Symmetric Two-electrode System Research Articles

PVA-assisted hydrated vanadium pentoxide/reduced graphene oxide films for excellent Li+ and Zn2+ storage properties

Low-cost, high safety and environment-friendly aqueous energy storage systems (ESSs) are huge potential for grid-level energy storage, but the (de)intercalation of metal ions in the electrode materials (e.g. vanadium oxides) to obtain superior long-term cycling stability is a significant challenge. Herein, we demonstrate that polyvinyl alcohol (PVA)-assisted hydrated vanadium pentoxide/reduced graphene oxide (V2O5∙nH2O/rGO/PVA, denoted as the VGP) films enable long cycle stability and high capacity for the Li+ and Zn2+ storages in both the VGP//LiCl (aq)//VGP and the VGP//ZnSO4 (aq)//Zn cells. The binder-free VGP films are synthesized by a one-step hydrothermal method combination with the filtration. The extensive hydrogen bonds are formed among PVA, GO and H2O, and they act as structural pillars and connect the adjacent layers as glue, which contributes to the ultrahigh specific capacitance and ultralong cyclic performance of Li+ and Zn2+ storage properties. As for Li+ storage, the binder-free VGP4 film (4 mg PVA) electrode achieves the highest specific capacitance up to 1381 F g−1 at 1.0 A g−1 in the three-electrode system and 962 F g−1 at 1.0 A g−1 in the symmetric two-electrode system. It also behaves the outstanding cyclic performance with the capacitance retention of 96.5 % after 15000 cycles in the three-electrode system and 99.7 % after 25000 cycles in the symmetric two-electrode system. As for Zn2+ storage, the binder-free VGP4 film electrode exhibits the high specific capacity of 184 mA h g−1 at 0.5 A g−1 in the VGP4//ZnSO4 (aq)//Zn cell and the superb cycle performance of 98.5 % after 25000 cycles. This work not only provides a new strategy for the construction of vanadium oxides composites and demonstrates the potential application of PVA-assisted binder-free film with excellent electrochemical properties, but also extends to construct other potential electrode materials for metal ion storage cells.

Single-step hydrothermal synthesis of nitrogen-doped ZnO nanostructures and an insight into its electrochemical properties

Zinc oxide (ZnO) nanostructures have been extensively used as electrochemical sensing material for the development of biosensors and bioimplantable devices. It is important to evaluate their electrochemical performance while developing materials with rapid response time and higher sensitivity. Herein, we present a novel one-step low-temperature hydrothermal technique for simultaneous nitrogen doping and growth of ZnO (N-ZnO) nanostructures. Nitrogen addition is expected to enhance the electron mobility and hence the electrical conductivity of ZnO. The nanostructures were characterized by X-ray diffraction, UV–Vis spectroscopy and field emission scanning electron microscopy. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry using an N-ZnO/Ag/Glass symmetric two-electrode system. The nitrogen addition to ZnO lattice is suggested by XRD peak shift, changing lattice parameters and dislocation density as compared to pristine ZnO. A substantial increase in the electrochemical response and conductivity can be attributed to nitrogen incorporation into ZnO lattice.

Intercalation pseudocapacitance in Bi2Se3−MnO2 nanotube composite for high electrochemical energy storage

