Symmetric Electrochemical Capacitor Research Articles

Interfacial Insights into the Polarization Protocol: Toward Reducing Corrosion and Improving the Cycle Life of Electrochemical Capacitors.

The number of scientific publications on the impact of corrosion on current collectors on the working parameters of electrochemical capacitors is very limited. The aim of current research is to search for new, environmentally friendly chemical power sources and energy storage devices and to improve existing ones. Therefore, this article presents a simple and effective way to improve the life of a symmetric electrochemical capacitor by changing the direction of electrode polarization, which in turn inhibits the corrosion of the current collector. This slows the degradation of current collectors of positive electrode over long durations. However, activated carbon electrode corrosion also occurs. Experiments on capacitors with stainless steel and gold current collectors indicate that the lifespan of the latter is much longer than that of the former. Therefore, current collector corrosion has a distinct and detrimental impact on electrochemical capacitor operation. Moreover, the research results indicate that carbon corrosion results from current collector corrosive damage.

Fabrication of solid-state high capacitance supercapacitor from N-doped biomass porous carbon

Heteroatom-doped porous carbon material fabricated from bio-resources has greatly attracted extensive interest in the energy storage field. In this work, we report the cheese-like porous carbon material enriching more heteroatoms such as oxygen and nitrogen fabricated from silkworm pupa in a facile carbonization and activation way. Benefited from the compromise between activator ratio and activation temperature in the activation process, the optimized sample of NBC600-1:3 presents not only a substantial surface of 2005.04 m2 g−1 but also a high heteroatom doped level of 11.90 %, leading to the achievement of the maximal mass specific capacitance of 406 F g−1 at 1 A g−1 and good rate capability up to 70.44 % (286 F g−1) at 20 A g−1 in 6 M KOH solutions. The symmetric electrochemical capacitor assembled displays a high energy density of 21.78 W h kg−1 (at 450 W kg−1) and a power density of 4500 W kg−1 (at 13.75 W h kg−1) in 1 M Na2SO4 solutions. Noticeably, the as-prepared quasi-solid device also presents a perspective performance in various bending angles, indicating a good flexible performance. This work provides the possibility for the application prospects of biomass carbon in flexible electronic.

Binder mediated enhanced electrochemical capacitance in sodium silicate-graphite paint coated filter paper electrodes for all-solid-state symmetric electrochemical capacitors

In this study, we have prepared a conductive paint by mixing graphite powder, fumed SiO2 particles, NaOH and water in a suitable ratio. The paint was coated on the surface of low-cost laboratory filter paper to prepare paper-based electrodes for electrochemical capacitors. Electrochemical parameters such as specific capacitance, specific energy and specific power of the electrodes were determined for 1 M H2SO4, H3PO4 and KOH electrolytes using 3-electrode electrochemical cells. All-solid-state symmetric electrochemical capacitors were constructed by using three different gel-electrolytes: PVA-H2SO4, PVA-H3PO4 and PVA-KOH. The areal capacitance values obtained for all-solid-state symmetric electrochemical capacitors with PVA-H2SO4, PVA-H3PO4 and PVA-KOH gel-electrolytes were 123.8, 94.8 and 74.7 mF cm−2 respectively. In presence of acidic electrolyte, there is significant pseudocapacitance contribution from the electrode due to presence of binder. Thus, the value of areal capacitance and hence the energy density of electrochemical capacitor with PVA-H2SO4 is highest followed by PVA-H3PO4 and lowest with PVA-KOH gel-electrolyte. It is interesting to note that in acidic electrolyte, although there is enhancement of areal capacitance, it is associated with significant reduction of cyclic stability due to the structural change of the binder. Thus, electrochemical capacitor with PVA-KOH gel-electrolyte has shown highest cyclic stability.

