Areal Specific Capacitance Research Articles

Achieving Self-Supported Hierarchical Cu(OH)2/Nickel-Cobalt Sulfide Electrode for Electrochemical Energy Storage.

Herein, nickel-cobalt sulfide (NCS) nanoflakes covering the surface of Cu(OH)2 nanorods were achieved by a facile two-step electrodeposition strategy. The effect of CH4N2S concentration on formation mechanism and electrochemical behavior is investigated and optimized. Thanks to the synergistic effect of the selected composite components, the Cu(OH)2/NCS composite electrode can deliver a high areal specific capacitance (Cs) of 7.80 F cm-2 at 2 mA cm-2 and sustain 5.74 F cm-2 at 40 mA cm-2. In addition, coulombic efficiency was up to 84.30% and cyclic stability remained 82.93% within 5000 cycles at 40 mA cm-2. This innovative work provides an effective strategy for the design and construction of hierarchical composite electrodes for the development of energy storage devices.

Fabrication of Fe-Fe1-xO based 3D coplanar microsupercapacitors by electric discharge rusting of pure iron substrates.

Iron oxides with advanced functional properties show great potential for applications in the fields of water splitting, drug delivery, sensors, batteries and supercapacitors. However, it is challenging to develop a simple and efficient strategy for fabricating patterned iron oxide based electrodes for supercapacitor applications. Herein, a facile, simple, scalable, binder-free, surfactant-free and conductive additive-free electric discharge rusting (EDR) technique is proposed to directly synthesize Fe1-xO oxide layer on a pure iron substrate. This new EDR strategy is successfully adopted to fabricate Fe-Fe1-xO integrative patterned electrodes and coplanar microsupercapacitors (CMSC) in one step. The CMSC devices with different geometries could be directly patterned by EDR, which is automatically controlled by a computer numerical control system. The fabricated Fe-Fe1-xO based 3D 2F-CMSC exhibits a maximum areal specific capacitance of 112.4 mF cm-2. Another important finding is the fabrication of 3D 2F-CMSC devices, which show good capacitive behavior at an ultra high scanning rate of 20 000 mV s-1. The results prove that EDR is a low-cost and versatile strategy for the scalable fabrication of high-performance patterned supercapacitor integrative electrodes and devices. Furthermore, it is a versatile technique which shows a great potential for development of next generation microelectronic devices, such as microbatteries and microsensors.

Insight into thermal regulation of supercapacitors via surface-engineered phase change microcapsules.

Constructing efficient thermal management system to settle the thermal runaway of energy storage devices via employing phase change microcapsules (MEPCMs) is of great significance. However, it is still a challenge that the conventional MEPCMs go against the electrochemical performance and hardly be homogenously fixed in the electrodes. In order to conquer these long-standing critical issues, we designed a novel electrochemically active double-shell phase change microcapsule by introducing polypyrrole on the surface of dense amine resin shell of the conventional inert MEPCM. The active MEPCMs@PPy are uniformly immobilized on the surface of the electrode material using reduced graphene oxide to ensure the stable and efficient operation of the flexible supercapacitor. The assembled all-solid-state supercapacitor containing MEPCMs@PPy (SCs@MEPCMs@PPy) lagged 103s to 55°C than the SCs@00 without the added phase change material. At a high temperature of 55°C and a scan rate of 50mVs-1, SCs@MEPCMs@PPy exhibits an areal specific capacitance of 110.6mAcm-2, which is higher than that of the original SCs@MEPCMs. A capacitance retention of 79.8% and coulombic efficiency of 98.4% can be reached after 3000 cycles. This study opens a new avenue for developing applicable microencapsulated phase change materials in temperature-regulated electrode systems for supercapacitors and alkaline-ion batteries.

A general strategy to in situ synthesize hollow metal sulfide/MOF heterostructures for high performance supercapacitors.