Layered materials exhibit exclusive electrochemical properties centered on interlayer spaces. However, slow kinetics and poor cycling stability restrict overall performance. A possible solution to deliver high energy storage is by interfacial modification of layered materials, which can structurally allow the occurrence of intercalation pseudocapacitance at redox-capacitance timescale. In this work, MnO2 has been intercalated in-situ in layered Bi2Se3 for the first time to give Bi2Se3−MnO2 nanotube composite. Structural and morphological characterizations have been conducted elaborately by several experimental and theoretical studies. Electrokinetic measurements reveal a dominant capacitive mechanism of 69% at 60 mV s − 1. Ex-situ XRD analysis after electrochemical charge-discharge cycles show reversible shifts in c-axis containing Bi2Se3 (015) plane, which confirms intercalation pseudocapacitance. The nanocomposite demonstrates high specific capacitance (438 F g − 1 at 1 A g − 1 in a three-electrode system) in a wide potential window of 2 V. Moreover, a symmetric two-electrode system for Bi2Se3−MnO2 exhibits a high energy density of 62 Wh kg−1 and a power density of 2.7 kW kg−1 at 1 A g − 1 and 10 A g − 1, respectively, along with capacitance retention of 86% after 2000 cycles. The study gives promising direction to design integrated high energy and power density intercalation pseudocapacitive materials.

Facile synthesis of NiO@Ni(OH)2-α-MoO3 nanocomposite for enhanced solid-state symmetric supercapacitor application

Electrochemical supercapacitor fabrication using heterogeneous nanocomposite is one of the most promising pathways for energy storage technology. Herein, heterostructure based nickel-molybdenum (NiO@Ni(OH)2-α-MoO3) nanocomposites have been successfully prepared on nickel foil via hydrothermal route for supercapacitor application. The mixed phases of cubic, hexagonal, and orthorhombic crystal structure for NiO, Ni(OH)2, and α-MoO3, respectively were observed by X-ray diffraction. Heterostructures of nanosheet and nanosphere morphologies were confirmed by high resolution transmission electron microscopy. Impressively, the NiO@Ni(OH)2-α-MoO3 composite working electrode exhibits a high specific capacitance of 445 Fg−1 at current density of 1 Ag−1 and shows outstanding rate capability (97.3% capacity retention after 3000 cycles at 10 Ag−1), compared to that of NiO@Ni(OH)2 nanoparticles. Notably, two-electrode symmetric supercapacitor of NiO@Ni(OH)2-α-MoO3 working electrode shows a high specific capacitance of 172 Fg−1 at 0.5 Ag−1, excellent rate capability and good cycling stability. Also, an excellent cycling stability (capacity retention of 98% after 5000 cycles) is observed for NiO@Ni(OH)2-α-MoO3 as a working electrode in the symmetric two-electrode system. The obtained attractive results demonstrate that nanocomposite anode material can be used for development of a wide-range of energy storage devices.

Electrochemical performance of supercapacitor with glass wool separator under TEABF4 electrolyte

The paper presents the electrochemical performance of supercapacitor with glass wool separator under organic electrolyte of tetraethylammonium tetrafluoroborate (TEABF4). The performance was evaluated using symmetrical two-electrode system and compared to an identical supercapacitor with commercially available cellulose paper separator under 1 M TEABF4. The application of glass wool separator reduces the bulk resistance of supercapacitor by 19.6%, promotes more efficient ions transfer across active surface of electrode and significantly improves specific capacitance by 19.1% compared to cellulose paper. The application of higher concentration TEABF4 (1.5 M) even improves the overall performance of glass wool-based supercapacitor by 32.2% reduction of bulk resistance and 61.9% increment in specific capacitance compared to 1 M TEABF4. In addition, the energy and power densities are significantly improved by 64% and 165%, respectively for the one with 1.5 M TEABF4. In general, the low-cost material glass wool material has great potential to replace commercially available cellulose paper as separator in developing much better supercapacitor.

In-situ hydrothermal synthesis of δ-MnO2/soybean pod carbon and its high performance application on supercapacitor

Manganese dioxide, with large theoretical capacitance, is a promising electrode material of supercapacitors, while the poor cyclic stability limits its practical application. Traditional carbon loading using graphene or carbon nanotube is still unsatisfactory due to high cost. In this study, renewable waste of soybean pod was utilized as the precursor of carbon matrix. The MnO2/soybean pod carbon composite material was synthesized by a one-step in-situ hydrothermal method. The composite material displayed natural tube structure, and its surface was sheathed with numerous δ-MnO2 nanorods. After carbon loading, the MnO2/soybean pod carbon delivered a superior specific capacitance of 530 F g–1 in Na2SO4 electrolyte as the three-electrode system, 46% higher than 362 F g–1 of pristine MnO2. Using the symmetrical two-electrode system, such the composite electrode further revealed high capacitance retention of 91% and reversible capacitance of 189 F g–1 after 6000 charge/discharge cycles. It demonstrates that this work develops a scalable strategy to obtain high-performance and cost-effective electrode material of next-generation supercapacitors.