Choline chloride-based deep eutectic solvents as electrolytes for wide temperature range supercapacitors

Deep eutectic solvents (DESs) are a promising new class of environmentally friendly versatile solvent systems. In this work, a new approach for applying choline chloride-based DESs as cost-effective, and anti-corrosion electrolytes for activated carbon-based electrochemical capacitors (ECs) is proposed for the first time. In this regard, DESs of choline chloride/glycerol and choline chloride/propionic acid were prepared with molar ratios of 1:2. Important properties such as viscosity, electrical conductivity, and electrochemical measurements were studied in the range of room temperature up to 373 K. With the rising temperature, the viscosity of DESs decreased and their electrical conductivity increased. High energy is provided by the symmetric ECs in the choline chloride-based electrolytes, which exhibit excellent electrochemical stability at a maximum voltage up to 2.5 V. The electrolyte with DES ChCl/PA under 373 K has a specific capacitance of 198 F g−1 (with an energy density of 110 Wh kg−1), which can be reduced to 145 F g−1 (with an energy density of 16.3 Wh kg−1) at room temperature. In addition, 93 % capacity retention was achieved in the supercapacitor prepared based on DES ChCl/PA up to 5000 cycles at 373 K. According to the results, important implications are presented for expanding the application of green, non-toxic and cheap electrolytes for high-performance ECs with wide voltage windows and superior lifetime.

Evaluation of kinetic parameters of non-faradic processes in carbon-based electrodes using multisine dynamic electrochemical impedance spectroscopy

Dynamic Electrochemical Impedance Spectroscopy is a valuable tool to investigate kinetic parameters of non-Faradic processes in symmetric Electrochemical Double Layer Capacitors. Compared to classic Electrochemical Impedance Spectroscopy, the dynamic technique measures the impedance under non-equilibrium condition removing the stationarity requirement and, at the same time, giving the frequency-dependent information of a dynamic process in presence of overpotential. Despite not being a new technique, there is an inherent complexity in the signal sampling and data manipulation to obtain the impedance spectra down to low frequencies (the interesting band for energy storage devices impedance). Few methods to compute the impedance from sampled signals are reported in the literature and under development. For this work the Dynamic Multi-Frequency Analysis algorithm was used to compute the impedance and reconstruct the cyclic voltammetry profile as well. The time-dependency of the kinetic parameters, namely capacitances of double layer and adsorption phenomenon, were extracted from equivalent circuit model regression and the adsorption time constants with a graphical analysis of the impedance spectra dataset during a full charge/discharge cycle. The values of the adsorption capacitance from the model regression are, on average, compatible with the values computed with a common formula showing the reliability of the model regression. The use of a three-electrode compact cell allowed the characterization of both active electrodes independently during operation showing a strong potential dependence on the active material properties. Furthermore, the impedance showed the presence of a side reaction (likely oxygen evolution) connected to the increase of adsorption and double layer capacitances localized on the positive electrode in a clearer way than what was possible to observe from the voltametric profile.

Layered graphite foil/poly(3,4-ethylenedioxythiophene) electrode-enabled flexible electrochemical capacitors with observably boosted performances

• A simple mechanically exfoliated method is proposed to prepare LGF current collector. • LGF shows a unique layered microstructure with observably enlarged surface area. • The electrochemical properties of PEDOT are significantly affected by polymerized parameters. • LGF-constructed electrodes show observably enhanced electrochemical properties. • LGF/PEDOT flexible EC features high electrochemical properties and mechanical flexibility. Seeking a cheap flexible current collector and further enhancing charge storage capacity are still two crucial challenges to promote the practical applications of flexible electrochemical capacitors. In this work, we first fabricate layered graphite foil (LGF) current collector from low-cost GF by a facile and scalable mechanically exfoliated method. And meanwhile, the electropolymerization parameter-dependent supercapacitive performance of the poly(3,4-ethylenedioxythiophene) (PEDOT) as the electroactive material is investigated in detail. Electrochemical measurements verify that the electrochemical performances of PEDOT are notably improved via optimizing the electropolymerization parameters. More importantly, the capacitive behaviors of PEDOT electrodes are further observably boosted through using LGF current collector compared to GF, attributed to the 3D interface established between the PEDOT films and LGF. The LGF/PEDOT electrodes yield an areal-specific capacitance of 122.3 mF cm −2 and achieve high rate capability. Furthermore, a symmetrical electrochemical capacitor assembled by the LGF/PEDOT electrodes show superior electrochemical capacitive properties and highly mechanical flexibility. Even more impressively, it retains 92.1% and 94.3% of initial capacitance after 10,000 charge–discharge cycles and harsh mechanical deformation for 500 times, respectively. The LGF we develop not only ensures its high flexibility but distinctly enhances its electrochemical properties.

