Electrochemical Capacitors Research Articles

Progress in Conducting Polymer‐Based Electrospun fibers for Supercapacitor Applications: A Review

AbstractThe ever‐growing need for energy storage has been at the forefront of research for the past few decades. A supercapacitor is an attractive candidate for storage needs with widespread applications in electronic gadgets, electric vehicles and hybrid vehicles, especially in space and the military. The significant role of electrodes in the performance of supercapacitors has led to the development of materials endowed with exceptional electrochemical performance and mechanical stability. Conducting polymers with intriguing properties like tuneable electronic conductivity, broad voltage window, tuneable redox activity etc., are excellent candidates as electrode materials for electrochemical capacitors with superior performance parameters. Electrospun conducting polymer nanofibers exhibit unique characteristics and favourable morphologies that have the potential to enhance the performance of supercapacitors. The review covers the fundamentals of electrochemical capacitors and introduces electrospinning as a versatile method to fabricate nanofibers using conducting polymers and their composites. The application of these nanofibers as electrodes in supercapacitors is discussed in detail and the performance parameters are compared. The article also discusses the challenges and prospects in using these electrospun nanofibers as effective supercapacitor electrodes.

Inside Front Cover: Carbon Neutralization, Volume 2, Issue 3, May 2023

Inside front cover image: The ambitious goal of cabron neutralization requires the further development of fast energy storage devices like supercapacitors, while the severe self-discharge of conventional electrochemical double-layer capacitors has greatly limited their development. The recent emergence of conjugately configured supercapacitor has brought a new frontier for alleviating self-discharge. In article number CNL255, The researchers explored how the carbon coating strategy, which has already been widely used to modify active materials to enhance conductivity and cycling stability, could introduce profound and complex influence to self-discharge property for active materials specifically used for conjugatedly configured supercapacitors. The proposed conjugated configuration as well as the optimization strategy specifically for such device is expected to provide a general and powerful approach for alleviating self-discharge.

Enhanced optoelectronic and supercapacitive performance of electrodeposited Mn3O4 thin film prepared from two-electrode: An effect of Zn-ion incorporation

Here in, we report electrodeposited Mn3O4 thin film doped with various level of Zn dopant (0≤x≤5.0,%), on a layer of indium tin oxide (ITO) on glass substrate. The deposition route involves the use of two-electrode electrochemical cell system comprising graphite and the substrate as counter and working electrodes, respectively. Some surface properties such as those of morphological, crystal structure, optical, electrical and electrochemical were studied to evaluate the films’ potentials in energy conversion and storage devices. Microstructural studies revealed the films grew with isotropic morphology of good tetragonal shaped crystal structure with even distribution and possessing required surface area on the substrate surfaces. Raman prominent peak at 659 cm −1 wave number indicates a typical A1g Raman vibrating mode of Mn2+ in a Mn3O4 spinel structure. The crystallite size and microstrain values were found varying from 38 to 43 nm and 5.6 × 10−3 to 3.2 × 10−3, with respect to increase in dopant content, respectively. Energy band gap and Urbach energy were varied from 3.28 to 2.68 eV and 1.59 to 2.17 eV with increasing level of dopant content, accordingly. Electrochemical charge storage area capacitance (12.62 to 21.35 mF cm −2)/capacity (5.1 to 8.1μAh cm −2) and rate capability of Mn3O4 electrode were found to improve with Zn dopant. The work therefore discusses the tailoring of band absorption and supercapacitive characteristic of electrodeposited Mn3O4 thin film with Zn-doping for enhanced energy application.

