possess excellent electrochemical performances owing to the synergistic effects from two components. Herein we report a novel CoMo2S4@Zn-Co-S core-shell structure as the electrode materials for asymmetric supercapacitor. The unique electrode structure is beneficial to rapid electron transport and the ion diffusion due to the existence of many vast channels. The as-synthesized core-shell structured electrode exhibits an overall improved electrochemical performance. Moreover, a quasi-solid state asymmetric supercapacitor is fabricated. It reveals a specific capacitance of 0.84 C/cm2 collected at 4 mA/cm2 and an energy density of 1.87 mWh/cm3 at a power density of 31.99 W/cm3.

Realizing an Asymmetric Supercapacitor Employing Carbon Nanotubes Anchored to Mn3O4 Cathode and Fe3O4 Anode.

A facile route to anchor pseudocapacitive materials on multiwalled carbon nanotubes (CNTs) to realize high-performance electrode materials for asymmetric supercapacitors (ASCs) is reported. The anchoring process is developed after direct decomposition of metal-hexacyanoferrate complex on the CNT surface. Transmission electron microscopy (TEM) analysis reveals that the nanoparticles (NPs) are discretely attached over the CNT surface without forming a uniform layer, thus making most of the entire NP surface available for electrochemical reactions. Accordingly, CNT-Mn3O4 nanocomposite cathode shows significantly improved capacitive performance as compared to pristine CNT electrode, validating the efficacy of designing the composite electrode. With CNT-Fe3O4 nanocomposite as the paired anode, the hybrid ASC delivers a specific capacitance of 135.2 F/g at a scan rate of 10 mV/s within a potential window of 0-1.8 V in the aqueous electrolyte and retains almost 100% of its initial capacitance after 15,000 cycles. The serially connected ASCs can power commercial light-emitting diodes (LEDs) and mobile phones, reflecting their potential in next-generation storage applications.

One-step electrodeposition fabrication of Ni3S2 nanosheet arrays on Ni foam as an advanced electrode for asymmetric supercapacitors

Ni3S2 nanosheet (NS) arrays on Ni foam were fabricated by a simple one-step electrodeposition strategy, and used as a kind of electrode material for asymmetric supercapacitors. The Ni3S2 NS arrays are interconnected, which can be regarded as bridges between these individual nanoparticle units. The electrochemical performances were evaluated by cyclic voltammetry and chronopotentiometry techniques in a three-electrode system. The Ni3S2 NS arrays display a specific capacitance of 773.6 F g−1 at 1 A g−1, and excellent rate property of 84.3% at 10 A g−1. The performance of the Ni3S2 NS arrays was further investigated in an asymmetric supercapacitor for potential practical application. The asymmetric supercapacitor using the Ni3S2 electrode and reduced graphene oxide electrode as positive and negative electrodes, respectively, exhibits an energy density of 41.2 W h kg−1 at 1.6 kW kg−1. When up to 16 kW kg−1, it holds 25.3 W h kg−1. These excellent electrochemical performances are attributed to the improved electronic conductivity and rich redox reaction sites from Ni3S2 NS arrays. Our results indicate that the Ni3S2 NS arrays have great potential for supercapacitors.

Polyaniline-modified porous carbon tube bundles composite for high-performance asymmetric supercapacitors

In this work, activated carbon tube bundles (ACTBs) with porous hollow structure are prepared using dandelion fluffs as precursors. The open-framework porous structure of the ACTBs contributes to large specific surface area and enhanced electrochemical performances. Then the ACTBs are further modified with polyaniline (PANI) using the in-situ polymerization method, the unique hollow tube structure of the ACTBs effectively increases the growth area for the PANI. The PANI modified ACTBs (PANI/ACTBs) composite exhibits an excellent rate performance due to the highly retained porous hollow tube structure, which promotes the electrolyte ions diffusion and electron transport. Meanwhile, the ACTBs and PANI/ACTBs serve as the cathode and anode electrode materials for asymmetric supercapacitor, respectively. As a result, the asymmetric supercapacitor displays a high energy density of 42 Wh kg−1 and a capable cycling stability. These results demonstrate that the PANI/ACTBs composite is a promising electrode material for the energy storage devices.

