Supercapacitor In Aqueous Electrolyte Research Articles

MgO templated carbons: Effect of synthesis methodology on the morphology, surface chemistry and supercapacitor performances

Templating method is a widely adopted route to prepare porous carbon, while the effect of methodology on the structure and performances of the derived porous carbon was rarely focused. Herein, we employed a commercial MgO as template and catechol/formaldehyde as starting materials to prepare porous carbon by incipient impregnation method (the derived product denoted as MgC-I) and aqueous self-assembly method (the derived product denoted as MgC-S), respectively. Systematically analysis indicates that impregnation method favors the construction of two-dimensional structure, while, aqueous self-assembly method benefits formation of densified structure. Concerning to the surface chemistry, aqueous self-assembly method enables more residual oxygenic functionalities than that of impregnation derived ones. As electrode for supercapacitor in aqueous electrolyte, the MgC-S achieves superior volumetric performances including high specific volumetric capacitance of 319 F/cm3@1.0 A/g and large energy density of 27.9 Wh/L@1193 W/L, showing a potential for practical energy storage devices. Whereas, in organic electrolyte of 1.0 M TEANBF4/AN, the MgC-I electrode show a superior energy storage ability with energy density of 40.5 Wh kg−1@1350 W kg−1, the value is about six times higher than that of MgC-S based one. This study provides a reference for how to choose synthesis methods for preparing carbon materials with specific target.

Fabrication and Development of a Biomass-Based Supercapacitor with Enhanced Energy Storage Characteristics

In this work, a raw carbon waste parali biomass is collected to develop a supercapacitor. The activated carbon developed is characterized using X-ray diffraction (XRD), Field effect scanning electron microscope (FESEM), Energy dispersive spectroscope (EDS), and Brunauer–Emmett–Teller (BET) analyses. The porous and crystalline activated carbon achieved a remarkably high carbonaceous value of 99.85% carbon from 35.71% in raw state. The specific surface area obtained is 151.42 m2 g−1 and the porosity (average pore diameter) is 2–10 nm of the optimized activated carbon. The activated carbon is explored as electrode material for supercapacitor in aqueous electrolyte and the specific capacitance was found to be a maximum of 247 F g−1 at 1.2 A g−1 to a stable value of 180 F g−1 at 10 A g−1. The symmetrical supercapacitor device, featuring electrodes composed of carbon material, attains an impressive energy density of 54 Wh kg−1 along with outstanding coulombic efficiency and stability. The laboratory prototype supercapacitor has successfully powered consumer electronics, such as a DC (direct current) motor for 12.5 min and an LED (Light emitting diode) bulb for 14 min, on a single charge in each case.

Kelp derived hierarchically porous carbon aerogels with ultrahigh surface area for high-energy-density supercapacitor in aqueous electrolyte

Nowadays, obtaining porous carbons from abundant and sustainable biomass as electrode materials for energy storage has been attracting tremendous attentions, to meet the requirement of energy consumption and environmental remediation. In this study, hierarchically porous carbon aerogels (HPCAs) with desirable micro-, meso- and macropores were obtained via decoloration, freeze-drying and subsequent carbonizing-activating process using kelp as sustainable, low-cost and massive precursors by adjusting the activation temperature. The effect of temperature on the pore structures and electrochemical performance of HPCAs were investigated in depth. At 800 °C, the as-obtained HPCA-800 had an appropriate combination of specific surface area and hierarchically porous networks, rendering the optimal capability of electrolyte ion's accumulation and transportation. The HPCA-800 exhibited highest specific capacitance of 278 F g−1 in 6 M KOH and 1965 F g−1 and 1 M KOH + 0.06 M K3Fe (CN)6 electrolyte, respectively, which are superior to those of the reported carbon aerogels. Moreover, an ultrahigh energy density of 93 W h kg−1 at high power density of 2109 W kg−1 was achieved in the redox electrolyte. The energy storage mechanism was also elucidated. The HPCAs from kelp should be promising and competitive electrode materials for constructing high-energy-density supercapacitor, owing to their outstanding supercapacitor performance together with the superior advantages of raw materials including abundance, low-cost and renewability.

