Pseudocapacitive Electrode Materials Research Articles

Fabrication of Mn3O4-WO3 nanoparticles based nanocomposites symmetric supercapacitor device for enhanced energy storage performance under neutral electrolyte

Development of pseudocapacitive electrode materials with wide potential windows is the major challenge for supercapacitor application to overcome the critical energy crisis. In this consequence, we have prepared Mn3O4-WO3 nanoparticles based nanocomposite with the variable stoichiometric amount of Mn sources via the one-pot solvothermal method. Among all the synthesized nanocomposite and bare samples, Mn3O4-WO3 (10:1) nanoparticles nanocomposite pursue excellent specific capacitance in three and two-electrode systems. In a three-electrode system the synthesized Mn3O4-WO3 (10:1) nanoparticles nanocomposite displays maximum specific capacitance 358 F g−1 using a neutral electrolyte with a wide working potential window. The electrokinetic analysis of the synthesized Mn3O4-WO3 (10:1) nanoparticles nanocomposite has been predominant capacitive contribution over the charge storage. Further the fabricated symmetric supercapacitor device (SSD) using Mn3O4-WO3 (10:1) nanocomposite pursues the maximum specific capacitance 101 F g−1 along with the energy density of 56.11 Wh kg−1 and power density 5 kW kg−1. Moreover the fabricated device of the synthesized Mn3O4-WO3 (10:1) nanocomposite demonstrates outstanding durability which has 95.5% specific capacitance retention upto 5000 continuous charge-discharge cycles. The improved stability and higher electrochemical activity are due to the nanocomposite effect, high pore volume and surface area, and low charge transfer resistance of the synthesized Mn3O4-WO3 (10:1) nanocomposite.

Single-step in situ synthesis of MoO2-faceted structures as highly efficient HER electrocatalysts and electrode materials for pseudocapacitors

The in situ developed intermediate MoO2-layered structures exhibited superior performance towards HER activity. The faceted and stacked MoO2 structures are potential candidates as electrode materials for pseudocapacitors.

Advances in pseudocapacitive and battery-like electrode materials for high performance supercapacitors

Systematic survey on the fabrication and electrochemical performance of the most promising classes of pseudocapacitive/battery-type electrode materials for supercapacitors.

Sol-gel synthesized nickel oxide nanostructures on nickel foam and nickel mesh for a targeted energy storage application

The nickel-based oxides are treated as favourable pseudocapacitive electrode materials for energy storage application owing to their inexpensive nature, well-defined redox activity, as well as liberty in tuning the microstructures by changing the synthesis process optimizing its vital parameters. However, a real challenge for fabricating nickel-based materials is to sustain the uniform morphology onto a conductive substrates like FTO, ITO, stainless steel, nickel foam, nickel mesh, and copper foam etc. Herein, nickel oxide (NiO) nanostructures (NSs) with high pseudocapacitive performance have been prepared via the sol-gel technique for energy storage application. The structural identity of NiO-NSs is documented by X-ray diffraction, which confirmed the monoclinic crystal structure of the synthesized NSs. The X-ray photoelectron spectroscopy confirmed the valence state of the nickel as ‘+2′ and oxygen as ‘-2′. The field-emission scanning electron microscopy of NiO-NSs revealed non-uniform large spherical clusters agglomerated onto the surface. The NiO-NSs manifested the mesoporous channels and exhibit a surface area of 31.4 m2g-1, which is evaluated through Brunauer-Emmett-Teller analysis. The fabricated NiO-nickel foam (NF) electrode exhibit a high specific capacitance of 871 Fg−1 at a scan rate of 5 mVs−1 in 4 M KOH solution. Moreover, the NiO−NF electrode displayed the cyclic retention of 86.5 % after 10,000 cycles. The mesoporous channels of the electrode material afford plentiful, accessible, active sites to the effective charge transportation of electrolyte charges over the electrolyte-electrode interface and boost the electrochemical performance of NiONF −electrodes. Moreover, an asymmetric supercapacitor device constructed with NiO−NF as the anode and AC−NF as the cathode delivers high specific energy and specific power (24 Whkg−1 at 2.9 kWkg−1), and good cycling stability (retention of 89.7 % over 5 000 cycles)

Fabrication of various metal hexacyanoferrates@CNF through acid-regulation for high-performance supercapacitor with superior stability