Hydrogen-bonding interaction promoted supercapacitance of polylactic acid-graphene-microcrystalline cellulose/polyaniline nanofiber

Electrospinning polylactic acid-graphene-microcrystalline cellulose/polyaniline (PLA-GN-MCC/PANI) nanofiber is fabricated as superior supercapacitor electrode material, which involves flexible substrate of PLA, conductivity additive of GN, GN dispersion additive of MCC and electroactive substance of PANI. PLA-GN-MCC is optimized as a component mass ratio of 10:0.6:1 to achieve superior interface affinity properties. The ultimate tensile strength and the elongation at break of the optimized PLA-GN-MCC are 568 kPa and 93%, better than the 496 kPa and 87% of PLA, exhibiting both superior strength and flexibility. The PLA, PLA-GN-MCC and PLA-GN-MCC/PANI keep the reduced ohmic resistance from 18.73 to 9.58 to 8.00 Ω, the dwindled charge transfer resistance from 323.2 to 181.7 to 17.8 Ω, the declined electronic band gap from 4.084 to 0.557 to 0.142 eV, the reduced Frontier molecular orbitals energy gap from 3.6505 to 0.7964 to 0.7694 eV, the increased density of states from 4.7983 to 5.7842 to 8.6671 electrons eV−1. These results indicate more feasible electron transition and highly improved electronic conductivity. The hydrogen bonding interaction between PLA-GN-MCC and PANI contributes to increasing interface affinity and decreasing total surface energy, achieving superior electrochemical capacitance increased from 2.72 to 3.72 up to 221.64 mF/cm2. Experimental measurement and simulation calculation keep consistent results, demonstrating the promise of PLA-GN-MCC/PANI nanofibers for electrochemical energy storage.

2D Materials-based Electrochemical Triboelectric Nanogenerators.

The integration of 2D materials in triboelectric nanogenerators (TENGs) is known to increase the mechanical-to-electrical power conversion efficiency. 2D materials are used in TENGs with multiple roles as triboelectric material, charge-trapping fillers, or as electrodes. Here, novel TENGs based on few-layers graphene (FLG) electrodes and stable gel electrolytes composed of liquid phase exfoliated 2D-transition metal dichalcogenides and polyvinyl alcohol are developed. TENGs embedding FLG and gel composites show competitive open-circuit voltage (≈ 300 V), instant peak power (530 mW m-2 ), and stability (> 11 months). These values correspond to a seven-fold higher electrical output compared to TENGs embedding bare FLG electrodes. It is demonstrated that such a significant improvement depends on the high electrical double-layer capacitance (EDLC) of FLG electrodes functionalized with the gel composites. The wet encapsulation of the TENGs is shown to be an effective strategy to increase their power output further highlighting the EDLC role. It is also shown that the EDLC is dependent upon the transition metal (W vs Mo) rather than the relative abundance of 1T or 2H phases. Overall, this work lays down the roots for novel sustainable electrochemical-(e)-TENGs developed exploiting strategies typically used in electrochemical capacitors.

Electrodeposition of manganese dioxide coatings onto graphene foam substrates for electrochemical capacitors

Optimisation of electrodeposition routes of birnessite manganese dioxide (MnO2) coatings onto 3D graphene foam substrates enabled greater attainable capacitances. Current pulse deposition method resulted in highest achievable areal capacitance of 530 mF/cm2 under a 10 mA/cm2 current rate, cycling performance with 91% retention after 9000 cycles, as well as improved rate capability when compared to the cyclic voltammetry or galvanostatic deposition. Introduction of oxygen functional groups to the graphene foam added initial pseudocapacitance and accelerated the rate for nucleation and growth of the MnO2 crystal grains, resulting in an areal capacitance of 410 mF/cm2 under a 10 mA/cm2 current rate. However, in this case the increase in specific capacitance was accompanied by sluggish kinetics for charge storage seen via impedance spectroscopy. The charge storage mechanism of the deposited MnO2 films was investigated using in situ Raman microscopy and analysis of peak shifts revealed expansion and contraction of birnessite MnO2, relating to exchange of Na+ and H2O at the MnO2 interface.

Advanced Electrode Coatings Based on Poly-N-Phenylanthranilic Acid Composites with Reduced Graphene Oxide for Supercapacitors.