Doable high energy density supercapacitors using rice husk-derived carbon in dihydroxybenzenes as redox-additive electrolytes

Though activated carbon made from various bio wastes is quite affordable and plentiful, the energy density of these electrodes in aqueous electrolytes is still questionable. Therefore, increasing the energy density of activated carbon for use in supercapacitors is a challenging issue. The ideal way to boost the energy density of supercapacitors in aqueous electrolytes is by using redox-additive electrolytes. Redox-additive electrolytes are the impeccable solution for thriving the energy density of supercapacitors in aqueous electrolytes. Here, three additives namely 1, 2-benzene diol, 1, 3-benzene diol, and 1, 4-benzene diol were utilized as redox-additives with 1 M H2SO4 to study the influence of the position of OH on their redox activity and electrochemical performance. The activated carbon derived from rice-husk delivered a high specific capacitance of 1414 F/g at 4 A/g with 1, 4-benzene diol/H2SO4 among the three redox additives. A symmetric supercapacitor was fabricated, which exhibited a remarkable energy density of 38 Wh/kg at 2 A/g with 1, 4-benzene diol/H2SO4, which is almost 4 times superior to the energy density of the same electrode with H2SO4 (10.6 Wh/kg at 2 A/g).

The role of nitrogen-doping on the electrochemical behavior of MOF-derived carbons in ionic liquid electrolytes

Metal-organic frameworks (MOFs) derived nanoporous carbons have been intensively studied as electrode materials for electric double-layer capacitors. However, the current research on MOF-derived carbons were mainly focused on investigating electrochemical performances of supercapacitors in aqueous electrolytes, and there were only a few studies involved ionic liquids electrolytes. In addition, the research of nitrogen doping effect on MOF-derived carbons in ionic liquids electrolytes has rarely been reported. Nitrogen doping is considered to be the common and effective way to improve the electrochemical performances of carbonaceous electrodes because it can not only enhance the electrical conductivity but also bring about pseudocapacitances in aqueous electrolytes. However, the nitrogen doping effect in ionic liquids electrolytes need to be further investigated especially for MOF-derived carbons with large quantities of micropores. In this study, MOF-derived nitrogen-doped carbons were synthesized by carbonization of urea functionalized Zn-MOF-74, and their electrochemical behavior in EMIMBF4 and EMIMTFSI ionic liquid electrolytes were investigated. The nitrogen-doping degree was tuned by adjusting the amount of urea. Electrochemical test showed that nitrogen-doped carbons exhibited a maximum capacitance enhancement of 24.4 % than pristine sample in ionic liquid electrolytes. Nevertheless, nitrogen-doping contributed few pseudocapacitances in ionic liquid electrolytes, and the enhanced electrochemical performances could be ascribed to the increased electrical conductivity and the matched pore structures.

Hafnium oxide - graphene electrodes for highly efficient aqueouselectrolyte supercapacitors

Hafnium Oxide (HO) has emerged as a novel material which has significantly revolutionized semi-conductor industry while role of this high-k metal oxide has not been investigated in-depth when it comes to the discovery of electroactive species for energy storage applications. In this context, herein we have reported the excellent electrochemical energy storage of stoichiometrically synthesized (HO)x – (GNPs)1-x nanocomposites (where x = 1, 0.75, 0.50, 0.25, 0) in different weight ratios. The presented research work aims to provide an insight into the charge storage mechanism in HO based energy storage devices by linking structural aspects with physical factors that are instrumental in impacting specific capacitance. Agile experimental techniques have been applied for structural authentication followed by a series of electrochemical experiments that have been conducted to provide in depth account of various physical parameters and their impact in achieving a superior charge storage of 925 F g−1 at a scan rate of 5 mV s−1 in 1 M H2SO4. Moreover, an energy density of 30.67 Wh - kg−1 and a power density of 235 W - kg−1 has been achieved, with a capacity retention of 80 % over 1000 cycles.