Prussian blue analogs, as a pseudo-capacitor electrode materials hold great potential due to their unique framework structure, excellent electrochemical activity and high specific capacity. Herein, a versatile method for the growth of series of metal hexacyanoferrates (MHCF) on carbon nanofiber with high conductivity and flexibility was proposed. By controlling the releasing rate of metal ions through acid modulation of solution, the series of MHCF nanocubes were successfully embedded on the carbon nanofibers with super stability. Different MHCF presented various loading density. Among the MHCFs, nickel hexacyanoferrate (NiHCF) is the most easily formed with high density and uniform distribution. The obtained self-supporting NiHCF@CNF, as a representative electrode, exhibited high specific capacitance (507 F g−1, 1 A g−1) and remarkable rate performance (67% retention at 10 A g−1). Moreover, the NiHCF@CNF-based hybrid supercapacitor cell delivered a high energy density of 60 Wh kg−1 at the power density of 810 W kg−1. Meanwhile, the capacitor showed extremely high stability due to tight anchoring of NiHCF on CNFs. This work provides a simple and versatile method to produce self-supporting MHCF@CNF composites for constructing high performance supercapacitor.

In Situ Growth of Ni–Zn–Fe Layered Double Hydroxide on Graphene Aerogel: An Advanced Two‐in‐One Material for Both the Anode and Cathode of Supercapacitors

The push toward high‐performance supercapacitors calls for the development of efficient pseudocapacitive negative electrode materials that can better match the high capacitance of the typical positive electrodes. Herein, a facile and one‐pot hydrothermal approach for the in situ growth of the nickel–zinc–iron layered double hydroxide (LDH) onto the graphene aerogel (GA) substrate is introduced. Proper selection of the metal precursors with prominent pseudocapacitive behavior over a wide potential range coupled with the excellent double‐layer capacitive and charge transport properties of the GA network results in an LDH–GA nanocomposite that displays outstanding supercapacitive performances as both negative (387 F g−1, 101 mA h g−1, at 1.0 A g−1) and positive (1235 F g−1, 103 mA h g−1) electrodes. An aqueous LDH–GA//LDH–GA device with a wide voltage window (1.55 V) that demonstrates a significantly enhanced specific capacitance (304 F g−1 at 1.0 A g−1), outstanding specific energy (95 W h kg−1), appreciable specific power (81 kW kg−1), along with 88% retention of the initial capacitance after 10 000 cycles, is also fabricated. The superior supercapacitive performance of the Ni–Zn–Fe LDH–GA nanocomposite over both negative and positive voltage ranges opens a promising pathway toward manufacturing high‐energy supercapacitors for state‐of‐the‐art applications.

MOF derived hierarchical carbon-enhanced MCo2S4 for high-performance hybrid supercapacitors

Ternary transition metal sulfides have attracted great research attention as effective pseudocapacitive electrode materials for high-performance supercapacitors. Herein, hierarchical carbon structure is derived from 2D zeolitic imidazolate framework to enhance overall electrochemical performances of MCo2S4 (M = Fe, Ni) nanospheres. Due to a positive synergistic effect induced by carbon substrate with excellent conductivity and the MCo2S4 with high electrochemical activity, the composite (C@MCo2S4) exhibits a specific capacity of 342.5 mAh g−1 at a current density of 1 A g−1 and a capacity retention of 69% at 10 A g−1. In addition, a hybrid supercapacitor with C@MCo2S4 and soybean derived porous carbon as the positive and negative electrodes delivers a high energy density of 45.9 Wh kg−1 at a power density of 775 W kg−1.

Simple, green organic acid-based hydrometallurgy for waste-to-energy storage devices: Recovery of NiMnCoC2O4 as an electrode material for pseudocapacitor from spent LiNiMnCoO2 batteries

A simple, green approach to recover NiMnCoC2O4 as an electrode material for high-performance pseudocapacitors from spent LiNiMnCoO2 (NMC) batteries is proposed. Four strategic metals (Li, Ni, Co, and Mn) were leached from spent NMC batteries using several organic acids as model green leachants. Among the various candidates of green leaching agents, 2 M citric acid and 5 wt% glucose were selected as the leachant and reductant, respectively. Microwave irradiation was conducted during the leaching step to maximize the performance of the leaching rate and efficiency. The leaching efficiencies within 0.5 h for Ni(II), Li(I), Mn(II), and Co(II) were 90.7 ± 1.6%, 98.3 ± 2.4%, 94.9 ± 4.3%, and 95.6 ± 1.4%, respectively, and were thus as efficient as using aqua regia leaching. After the leaching process, divalent metal ions, that is, Ni(II), Co(II), and Mn(II), were immediately separated at room temperature using oxalic acid. The recovered samples were not further treated and used directly for energy storage applications. The recovered NiMnCoC2O4⋅nH2O has been demonstrated as a promising electrode for pseudocapacitors, providing a specific capacitance of 1641 F/g, good rate-retention capability (80% of low-current capacitance), and good cycle stability over 4000 charge–discharge cycles.