The electrochemical behavior of new electrode materials based on poly-N-phenylanthranilic acid (P-N-PAA) composites with reduced graphene oxide (RGO) was studied for the first time. Two methods of obtaining RGO/P-N-PAA composites were suggested. Hybrid materials were synthesized via in situ oxidative polymerization of N-phenylanthranilic acid (N-PAA) in the presence of graphene oxide (GO) (RGO/P-N-PAA-1), as well as from a P-N-PAA solution in DMF containing GO (RGO/P-N-PAA-2). GO post-reduction in the RGO/P-N-PAA composites was carried out under IR heating. Hybrid electrodes are electroactive layers of RGO/P-N-PAA composites stable suspensions in formic acid (FA) deposited on the glassy carbon (GC) and anodized graphite foil (AGF) surfaces. The roughened surface of the AGF flexible strips provides good adhesion of the electroactive coatings. Specific electrochemical capacitances of AGF-based electrodes depend on the method for the production of electroactive coatings and reach 268, 184, 111 F∙g-1 (RGO/P-N-PAA-1) and 407, 321, 255 F∙g-1 (RGO/P-N-PAA-2.1) at 0.5, 1.5, 3.0 mA·cm-2 in an aprotic electrolyte. Specific weight capacitance values of IR-heated composite coatings decrease as compared to capacitance values of primer coatings and amount to 216, 145, 78 F∙g-1 (RGO/P-N-PAA-1IR) and 377, 291, 200 F∙g-1 (RGO/P-N-PAA-2.1IR). With a decrease in the weight of the applied coating, the specific electrochemical capacitance of the electrodes increases to 752, 524, 329 F∙g-1 (AGF/RGO/P-N-PAA-2.1) and 691, 455, 255 F∙g-1 (AGF/RGO/P-N-PAA-1IR).

Insight into the Effect of Glycerol on Dielectric Relaxation and Transport Properties of Potassium-Ion-Conducting Solid Biopolymer Electrolytes for Application in Solid-State Electrochemical Double-Layer Capacitor.

The increased interest in the transition from liquid to solid polymer electrolytes (SPEs) has driven enormous research in the area polymer electrolyte technology. Solid biopolymer electrolytes (SBEs) are a special class of SPEs that are obtained from natural polymers. Recently, SBEs have been generating much attention because they are simple, inexpensive, and environmentally friendly. In this work, SBEs based on glycerol-plasticized methylcellulose/pectin/potassium phosphate (MC/PC/K3PO4) are investigated for their potential application in an electrochemical double-layer capacitor (EDLC). The structural, electrical, thermal, dielectric, and energy moduli of the SBEs were analyzed via X-ray diffractometry (XRD), Fourier transforms infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), transference number measurement (TNM), and linear sweep voltammetry (LSV). The plasticizing effect of glycerol in the MC/PC/K3PO4/glycerol system was confirmed by the change in the intensity of the samples' FTIR absorption bands. The broadening of the XRD peaks demonstrates that the amorphous component of SBEs increases with increasing glycerol concentration, while EIS plots demonstrate an increase in ionic conductivity with increasing plasticizer content owing to the formation of charge-transfer complexes and the expansion of amorphous domains in polymer electrolytes (PEs). The sample containing 50% glycerol has a maximal ionic conductivity of about 7.5 × 10-4 scm-1, a broad potential window of 3.99 V, and a cation transference number of 0.959 at room temperature. Using the cyclic voltammetry (CV) test, the EDLC constructed from the sample with the highest conductivity revealed a capacitive characteristic. At 5 mVs-1, a leaf-shaped profile with a specific capacitance of 57.14 Fg-1 was measured based on the CV data.