Metal-organic frameworks (MOFs) have been extensively applied in supercapacitors. Unfortunately, metal active sites in MOFs are commonly blocked and saturated by organic ligands, leading to insufficient positions available for the electrochemical reaction. To address this issue, we develop a novel strategy to design and prepare a series of hollow metal sulfide/MOF heterostructures, which simultaneously alleviate the large volume expansion, avoid slow kinetics of metal sulfides and expose more electrochemically active sites of the MOF. Consequently, the optimized Co9S8/Co-BDC MOF heterostructure presents outstanding electrochemical performance with a high areal specific capacitance of 15.84 F cm-2 at 2 mA cm-2 and a capacitance retention rate of 87.5% after 5000 charge-discharge cycles. The asymmetric supercapacitors based on the heterostructure deliver a high energy density of 0.87 mW h cm-2 and a power density of 19.84 mW cm-2, as well as long cycling stability. This study provides a new strategy for the rational design and in situ synthesis of metal sulfide/MOF heterostructures for electrochemical applications.

Novel Fe2O3 microspheres composed of triangular star-shaped nanorods as an electrode for supercapacitors.

Fe2O3 microspheres with a unique structure were reported for the first time in this article and showed excellent cycling stability as a negative electrode for supercapacitors. A high areal specific capacitance of 1465.26 mF cm-2 was also achieved in sulfur-doped Fe2O3. An asymmetric supercapacitor was assembled demonstrating its potential for practical use.

MXene (Ti3C2Tx)/cellulose nanofiber/polyaniline film as a highly conductive and flexible electrode material for supercapacitors

In recent years, supercapacitors based on cellulose nanofiber (CNF) films have received considerable attention for their excellent flexibility, lightweight, and unique structure. In this study, MXene (Ti3C2Tx) /CNF/polyaniline (PANI) hybrid films with good conductivity and flexibility were prepared by a convenient vacuum filtration method. Combined with PANI, MXene creates an open structure with high conductivity, which facilitates ion and electron transport among the materials and provides the composite with high electrochemical activity. The MXene/CNF/PANI electrode presents a high areal specific capacitance of 2935 mF cm−2 at the current density of 1 mA cm−2, excellent cycling stability with high capacitance retention of 94 % after 2000 cycles at 10 mA cm−2 and high electrical conductivity (634.4 S∙cm−1). As a further application of this film, it is used as a free-standing electrode to fabricate a quasi-solid-state supercapacitor with high performance, which has an ultra-thin thickness of 0.344 mm, a significantly high areal specific capacitance (522 mF cm−2) at 5 mA cm−2, a high areal energy density of 94.7 μWh∙cm−2 and a high areal power density of 573 μW∙cm−2. This work shows the great potential of the developed high-performance and flexible cellulose-based composites for fabricating electrodes as well as supercapacitors.

Ultrafine Carbon-Nanofiber-Reinforced Graphene Fiber Electrodes for Flexible Supercapacitors with High Specific Capacitance and Durable Cycle Stability

Graphene fiber-based supercapacitors (FSCs) are one of the most promising energy storage devices for flexible electronics. However, the electrochemical performance of conventional graphene fiber electrodes fabricated by wet spinning is still limited by the low specific surface area (SSA), mismatched pore size distribution, and considerable interface resistance. Herein, we developed a scalable method to produce hierarchical porous carbon nanofibers/graphene hybrid fibers (CNGFs) for flexible supercapacitor electrodes with high specific capacitance and durable cycle stability. For energy storage applications, both ion storage accommodation and rapid electronic transfer are required, which could be achieved by the ultrahigh SSA and exceptional conductivity of CNGF electrodes. Therefore, the electrodes of CNGF30 (hybrid fibers with 30% carbon nanofiber loading) exhibit excellent electrochemical performance in terms of the area of areal-specific capacitance (409.1 mF/cm2) and cycle stability (97.7% over 10 000 cycles). Moreover, the well-designed CNGF30 offers remarkable mechanical flexibility for assembled FSCs.

Optimization of ion/electron channels enabled by multiscale MXene aerogel for integrated self-healable flexible energy storage and electronic skin system

MXenes have received extensive attention in the fields of energy storage and flexible electronics due to their excellent physicochemical properties. However, MXenes are prone to self-stacking, which would result in severely degraded performance of the electronic devices. Unlike the optimization of the structure-property relationship of MXene at specific scale in most reported studies, the current work is based on the multiscale design concept: MXene aerogels with abundant ion/electron channels are constructed through an efficient chemical oxidation and rapid gas foaming strategy. Nanoscale in-plane nanoporous MXenes can lead to increased ion channels and effectively shortened ion transport distances. Micron-scale MXene aerogels can provide abundant ionic active sites and maximized electron channels. The fabricated integrated self-healable flexible zinc-ion energy storage and pressure sensing system offers high areal specific capacitance of 576 mF cm−2, sufficient energy density of 156.8 uWh cm−2 at a power density of 4200 uW cm−2, and ultra-high pressure sensitivity (1024.9 kPa−1), which has great potential in applications including self-healing and flexible wearable devices. The multiscale design concept achieves the maximization of ion/electron channels, realizing a thoughtful strategy for the optimization of flexible electronic devices.