Boosting the Utilization and Electrochemical Performances of Polyaniline by Forming a Binder-Free Nanoscale Coaxially Coated Polyaniline/Carbon Nanotube/Carbon Fiber Paper Hierarchical 3D Microstructure Composite as a Supercapacitor Electrode.

Nanoscale polyaniline (PANI) is formed on a hierarchical 3D microstructure carbon nanotubes (CNTs)/carbon fiber paper (CFP) substrate via a one-step electrochemical polymerization method. The chemical and structural properties of the binder-free PANI/CNTs/CFP electrode are characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The specific capacitance of PANI/CNTs/CFP tested in a symmetric two-electrode system reaches 731.6 mF·cm–2 (1354.7 F·g–1) at a current density of 1 mA·cm–2 (1.8 A·g–1). The symmetric supercapacitor device demonstrates excellent cycling performance up to 10,000 cycles with a capacitance retention of 81.4% at a current density of 1 mA·cm–2 (1.8 A·g–1). The results demonstrate that the binder-free CNTs/CFP composite is a strong backbone for depositing ultrathin PANI layers at a high mass loading. The hierarchical 3D microstructure PANI/CNTs/CFP provides enough space and transporting channels to form an efficient electrode–electrolyte interface for the supercapacitance reaction. The formed nanoscale PANI film coaxially coated on the sidewalls of CNTs enables efficient charge transfer and a shortened diffusion length. Hence, the utilization efficiency and electrochemical performances of PANI are significantly improved. The rational design strategy of a CNT-based binder-free hierarchical 3D microstructure can be used in preparing various advanced energy-storage electrodes for electrochemical energy-storage and conversion systems.

Three-dimensional self-supported iron-doped nickel sulfides for sustainable overall water splitting

In this short communication, a three-dimensional (3D) iron-doped nickel sulfides catalyst supported was successfully prepared on commercial Ni–Fe foam through one-step heat sulfurization, and its electrocatalytic performance for water splitting in 1 M KOH was investigated. In a symmetric two-electrode system assembled by the prepared electrocatalyst, an ultralow cell voltage of 1.46 V was required to drive 10 mA cm−2, which was much lower than that of the symmetric two-electrode system assembled by bare Ni foam, bare Ni–Fe foam, or nickel sulfides without iron doping. The iron-doped nickel sulfides had desirable stability for overall water splitting, and the electrocatalytic performance showed no significant degradation during long-term durability test (70 h at 10 mA cm−2). The 3D porous structure of Ni–Fe foam, the in-situ growth of catalyst, and the combined iron doping effects contributed to the outstanding performance of our prepared catalyst for overall water splitting.

Hybrid supercapacitors from porous boron-doped diamond with water-soluble redox electrolyte