Nanostructured conversion-type anode materials of metal-organic framework-derived spinel XMn2O4 (X = Zn, Co, Cu, Ni) to boost lithium storage

Bimetallic spinel transition metal oxides play a major part in actualizing eco-friendly electrochemical energy storage systems (ESSs). However, structural precariousness and low electrochemical capacitance restrict their actual implementation in lithium-ion batteries (LIBs). To address these demerits, the sacrificial template approach has been considered as a prospective way to strengthen electrochemical stability and rate performance. Herein, metal-organic frameworks (MOFs) derived XMn2O4-BDC (H2BDC = 1,4-dicarboxybenzene, X = Zn, Co, Cu, Ni) are prepared by a hydrothermal approach in order to discover the effects of various metal cations on the electrochemical performance. Among them, ZnMn2O4-BDC displays best electrochemical properties (1321.5 mAh g−1 at the current density of 0.1 A g−1 after 300 cycles) and high efficiency with accelerated Li+ diffusivity. Density functional theory (DFT) calculations confirm the ZnMn2O4 possesses the weakest adsorption energy on Li+ with a minimized value of −0.92 eV. In comparison with other XMn2O4 through traditional fabrication method, MOF-derived XMn2O4-BDC possesses a higher number of Li+ transport channels and better electric conductivity. This tactic provides a feasible and effective method for preparing bimetallic transition metal oxides and enhances energy storage applications.

Nitrogen, nickel and graphene oxide doped carbon xerogel as an active electrode of an electrochemical capacitor

N-, Ni-, and graphene oxide (GO)-doped carbon xerogel were synthesized from melamine-resorcinol-formaldehyde gels by drying followed by pyrolysis at 950 °C. The mass of nickel and GO in carbon xerogel, formed after carbonization was 5 and 1%, respectively. The obtained product was characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The characteristics were completed by measurements of BET specific surface area as well as pore distribution. For graphene oxide and nickel doped carbon xerogel, a decrease in the BET surface area of about 2% compared to unmodified carbon xerogel was observed with a simultaneous increase of cumulative pore volume and average pore diameter of about 50 and 32%, respectively. Electrochemical properties of doped carbon xerogel were evaluated in 6 M KOH by cyclic voltammetry (CV) and galvanostatic modes. It was revealed, that the highest specific capacitance of 222 Fg−1 was reached for N-Ni-GO-doped carbon xerogel during the process of galvanostatic charge-discharge (GCD). Moreover, this sample also exhibited 100% stability during GCD and about 98% stability during 3000 cycling tests.Graphical abstractCharacterization of morphology, structure and electrochemical properties of xerogels where:MRF-CX - melamine-resorcinol-formaldehyde xerogel,MRF-GO-Ni-CX - melamine-resorcinol-formaldehyde-graphene oxide-nickel xerogel

Oxygen and nitrogen-doped carbon particles derived from pyrolysis of Chlorella vulgaris and Spirulina platensis microalgae as an efficient electrode material for supercapacitor application

This study consists of the thermal activation of Chlorella vulgaris and Spirulina platensis microalgae with a potassium hydroxide (KOH) chemical agent in a carbon dioxide (CO2) atmosphere and the formation of nitrogen and oxygen-doped material from the hydrothermal interaction of the obtained activated carbons with nitric acid. The obtained nitrogen and oxygen-doped activated carbons were used in the production of electrochemical super capacitors. The morphological properties of the obtained pores were evaluated by transmission electron microscopy (TEM). Electrochemical properties were evaluated according to the cyclic voltammetry (CV) method in sulphuric acid (H2SO4), potassium chloride (KCl), and sodium hydroxide (NaOH) electrolytes with a scanning rate in the range of 2.5–50 mVs−1. Nitrogen and oxygen doped electrode electrochemical capacitor based on Spirulina platensis microalgae showed the highest specific capacitance of 99.53 Fg−1 at a scanning rate of 2.5 mV s−1 in 1 M H2SO4 electrolyte. In contrast, the supercapacitor based on an activated carbon electrode from Chlorella vulgaris microalgae showed the highest specific capacitance of 156.04 Fg−1 at a scan rate of 2.5 mV s−1 in 1 M KCl electrolyte.