In-situ growth of Ni(OH)2 nanoplates on highly oxidized graphene for all-solid-state flexible supercapacitors

Pseudocapacitive materials are vitally important to the development of flexible supercapacitors but usually suffer from poor conductivity and stability. In this work, a Ni(OH)2/HGO nanocomposite was fabricated by in-situ growth of Ni(OH)2 nanoplates on highly-oxidized graphene oxide (HGO). A series of characterizations reveal the abundant out-of-plane active sites of HGO enable the uniformly grown Ni(OH)2 nanoplates with smaller crystalline size and stronger anchoring with HGO substrates. Furthermore, benefit from the porous structure and improved conductivity of HGO substrates together with more exposed active sites of Ni(OH)2 nanoplates, the complex Ni(OH)2/HGO electrode exhibits a remarkable specific capacitance of 1430.9F/g at 5 A/g, which is much higher than those of the pure Ni(OH)2 of 329.8F/g and Ni(OH)2 on the untreated GO (Ni(OH)2/GO) of 538.3F/g. Even under an ultrahigh current density of 60 A/g, the specific capacitance of Ni(OH)2/HGO electrodes still reach up to 850F/g, delivering a superior rapid-charging capability. In addition, by using screen-printing techniques, an all-solid-state Ni(OH)2/HGO//activated carbon-based asymmetric flexible supercapacitor is fabricated and displays an excellent areal specific capacitance of 322 mF/cm2, outstanding energy density (0.134 mW h/cm2) and power density (33.6 mW/cm2). Moreover, the capacity of all-solid-state flexible supercapacitors (AFSCs) remains 80 %, even bending to various angles and for 1000 times, showing good flexibility. This work provides inspiration for rational development of Ni(OH)2-based pseudocapacitive materials and high-performance AFSCs for portable and wearable electronics.

Porous network of ultrathin V6O13-polyoxometalates nanosheets grown on carbon cloth as anode materials for high-performance lithium-ion batteries

Polyoxometalates (POM) have a wide range of applications in electrochemistry, catalysis, and energy storage due to their variable structure and nature. Here, we designed a novel 3D porous network of ultrathin V6O13-POM nanosheets on carbon cloth (V6O13-POM//CC) for the first time by one-pot hydrothermal method with the help of phosphotungstic acid. Serving as inorganic ligands, the anions of phosphotungstic acid coordinate with V cations, facilitating the assembly of nanoclusters and guiding to control of the morphology of V6O13-POM composites, which increases the specific surface area and multiple active sites for the reaction of lithium ions batteries (LIBs). Furthermore, the synergistic effect of V6O13 and POM improves the stability of the structure and increases the capacity of the electrode in LIBs. V6O13-POM//CC as an anode material exhibited a high reversible capacity of 2.03 mAh cm-2 at a high current density of 2 mA cm-2 after 120 cycles. To illustrate the generality of the synthesis strategy, we also obtained MoO3-POM//CC via a similar method. By using V6O13-POM//CC and MoO3-POM//CC as the anode materials, LIBs exhibited high reversible areal specific capacity and excellent cycling stability which are expected to achieve commercial applications.