Enhancing the materials circularity: from laboratory waste to electrochemical capacitors

Enhancing the circularity of materials is at the forefront of sustainability; this paper addresses smart reuse of a laboratory waste, i.e., paper towels, as one of the main components (electrodes) in an energy storage device (electrochemical capacitor, EC). We obtained carbon from wastepaper towels by converting them into cellulose through alkali treatment, subsequent enhancement of porosity via nitric acid reflux, and enhancement of chemical purity via controlled annealing. The porous carbon thereby optimized is characterized for chemical structure, surface structure, and morphology as well as electrochemical charge storability. The carbon sample obtained at 800 °C showed graphitization and interconnected morphology displaying a combination of micro and mesopores, superior surface area (∼528 m2/g), desirable pore diameter for efficient ion adsorption (∼3.3 nm), and specific capacitance ∼230 F/g in 1 M KOH and ∼160 F/g in 1 M Na2SO4 electrolytes. Symmetrical electrochemical capacitors are also fabricated using the best performing carbon electrode in the above two electrolytes, which delivered desirable specific energy and specific power with high cycling stability. Given the longer cycling stability of the device and considering the acceptable properties, the present work is a way forward for enhancing the circularity of the laboratory wastepaper towels.

Biosourced quinones for high-performance environmentally benign electrochemical capacitors via interface engineering

Biosourced and biodegradable organic electrode materials respond to the need for sustainable storage of renewable energy. Here, we report on electrochemical capacitors based on electrodes made up of quinones, such as Sepia melanin and catechin/tannic acid (Ctn/TA), solution-deposited on carbon paper engineered to create high-performance interfaces. Sepia melanin and Ctn/TA on TCP electrodes exhibit a capacitance as high as 1355 mF cm−2 (452 F g−1) and 898 mF cm−2 (300 F g−1), respectively. Sepia melanin and Ctn/TA symmetric electrochemical capacitors operating in aqueous electrolytes exhibit up to 100% capacitance retention and 100% coulombic efficiency over 50,000 and 10,000 cycles at 150 mA cm−2 (10 A g−1), respectively. Maximum power densities as high as 1274 mW cm−2 (46 kW kg−1) and 727 mW cm−2 (26 kW kg−1) with maximum energy densities of 0.56 mWh cm−2 (20 Wh kg−1) and 0.65 mWh cm−2 (23 Wh kg−1) are obtained for Sepia melanin and Ctn/TA.

Hydrothermally prepared sugar-derived carbon spheres for all-solid-state symmetric electrochemical capacitors

Carbon spheres were prepared by template-free hydrothermal process and further modified via heat treatment and activation to form oxygen doped graphitic carbon spheres with higher surface area. FTIR, XRD, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analysis, cyclic voltammetry (CV), galvanic charge-discharge (GCD) experiments and electrochemical impedance spectroscopy (EIS) techniques were used for analyzing structural and chemical composition, morphological features and electrochemical properties of the prepared materials. The electrochemical properties of materials were thoroughly investigated by using three electrode systems. In two electrode studies, all-solid-state symmetric supercapacitor devices were constructed where hydrothermally prepared carbon spheres showed areal capacitance, energy density and power density values 20.5 mF cm−2, 2.9 μWh cm−2 and 50.0 μW cm−2 respectively at current density 0.1 mA cm−2. Under identical condition, these parameters for activated carbon sphere were 70.5 mF cm−2, 9.8 μWh cm−2 and 50.0 μW cm−2 respectively. Moreover, hydrothermally prepared carbon sphere exhibits remarkable cyclic stability by retaining 102% of its initial areal capacitance even after completion of 5000 cycles. Thus hydrothermally prepared carbon spheres without activation may be a promising low cost material for supercapacitors of low energy density with excellent cyclic stability.