Unique porous Mn2O3/C cube decorated by Co3O4 nanoparticle: Low-cost and high-performance electrode materials for asymmetric supercapacitors

A unique interconnected porous Mn2O3/C@Co3O4 cubic composite, as efficient electro-active electrode for supercapacitors, was successfully synthesized via a facile two-step hydrothermal method. Novel cube-like Mn2O3/C@Co3O4 composite, with a high specific surface area (SBET) and conductivity, could promote charge transfer and improve the overall electrochemical performance. The as-prepared Mn2O3/C@Co3O4 composite exhibited the excellent reversible specific capacitance (523.8 F g−1 at a current density of 0.3 A g−1, much higher than Mn2O3/C), good rate performance (57.2% capacitance retention) and superior cycling stability (90.6% capacitance retention after 3000 cycles). In addition, an asymmetric supercapacitor (Mn-Co//AC) with Mn2O3/C@Co3O4 as the positive electrode and activated carbon (AC) as the negative electrode delivered a maximum energy density of 45.8 Wh kg−1 at a power density of 0.3 kW kg−1.

Hierarchical self-assembly flower-like ammonium nickel phosphate as high-rate performance electrode material for asymmetric supercapacitors with enhanced energy density

Ammonium nickel phosphate has a large specific capacitance as an electrode material at low current density, but its capacitance decays fast at high current density, which directly affects the rate performance of supercapacitors. Herein, we demonstrate a facile route for the controllable synthesis of hierarchical self-assembly flower-like ammonium nickel phosphate as a high-rate electrode material for asymmetric supercapacitors, which is an important strategy to enhance the energy density at high power density. The flower-like structures are hierarchically assembled by a mass of rectangular sheets, which can provide fast electron transport and short ion diffusion path, thereby exhibiting excellent electrochemical performance with ultrahigh specific capacitance of 1016 F g−1 at 1.0 A g−1. More importantly, the NH4NiPO4 · H2O materials exhibit outstanding rate performance (800 F g−1 even at large current density of 30 A g−1) and superior long-term cycle life (83% of capacity retention up to 3000 cycles at 5 A g−1). Furthermore, the NH4NiPO4 · H2O//AC asymmetric supercapacitors are assembled in aqueous KOH electrolyte, and exhibit high energy density (46.2 Wh kg−1 at 160 W kg−1 and 26.7 Wh kg−1 at a large power density of 4000 W kg−1, respectively). Due to the outstanding electrochemical performance, the all-solid-state asymmetric supercapacitors are successfully constructed using these materials.

Mn3O4-Anchored Carbon-Nanotube Based Asymmetric Supercapacitor

A facile route to anchor pseudocapacitive materials on multi-walled Carbon Nanotubes (CNTs) to realize high-performance electrode materials for Asymmetric Supercapacitors (ASCs) is achieved. The anchoring process is achieved after direct decomposition of metal-hexacyanoferrate complexes on the CNT surface. Transmission electron microscopy (TEM) analysis reveals that the nanoparticles (NPs) are discretely attached over CNT surface without forming a uniform layer, thus making almost entire NP surface available for electrochemical reactions. Accordingly, CNT-Mn3O4 nanocomposite cathode shows significantly improved capacitive performance as compared to bare CNT electrode, validating the efficacy of designing the composite electrode. With CNT-Fe3O4 nanocomposite as paired anode, the hybrid ASC delivers a specific capacitance of 135.2 F/g at a scan rate of 10 mV/s within a potential window of 0-1.8V in the aqueous electrolyte and retains almost 100% of its initial capacitance even after 15000 cycles.