Ultramicroporous N-Doped Activated Carbon Materials for High Performance Supercapacitors

Porous carbon electrode materials are utilized in supercapacitors with very fast charge/discharge and high stability upon cycling thanks to their electrostatic charge storage mechanism. Further enhancement of the performance of such materials can be achieved by doping them with heteroatoms which alter the kinetics of charge/discharge of the adsorbed species and result in pseudocapacitance phenomena. Here, microporous N-doped activated carbons were synthesized by thermochemical activation process. The structure and composition of the final material were adjusted by tuning the synthesis conditions and the choice of precursor molecules. In particular, N-doped activated carbons with a controlled specific surface area in the range of 270–1380 m2/g have been prepared by KOH-activation of sucrose/ammonium citrate mixture. By adjusting the composition of precursors, N-doping was varied from ca. 1.5 to 7.3 at%. The role of the components and synthesis conditions on the composition and structure of final products has been evaluated. The N-doped activated carbon with optimized structure and composition has demonstrated an outstanding performance as electrode material for aqueous electrolyte supercapacitors. The specific capacitance measured in a 3-electrode cell with 0.75 mg/cm2 loading of optimized activated carbon in 1M H2SO4 changed from 359 F/g at 0.5 A/g charging rate to 243 F/g at 20 A/g. Less than 0.01% of capacitance loss has been detected after 1000 charging/discharging cycles.

A High-Performance Redox Electrochemical Capacitor: Confinement of Sodium Anthraquinone-2-Sulfonate in Porous Carbons with Electric-Field Assistance

Redox electrolytes bridge the energy density gap between carbon-based supercapacitors and batteries. However, across-diffusion of soluble redox couples results in subpar rate performance, therefore, how to deal with this impasse becomes the focus of the field’s attention. In this study, we put forth the idea that the problem can be solved by using activated carbon nanopores as reservoirs to retain redox species and prevent their diffusion. The electric field is used to help confine sodium anthraquinone-2-sulfonate (AQS, size is around 1.634 × 0.634 × 0.864 nm3) to the nanopores of the tea-leaf biomass carbon electrode (TAC, 59.65% of micropores). We show that AQS molecules occupy small micropores (less than 1 nm), resolving the problem of cross-diffusion that arises naturally in redox-enhanced electrochemical capacitors. Thus, in the 1 M H2SO4 electrolyte, a high specific capacitance of 733.3 F g–1 is produced in a three-electrode system at a current density of 1 A g–1, and only 7% of the specific capacitance decays at a current density of 10 A g–1. Besides, the TAC/AQS-5 electrode-based symmetric device delivers a maximum energy density of 41.48 Wh kg–1 and excellent capacitance retention of 86.2% after 5000 charge and discharge cycles at 2 A g–1. The maximum energy density obtained by our symmetrical supercapacitor is higher than that of currently reported aqueous electrolyte supercapacitors.

Biomass-derived hierarchically porous carbon-supported MnOx enable fast ion/electron transport at high operating voltages

Metal oxide/carbon composite systems have been investigated extensively for fabrication of supercapacitors. To obtain high capacitance, a thick pseudocapacitive layer loaded on a conventional carbon support inevitably leads to high dead volume and poor rate/power characteristics. Herein, we propose a strategy with biomass-derived hierarchical porous carbon as supports to bridge two critical but mutually exclusive properties of supercapacitors: high capacitance and rapid ion/charge transport. Highly dispersed deposition of nanosized MnO2 and MnO on hierarchically porous carbon were achieved through slow redox reaction controlled by gradual hydrolysis of fibrous polymers remaining in the hydrothermal carbon. High surface area, ultrathin pseudocapacitance layer, and wide voltage window (1.6–2 V) improve the synergy between the high energy density of MnOx and the high power density of porous carbon. The maximum energy density of 40.95 Wh kg−1 (at 180 W kg−1) and power density of 9000 W kg−1 (at 23.85 Wh kg−1) was realized for the assembled asymmetric/symmetric supercapacitors in aqueous electrolytes. More importantly, a cycle life comparable to that of carbon-based double-layer capacitors (95.6% capacitance retention after 10,000 charge/discharge cycles) could be achieved. Furthermore, density functional theory (DFT) was also conducted to elaborate the differences between manganese valence states for in-depth understanding. The characteristics of low cost, environmental friendliness, and excellent performance highlight the great promise of biomass waste in designing carbon supports for electrochemical applications.

