Specific Capacitance Of Electrode Research Articles

Sodium lignosulfonate/graphene composites for efficient desalination by incorporating CoS to control pore size

The phenomenon of overlapping double layers due to micropores inhibits capacitive deionization performance, which is improved by increasing the pore size. In this study, a novel ternary composite electrode (sodium lignosulfonate/reduced graphene oxide/cobalt sulfide, LGC) was designed using a two-step hydrothermal method. CoS with high pseudocapacitance modifies sodium lignosulfonate and graphene connected by hydrogen bonding, benefiting from the constitutive steric structure. The electrochemical performance was significantly enhanced, and the desalination capacity substantially improved. The LGC electrode specific capacitance was as high as 354.47 F g−1 at a 1 A g−1 current density. The desalination capacity of the capacitive deionization device comprising LGC and activated carbon in 1 M NaCl electrolyte reached 28.04 mg g−1 at an operating condition of 1.2 V, 7 mL min−1. Additionally, the LGC electrodes degraded naturally post the experiment by simply removing the CoS, suggesting that the LGC composites are promising material for capacitive deionization electrodes.

Enhancing electrochemical capacitor performance of N-doped tannin-derived carbons by hydrothermal treatment in ammonia

This study demonstrates that ammonia concentration when doping carbons using hydrothermal treatment has crucial impact on textural properties. The latter translates into an improvement of the electrochemical performance of carbon materials, when used into electrochemical capacitors, especially at high-rate performance. Nitrogen-doped carbons were synthesized by subjecting tannin to hydrothermal carbonization in ammonia solutions of varying concentrations. After carbonization and CO2 activation, the as-produced activated carbons (ACs) were tested as electrodes for electrochemical capacitors in symmetric configuration using 1 M H2SO4 as aqueous electrolyte. Interestingly, ammonia concentration during the hydrothermal synthesis step did not significantly affect the final N content (ca. 3 and 4 at. %) nor the nitrogen and oxygen functionalities on the surface. However, the use of ammonia had crucial impact on the textural properties developed by CO2 activation, and therefore on the electrochemical performance of the ACs. The best-performing N-doped AC showed specific electrode capacitance values, based on carbon material, of 212 F g−1 at 0.5 A g−1 and outstanding capacitance retention of ca. 71 % at 40 A g−1. It also showed high cycling stability, with capacitance retention of ca. 96 % after 30,000 cycles. Furthermore, this AC outperformed similar reported materials, achieving a specific energy of 4.6 W h kg−1 at 12.1 kW kg−1.

Enhanced electrochemical properties of multiwalled carbon nanotubes modified with silver nanoparticles for energy storage application

This work reports an easy, straightforward, and cost-effective method to synthesize a composite material using multiwalled carbon nanotubes (MWCNTs) and silver nanoparticles (Ag NPs) for application as an electrode in supercapacitors. The objective of this work was to enhance the charge transfer mechanism in supercapacitor cells by introducing the conductive particles in the MWCNT framework. The pivotal studies, like scanning (SEM), and transmission (TEM) electron microscopy, X-ray diffraction (XRD), Raman, and X-ray photoelectron (XPS) spectroscopy confirmed the formation of the composite as well as a successful deposition of Ag NPs on MWCNT. The surface area of the composite was evaluated by using the N2 adsorption-desorption studies and it was found to be of the order of 358 m2 g−1. Electrochemical studies were performed using a two-electrode system. Magnesium ion-based polymer gel electrolyte was used as an electrolyte material. The single electrode-specific capacitance was observed to be ∼31.9 F g−1 with power density and energy density values of ∼4.4 kW kg−1 and 1.2 Wh kg−1, respectively, at a current density of 0.46 A g−1. The cell was stable up to ∼5000 charge-discharge cycles with ∼96% of capacitance retention at the end of 5000 cycles.