Hybrid supercapacitors (HSCs) can simultaneously achieve battery-level energy as well as capacitor-level power and cycle life in a single device. To construct such HSCs, porous boron-doped diamond (BDD) films fabricated by a template-free method via regrowth of diamond nanoparticles were employed as the electrodes and water-soluble redox couples (Fe (CN)63−/4−) as the electrolyte. For the three-electrode system, the porous BDD electrode delivers a capacitance of 13.08 mF cm−2 in 1.0 M Na2SO4, and a capacity of 78.23 mAh g−1 in 0.05 M Fe (CN)63−/4− + 1.0 M Na2SO4 when a scan rate of 10 mV s−1 is applied. For the symmetric two-electrode system, the porous BDD electrode exhibits a capacitance of 13.04 mF cm−2 in 1.0 M Na2SO4 and a capacity of 34.74 mAh g−1 in 0.05 M Fe (CN)63−/4− + 1.0 M Na2SO4 at the same scan rate. The capacitance (capacity) remains about 92% of its initial value after 5000 cyclic voltammetry cycles in all conditions. The specific power densities (normalized by the mass of electrode active material only) are 0.17 and 1.05 kW kg−1, with their specific energy densities of 5.51 and 38.10 W h kg−1, respectively. Thus, the porous BDD films, together with the water-soluble redox electrolyte, have profound applications in high-performance hybrid supercapacitors construction for future power devices.

Electrodeposited NiSe on a forest of carbon nanotubes as a free-standing electrode for hybrid supercapacitors and overall water splitting

NiSe nanoparticles are electrodeposited over a forest of carbon nanotubes (CNTs) to form an intertwined and porous network. The assynthesized composite (denoted as CNT@NiSe/SS) is used as a free-standing and multifunctional electrode for bothsupercapacitorsand overallwater splitting applications. For a supercapacitor application, CNT@NiSe/SS exhibits higher specific capacity and improved rate capability compared with individual NiSe and CNTs. A hybrid supercapacitor device consisting of battery-like CNT@NiSe/SS and EDLC-like graphene delivers a maximum energy density of 32.1 Wh kg−1 at a power density of 823 W kg−1 and has excellent stability after a floating test of 50 h. On the other hand, CNT@NiSe/SS also serves as a bifunctional electrocatalyst with high activity for overall water splitting. The CNT@NiSe/SS electrode displays excellent hydrogen and oxygen evolution reaction performance with the lowest overpotential of 174 mV at 10 mA cm−2 and 267 mV at 50 mA cm−2, respectively. The symmetrical two-electrode system requires an operating potential of 1.71 V to achieve a current density of 10 mA cm−2. Furthermore, this electrolyzer shows a negligible increment in potential after 24 hof continuouswater splitting. The outstanding performances of CNT@NiSe/SS can be attributed to the synergistic effect of NiSe and CNTs.

Valorization of composting leachate for preparing carbon material to achieve high electrochemical performances for supercapacitor electrode

Composting leachate, a potential precursor, was attempted to prepare the activated carbons via hydrothermal carbonization plus KOH activation in this work. The obtained carbons were further investigated to check their electrochemical performances as electrode materials of supercapacitor. The carbon material that activated at 700 °C (CL-700) exhibits the highest specific surface area of 2184.9 m2 g−1 and the largest pore volume of 1.55 cm3 g−1 comparing to the activated carbons at other temperatures. In a three-electrode system, CL-700 displayed an excellent capacitance of 228 F g−1 at 0. 5 A g−1, and it was 178 F g−1 even though at a higher current density of 10 A g−1. After 5000 tests on the charge-discharge cycle, CL-700 showed a superior stability with 83.2% capacity retention and almost 100% coulombic efficiency at 5 A g−1. Moreover, CL-700 had a good energy density of 7.1 Wh kg−1 at a power density of 124.9 W kg−1 in a symmetric two-electrode system. Based on the comparison with the currently reported biomass-deriver carbons, the composting leachate can be regarded as a feasible precursor to harvest carbon materials for supercapacitor electrode, which was meaningful to offer a novel path for the valorization of the leachate fraction from bio-wastes.