Fabrication of 3D graphene-CNTs/α-MoO3 hybrid film as an advance electrode material for asymmetric supercapacitor with excellent energy density and cycling life

Recently, three-dimensional (3D) architectures of graphene-carbon nanotubes (CNTs) have attracted a lot of attention due to their multifunctional properties. In this study, we have reported a novel 3D graphene-CNTs/MoO3 hybrid film as a binder free electrode material with unique morphology and outstanding electrochemical performance. The optimized 3D graphene-carbon nanotubes (GF-CNTs) framework was fabricated by a chemical vapor deposition (CVD) process on Ni foam skeleton. Further, controlled loading of MoO3 nanoplates were grown on the GF-CNTs framework as a hybrid film, using an easy and low cost hydrothermal method. The as-fabricated hybrid electrode exhibits remarkable specific capacitance of 1503 F g−1 at 1 A g−1 and 798.93 F g−1 at a current density of 10 A g−1, as well as exceptional capacitance retention of 96.5% after 10,000 cycles. The excellent electrochemical performance of the electrode material can be attributed to the combination of pseudocapacitance and electric double layer capacitance contributed by the MoO3 nanoplates and graphene foam/CNTs in the hybrid system, respectively. The asymmetric supercapacitor (ASCs), assembled from GF-CNTs/MoO3 and GF-CNTs as positive and negative electrode, respectively, delivers excellent specific capacitance of 211.71 F g−1 at current density of 1 A g−1. The ASCs device also exhibits a maximum energy density of 75.27 W h kg−1 at a power density of 816.67 W kg−1 with excellent cycling ability of 94.2% of the initial capacitance after 10,000 cycles. These results suggest that the as-fabricated GF-CNTs/MoO3 hybrid architecture can be used as a promising electrode material for the next generation supercacitor devices.

Excellent electrochemical behavior of graphene oxide based aluminum sulfide nanowalls for supercapacitor applications

Graphene oxide based electrode materials show remarkable electrochemical properties due to the improved specific surface area and electrical conductivity for supercapacitor applications. Hydrothermally synthesized graphene oxide based aluminum sulfide nanowalls on nickel foam (NF) have revealed excellent pseudocapacitive behavior with the specific capacitance 2362.15 F g-1 at 2 mVs-1 as observed through cyclic voltammetry. The galvanostatic charge-discharge measurements confirmed a specific capacitance 2373.51 F g-1 at 3 mAcm−2. Hexagonal phase of the graphene oxide (GO) based Al2S3 nanowalls also showed good discharge time of 820 s and energy density 118.68 WhKg−1 at 3 mAcm−2. Moreover, the fabricated electrode material exhibited good power density 2663.58 W kg-1 at 20 mAcm−2. The impedance results also confirmed the pseudocapacitive characteristics and revealed weak contact and Warburg resistances for the electrode material in half cell. Hence, GO based Al2S3 nanowalls performed as a prominent electrode material for asymmetric supercapacitors. Additionally, electrode material also exhibited excellent symmetric behavior, which again suggested a good electrode structure for supercapacitor applications.

One-step synthesis of Nickle Iron-layered double hydroxide/reduced graphene oxide/carbon nanofibres composite as electrode materials for asymmetric supercapacitor

A novel NiFe-LDH/RGO/CNFs composite was produced by using a facile one-step hydrothermal method as electrode for supercapacitor. Compared with NiFe-LDH/CNFs, NiFe-LDH/CNTs and NiFe-LDH/RGO, NiFe-LDH/RGO/CNFs demonstrated a high specific capacitance of 1330.2 F g−1 at 1 A g−1 and a super rate capability of 64.2% from 1 to 20 A g−1, indicating great potential for supercapacitor application. Additionally, an asymmetric supercapacitor using NiFe-LDH/RGO/CNFs composite as positive electrode material and activated carbon as negative electrode material was assembled. The asymmetric supercapacitor can work in the voltage range of 0–1.57 V. It displayed high energy density of 33.7 W h kg−1 at power density of 785.8 W kg−1 and excellent cycling stability with 97.1% of the initial capacitance after 2500 cycles at 8 A g−1. Two flexible AC//LDH-RGO-CNFs ASC devices connected in series were able to light up a red LED indicator after being fully charged. The results demonstrate that the AC//LDH-RGO-CNFs ASC has a promising potential in commercial application.