Ceria nanoflowers decorated Co3O4 nanosheets electrodes for highly efficient electrochemical supercapacitors

Overcoming a low energy density (1–50 Whkg−1) limitation is a challenge for supercapacitor electrode materials. To achieve higher performance (up to 100 Whkg−1), the transition metal-based pseudocapacitors (PCs) have been utilized owing to advantages viz. Faradaic reversible redox reaction significantly boosts the capacitance compared to that of the traditional electrical double layers capacitors (EDLCs). In this work, ceria nanoflowers decorated Co3O4 nanosheets structured active material deposited on nickel foam (denoted as CeO2@Co3O4/NF) by hydrothermal synthesis, demonstrates enhanced supercapacitor performance due to high conductivity, large surface area, and stable reversible oxidation states of Ce3+/Ce4+ and Co2+/Co3+ and greatly supported the Faradaic redox reaction of PCs. The CeO2@Co3O4/NF electrode showed a high areal-specific capacitance of 1598 mFcm−2 at 1 mAcm−2 for the 0–0.5 V potential windows and stability up to 96.6% after 6000 cycles. In an asymmetric supercapacitor (ASC) device, the CeO2@Co3O4/NF was used as a positive electrode which revealed an excellent energy density and power density viz. 92 Whkg−1 and 1580 Wkg−1, respectively. Overall, the present research findings signify the advantages of the novel combination of nanostructured ceria and cobalt oxide active materials for enhanced supercapacitor performance.

One-dimensional conductive Ni3(HHTP)2 @ woven fabrics with controlled engineering design towards high-efficiency EDL electrodes

In this work, one-dimensional (1D) conductive MOFs Ni3(HHTP)2 with nanorod-like morphology on the surface of a woven fabric was synthesized by an in-situ growth method. Based on a three-electrode system, the effects of substrate concentration, scan rate and current density on electrode properties were investigated, respectively. The results showed that Ni3(HHTP)2 @ woven fabric-3 (NHWF-3) demonstrated the largest area capacitance at 5 mV s−1 and reached up to 360 μF cm−2 at 20 μA cm−2. Most importantly, the material still maintained 58.3% (210 μF cm−2) of the initially areal specific capacitance when the current density was increased 5 times to 100 μA cm−2. According to the electrochemical impedance spectroscopy (EIS) curve, NHWF-3 has the smallest semicircle radius in the high-frequency region, indicating that it has the lowest internal transfer resistance and the best conductivity. Thus, this study provides a good example for the simple preparation and practical applications of conductive MOFs composites.

Flexible Transparent Bifunctional Capacitive Sensors with Superior Areal Capacitance and Sensing Capability based on PEDOT:PSS/MXene/Ag Grid Hybrid Electrodes

AbstractFlexible transparent supercapacitors (FTSs) have aroused considerable attention. Nonetheless, balancing energy storage capability and transparency remains challenging. Herein, a new type of FTSs with both excellent energy storage and superior transparency is developed based on PEDOT:PSS/MXene/Ag grid ternary hybrid electrodes. The hybrid electrodes can synergistically utilize the high optoelectronic properties of Ag grids, the excellent capacitive performance of MXenes, and the superior chemical stability of PEDOT:PSS, thus, simultaneously demonstrating excellent optoelectronic properties (T: ≈89%, Rs: ≈39 Ω sq−1), high areal specific capacitance, superior mechanical softness, and excellent anti‐oxidation capability. Due to the excellent comprehensive performances of the hybrid electrodes, the resulting FTSs exhibit both high optical transparency (≈71% and ≈60%) and large areal specific capacitance (≈3.7 and ≈12 mF cm−2) besides superior energy storage capacity (P: 200.93, E: 0.24 µWh cm−2). Notably, the FTSs show not only excellent energy storage but also exceptional sensing capability, viable for human activity recognition. This is the first time to achieve FTSs that combine high transparency, excellent energy storage and good sensing all‐in‐one, which make them stand out from conventional flexible supercapacitors and promising for next‐generation smart flexible energy storage devices.

3D hollow NiCo LDH nanocages anchored on 3D CoO sea urchin-like microspheres: A novel 3D/3D structure for hybrid supercapacitor electrodes

The research on the structure of advanced electrode materials is significant in the field of supercapacitors. Herein, for the first time, we propose a novel 3D/3D composite structure by a multi-step process, in which 3D hollow NiCo LDH nanocages are immobilized on 3D sea urchin-like CoO microspheres. Results show that the 3D CoO acts as an efficient and stable channel for ion diffusion, while the hollow NiCo LDH provides abundant redox-active sites. The calculated results based on density function theory (DFT) show that the CoO@NiCo LDH heterostructure has an enhanced density of states (DOS) near the Fermi level and strong adsorption capacity for OH−, indicating its excellent electrical conductivity and electrochemical reaction kinetics. As a result, the CoO@NiCo LDH electrode has an areal specific capacity of 4.71C cm−2 at a current density of 3 mA cm−2 (440.19C g−1 at 0.28 A g−1) and can still maintain 88.76 % of the initial capacitance after 5000 cycles. In addition, the assembled hybrid supercapacitor has an energy density of 5.59 mWh cm−3 at 39.54 mW cm−3.