Capacitor lifetime prolonged by addition of organic ammonium salt with cyclohexyl substituent and 2,5-dihydroxybenzenesulfonic anion

It is well known that the electrochemical corrosion negatively affects the functional properties of metal and steel materials that constitute a part of systems conducting electric charge. On the other hand, the phenomenon of corrosion is rarely associated with the degradation of chemical power sources and energy storage devices. This article is aimed to fill this gap by describing the effect demonstrated by a substituted ammonium salt with cyclohexyl substituent and 2,5-dihydroxybenzenesulfonate anion used as a corrosion inhibitor in symmetrical electrochemical capacitor system. The accelerated ageing test of capacitor systems has shown that the addition of substituted ammonium salt to capacitor electrolyte allows to extend the service lifetime of the entire system by inhibiting the corrosion of 316L stainless steel current collectors. The inhibitory effect of substituted ammonium salt additives on the electrochemical corrosion of 316L stainless steel surface has been also confirmed by cyclic potentiodynamic polarization (CPP) tests and X-ray photoelectron spectroscopy (XPS) measurements.

Ruthenium dioxide anchored on reduced graphene oxide nanocomposite for 1.2 V symmetric supercapacitor devices

In this work, the high-performance symmetric electrochemical capacitor based on ruthenium dioxide anchored on reduced graphene oxide nanostructures was developed. The created system consists of the negative and positive electrodes with Na2SO4 aqueous electrolyte. The symmetric capacitor devices electrodes were tested in the potential range of 0 to 1.2 V. As a result, at 2 A/g,the rGO/RuO2 and RuO2 electrodes gained higher energy (41 Wh kg−1 and 31 Wh kg−1) and power densities (1.2 kW kg−1 and 0.98 kW kg−1). After the 2000th cycle,the rGO/RuO2 electrode has such a high cyclic efficiency of 96%, which is considerably higher than the pure RuO2 (88%).This is due to the anchoring of high conducting rGO in rGO/RuO2 nanocomposite. These findings reinforce the idea of graphene-based nanocomposites having as a safe aqueous electrolyte in high-voltage energy storage devices.

Sustainable production of lignin-derived porous carbons for high-voltage electrochemical capacitors

• CuCl 2 activation mechanism is elucidated. • Lignin-derived porous carbon with high specific surface area. • Lignin-derived porous carbon with high yields up to 49.4%. • High-voltage electrochemical capacitors are fabricated. The high energy storage cost is a crucial factor limiting the wide application of electrochemical capacitors. Herein, we proposed a comprehensive strategy to reduce the cost of electrochemical capacitors with aqueous electrolytes, i.e. , reducing the cost of electrode materials and increasing the energy density of electrochemical capacitors. Low-cost lignin-derived porous carbon electrode materials with high specific surface area and hierarchical porous structure were prepared by CuCl 2 activation. The CuCl 2 activation agent was recycled and thus can be reused. What is more, we proposed that the mechanism of CuCl 2 activation is a solid-phase reaction in which the chloride ions in copper chloride deprive the hydrogen atoms in lignin, resulting in the loss of hydrogen atoms and the formation of pores. High energy density C//C symmetric electrochemical capacitors, Zn//C and Pb//C asymmetric electrochemical capacitors based on lignin-derived porous carbon were fabricated using sulfate electrolytes which endow high working voltage window. This work provides a comprehensive strategy for designing electrochemical capacitors with high energy densities and low cost of energy storage, which is expected to promote the industrial application of electrochemical capacitors with aqueous electrolytes.

Additive manufacturing of polyaniline electrodes for electrochemical applications

Polyaniline (PANI), particularly in its emeraldine salt form (PANI-ES), possesses several desirable properties such as high tuneable conductivity, pseudocapacitance and chemical stability, which make PANI a promising material for a wide range of electrochemical applications. However, its use is severely limited by its poor processability due to its non-thermoformable nature. In this work, a novel additive manufacturing method to process PANI is introduced, which enables the fabrication of electrodes with complex geometries exhibiting conductivities of up to 20000 mS/cm. This novel additive manufacturing process is based on the thermal doping of PANI in its low-conductive emeraldine base form (PANI-EB) with dodecyl benzene sulfonic acid (DBSA). For this purpose, a commercially available 3D printer was modified with a custom-made syringe extrusion system to enable the extrusion of a viscous PANI-EB/DBSA paste. The influence of the additive manufacturing process parameters on the conductivity of printed electrodes was evaluated, and the resulting printed materials were characterised by Fourier-transform infrared spectroscopy – attenuated total reflection, X-ray powder diffraction, thermo-gravimetric analysis and scanning electron microscopy. The feasibility of the 3D printed PANI-ES/DBSA electrodes was studied by conducting a proof-of-concept electrochemical study of 3D printed interdigitated symmetric electrochemical capacitors, demonstrating how the printed structures could be easily integrated in prototypes of electrochemical devices. Although the fabricated devices did not exhibit superior capacitance, they presented a memristive behaviour with a potential for other applications such as artificial neural networks. Moreover, the results of this proof-of-concept study illustrate the significant importance of the conductivity of the printed electrodes, hence the importance of the additive manufacturing process parameters on the electrochemical performance.