Improved electrochemical performance of sandwich-structured N-rich C@MnO2@C electrodes

This paper reports the capacitive behavior of N-enriched carbon nanofiber/MnO2/carbon nanofibers with a triple layer structure (N-rich C@MnO2@C) prepared by continuous electrospinning. N-functional groups were introduced into the upper (or lower) or middle layer of the triplex and the structures and electrochemical properties of each are compared. N-functional groups introduced into the lower (or upper) layer induce a high surface area, numerous pyrrolic-N, high electrical conductivity, and low contact angle in N-rich C@MnO2@C composites. The optimized material provides a specific capacitance of 201 Fg−1 (1 mAcm−2) with more than 84% specific capacitance retention in a symmetric two-electrode cell configuration using a 6 M KOH electrolyte. In addition, it shows a maximum energy density of 24.8 and 13.41 Whkg−1 at power densities of 400 and 10,000 Wkg−1 with excellent cycling stability (95% capacity retention after 10,000 cycles at 1 mAcm−2). An assembled asymmetric device, consisting of optimized N-rich C@MnO2@C as the positive electrode and C@MnO2@C as a negative electrode, delivers a high energy density of 41 Whkg−1 at a power density of 400 Wkg−1. This material has excellent potential as an electrode for constructing high-voltage asymmetric supercapacitors in aqueous electrolytes.

Biaxial strain tunable quantum capacitance and photocatalytic properties of Hf2CO2 monolayer

MXenes have great potential applications in energy storage and photocatalyst. The photocatalytic activity and the quantum capacitance of Hf2CO2 monolayer under biaxial strain are investigated in this paper. The result indicates that Hf2CO2 monolayer under biaxial strain can reduce H+ to H2 at pH = 0 and has the strongest reducing ability at 12% tensile strain. Hf2CO2 monolayer under strain has the photocatalytic capacity for overall water splitting within appropriate pH range. The tensile strain can enhance the CO2 reduction ability of Hf2CO2 monolayer. The reducing ability of Hf2CO2 for N2 is improved under tensile strain and reduced under compressive strain. The analysis of exciton binding energy further confirms the potential photocatalytic activity of Hf2CO2 monolayer under strain. Hf2CO2 monolayers under strain are potential cathode materials for supercapacitors in aqueous electrolyte, the wide voltage makes Hf2CO2 monolayer under −6% strain transform into electrode material of symmetric supercapacitors. The effect of temperature on the electrode type of materials is further explored.

Flexible Solid Supercapacitors of Novel Nanostructured Electrodes Outperform Most Supercapacitors.

Sustainable and scalable fabrication of electrode materials with high energy and power densities is paramount for the development of future electrochemical energy storage devices. The electrode material of a supercapacitor should have high electrical conductivity, good thermal and chemical stability, and a high surface area per unit volume (or per unit mass). Researchers have made great efforts to use two-dimensional (2D) nanomaterials, but the separated 2D plates are re-stacked during processing for electrode fabrication, impeding the transport of ions and reducing the number of active sites. We developed a novel process for manufacturing thin and flexible electrodes using a 2D material (MXene,Ti3AlC2) and a conducting polymer (poly(3,4-ethylenedioxythiophene), PEDOT). Because the PEDOT layer is electrochemically synthesized, it does not contain the activator poly(styrene sulfonate). The electrospray deposition technique solves the restacking problem and facilitates the infilling of the gel electrolyte by forming a highly porous open structure across the entire electrode. In the PEDOT/MXene multilayered electrode, the double-layer capacitance increased substantially because of a dramatic increase in the number of accessible sites through the MXene layer. Although applied to solid supercapacitors, these new supercapacitors outperform most aqueous electrolyte supercapacitors as well as other solid supercapacitors.