Functionalized graphene–polyaniline nanocomposite as electrode material for asymmetric supercapacitors

A polyaniline/sulfonated graphene (PANI/SG) nanostructure was synthesized as electrode material for an asymmetric supercapacitor via a novel in situ chemical oxidative polymerization method including two oxidants. The composite’s structure and morphology were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) measurements. Furthermore, the electrochemical performances of the composite were characterized by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques in detail. In addition, we have triumphantly manufactured an asymmetric supercapacitor (ASC) employing activated carbon (AC) and PANI/SG as the positive and negative electrodes, respectively. The ASC possessed an extended potential window (1.4 V), a remarkable cycling property (85.9% capacitance retention after 5000 cycles), and a satisfactory average energy and power density (23 Wh/kg and 6.1 kW/kg).

Preparation and Electrochemical Properties of Nickel Iron Carbonate Hydroxide as a Cathode Electrode Material for Asymmetric Supercapacitors

Preparation and Electrochemical Properties of Nickel Iron Carbonate Hydroxide as a Cathode Electrode Material for Asymmetric Supercapacitors

One-step engineered self-assembly Co3O4 nanoparticles to nanocubes for supercapacitors

Tricobalt tetraoxide or cobalt oxide (Co3O4) nanocubes (NCs) were synthesized from the self-assemblies of Co3O4 nanoparticles (NPs) via a simple one-step hydrothermal method. X-ray diffraction analysis confirmed the cubic crystal structure of Co3O4 NCs. The surface properties were investigated by x-ray photoelectron spectroscopy, which suggests the co-existence of Co in +2 and +3 states. The self-assemblies of aggregation of NPs to NCs were inspected using scanning electron microscopy, which is supported by transmission electron microscopy. The electrochemical properties of Co3O4 NCs were carried out by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) curves and impedance analysis. The areal capacitance of 3.04 mF cm−2 was obtained at current density of 10 μA cm−2. The Co3O4 NCs electrode exhibits good long-cyclic stability with 92.1% capacitance retention over 3000 cycles. The CV, GCD and impedance curves of Co3O4 NCs were recorded after cyclic test, which are similar to the curves recorded before the test. Therefore, the Co3O4 NCs serves good candidate as positive electrode materials for asymmetric supercapacitors.

Facile synthesis of electrostatically anchored Nd(OH)3 nanorods onto graphene nanosheets as a high capacitance electrode material for supercapacitors

Nd(OH)3/G hybrid is prepared by a solvothermal reduction process and used as an electrode material for asymmetric supercapacitors.

Synthesis of a MnS/Ni x S y composite with nanoparticles coated on hexagonal sheet structures as an advanced electrode material for asymmetric supercapacitors.

Herein, a facile hydrothermal method was designed to synthesize a novel structure of micro-flowers decorated with nanoparticles. The micro-flower structure consists of enormous cross-linked flat hexagonal nanosheets with sufficient internal space, providing fluent ionic channels and enduring volume change in the electrochemical storage process. As expected, the MnS/NixSy (NMS) electrode exhibits a relatively high specific capacitance of 1073.81 F g−1 (at 1 A g−1) and a good cycling stability with 82.14% retention after 2500 cycles (at 10 A g−1). Furthermore, the assembled asymmetric supercapacitor achieves a high energy density of 46.04 W h kg−1 (at a power density of 850 W kg−1) and exhibits excellent cycling stability with 89.47% retention after 10 000 cycles. The remarkable electrochemical behavior corroborates that NMS can serve as an advanced electrode material.