Tween modified CuFe2O4 nanoparticles with enhanced supercapacitor performance

Binary metal oxides CuFe2O4 can be a low-cost and high-performance pseudo-capacitive electrode material. However, their large size distributions and low dispersion caused by agglomeration can not exert their potential capacity. Hence, we used tween to modify CuFe2O4 (CuFe2O4-T) nanoparticles via a facile hydrothermal method. The composite nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis reflectance spectroscopy, and Fourier transform infrared spectroscopy. After modification, CuFe2O4-T showed high purity, greatly reduced particle size with the diameter about 10–20 nm, and decreased bandgap energy. When serving as supercapacitor electrodes, their electrochemical behaviors were examined by cyclic voltammetry, galvanostatic charge-discharge study, and electrochemical impedance spectroscopy. CuFe2O4-T exhibited improved supercapacitor behavior, with a specific capacitance of 437.3 F g−1 at the scan rate of 0.004 Vs−1 in 0.5 M H2SO4 electrolyte, 88.6% capacitance stability retention over 2000 cycles. An asymmetric supercapacitor device was assembled by using CuFe2O4-T as a positive electrode, which showed good capacitive behavior and cyclic stability. This work indicates that tween can effectively improve the performance of CuFe2O4 nanoparticles, and CuFe2O4-T will have great promise for wide electrochemical application.

Ultrafine Mn3O4 nanowires synthesized by colloidal method as electrode materials for supercapacitors with a wide voltage range

Manganese oxide is considered an ideal pseudo-capacitive electrode material for supercapacitors due to its low cost, environmental friendliness and large theoretical capacity. However, it is difficult to obtain manganese electrodes with a high specific capacitance and a large voltage range. In this study, ultrafine Mn3O4 nanowires with an average diameter of 4.0 nm were synthesized using a colloidal method. They have a large specific surface area of 175.1 m2 g−1, and can provide numerous active sites to enhance their specific capacitances. They also show a large pore volume of 0.7960 cm3 g−1, which can provide essential channels for ion transport during charging and discharging processes. The supercapacitor electrode made of these ultrafine Mn3O4 nanowires exhibits a predominant surface capacitive behavior during charge/discharge processes, and achieves a large specific capacitance of 433.1 F g−1 at a current density of 0.5 A g−1 with a very wide voltage range from -0.5 to 1.1 V in 1 M Na2SO4 electrolyte. An asymmetric supercapacitor (ASC) was assembled using a cathode electrode made of these ultrafine Mn3O4 nanowires and an active carbon (AC) anode electrode, and a high energy density of 26.68 Wh kg−1 at a power density of 442 W kg−1 was achieved. The ASC showed a good cycling stability, and its capacitance value was still maintained at 75.8% after 64,000 charge/discharge cycles.

Pseudocapacitance improvement of polymolybdates-based metal–organic complexes via modification with hydrogen molybdenum bronze by electrochemical treatment