Advancing capacitive deionization via intelligent optimization approach part 1: Development of tunable low-cost carbon electrodes

This work introduces a novel approach based on utilizing intelligent data-based optimization techniques to fabricate high-quality and low-cost carbon electrodes for capacitive deionization (CDI). The effects of synthesis parameters of peanut shell-derived porous carbon (PSPC) (KOH to Raw ratio, pyrolysis temperature and time) on five factors (production yield, BET surface area, electrode specific capacitance, and ion transfer resistances, including interface and diffusion) were investigated using combined design-of-experiment (DOE), response-surface-methodology (RSM), and Sobol's sensitivity analysis (SA). Optimal scenarios providing maximum production yield, surface area, and specific capacitance, and minimum ion transfer resistances were found using a multi-objective genetic algorithm (GA). Results uncover that increasing the impregnation ratio, pyrolysis temperature and time enhances the PSPC porosity that causes the carbon surface area and electrode specific capacitance to promote, the production yield to reduce and ion transfer resistances to raise. From Sobol's SA, pyrolysis temperature was the most impacting parameter on all decision factors. The optimal PSPC prepared at 750 °C and minimum KOH:Raw = 1 and time = 30 min offered a developed mesoporous structure with BET surface area of 685 m2/g and the resulting electrode had an outstanding specific capacitance (127.13 at 5 mV/s), with reliable durability after 100 cycles and showing the lowest possible ion transfer resistances.

A novel CoS/Ti3C2Tx MXene conductive filler effectively improves the pseudocapacitive performance of conductive hydrogel electrode materials for all-solid-state supercapacitors

It is currently an essential research direction to develop a low-cost, cost-effective, and environmentally friendly high-performance flexible electrode material. The electrode materials prepared from Ti3C2Tx MXene based hydrogels showed favorable physical and chemical properties (e.g., extreme flexibility, excellent mechanical strength, and electrical conductivity), and CoS (cobaltous sulfide) nanoparticles were grown by in-situ hydrothermal growth on the “accordion-like” Ti3C2Tx MXene surfaces, which were then synthesised into PCCT (PAA/chitosan/CoS/Ti3C2Tx) conductive hydrogels with physical crosslinked networks in a two-step process. This 3D porous structure containing highly conductive materials can provide suitable geometrical space and electronic structure, which can help to suppress the accumulation of active material at high mass loading and improve the specific capacitance of the electrode material. With a current density of 4 mA/g, the specific capacitance of the PCCT conductive hydrogel electrode was 3.6F/g. At a current density of 10 mA/g, the cycling stability was still 80 % after 2000 cycles. The elongation at break of PCCT conductive hydrogel wass about 349 %. After 48 h of healing at room temperature, the self-healing efficiency can reach 66.88 %. A foundation has been laid for obtaining flexible all-solid-state supercapacitors with stable structures and excellent electrochemical properties.

Sustainable supercapacitor with a natural rubber‐based electrolyte and natural graphite‐based electrodes

AbstractSupercapacitors are at the forefront of energy storage devices due to their ability to fulfill quick power requirements. However, safety and cost are important parameters for their real‐world applications. Green materials‐based electrodes and electrolytes can make them safer and cost‐effective. Herein, a supercapacitor based on a methyl‐grafted natural rubber/salt‐based electrolyte and natural graphite (NG)‐based electrodes are fabricated and characterized. Zinc trifluoromethanesulfonate [Zn(CF3SO3)2] is used as the salt for the electrolyte. A mixture of NG, activated charcoal, and polyvinylidenefluoride is used for electrodes. Our supercapacitor shows a single electrode specific capacitance, Csc of 4.2 Fg−1 from impedance measurement. Moreover, the capacitive and resistive features are dominant at low and high frequencies, respectively. The cyclic voltammetry test shows the dependence of Csc on the scan rate with a high value at slow scan rates. Performance of the supercapacitor during 5000 charge and discharge cycles at a constant current of 90 μA shows a rapid decrease of single electrode specific discharge capacitance at the beginning, but it starts to stabilize after about 2500 cycles. These findings are relevant to further developments of green materials‐based supercapacitors, offering opportunities to expand the functionalities of supercapacitors in green technologies.