An unprecedented hybrid polyoxometalate based on niobium oligomers: A notable application as redox supercapacitor electrode

An unprecedented polyoxoniobate (PONb) oligomer was obtained by addition of a methylene blue (MB) dye solution over the PONb solution formed a blue nanogel that was converted into a stable blue solid through a lyophilization process. The new solid composite, so-called “blue polyoxoniobate” (blue-PONb), presents a two-dimensional (2D) morphology with electrochemical performance that stand out among the materials used in redox supercapacitor technology. This new material was evaluated as supercapacitor electrode showing a high areal specific capacitance and power density that reaches 110.50 mF cm−2 and 8.49 mW cm−2. In addition, in this composite the redox additive (MB) and the PONb presented a peculiar electrochemical behavior, the reduction of the niobium species and the transfer of electrons necessary for the accumulation of charge occurring simultaneously. As a result, blue-PONb electrode maintains the cycling performance with high coulombic efficiency (∼99 %) over the 50,000 cycles evaluated. Here, the origins of the electrochemical stability and the mechanism of operation of the blue-PONb electrode are analyzed and discussed. Finally, this work presents a PONb as a new and promising class of redox-capacitive materials with matrix/redox shuttle synergism.

Solvent-free MOF-CVD prepared ZIF-67 film with hollow and opened morphology for supercapacitor application

Metal organic frameworks (MOFs) have demonstrated excellent properties for application in energy storage field. In this work, we use a facile and solvent-free method to fabricate ZIF-67 films on foam Ni, Cu, Fe and Zn substrates. The pre-electrodeposited films are exposed to 2-methylimidazole vapor to generate ZIF-67 films. The morphology of the ZIF-67 films depends on the substrates and reaction duration. Specially, a hollow and opened polyhedron appearance is generated on the foam Ni substrate, which presents a uniform and smooth distribution. All ZIF-67 films on different substrates demonstrate good electrochemical performances when they are utilized as the active materials in the supercapacitors. The ZIF-67 film on the foam Ni substrate has 105 mF/cm2 areal specific capacitance at 10 mA/cm2 current density, showing superior electrochemical properties than that on other substrates. The specific energy can reach 24.5 μWh/cm2 at a high specific power of 14 mW/cm2 in an asymmetric supercapacitor, with Ni@Z67 as the cathode material and active carbon as anode electrode material. The process combining a simple electrodeposition method with solvent-free CVD transformation will be useful for the fabrication of MOFs films and their potential applications in various fields.

Introducing oxidant to expand laser-induced in-plane microsupercapacitor in depth

Laser-induced graphene (LIG) technology is a method to manufacture carbon material quickly. However, it is usually limited to the thin in-plane carbonized structure produced on the surface of substrate only, so that the thickness of substrate cannot be fully used in depth. In this work, we put forward a feasible scheme which can substantially thicken the carbonized structure by creatively introducing oxidant to promote the laser ablation. The thickness of obtained laser-induced thickened graphene (LITG) with porous morphology can reach ∼10 times of the classic material. When the concentration of oxidant is moderate, there are many micropores in the material and the surface area of the material increases by ∼30 times. The change of functional groups is obvious. Introduced oxidant does not decrease the yield of carbon, but can double it. Furthermore, the specific areal capacitance of assembled microsupercapacitor (MSC) is up to 65.2 mF cm−2 and is nearly 1000 times of the control. The electrochemical impedance of the device is reduced. The device keeps 96% capacitance retention after 10000 cycles at high rates. Profiting from this simple strategy, traditional in-plane laser-induced technology can easily prepare carbon material with high thickness now.