The preparation of highly pseudocapacitive electrode materials is important for development of supercapacitors. In this work, a kind of new electrode material, namely, hydrogen molybdenum bronze (HMB) modified polymolybdate-based metal–organic complex {Cu(3-H2bptzh)(H2O)2[γ-Mo8O26]}·(3-H2bptzh)·H2O (1) (1-HMB) was prepared by electrochemical treatment (3-bptzh = 1,4-bis(5-(3-pyridyl)tetrazolyl) -hexane), aiming for promoting the pseudocapability of polymolybdates-based complexes. The carbon cloth-based electrode with 1-HMB (1-HMB/CC-0.15), which was obtained through electrochemical treatment between potential range of − 0.15 and 0.5 V (vs. SCE) achieved a high specific capacitance of 807.2F g−1 at the current density of 1 A g−1. The active sites and the mixed valence brought by the amorphous HMB layer give rise to the improved pseudocapacitance. 1-HMB/CC-0.15 can maintain 89.7% of its initial capacitance after 5000 galvanostatic charge/discharge cycles. In order to probe the effect brought by the structure of complex precursor, two new polymolybdates-based complexes {Cu(3-H2bptzpe)2[γ-Mo8O26]} (2) and {Cu2(3-bptzp)2(H2O)4[γ-Mo8O26]} (3) (3-bptzpe = 1,4-bis(5-(3-pyridyl)tetrazolyl)-pentane, 3-bptzp = 1,4-bis(5-(3-pyridyl)tetrazolyl)-butane) were synthesized and used as electrode material precursors as well. However, no HMB was produced on the surface of complexes 2 and 3 by similar electrochemical treatment. 1-HMB/CC-0.15 is taken as cathode to assemble an asymmetric supercapacitor (ASC) device, which demonstrates an ultrahigh energy density of 23.71 Wh kg−1 at the power density of 0.7 KW kg−1. After 5000 galvanostatic charge/discharge cycles, the aqueous ASC device can retain 86.8% of its capacitance, showing good cyclic stability. The effects brought by the electrochemical treatment and the structure of complexes on the pseudocapacitive behavior are discussed, respectively.

Design rules of pseudocapacitive electrode materials: ion adsorption, diffusion, and electron transmission over prototype TiO2

The development of a high-performing pseudo-capacitor requires a comprehensive understanding of electrode materials from the aspects of electron transfer and electrolyte ion adsorption and diffusion. Herein, these factors are considered over the prototype TiO2, and a high pseudo-capacitance is achieved via the introduction of various defects, i.e., oxygen defect (VO) and co-doped defect (VO+NO). The study is based on joint explorations of first-principle calculations and the transfer matrix method. Relative to pristine TiO2 (300 F g−1), defective TiO2 produces pseudocapacitance as high as 1700 F g−1. Moreover, defects induce small barriers for electron transmission caused by surface band bending. The climbing image nudged elastic band diffusion of H ions displays a much higher barrier in TiO2−VO than in TiO2−VO+NO. Such a result indicates easy H diffusion in the co-doped system. This work provides insights into the adsorption and diffusion of electrolyte ions and the influence of defects on electron transfer. The results are also significant for the design and optimization of electrode materials for the next generation of supercapacitors.

Nanosheet-assembled NiCo-LDH hollow spheres as high-performance electrodes for supercapacitors

Layered double hydroxides (LDHs) have been considered as favorable pseudocapacitive electrode materials for supercapacitors due to their tunable layered structure/compositions and low cost. Here, we report the NiCo-LDH hollow spheres prepared with Co-glycerate as the sacrificial template and cobalt source. The hollow spheres are assembled with frizzy NiCo-LDH nanosheets, where the hollow structure can inhibit agglomeration of the LDH nanosheets to expose more active sites and shorten the diffusion path of electrolyte ions. The prepared NiCo-LDH hollow spheres show a high specific capacitance of 1962 F g−1 at 1 A g−1 and good capacitance retention rate of 66.4 % at 30 A g−1. The asymmetric supercapacitors fabricated using NiCo-LDH hollow spheres as positive electrode yields a large energy density 62.9 Wh kg−1 at the power density of 0.8 kW kg−1. This research may develop a facile synthesis way to prepare LDH hollow spheres for supercapacitors.

An aqueous high-performance hybrid supercapacitor with MXene and polyoxometalates electrodes

Two-dimensional (2D) titanium carbide (Ti3C2Tx), MXene, is an attractive pseudocapacitive electrode material that exhibits its highest capacitance at a negative potential in an aqueous protic (H2SO4) electrolyte. Developing hybrid supercapacitors (HSCs) using diverse cathode materials is the best way to identify a material with high energy density in aqueous electrolytes. However, it is difficult to find redox-active positive cathode materials that are suitable for use with MXene in an H2SO4 electrolyte. Here, 2D nanocomposite of reduced graphene oxide (rGO) decorated with phosphomolybdic acid (PMo12) polyoxometalates (POMs) are reported as promising cathode materials suitable for use against an MXene anode. The complementary potential window of MXene and rGO-POMs along with the redox activity and 2D nanostructured features of these materials can significantly enhance the electrochemical properties of HSC cell. An all-redox active HSC cell with rGO-POM cathode and MXene anode can deliver a maximum specific energy and power of 50.46 Wh/kg and 7000 W/kg, respectively, with capacitance retention of 87.12 % over 10,000 cycles and superb energy and coulombic efficiency over all applied current densities. These results suggest that the rGO-POMs cathode can be potentially coupled with an MXene anode in a protic electrolyte to enhance the electrochemical parameters of the HSC cells.