“Frying” milk powder by molten salt to prepare nitrogen-doped hierarchical porous carbon for high performance supercapacitor

A simple method similar to frying was used to pyrolysis of renewable biomass carbon milk powder in NaCl/Na2CO3 molten salt at 700 °C under the air atmosphere to prepare nitrogen-doped hierarchical porous carbon. This preparation method displayed a simple preparation process with the low requirements for equipment and low-cost raw materials. The prepared optimal nitrogen-doped porous carbon material exhibited a hierarchical porous with macropores, mesopores, and micropores and had a high specific surface area of 1095 m2 g−1. As supercapacitors electrodes, The prepared optimal sample displayed a high specific capacitance of 391.5 F g−1 at 0.5 A g−1 and an excellent rate performance. It also exhibited excellent cycle stability (only loss of 4.4% capacitance) at 4 A g−1 over 5000 cycles. Moreover, In a symmetrical two-electrode system of 1 M Na2SO4, the assembled supercapacitor displayed a high energy density of 33.0 Wh kg−1 at 0.25 A g−1, maintained a high energy density of 22.3 Wh kg−1 at 20 A g−1 and exhibited excellent stability at 5 A g−1 over 5000 cycles. The assembled symmetrical PVA/Na2SO4 solid supercapacitor can successfully light up the light emitting diode (LED). This work provided a sample and low consumption way to prepare N doped hierarchical porous carbon electrode material for high performance supercapacitors.

Facile and Scalable Fabrication of Nitrogen-Doped Porous Carbon Nanosheets for Capacitive Energy Storage with Ultrahigh Energy Density.

Porous carbon materials are the most commonly used electrode materials for supercapacitors because of their abundant structures, excellent conductivities, and chemical stability. However, the manufacture of carbon materials possessing sizable pores and remarkable wettability with the electrolyte remains challenging. Herein, we developed a facile and industrially scalable method for the production of nitrogen-doped porous carbon nanosheets (PNDC-4) with excellent pore size distribution, large specific surface area (>1200 m2 g-1), high conductivity (>700 S m-1), and superb wettability either in aqueous or organic electrolyte. Particularly, PNDC-4 shows a high capacitance of 387 F g-1 (1 A g-1) in a three-electrode system with 3 M KOH and 80 F g-1 (1 A g-1) in a symmetric two-electrode system with EMIMBF4. The device exhibits an ultrahigh energy density of 81 W h kg-1 at a power density of 1.3 kW kg-1 and can still maintain at 60.8 W h kg-1 when the power density is increased to 266.6 kW kg-1. Moreover, the devices show superb stability that 94% of its initial capacitance is still maintained after 100 000 cycles at 20 A g-1.

Mesoporous nickel sulphide nanostructures for enhanced supercapacitor performance

The nanostructured electrode material with high surface area, good porous texture and appropriate pore-size distribution are facilitating more active sites for accumulation of ions and a large rate of ionic diffusion. Here, the mesoporous Ni3S4 nanostructures were prepared through a one-pot hydrothermal method. Annealing temperature which is known to affect the structural, morphological and electrochemical properties of the nanostructure has been optimized. Mesoporous Ni3S4 nanoflakes show a high surface area of 73 m2 g−1 at an annealing temperature of 200 °C (N2). This porous nanostructure exhibits a high specific capacitance of 1184 ± 71 to 548 ± 9 F g−1 at realistic specific currents of 5 to 40 A g−1. The symmetric two-electrode system (N2//N2) made up of mesoporous nanoflakes delivers a maximum energy density of 9 W h kg−1 at 2 A g−1 and maximum power density of 4.6 kW kg−1 at 40 A g−1. It retains 72% of initial capacitance after 5000 repeated cycling process. In addition, we have used two such symmetric devices to power a red LED. It demonstrates the intrinsic capability of porous Ni3S4 nanoflakes annealed at 200 °C to offer enhanced electrochemical performance and further appear to be a promising electrode material for real-life supercapacitors.