Bamboo-based self-supporting electrodes via green activation for high-performance supercapacitors

As a potential high-efficiency energy storage device, supercapacitor electrode materials encounter persistent challenges, including limitations in energy density and stability, particularly at large loadings. In this work, a bamboo-based self-supporting thick electrode (∼30 mg cm−2) is prepared. The electrode takes full advantage of the vertical growth channels and surface oxygen-containing functional groups of bamboo, which improves the ion transport kinetics within its structure. Inspired by the fermentation process of bread with baking soda, the electrode material is prepared by KHCO3 activation at 1000 °C. The optimal sample exhibits a specific surface area of 903 m2 g−1 and an electrode specific capacitance of 142.7 F g−1 at current density of 1 A g−1. Furthermore, the assembled supercapacitor device exhibits excellent electrochemical performance even at high loadings. Specifically, the supercapacitor exhibits high energy density of 20.36 Wh kg−1 at 400 W kg−1. The device also has excellent cycling stability with a capacitance retention of 104.4 % after 10,000 cycles at a high current of 5 A g−1. Benefiting from the green preparation process, high energy density, and excellent cycling stability, the bamboo-based self-supporting thick electrode exhibits immense potential for further development and utilization.

Metal‐free nanostructured‐carbon inks for a sustainable fabrication of zinc/air batteries: From ORR activity to a simple prototype

AbstractZinc/air batteries are convenient energy storage devices for both small and massive applications. While future perspectives indicate the need for low‐cost components and sustainable fabrication processes, the battery performance is in part controlled by the kinetics of the oxygen reduction reaction (ORR), which typically involves transition metals as catalysts. In this context, we prepare a series of metal‐free water‐based carbon inks, which are tested for their catalytic performance, once deposited on a gas‐diffusion substrate, in the air cathode of a simple battery prototype. The inks contain a variety of well‐defined carbon nanomaterials and additives, exhibiting different physicochemical properties that critically influence the interaction with the gas diffusion hydrophobic substrate. The intrinsic ORR catalytic activity of the ink material is also analyzed on a glassy carbon electrode by the rotating ring‐disc electrode (RRDE) method and specific capacitance measurements. The discharge capacity on our zinc/air battery prototype correlates well with the intrinsic catalytic activity in the RRDE. However, only the activity in the RRDE does not actually assure the performance on the commercial cathode of the prototype, since other chemical compatibility issues play a role. Thus, we highlight the importance of catalyst testing, not only on the RRDE but also under realistic device conditions.

Comparative study on flower-like polyimide-based carbon electrodes activated by KOH and HNO3

Polyimide (PI)-based flower-like carbon superstructures have recently attracted extensive attention due to their relatively high specific surface area and abundant chemically active sites. However, their practical application for supercapacitor (SC) is still limited by lower specific capacitances. In this study, a kind of PI-based flower-like carbon (PC) materials is firstly prepared by hydrothermal process and further carbonization at 800 °C. Then, the activated PI-based carbon materials (APC) are separately obtained by using chemical activators KOH and HNO3. On the basis of optimizing the activation conditions respectively, the structures and electrochemical performances of the two preferred APC samples are compared. The experimental results show that the APC-1 activated by KOH and APC-2 treated by HNO3 exhibit extremely similar single electrode specific capacitance of 314.7 and 310.3 F g−1 at 0.5 A g−1. After being assembled into symmetrical supercapacitors, the two SC devices display energy densities of 20.28 and 19.54 Wh kg−1 at a power density of 260 W kg−1, respectively. Although the activation method and mechanism are different, the two optimized APCs exhibit similar electrochemical performance. Thus, in this work, we compare the two activation method and prepare a kind of valuable flower-like carbon electrode materials for SCs.

MOF-derived porous NiCo2O4 nanofile arrays as an efficient anode material for rechargeable Li-ion batteries

Due to their vast surface area and superior porosity structure, metal-organic frameworks (MOFs) derived materials have recently presented a significant promise for better lithium-ion batteries (LIBs). Herein, we synthesised MOF-derived porous NiCo2O4 nanofile arrays from a simple solvothermal technique followed by calcination at 450 °C. The prepared sample was characterized by X-ray diffraction, thermogravimetric, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. The acquired nanofile array morphology achieved a large specific surface area of 189 m2/g can shorten the Li ions (Li+) transport and enhance the electrochemical performance. As expected, the prepared electrode reveals a discharge-specific capacity of around 1120 mAh/g at a 0.1 C rate. At 2 C rate, the electrode's specific capacity can still reach 210 mAh/g after 100 cycles. The pseudocapacitive nature of NiCo2O4 was determined by kinetic analysis, revealing the diffusion-controlled faradaic behaviour. Our prepared electrode material is considered an attractive option for the anode material in rechargeable Li-ion batteries because it has been proven to have a relatively good specific capacity and cycling stability.