High-performance flexible supercapacitor enabled by Polypyrrole-coated NiCoP@CNT electrode for wearable devices

As a pseudocapacitive electrode material, nickel–cobalt bimetallic phosphide has attracted wide attention with its advantage in capacitance and chemical activity. While, like Ni-Co oxides or sulfides, the application of nickel–cobalt bimetallic phosphide is generally hampered by its confined conductivity, low chemical stability and unsatisfactory cycle durability. Herein, this work demonstrates a NiCoP@CNT@PPy (NCP@CNT@PPy) composite that is obtained by polymerizing pyrrole monomer on the surface of NiCoP@CNT complex. According to density functional theory (DFT), it is theoretically demonstrated that the bimetallic Ni-Co phosphide (NiCoP) can exhibit more electrons near the Fermi level than single Ni or Co phosphide. Under the combined effects of carboxylic carbon nanotubes (c-CNTs) and polypyrrole (PPy), the NCP@CNT@PPy electrode exhibits excellent electrochemical performance. In addition, a flexible asymmetric supercapacitor (ASC) is prepared, which demonstrated high energy density and admirable heat-resistance and flexibility performance, showing huge potential in the application of heat-resistant storage energy systems and portable wearable devices.

Studies on electrochemical mechanism of nanostructured cobalt vanadate electrode material for pseudocapacitors

The supercapacitive behaviour of chemically synthesized cobalt vanadate nanostructures was reported in this work. Various analytical techniques along with optical studies were utilized to investigate the crystallographic information's and optical response. Crystallographic information of the prepared nanostructures was revealed by the XRD analysis and it's formation was confirmed by the FTIR and XPS techniques. The nano-layered structural and surface morphology was observed through scanning electron microscopy and high-resolution transmission electron microscopy. Electrochemical performances in aqueous electrolytic medium were examined for supercapacitive behaviour of prepared Co3V2O8. Specific capacitance value of about 790 F/g was achieved at 1 A/g current density and the superior capacitive retention of 90.1 % after 10000 cycles had been imparted by the prepared Co3V2O8. Based on the results, it was confirmed that the prepared cobalt vanadate nanostructures can be used as an electrode material for future energy storage devices.

Recent Development of Flexible and Stretchable Supercapacitors Using Transition Metal Compounds as Electrode Materials.

Flexible and stretchable supercapacitors (FS-SCs) are promising energy storage devices for wearable electronics due to their versatile flexibility/stretchability, long cycle life, high power density, and safety. Transition metal compounds (TMCs) can deliver a high capacitance and energy density when applied as pseudocapacitive or battery-like electrode materials owing to their large theoretical capacitance and faradaic charge-storage mechanism. The recent development of TMCs (metal oxides/hydroxides, phosphides, sulfides, nitrides, and selenides) as electrode materials for FS-SCs are discussed here. First, fundamental energy-storage mechanisms of distinct TMCs, various flexible and stretchable substrates, and electrolytes for FS-SCs are presented. Then, the electrochemical performance and features of TMC-based electrodes for FS-SCs are categorically analyzed. The gravimetric, areal, and volumetric energy density of SC using TMC electrodes are summarized in Ragone plots. More importantly, several recent design strategies for achieving high-performance TMC-based electrodes are highlighted, including material composition, current collector design, nanostructure design, doping/intercalation, defect engineering, phase control, valence tuning, and surface coating. Integrated systems that combine wearable electronics with FS-SCs are introduced. Finally, a summary and outlook on TMCs as electrodes for FS-SCs are provided.

Polyaniline nanowires aligned on MOFs-derived nanoporous carbon as high-performance electrodes for supercapacitor

Polyaniline, as the pseudocapacitive electrode material, has been extensively studied for supercapacitors. However, their cycling stability is limited by the structural instability arising from large volumetric swelling/shrinking, which has been the main obstacle to their practical applications. Herein, this work reports metal organic frameworks(MOFs)-derived porous carbon frameworks as the substrate and further deposit polyaniline by in situ chemical polymerization. Benefit from the structurally stable MOFs-derived porous carbon frameworks and the uniformly-deposited conducting polyaniline nanowires with controlled lengths, the synthesized MOFs-derived porous carbon/polyaniline hybrid electrode displays a maximum specific capacitance of 534.16 F g−1 at 0.2 A g−1 and a maximum capacitance retention of 211% at 2 A g−1 after 20000 cycles, demonstrating promising applications for pseudocapacitive devices. The assembled semi-solid symmetrical supercapacitors delivers good electrochemical performance (energy density of 9.72 μWh cm−2) and excellent cyclic stability (94.4% at 10000 cycles), which can also power a commercial LED.