Hierarchically porous carbon from biomass tar as sustainable electrode material for high-performance supercapacitors

The byproduct tar from biomass gasification process had seriously impeded development and applications of this technology, thus novel path for biomass tar valorization is had been continuously pursued. Given its high carbon content, this work attempted to convert biomass tar into hierarchically porous carbon by thermal activation with acetate potassium. The optimal product produced with mass ratio of biomass tar to acetate potassium of 1:3 and activation temperature at 800 °C was revealed as excellent electrode material for high-performance supercapacitor, which demonstrated electrochemical capacitance up to 310.4 F/g at 0.2 A/g, whilst preserved 91% of initial capacitance after 5000 charge-discharge circles at current density of 5 A/g. These excellent properties had arisen from the open and hierarchical porosity and large surface area. This work disclosed the great potential of biomass tar as sustainable and competent candidate for fabricating high-performance electrode material for electrochemical energy devices, and may bring up new opportunities to development of biomass gasification technologies.

Intrinsic Properties of GO/RGO Bilayer Electrodes Dictate Their Inter-/Intralayer Intractability to Modulate Their Capacitance Performance.

The demand for high-capacity energy storage along with high power output and faster charging has made supercapacitors a key area of energy research. The charge storage capacity of capacitors is largely dependent on the electrode materials utilized. To that end, graphene oxide (GO) and reduced GO (RGO) have been extensively employed for preparing supercapacitors. However, to date, no study has reported utilizing a GO/RGO bilayer electrode material for supercapacitor application. Herein, we report the synthesis of GO/RGO bilayer electrodes on fluorine-doped tin oxide (FTO) conducting substrates with four different combinations, namely, RGO-RGO, RGO-GO, GO-RGO, and GO-GO. Electrochemical capacitance analysis based on a symmetrical electrode configuration revealed that FTO-GO-RGO electrodes had the best areal capacitance performance. However, the highest specific areal capacitance (27.85 mF/cm2) for both symmetric/asymmetric configurations was achieved with FTO-GO-RGO as the anode and FTO-GO-GO as the cathode. The heterogeneous capacitance performance of the GO/RGO bilayer systems was analyzed based on structural characterization and computational simulation methods. Based on our analysis, we identified that inter-/intralayer molecular interaction of the GO/RGO bilayer sheets through the confinement pressure effect might have prompted their unique physicochemical properties. This work highlights the importance of probing multilayer GO/RGO electrode fabrication methods for preparation of high-capacity supercapacitors through fine-tuning their structural and molecular properties.

Constant chemical potential-quantum mechanical-molecular dynamics simulations of the graphene-electrolyte double layer.

We present the coupling of two frameworks-the pseudo-open boundary simulation method known as constant potential molecular dynamics simulations (CμMD), combined with quantum mechanics/molecular dynamics (QMMD) calculations-to describe the properties of graphene electrodes in contact with electrolytes. The resulting CμQMMD model was then applied to three ionic solutions (LiCl, NaCl, and KCl in water) at bulk solution concentrations ranging from 0.5 M to 6 M in contact with a charged graphene electrode. The new approach we are describing here provides a simulation protocol to control the concentration of electrolyte solutions while including the effects of a fully polarizable electrode surface. Thanks to this coupling, we are able to accurately model both the electrode and solution side of the double layer and provide a thorough analysis of the properties of electrolytes at charged interfaces, such as the screening ability of the electrolyte and the electrostatic potential profile. We also report the calculation of the integral electrochemical double layer capacitance in the whole range of concentrations analyzed for each ionic species, while the quantum mechanical simulations provide access to the differential and integral quantum capacitance. We highlight how subtle features, such as the adsorption of potassium graphene or the tendency of the ions to form clusters contribute to the ability of graphene to store charge, and suggest implications for desalination.

Why electrochemical capacitor electrolytes should not be ignored?