Self-supporting electrode for flexible supercapacitors: NiCo-layered double hydroxide derived from metal organic frameworks wrapped on graphene/polyaniline nanotubes@cotton cloth

Nowadays, constructing hetero-structure materials is an efficacious procedure to uplift the electrochemical performance of layered double hydroxide (LDH) materials. The logical design of such elegant nanostructures is still challenging. Herein, NiCo-LDH nanosheets derived from Co-ZIF grown on graphene/polyaniline nanotube (G/PANI-NT)@cotton cloth (CC) was synthesized by a facile and novel two-step strategy for supercapacitors. Such hetero-structures give a 30.63 m2 g−1 surface area and more subjected electrochemical active sites. The supercapacitor performance results exhibit that the NiCo-LDH/G/PANI-NT@CC electrode has the best supercapacitor performance when it is used as a pseudocapacitor. By the ratio of Ni/Co = 2:1 in the precursor solution, the electrode shows an areal specific capacitance of 88.15 mF cm−2 at a current density of 0.075 mA cm−2. The electrochemical performance of the electrodes was perused using a redox-additive electrolyte. The electrochemical performance of the NiCo-LDH/G/PANI-NT@CC electrode was amended using K2S2O8 in a 3 M KOH solution. Considerably, the areal specific capacitance of NiCo-LDH/G/PANI-NT@CC (181.17 mF cm−2) increased to 431.30 mF cm−2, by changing the K2S2O8 concentration in KOH solution at a current density of 0.075 mA cm−2. Long-term stability test demonstrates that 84.05 % of the original capacitance remains after 10,000 cycles at the current density of 0.2 mA cm−2. The results indicate that NiCo-LDH/G/PANI-NT@CC will be an appropriate candidate for high-performance supercapacitors. The NiCo-LDH/G/PANI-NT@CC//NiCo-LDH/G/PANI-NT@CC flexible solid-state supercapacitor was assembled with the PVA/KOH gel electrolyte.

A Simple Trick to Increase the Areal Specific Capacity of Polypyrrole Membrane: The Superposition Effect of Methyl Orange and Acid Treatment.

Polypyrrole (PPy) is one of the attractive conducting polymers that have been investigated as energy storage materials in devices like supercapacitors. Previously, we have reported a free-standing soft PPy membrane synthesized through interfacial polymerization in which methyl orange (MO) and ferric chloride were used as nano template and oxidant. In this work, we report that the presence of MO and the treatment of the PPy-MO membrane with sulfuric acid can dramatically increase the specific capacitance of the membrane. The properties of the membranes were evaluated using scanning electron microscope (SEM) for morphology, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) for chemistry, thermogravimetric analysis (TGA) for thermal stability, and cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) for electrochemical activity. It was found that the areal specific capacitance of the PPy membrane increased from 2226 mF/cm2 to 6417 mF/cm2 and the charge transfer resistivity decreased from about 17 Ω to 3 Ω between 10,000 and 0.1 Hz due to the presence of MO and the acid treatment. It is likely that the superposition effect of MO and acid treatment helped the charge transfer process and consequently enhanced the charge storage performance and specific capacitance of the PPy membrane.

Flexible freestanding conductive nanopaper based on PPy:PSS nanocellulose composite for supercapacitors with high performance

A freestanding, binder-free flexible polypyrrole: polystyrene sulfonate/cellulose nanopaper (PPy:PSS/CNP) electrode is successfully fabricated by a low-cost, simple, and fast vacuum filtration method for the first time. The hierarchical structure of CNP with high surface area and good mechanical strength not only provides a high electroactive region and shortens the diffusion distance of electrolyte ions, but also mitigates the volumetric expansion/shrinkage of the PPy during the charging/discharging process. The optimized PPy:PSS/CNP exhibits a high areal specific capacitance of 3.8 F cm−2 (corresponding to 475 F cm−3 and 240 F g−1) at 10 mV s−1 and good cycling stability (80.9% capacitance retention after 5000 cycles). The cyclic voltammetry curves of PPy:PSS/CNP at different bending angles indicate prominent flexibility and electrochemical stability of the electrode. Moreover, a symmetric supercapacitor device is assembled and delivers a high areal energy density of 122 µ cm−2 (15 W h cm−3) at a power density of 4.4 mW cm−2 (550 mW cm−3), which is superior to other cellulose-based materials. The combination of high supercapacitive performance, flexibility, easy fabrication, and cheapness of the PPy: PSS/CNP electrodes offers great potential for developing the next generation of green and economical portable and wearable consumer electronics.