V2O5@RuO2 core–shell heterojunction nano-arrays as electrode material for supercapacitors

V2O5 nanobelt arrays (VNBs) are directly synthesized on porous nickel as the primary structure, and then the VNBs are completely covered by RuO2 nanosheets (RNSs) as the secondary structure to create a core–shell heterojunction. The as-prepared VNBs@RNSs core–shell heterojunction is systematically researched through SEM, EDS, XRD, XPS and TEM, and the growth process is investigated in detail by sampling at different time. The VNBs@RNSs has a superb specific capacitive value of 971F g−1 at a voltage scanning speed of 5 mV s−1, a better cyclic steadiness of 80.4 % after recycling 10,000 times, a small charge transferring resistance value of 1.8 Ω and a fast effective diffusion coefficient of 1.01 × 10−8 cm2 s−1 calculated by CV, GCD, AC impedance and CA electrochemical techniques in a three-electrode testing system. A symmetrical electrochemical capacitor assembled by the as-prepared VNBs@RNSs electrode material has a superior energy density of 174.2 W h kg−1 at a power density of 450 W kg−1 and still retains 95.9 W h kg−1 at 9000 W kg−1 in a two-electrode testing system. The improved supercapacitive performance makes the VNBs@RNSs as a superior electrode material for supercapacitor.

One-Pot Synthesis of rGO@Cu2V2O7 Nanocomposite as High Stabled Electrode for Symmetric Electrochemical Capacitors

The rGO anchored copper vanadate nanostructures have been synthesized through facile hydrothermal synthesis for the high efficient energy storage applications. The prepared Cu2V2O7 and rGO@Cu2V2O7 nanostructures are fabricated as the electrode materials for three electrode and symmetric type electrochemical supercapacitors. Based on the electrochemical the electrodes shows the outstanding areal capacitance values of 340 and 545 F g−1 for Cu2V2O7 and rGO@Cu2V2O7 electrodes, respectively. Also the charge discharge curves of the rGO@Cu2V2O7 electrode revealed the higher specific capacitance values of 520 F g−1 at 1 A g−1 which is higher capacitance value than Cu2V2O7 electrode (318 F g−1 at 1 A g−1). Based on the cyclic performance the rGO@Cu2V2O7 electrode enumerate 98.6% withstand even the 1000th cycle. The symmetric electrode based device have been shows the higher capacitance values of 190 F g−1 at 1 A g−1 for rGO@Cu2V2O7 it is higher than pure Cu2V2O7 (148 F g−1 at 1 A g−1). With the synergitic reaction of rGO@Cu2V2O7 electrode shows the high energy 29.7 Wh kg−1 and power 4.8 kW kg−1 and the Cu2V2O7 and rGO@Cu2V2O7 electrodes. Also the rGO@Cu2V2O7 symmetric electrode device shows the higher cyclic efficiency about 97.5% at the 2000th cycle. These findings assess the rGO@Cu2V2O7 electrode is a promising candidate for the energy storage application.

Enzymatic Hydrolysis Lignin-Derived Porous Carbons through Ammonia Activation: Activation Mechanism and Charge Storage Mechanism.

The low energy density and low cost performance of electrochemical capacitors (ECs) are the principal factors that limit the wide applications of ECs. In this work, we used enzymatic hydrolysis lignin as the carbon source and an ammonia activation methodology to prepare nitrogen-doped lignin-derived porous carbon (NLPC) electrode materials with high specific surface areas. We elucidated the free radical mechanism of ammonia activation and the relationship between nitrogen doping configurations, doping levels, and preparation temperatures. Furthermore, we assembled NLPC∥NLPC symmetric ECs and NLPC∥Zn asymmetric ECs using aqueous sulfate electrolytes. Compared with the ECs using KOH aqueous electrolyte, the energy densities of NLPC∥NLPC and NLPC∥Zn ECs were significantly improved. The divergence of charge storage characteristics in KOH, Na2SO4, and ZnSO4 electrolytes were compared by analyzing their area surface capacitance. This work provides a strategy for the sustainable preparation of lignin-derived porous carbons toward ECs with high energy densities.