Nanoporous Carbon Electrodes Derived from Coffee Side Streams for Supercapacitors in Aqueous Electrolytes.

Coffee, as one of the most traded resources, generates a vast amount of biogenic by-products. Coffee silver skins (CSS), a side stream from the roasting process, account for about 4 wt.%. Despite the abundancy of CSS, possible routes to generate added value for broad applications are limited. Herein, we present an approach to use CSS as a precursor material for supercapacitor electrodes. KOH activated carbon (AC) was produced from CSS. The resulting AC—CSS was characterized by X-ray diffraction, gas sorption analysis, scanning electron microscopy, and Raman spectroscopy. The highly porous AC—CSS exposes a specific surface area of more than 2500 m2 g−1. Electrodes formed with AC—CSS were electrochemically characterized by performing cyclic voltammetry and galvanostatic cycling. The electrodes were further assembled into a supercapacitor device and operated using 1 M sulfuric acid as electrolyte. In addition, various quinones were added to the electrolyte and their impact on the capacitance of AC—CSS electrodes was analyzed. In this work, we were able to show that CSS are a valuable source for supercapacitor applications and that coffee-waste-derived quinones can act as capacitance enhancers. Thus, the findings of this research show a valuable path towards sustainable and green energy storage solutions.

CO2 outperforms KOH as an activator for high-rate supercapacitors in aqueous electrolyte

Although high-surface area activated carbons used as supercapacitor (SC) electrodes are frequently produced by KOH activation, this study shows that, when aqueous electrolytes are used, CO2 activation is a better choice from the point of view of SC performance, environment and economy. Ordered mesoporous carbons (OMCs) produced by a mechanochemical synthesis method from mimosa tannin are activated with KOH to use these materials as electrodes for SCs. A comparative analysis of the same OMCs but activated with CO2 is presented to examine the effect of the activation process on materials performance. KOH-activated materials exhibit good electrochemical performance at low charging rates, reaching specific cell capacitance values of 49 F g−1 at 0.5 Ag−1, however, restricted access to microporosity and low water affinity water reduces their performance at high charging rates. In contrast, the best performing CO2-activated material can retain 81% of capacitance at 20 A g−1, compared to 25% for a KOH-activated OMC with similar properties and tested under the same conditions. A thorough review of the open literature suggests that CO2 activation would produce materials with a suitable combination of pore network connectivity and water affinity, resulting in SCs with high rate capability in an aqueous electrolyte. These conclusions were drawn by judiciously integrating the analysis of: (i) the hysteresis loop scanning of N2 adsorption-desorption isotherms; and (ii) water adsorption isotherms as tools to more accurately assess the pore network connectivity and water affinity of the materials, which are not generally considered when studying SC performance.

Reassembly of MXene Hydrogels into Flexible Films towards Compact and Ultrafast Supercapacitors

AbstractThe freestanding MXene films are promising for compact energy storage ascribing to their high pseudocapacitance and density, yet the sluggish ion transport caused by the most densely packed structure severely hinders their rate capability. Here, a reassembly strategy for constructing freestanding and flexible MXene‐based film electrodes with a tunable porous structure is proposed, where the Ti3C2Tx microgels disassembled from 3D structured hydrogel are reassembled together with individual Ti3C2Tx nanosheets in different mass ratios to form a densely packed 3D network in microscale and a film morphology in macroscale. The space utilization of produced film can be maximized by a good balance of the density and porosity, resulting in a high volumetric capacitance of 736 F cm−3 at an ultrahigh scan rate of 2000 mV s−1. The fabricated supercapacitor yields a superior energy density of 40 Wh L−1 at a power density of 0.83 kW L−1, and an energy density of 21 Wh L−1 can be still maintained even when the power density reaches 41.5 kW L−1, which are the highest values reported to date for symmetric supercapacitors in aqueous electrolytes. More promisingly, the reassembled films can be used as electrodes of flexible supercapacitors, showing excellent flexibility and integrability.