High-temperature-operating (over 140 °C) Li-ion supercapacitor via water-locking bimodal cross-linked hydrogel

The utilization of quasi-solid conducting medium possessing superior interfacial properties represents a significant approach in tackling the issue of leakage and stability in supercapacitors. However, preserving the conductivity of ions like Li+ and enabling their adaptability to high-temperature environments pose significant challenges to the improvement of water-locking capacity. Herein, a bimodal cross-linked hydrogel with a mesoporous structure has been developed based on the polyacrylamide-lithium chloride (PAM-LiCl) hydrogel system using polyethylene glycol (PEG). This hydrogel not only exhibits a high water-binding capacity but also facilitates the migration of Li-ions. Using activated carbon as the electrode material, the assembled quasi-solid state supercapacitor devices achieve a single electrode specific capacitance of 32.6 F/g at 0.1 A/g and an energy density of 1.77 W h/kg by varying the ratio of acrylamide and polyethylene glycol (AM/PEG). The findings of this study demonstrate that utilizing a bimodal cross-linked hydrogel can enable the operation of a supercapacitor at high temperatures above 140 °C.

The Performance of Chitosan-based Activated Carbon for Supercapacitor Applications towards Sustainable Energy Technologies

In sustainable technologies, the application of supercapacitors (SC) for energy conversion and storage systems is rapidly increasing. Supercapacitors are widely employed in applications that require fast charge and discharge phases, such as in the automobile industry, where they are utilized in energy storage. Chitosan (CS) is a natural polymer material utilized in supercapacitor fabrication. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period, and longer lifetime. In this research, the fabrication of symmetric supercapacitors with activated carbon (AC) electrodes has been investigated in order to analyze their performance characteristics. AC is derived from CS biomass, which has remarkable biodegradability. It has been chemically activated using ZnCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as the activating agent. CS has been activated inside a furnace at 500, 600, and 700°C in an inert N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> atmosphere. A 1M aqueous potassium hydroxide (KOH) solution is used as the electrolyte. The test using electrolytes (KOH) revealed that the electrode's specific capacitance was 74.7 Fg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , the highest value discovered. However, using organic electrolytes would have produced better results that can be used as a guide for future advancements. The influence of activation temperature on the porous characteristics of prepared AC was investigated utilizing surface area and pore size analyses. The morphological characteristics of synthesized AC were analyzed through scanning electron microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDX). Symmetric SC electrodes fabricated is analyzed in a two-electrode system applying standard electrochemical characterization methods using the potentiostat. Symmetric SC electrodes fabricated are analyzed in a two-electrode system applying standard electrochemical characterization methods using the potentiostat.

Application of long fibrous coconut silk-based porous carbon in flexible supercapacitor

All-solid-state flexible supercapacitors are considered to be one of the ideal candidates for energy storage in the next generation of wearable electronic devices due to their high capacitance performance and excellent mechanical flexibility. Biomass-based carbon materials are regarded as the ideal precursors for carbon-based electrode materials due to their wide sources, low cost, natural and abundant biological features. In this work, long-fiber coconut silk with vascular bundle structure was selected as the precursor, the controllable adjustment of the pore structure and conductive characteristics of the electrode material was achieved by changing the KOH activation temperature. The specific surface area of the activated carbon electrode material etched with KOH at 900 °C can reach 2794 m2·g−1. The high specific surface area and reasonable pore size distribution provide abundant active sites for the adsorption of electrolyte ions, which leads to the excellent electrode specific capacitance (2 mV·s−1，634 F·g−1，10.73 Wh·kg−1) of the symmetric flexible supercapacitor combined with PVA (polyvinyl alcohol)/H2SO4 gel electrolyte. At the same time, the long-fiber carbon skeleton has intrinsically high Young's modulus, which enables the flexible all-solid-state supercapacitor to maintain better electrochemical stability and mechanical durability under mechanical deformation, and it's retention rate can reach 101.5 % after 10,000 bending experiments at an inner angle of 140°. It proves the great advantages and potential of coconut silk-based biomass carbon materials in the field of preparing flexible supercapacitors, and promotes the development of energy storage units for next-generation wearable electronic devices.