Hydrothermally Prepared Sugar-Derived Carbon Spheres for All-Solid-State Symmetric Electrochemical Capacitors

Hydrothermally Prepared Sugar-Derived Carbon Spheres for All-Solid-State Symmetric Electrochemical Capacitors

Optimal Charging Profile Design for Attaining Desired State of Charge in Symmetric Electrochemical Capacitor With Efficiency Analysis

The optimal utilization of ultracapacitor (symmetric electrochemical capacitor) for vehicular applications demands continuous monitoring and maintenance of its state of charge (SOC). The online estimation of SOC plays a vital role in the effective utilization of the energy storage capacity of ultracapacitors. In addition to monitoring SOC, high reliability in vehicle operation requires a predefined SOC level, as per the dynamic load requirement. For the ultracapacitor undergoing series of charge-discharge cycles, proper regulation of the SOC in accordance with the vehicle drive profile, increases the ultracapacitor life by avoiding possible stress due to undercharging/overcharging. Achieving the desired SOC in real-time warrants a mechanism for the optimal charging of the ultracapacitor. In this regard, the present article proposes an optimal charging scheme to attain a predefined SOC from any initial value, within a given time-frame. The proposed noniterative fractional calculus-based approach allows for analytically representing the charging current as a function of the desired SOC, charging duration and ultracapacitor model parameters. The scheme has been extensively validated experimentally for its effectiveness in attaining the desired SOC. Further, the appropriateness of the derived charging profiles for different operating scenarios has also been analyzed in terms of maintaining a tradeoff between faster charging and high charging efficiency.

Improvement of Electrochemical Properties of Poly(3,4-ethylene dioxythiophene) (PEDOT) Thin Film by UV Irradiation.

Electrochemical redox supercapcitor is one of promising rechargeable power sources for portable electronic, display or telecommunication devices since it has a large energy density, very fast charge/discharge time and long life cycle. In this study, poly(3,4-ethylene dioxythiophene) (PEDOT) thin film as the electrode of electrochemical supercapacitor was deposited on a metal current collector by in-situ polymerization method. Symmetrical electrochemical capacitor was then assembled using PEDOT films as working and counter electrodes, where 0.1 M lithium perchlorate (LiClO₄) solution in acetonitrile was used as the electrolyte solution. Typical specific discharge capacitance of the capacitor was about 70 F/g and showed little decrease after 1,000 charge/discharge cycles. We also found that UV irradiation improved the electrochemical properties of redox capacitor by formation of hydrophilic polar groups on PEDOT film surface. After UV irradiation on the surface of PEDOT film for 2 hours with the intensity of 30 mW/cm², the specific discharge capacitance increased by about 10% compared to capacitance of pristine PEDOT film.

Chitin and chitin-cellulose composite hydrogels prepared by ionic liquid-based process as the novel electrolytes for electrochemical capacitors

This paper reports on the preparation and electrochemical performance of chitin- and chitin-cellulose-based hydrogel electrolytes. The materials were prepared by a casting solution technique using ionic liquid-based solvents. The method of chitin dissolution in ionic liquid with the assistance of dimethyl sulfoxide co-solvent was investigated. The obtained membranes were soaked with 1-M lithium sulfate aqueous solution. The prepared materials were preliminarily characterized in terms of structural and physicochemical properties. Further, the most promising biopolymer membranes were assembled with activated carbon cloth electrodes in symmetric electrochemical capacitor cells. The electrochemical performances of these devices were studied in a 2-electrode system by commonly known electrochemical techniques, such as cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The devices operated at a maximum voltage of 0.8 V. All the investigated materials have shown high efficiency in terms of specific capacitance, power density, and cyclability. The studied capacitors exhibited specific capacitance values in the range of 92–98 F g−1, with excellent capacitance retention (ca. 97–98%) after 20,000 galvanostatic charge and discharge cycles. Taking into account the above information and the eco-friendly nature of the biopolymer, it appears that the prepared chitin- and chitin-cellulose-based hydrogel electrolytes can be promising components for green electrochemical capacitors.