Boron-Doped Diamond Powders for Aqueous Supercapacitors with High Energy and High Power Density

The electrochemical properties of boron-doped diamond powder (BDDP) were investigated as a step toward its application to aqueous electric double-layer capacitors (EDLCs). Conductive BDDPs (particle size: 150, 350, and 3500 nm) were prepared by depositing a BDD layer on the surface of a diamond powder (DP) core with various particle sizes (100, 300, and 2600 nm) via microwave plasma-assisted chemical vapor deposition. The 150-nm-sized BDDP (BDDP-150) had a relatively large Brunauer–Emmett–Teller (BET) specific surface area (106 m2/g). Cyclic voltammetry of the BDDP electrodes in 1.0 M H2SO4 with a symmetric two-electrode system showed an operating voltage of 1.5 V, which is much larger than that of an activated carbon (AC) electrode (0.8 V). In addition, compared to the AC electrode, the BDDP electrodes showed lower capacitance-decrease ratios at fast scan rates. Hence, BDDP-150 had greater energy and power densities than the AC electrode under high rate conditions in the aqueous electrolyte. As the BDDP electrode had a larger bulk density than the AC electrode, aqueous EDLC using BDDP can be expected to be used as a space-saving electric energy storage system suitable for high-speed charging and discharging.

Preparation of S/N co-doped graphene through a self-generated high gas pressure for high rate supercapacitor

At present, the application of doped graphene have been widely studied in supercapacitor, but the preparation of co-doped graphene electrode materials for high rate performance supercapacitor is still a challenge. In this work, we reported an effective method to prepare S/N co-doped graphene (SNG-H) through a self-generated high gas pressure by heating graphene with (NH4)2SO4 and melamine in a sealed vacuum copper tube under 600 °C. During heating treatment, the self-generated high gas pressure was formed by pyrolysis of the precursors in a sealed space. The X-ray photoelectron spectroscopy result showed that N and S atomic percentage of SNG-H were 6.22 at% and 2.82 at% which higher than that doped method using inert gas. This result indicated that the self-generated high gas pressure by pyrolysis of the precursors in a sealed space promoted the incorporation of heteroatoms into the lattice of graphene. Meanwhile, this method avoided the resources consumption of using inert gas (N2 and Ar) and effectively reduced gas pollution emissions. As the supercapacitor electrode material, the specific capacitance of SNG-H electrode material reached 264.3 F g−1 at 0.5 A g−1 and showed excellent rate capability at 200 mV s−1 in a three-electrode system. SNG-H also exhibited high capacitance performance, excellent rate capability (82% capacitance retention from 1 to 20 A g−1) and excellent cycling stability (95%) after 5000 cycles at 5 A g−1 in a symmetric two-electrode system. SNG-H was prepared through a self-generated high gas pressure in a sealed vacuum copper tube under 600 °C. This method improved the content of doped heteroatoms in SNG-H and enhanced the supercapacitor rate performance of SNG-H as an electrode material.

High-performance symmetric supercapacitors based on carbon nanotube/graphite nanofiber nanocomposites

This work reports the nanocomposites of graphitic nanofibers (GNFs) and carbon nanotubes (CNTs) as the electrode material for supercapacitors. The hybrid CNTs/GNFs was prepared via a synthesis route that involved catalytic chemical vapor deposition (CVD) method. The structure and morphology of CNTs/GNFs can be precisely controlled by adjusting the flow rates of reactant gases. The nest shape entanglement of CNTs and GNFs which could not only have high conductivity to facilitate ion transmission, but could also increase surface area for more electrolyte ions access. When assembled in a symmetric two-electrode system, the CNTs/GNFs-based supercapacitor showed a very good cycling stability of 96% after 10 000 charge/discharge cycles. Moreover, CNTs/GNFs-based symmetric device can deliver a maximum specific energy of 72.2 Wh kg−1 at a power density of 686.0 W kg−1. The high performance of the hybrid performance can be attributed to the wheat like GNFs which provide sufficient accessible sites for charge storage, and the CNTs skeleton which provide channels for charge transport.