Do specific ion effects influence the physical chemistry of aqueous graphene-based supercapacitors? Perspectives from multiscale QMMD simulations

Whether or not specific ion effects determine the charge storage properties of aqueous graphene and graphite-based supercapacitors remains a highly debated topic. In this work we present a multiscale quantum mechanics – classical molecular dynamics (QMMD) investigation of aqueous mono- and divalent salt electrolytes in contact with fully polarizable charged graphene sheets. By computing both the electrochemical double layer (EDL) and quantum capacitance we observe a constant electrode specific capacitance with cationic radii and charge. Counterintuitively, we determine that a switch in the cation adsorption mechanism from inner to outer Helmholtz layers leads to negligible changes to the EDL capacitance, this appears to be due to the robust electronic structure of the graphene electrodes. However, the ability of ions (such as K+) with a relatively low hydration free energy to penetrate the inner Helmholtz plane and adsorb directly on the electrode surface is found to slow their diffusion parallel to the interface. Ions in the outer Helmholtz layer are found to have higher diffusivity at the surface due to their position in ion channels between water layers. Our results show that surface effects such as the surface polarization and the partial dehydration and local structuring of ions on the surface underpin the behaviour of cations at the interface and add a vital new perspective on trends in ion mobilities seen under confinement.

Create Rich Oxygen Defects of Unique Tubular Hierarchical Molybdenum Dioxide to Modulate Electron Transfer Rate for Superior High‐Energy Metal‐Ion Hybrid Capacitor

Metal‐ion capacitors could merit advantages from both batteries and capacitors, but they need to overcome the severe restrictions from their sluggish reaction kinetics of the battery type electrode and low specific capacitance of capacitor type electrode for both high energy and power density. Herein, we use the Kirkendall effect for the first time to synthesize unique tubular hierarchical molybdenum dioxide with encapsulated nitrogen‐doped carbon sheets while in situ realizing phosphorus‐doping to create rich oxygen vacancies (P‐MoO2‐x@NP‐C) as a sodium‐ion electrode. Experimental and theoretical analysis confirm that the P‐doping introduced oxygen defects can partially convert the high‐bond‐energy Mo–O to low‐bond‐energy Mo–P, resulting in a low oxidation state of molybdenum for enhanced surface reactivity and rapid reaction kinetics. The as‐prepared P‐MoO2‐x@NP‐C as an ion‐battery electrode is further used to pair active N‐doped carbon nanosheet (N‐C‐A) electrode for Na‐ion hybrid capacitor, delivering excellent performance with an energy density of 140.3 Wh kg−1, a power density of 188.5 W kg−1 and long stable life in non‐aqueous solution, which ranks the best among all reported MoOx‐based hybrid capacitors. P‐MoO2‐x@NP‐C is also used to fabricate a zinc‐ion hybrid capacitor, also accomplishing a remarkable energy density of 43.8 Wh kg−1, a power density of 93.9 W kg−1, and a long stable life@2A g−1 of 32 000 cycles in aqueous solutions, solidly verifying its universal significance. This work not only demonstrates an innovative approach to synthesize high‐performance metal ion hybrid capacitor materials but also reveals certain scientific insights into electron transfer enhancement mechanisms.