Technological advances in various fields are frequently hampered by the insufficient capacity of energy storage devices. Electrochemical capacitors (ECs) emerge as high-power effective energy storage devices with a short charge/discharge time, long-term cycle life, and wide temperature range. The electrolyte is an important component influencing EC performance because of its physical and chemical properties. There are various types of electrolytes including organic, ionic liquids, water in salt and redox active electrolytes which offer diverse behavior to the ECs. Liquid state electrolyte as well as solid-state systems are described. This review emphasizes the significance of the electrolyte type and its influence on the EC performance. Different aspects are discussed starting from the specific ion effect at the electrode/electrolyte interface that affects the EC charge/discharge mechanism. Furthermore, emerging electrolytes and new directions in ECs are highlighted. Herein, the progress and challenges in water in salt (WIS) and deep eutectic solvent (DES) electrolytes are presented. Moreover, a discussion on the redox-active electrolyte for hybrid capacitors is carried out. ECs electrolytes are governing the crucial metrics of the device like the voltage window, the energy and power density as well as the long-term cyclability. Hence, as “a rule of thumb” the EC electrolyte should not be ignored.

Reactive sputter deposition of β-Ni(OH)2 thin films in Ar + H2O mixed gas atmosphere at a substrate temperature of −80 °C

Nickel hydroxide [Ni(OH)2] is an electrochemically-active material used for rechargeable batteries, electrochemical capacitors, and electrochromic devices. Although there have been some studies on Ni(OH)2 thin films deposited by sputtering, the Ni(OH)2 formation has not been fully confirmed. In this study, a Ni metal target was reactively sputtered in atmospheres of O2 and Ar + H2O at substrate temperatures of RT (RT, around 20 °C), −80 °C, and −170 °C, and the aging treatment effects in the air at RT were studied. From optical, X-ray diffraction, and IR absorption measurements, β-Ni(OH)2 thin films were found to be formed after aging the films deposited at −80 °C in Ar + H2O, however, NiO thin films were formed at RT. These results corresponded well with a thermodynamic consideration of Ni(OH)2. At −170 °C, mixed metal and oxide films were formed, presumably because of insufficient Ni oxidation.

Graphene with KI-modified pore structure and its electrochemical capacitors application

AbstractThe use of electrochemical capacitors is greatly limited by their poor volumetric energy density, and the key for improving it is to develop porous yet compact carbon materials. In recent years, the densification of porous carbons by capillary forces during drying has been used as a main method to balance the density and porosity of porous carbons for high volumetric performance. But there are still deficiencies in fine tuning the pore structure, which limits the compatibility of porous carbons with high-voltage ionic liquids. We report a KI-assisted method to prepare graphene-based porous carbons with high density and high capacitance. During the synthesis of the carbons, graphene oxide was dispersed in KI solutions with concentrations of 12.5-37.5 mmol/mL followed by hydrothermal treatment at 180 °C for 6 h. The obtained hydrogels were dried in 0.01 MPa of air at 60 °C for 72 h. By this procedure, KI was loaded into a matrix of compact graphene and formed crystals to suppress over shrinkage of pores during drying to produce densification and pseudo-capacitance. Electrochemical characterization of the resulting materials indicated that the ion-accessible surface area and pseudo-capacitance of the porous carbons were increased. The KI/graphene composite with an optimum concentration of KI of 25 mmol/mL achieved both a high electrode density of 0.96 g cm-3 and a high volumetric capacitance of 115 F cm-3 (at 1 A g-1) in an ionic liquid electrolyte (1-alkyl-3-methylimidazolium tetrafluoroborate). A symmetric cell assembled using this material had a high volumetric energy density of 19.6 Wh L-1.