MOF derived nitrogen-doped carbon polyhedrons decorated on graphitic carbon nitride sheets with enhanced electrochemical capacitive energy storage performance

Three dimensional carbon materials with hirerarchically porous structure could exhibit superior energy storage performance than two dimensional stacked carbon nanosheet materials. In this work, we prepared a novel ZIF-8-derived nitrogen doped carbon nanoparticles/graphitic carbon nitride composite electrode material with high electrochemical energy storage performances, including high specific capacitances (495 F g−1 at 0.1 A g−1 and 188 F g−1 at 20 A g−1) and a stable cycling durability with no capacitance declination after 5000 charge-discharge cycles in three-electrode system. When assembled as electrode materials in symmetrical two-electrode system, the as-prepared composite electrode material could exhibit high specific capacitances of 349.7 F g−1 at 0.5 A g−1 and 261.2 F g−1 at 5 A g−1. Accordingly, a high energy density of 11.89 Wh/kg can be achieved at the power density of 247.40 W kg−1. The improvement stems from its hierarchically porous structure with dominant pore sizes at 3 nm and among 4–40 nm, as well as high exposed pyridinic nitrogen (8.58 at%) and pyrrolic nitrogen (3.59 at%) active sites caused by the insertion of ZIF-8-derived nitrogen doped carbon nanoparticles between g-CN layers. This study has provided a new idea on the design of graphitic carbon nitride nanostructures with improved doping level and hiearchically porous structure.

High performance symmetric supercapacitor based on zinc hydroxychloride nanosheets and 3D graphene-nickel foam composite

In this work, zinc hydroxychloride nanosheets (ZHCNs) were deposited on 3d graphene-nickel foam (NiF-G) by employing a simple hydrothermal synthesis method to form NiF-G/ZHCNs composite electrode materials. The fabricated NiF-G/ZHCNs electrode revealed a well-developed pore structures with high specific surface area of 119m2g−1, and used as electrode materials for symmetric supercapacitor with aqueous alkaline electrolyte. The specific areal capacitance and electron charge transfer resistance (Rct) were 222mFcm−2 (at current density of 1.0mAcm−2) and 1.63Ω, respectively, in a symmetric two-electrode system. After 5000 cycles with galvanostatic charge/discharge, the device can maintain 96% of its initial capacitance under 1.0mAcm−2 and showed low Rct of about 9.84Ω. These results indicate that NiF-G/ZHCNs composite is an excellent electrode material for electrochemical energy storage devices.

Aloe vera Derived Activated High-Surface-Area Carbon for Flexible and High-Energy Supercapacitors.

Materials which possess high specific capacitance in device configuration with low cost are essential for viable application in supercapacitors. Herein, a flexible high-energy supercapacitor device was fabricated using porous activated high-surface-area carbon derived from aloe leaf (Aloe vera) as a precursor. The A. vera derived activated carbon showed mesoporous nature with high specific surface area of ∼1890 m2/g. A high specific capacitance of 410 and 306 F/g was achieved in three-electrode and symmetric two-electrode system configurations in aqueous electrolyte, respectively. The fabricated all-solid-state device showed a high specific capacitance of 244 F/g with an energy density of 8.6 Wh/kg. In an ionic liquid electrolyte, the fabricated device showed a high specific capacitance of 126 F/g and a wide potential window up to 3 V, which results in a high energy density of 40 Wh/kg. Furthermore, it was observed that the activation temperature has significant role in the electrochemical performance, as the activated sample at 700 °C showed best activity than the samples activated at 600 and 800 °C. The electron microscopic images (FE-SEM and HR-TEM) confirmed the formation of pores by the chemical activation. A fabricated supercapacitor device in ionic liquid with 3 V could power up a red LED for 30 min upon charging for 20s. Also, it is shown that the operation voltage and capacitance of flexible all-solid-state symmetric supercapacitors fabricated using aloe-derived activated carbon could be easily tuned by series and parallel combinations. The performance of fabricated supercapacitor devices using A. vera derived activated carbon in all-solid-state and ionic liquid indicates their viable applications in flexible devices and energy storage.