Tough, self-healable, antifreezing and redox-mediated gel polymer electrolyte with three-role K3[Fe(CN)]6 for wearable flexible supercapacitors

Supercapacitors exhibiting toughness, self-healing, and high specific capacitance have practical significance for use in flexible and wearable electronic equipment. To meet these requirements, a novel multifunctional gel polymer electrolyte (GPE) consisting of polyvinyl alcohol (PVA)-sodium alginate (SA)-K3[Fe(CN)]6-Na2SO4 was prepared. In this GPE, K3[Fe(CN)]6 plays three crucial roles by serving as a carrier donor, ionic crosslinking agent and redox-active mediator. Consequently, the usual conflict between the conductivity and mechanical properties of GPEs is alleviated to some extent. In addition, the electrode specific capacitance and the energy density of the assembled supercapacitor are obviously improved because of the pseudocapacitance generated from the redox reaction of K3[Fe(CN)]6. Based on this GPE, the supercapacitor exhibits outstanding bending and stretching stabilities, significant self-healing, and anti-freezing properties. Therefore, the prepared GPE and super-capacitor are promising for application in flexible and wearable electronic equipment with complex service conditions.

Multifunctional Antifreezing Organogel Polyelectrolyte for a Flexible Supercapacitor

A multifunctional antifreezing mechanically tough conductive organogel polyelectrolyte was designed and prepared by simultaneously introducing poly(vinyl alcohol), tripentaerythritol, and H2O/dimethyl sulfoxide (DMSO) binary solvent. Based on the outstanding freeze resistance of the H2O/DMSO binary solvent, this organogel showed good mechanical properties and long-term stability in the temperature range of −20 to 20 °C. Meanwhile, the as-prepared flexible supercapacitor exhibits superior electrode specific capacitance (140 F g–1), high ionic conductivity (18.9 mS cm–1), outstanding cycling stability (only 5% capacitance decay over 2000 cycles), and excellent durability (85% weight retention after storing for 10 days) even at a low temperature of −20 °C. In addition, the prepared organogel exhibits tunable optical performances in diverse polar solvents and could act as information storage installations for recording and wiping.

Boosting the overall specific capacity of SiO electrodes for lithium-ion batteries using a multifunctional carbon cloth current collector

An approach of coating high-capacity active materials on current collectors with capacity-contributing ability is proposed to produce high-capacity electrodes.

Comparative Study of PEDOT- and PEDOT:PSS Modified δ-MnO2 Cathodes for Aqueous Zinc Batteries with Enhanced Properties

Chemically synthesized layered manganese dioxide (δ-MnO2) modified by poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) dispersion were used as cathode materials for aqueous Zn-ion batteries (AZIBs). A comparative study of electrochemical properties of cathodes with pristine MnO2 and materials chemically modified by conducting polymers in different forms was performed with cycling voltammetry and galvanostatic charge-discharge curves in Zn2+-containing electrolyte solutions. The results of electrochemical tests indicate the significant improvement in specific capacity of electrodes in the sequence MnO2, MnO2/PEDOT and MnO2/PEDOT:PSS composites. The MnO2/PEDOT:PSS electrode delivered a specific discharge capacity of 278 mAh·g−1 at a current density 0.3 A·g−1 after 100 cycles, whereas for MnO2/PEDOT and MnO2 electrodes the values were 238 and 121 mAh·g−1 (capacity retention is 99%, 99.5% and 89%, respectively). These specific capacity values obtained for manganese dioxide-based cathodes are demonstrating the positive role of intrinsically conducting polymer, especially in case of surface modification of electroactive particles by PEDOT:PSS dispersion.

The Potential of BiPO4 as Electrode Material and its Electrochemical Performance on AC-Mn2O3-BiPO4 Film Electrode

Supercapacitors as one of the energy storage have attracted attention. The advantages of using carbon materials have so far been widely developed and researched as electrodes for supercapacitors, but their volumetric capacity is still less than optimal and less practical in long-term use. Manganese (III) oxide (Mn2O3) materials show great potential as electrodes with high theoretical specific capacitance. On the other hand, BiPO4 as an anode has added battery characteristics to get maximum results. The blending method is applied in the manufacture of composites deposited on an aluminum foil substrate. The electrochemical properties of the developed samples were studied by cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The electrochemical results showed that the best electrode-specific capacitance at 20% BiPO4 percentage reached 56 Fg-1 at a current density of 1 Ag-1 with a potential window of 2 V for 50 cycles. It is hoped that these results can provide information on the potential of using the material as an optimal electrode.