3D Graphene Network with Covalently Grafted Aniline Tetramer for Ultralong‐Life Supercapacitors

AbstractThe conducting polymer polyaniline (PANI) has been considered to be a promising pseudocapacitive electrode material for supercapacitors due to its high specific capacitance, low cost, and environmental friendliness. However, the poor cycling stability of PANI during the charge–discharge processes limits its widespread practical application. Herein, a facile synthetic method is demonstrated for covalently grafting an aniline tetramer (TANI), the basic building block of PANI, onto 3D graphene networks via perfluorophenylazide coupling chemistry to create a hybrid electrode material for ultralong‐life supercapacitors. The design, which substitutes long‐chain PANI with short‐chain TANI and introduces covalent linkages between TANI and 3D graphene, greatly enhances the charge–discharge cycling stability of PANI‐based supercapacitors. The electrode material, as well as the fabricated symmetric all‐solid‐state supercapacitors, exhibit extraordinary long cycle life (>85% capacitance retention after 30 000 charge–discharge cycles). The capacitance can be further boosted through fast and reversible redox reactions on the electrode surface using a redox‐active electrolyte while maintaining outstanding cycling stability (82% capacitance retention after 100 000 cycles for a symmetric all‐solid‐state device). While conducting polymers are known to be limited by their poor cycling stability, this work provides an effective strategy to achieve enhanced cycle life for conducting polymer‐based energy storage devices.

Effect of Electrolyte Composition on the Performance of Coal Char-Derived Carbon Supercapacitors

Research regarding supercapacitors has vastly grown over the past decade. The advantages of supercapacitors include high power density, rapid charge/discharge capability, and a long cycle life. Current applications of supercapacitors are limited by the need to develop new, low-cost electrode materials for electric double layer capacitors and pseudocapacitors [1]. Coal char is the solid product of a low-temperature coal carbonization process, and is currently used primarily as an ultra-low-cost fuel for electric power generation. As such, coal char consists mainly of hard carbons and ash [2]. Upon ash removal, the hard carbons in coal char may serve as a promising, low-cost, supercapacitor electrode material. This research will present the use of inexpensive coal char as an electrode material for supercapacitors, with particular focus on the effects of various electrolyte compositions on the performance of coal-derived carbon supercapacitors.Electrolyte composition plays a large role in the electrochemical properties of a supercapacitor, affecting: ion interactions with electrode surface functional groups; electric double layer capacitance; thermal stability; and allowable voltage range. In this work, bituminous grade coal char from a Utah mine is pulverized, pyrolyzed, and washed in a base solution followed by an acid solution to remove residual ash. SEM imaging and BET surface area measurements are used to characterize the coal. The purified coal char is mixed into a slurry of coal char, Super P binder, and dimethylformamide, then applied on a stainless-steel plate to create supercapacitor electrodes. Three-electrode open-cell electrochemical measurements are used to characterize the supercapacitor performance of the coal char in varying electrolyte solutions using a Gamry Interface 1000E potentiostat. The different electrolytes explored include: aqueous acid 0.5 M H2SO4, aqueous base 6 M KOH, and aqueous neutral solutions 0.5 M Na2SO4, 4 M LiNO3, water-in-salt electrolyte using 12.5 M NaClO4, . Voltage range, specific capacitance, electrochemical impedance, and charge-discharge characteristics of the coal char in the different electrolytes are characterized by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy measurements. The results provide important insight into the optimal electrolyte composition for use with coal char supercapacitor electrodes, and contribute to current understanding of electrode-electrolyte interactions in carbon supercapacitors.This work is supported in-part by NSF Award #1742696.Reference1.Rakesh Kumar Gupta, Mukul Dubey, Parashu Kharel, Zhengrong Gu, Qi Hua Fan, Biochar activated by oxygen plasma for supercapacitors, Journal of Power Sources, Volume 274, 2015, Pages 1300-1305.2. H. H. Schobert, Coal; The Energy Source of the Past and Future, pg. 9, American Chemical Society, Washington (1987). Figure 1