Activated Carbon Derived from Cellulose and Cellulose Acetate Microspheres as Electrode Materials for Symmetric Supercapacitors in Aqueous Electrolytes

Activated Carbon Derived from Cellulose and Cellulose Acetate Microspheres as Electrode Materials for Symmetric Supercapacitors in Aqueous Electrolytes

Defect-domains enabling VO2 nanosheet arrays with fast charge transfer for 3.0 V aqueous supercapacitors

Defective metal oxides are of great significance to promote reaction activity for high energy and power densities supercapacitors in aqueous electrolytes. Herein, we demonstrate a monoclinic VO2 nanosheet arrays electrode with tailorable defect-domains by a simple thermal-induced strategy. It is found that the defect-domains stemmed from the residual trivalent vanadium of V2O3 precursor directly influence the intrinsic conductivity of VO2. The relationships between defect-domains and electrochemical performance are built and the defect-optimized VO2 can greatly accelerate the electrochemical reaction kinetics with decreased polarization effect. It exhibits a high specific capacitance of 180.3 F g-1 at 0.5 A g-1 and 78.8 F g-1 even at 10 A g-1 within a large potential window of -1.5 ~ 0.15 V with superior cycle stability in “water in salt” electrolyte. A 3.0 V aqueous asymmetric supercapacitor device is assembled with MnO2 nanosheet arrays as cathode, which delivers a very high energy density of 120.3 Wh kg-1 at 1.5 kW kg-1, almost as good as sodium/potassium ion batteries.

Transforming waste sugar solution into N-doped hierarchical porous carbon for high performance supercapacitors in aqueous electrolytes and ionic liquid

Waste sugar solution is a by-product in the process of manufacturing vitamin C. Nowadays, the unused industrial waste residues are transformed into high efficient energy storage devices, such as supercapacitors electrodes, which are worth exploring because they are consistent with the concept of green and sustainable development. In this paper, a nitrogen-doped hierarchical porous carbon are obtained via pre-carbonization and KOH activation. The as-prepared material, possessed proper pore size distribution, large specific surface area and nitrogen-doping, exhibits good electrochemical performance, such as a high specific capacitance of 342 F g−1 (0.1 A g−1), good stability with 95% capacitance retention after 15,000 cycles in 6 M KOH. Moreover, the supercapacitors deliver a high energy density of 25.6 and 65.9 W h kg−1 in the 1 M Na2SO4 and EMIMBF4, respectively. The good electrochemical performance illustrates that the nitrogen-doped hierarchically porous carbon derived from the waste sugar solution is a potential candidate for energy storage.

Additive manufacturing of monolithic supercapacitors with biopolymer separator

In this paper, additive layer-by-layer fabrication of a fully screen printed monolithic supercapacitor exhibiting performance comparable with supercapacitors prepared using lamination is reported. A novel separator material improves the performance of the monolithic supercapacitor, is easily applicable using scalable processes such as screen and stencil printing, and is based on sustainable biomaterials. The additive monolithic manufacturing offers advantages for system integration and avoids the need of an additional alignment step as needed in the fabrication of laminated supercapacitors. Previously, the monolithically fabricated supercapacitors showed higher equivalent series resistance (ESR) and leakage current than the laminated ones. By using microfibrillated cellulose (MFC) and chitosan as separator materials ESR and leakage current were decreased. These disposable and non-toxic aqueous electrolyte supercapacitors are optimized for autonomous sensor systems, for example in Internet-of-Things (IoT) applications, with capacitance of 200–300 mF and ESR of about 10 Ω. The new composite separator material consisting of MFC and chitosan has good adhesion on the electrodes and the substrate, is easy to apply using printing and coating processes, and does not diffuse into the porous electrode.Graphic

A Hierarchical Interconnected Nanosheet Structure of Porous δ-MnO2 on Graphite Paper as Cathode with a Broad Potential Window for NaNO3 Aqueous Electrolyte Supercapacitors

The potential window for aqueous supercapacitor cathodes greatly depends on the electrochemical stability of water, and thus is generally limited to ∼1.2 V. Herein, a 1.4 V potential window (vs Ag/...