Sustainable Porous Carbons with Ultrahigh Specific Surface Areas for High-performance Supercapacitors

Waste biomass residues are prospective precursors for the preparation of sustainable porous carbons. In this work, we used the residues from Lonicera japonica Thunb and Ligusticum chuanxiong Hort to prepare porous carbons with ultra-high specific surface area (> 3000 m2 g−1), which deliver excellent capacitive performance for electrochemical double-layer capacitor. Porous carbon derived from Ligusticum chuanxiong Hort displays a specific capacitance of 314.4 F g−1 (1 A g−1) in three electrode system. The energy density of Ligusticum chuanxiong Hort-based symmetric supercapacitor reaches 8.4 Wh kg−1 at the power density of 519 W kg−1 in 6 M KOH. The cell remains a high energy density of 5.1 Wh kg−1 at an increased power density of 10.8 kW kg−1. Our work indicates that the waste biomass residues are promising and competitive precursors for the preparation of ultrahigh specific surface area porous carbons for supercapacitor application.

A comparative study on electrochemical performance of KOH activated carbons derived from different biomass sources - Musa acuminata stem, Pongamia pinnata seed oil extract cake, cajanus cajan stem and Asclepias syriaca floss

In the present scenario of research, the recycling of inexpensive widely available agricultural waste/biowaste to activate carbon (AC) and procurement of value-added product has significant impact on energy storage systems, particularly in Electrochemical double layer capacitors (EDLCs). Herein, we report the production of KOH activated carbons from different biomass sources such as Musa Acuminata stem (MAC), Pongamia pinnata seed oil extract cake (PPC), Cajanus Cajan stem (CCC) and Asclepias syriaca floss (ASC) for the said purpose. Initially, the biomass materials were pyrolyzed at 550 °C and then activated with KOH at 800 °C. All the carbon materials were characterized for their physico-chemical properties by various analytical techniques and compared. Further, these materials were studied for their electrochemical performance using suitable electro-analytical techniques in 1 M KOH solution. ACs (Activated carbons) derived from MAC, PPC, CCC & ASC were estimated in three electrode system and were found to exhibit a specific capacitance (Cs) of 358, 343, 355 & 540 F/g at a scan rate of 2 mV/s and 102, 188, 253 & 256 F/g at a current density of 2.5 A/g respectively. The main novel objective of this work is to correlate the morphological and surface properties of these ACs obtained from different biomass sources with electrochemical performance. A symmetric coin cell constructed with ASC material exhibited Cs of 67 F/g at a current density of 2.5 A/g with maximum energy & power densities (ED & PD) of 37.2 W h/kg and 19.9 kW/kg respectively. Further the cell showed 25,000 cycles stability with 86% Cs retention and 100% coulombic efficiency.

Experimental and computational investigation on the charge storage performance of a novel Al2O3-reduced graphene oxide hybrid electrode

The advancements in electrochemical capacitors have noticed a remarkable enhancement in the performance for smart electronic device applications, which has led to the invention of novel and low-cost electroactive materials. Herein, we synthesized nanostructured Al2O3 and Al2O3-reduced graphene oxide (Al2O3-rGO) hybrid through hydrothermal and post-hydrothermal calcination processes. The synthesized materials were subject to standard characterisation processes to verify their morphological and structural details. The electrochemical performances of nanostructured Al2O3 and Al2O3- rGO hybrid were evaluated through computational and experimental analyses. Due to the superior electrical conductivity of reduced graphene oxide and the synergistic effect of both EDLC and pseudocapacitive behaviour, the Al2O3- rGO hybrid shows much improved electrochemical performance (~ 15-fold) as compared to bare Al2O3. Further, a symmetric supercapacitor device (SSD) was designed using the Al2O3- rGO hybrid electrodes, and detailed electrochemical performance was evaluated. The fabricated Al2O3- rGO hybrid-based SSD showed 98.56% capacity retention when subjected to ~ 10,000 charge–discharge cycles. Both the systems (Al2O3 and its rGO hybrid) have been analysed extensively with the help of Density Functional Theory simulation technique to provide detailed structural and electronic properties. With the introduction of reduced graphene oxide, the available electronic states near the Fermi level are greatly enhanced, imparting a significant increment in the conductivity of the hybrid system. The lower diffusion energy barrier for electrolyte ions and higher quantum capacitance for the hybrid structure compared to pristine Al2O3 justify improvement in charge storage performance for the hybrid structure, supporting our experimental findings.