A High-Performance Supercapacitor Based on Hierarchical Template-Free Ni/SnO2 Nanostructures via Hydrothermal Method

Novel flake-like Ni1-xSnxO2 particles were successfully prepared by template-free hydrothermal synthesis. The prepared samples were investigated for their properties by different characterization techniques. Scanning micrographs showed that the obtained particles consisted of nanoflakes. The X-ray diffraction results of the Ni1-xSnxO2 revealed the formation of mixed-phase Ni/SnO2 having the typical tetragonal structure of SnO2, and the cubic structure of Ni in a nanocrystalline nature. The doping with Ni had a certain influence on the host's lattice structure of SnO2 at different doping concentrations. Confirmation of the functional groups and the elements in the nanomaterials was accomplished using FTIR and EDS analyses. The electrochemical performance analysis of the prepared nanomaterials were carried out with the help of the CV, GCD, and EIS techniques. The specific capacitance of the synthesized nanomaterials with different concentrations of Ni dopant in SnO2 was analyzed at different scanning rates. Interestingly, a 5% Ni-doped SnO2 nanocomposite exhibited a maximum specific capacitance of 841.85 F g-1 at 5 mV s-1 in a 6 M KOH electrolyte. Further, to boost the electrochemical performance, a redox additive electrolyte was utilized, which exhibited a maximum specific capacitance of 2130.33 at 5 mV s-1 and an excellent capacitance retention of 93.22% after 10,000 GCD cycles. These excellent electrochemical characteristics suggest that the Ni/SnO2 nanocomposite could be utilized as an electrode material for high-performance supercapacitors.

Application of Copper-Sulfur Compound Electrode Materials in Supercapacitors

Supercapacitors (SCs) are a novel type of energy storage device that exhibit features such as a short charging time, a long service life, excellent temperature characteristics, energy saving, and environmental protection. The capacitance of SCs depends on the electrode materials. Currently, carbon-based materials, transition metal oxides/hydroxides, and conductive polymers are widely used as electrode materials. However, the low specific capacitance of carbon-based materials, high cost of transition metal oxides/hydroxides, and poor cycling performance of conductive polymers as electrodes limit their applications. Copper-sulfur compounds used as electrode materials exhibit excellent electrical conductivity, a wide voltage range, high specific capacitance, diverse structures, and abundant copper reserves, and have been widely studied in catalysis, sensors, supercapacitors, solar cells, and other fields. This review summarizes the application of copper-sulfur compounds in SCs, details the research directions and development strategies of copper-sulfur compounds in SCs, and analyses and summarizes the research hotspots and outlook, so as to provide a reference and guidance for the use of copper-sulfur compounds.

Fabrication of Flexible Films for Supercapacitors Using Halloysite Nano-Clay Incorporated Poly(lactic acid)

In the past few years, significant research efforts have been directed toward improving the electrochemical capabilities of supercapacitors by advancing electrode materials. The present work signifies the development of poly(lactic acid)/alloysite nano-clay as an electrode material for supercapacitors. Physico-chemical characterizations were analyzed by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and a universal testing machine. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge techniques were employed to evaluate electrochemical characteristics. The optimized poly(lactic acid)/halloysite nano-clay film revealed the highest specific capacitance of 205.5 F g-1 at 0.05 A g-1 current density and showed 14.6 Wh kg-1 energy density at 72 W kg-1 power density. Capacitance retention of 98.48% was achieved after 1000 cycles. The microsupercapacitor device presented a specific capacitance of 197.7 mF g-1 at a current density of 0.45 mA g-1 with 10.8 mWh kg-1 energy density at 549 mW kg-1 power density.

Electrodeposition of Polyaniline on Tantalum: Redox Behavior, Morphology and Capacitive Properties

Polyaniline (PANI) is among the most widely studied conducting polymers due to its potential technological applications in various fields. Recently, PANI-based hybrid materials have played an important role in the development of energy storage and conversion systems. The aim of the present work is the investigation of the simultaneous electrochemical growth of PANI and Ta2O5 on the Ta substrate and the characterization of the morphology, redox behavior and pseudocapacitive properties of the resulting micro- or nanostructured composite thin films. A well-adherent conductive Ta2O5-PANI composite film was first formed using cyclic voltammetry on Ta that facilitates the on-top electrodeposition of single PANI via an autocatalytic mechanism. The electrochemical characterization of the Ta|Ta2O5-PANI|PANI electrodes reveals unique redox properties of PANI not shown previously upon using PANI electrodeposition on Ta. Scanning electron microscopy shows that the morphology of the electrodeposited films comprises nano- or microspheres that may develop into nano- or microrods when the polymerization proceeds. Preliminary evaluation of the capacitive properties of the Ta|Ta2O5-PANI|PANI electrode shows adequately high specific capacitance values as high as 1130 F g-1 (at 9.2 mA cm-2), depending on the electrochemical parameters, as well as adequate stability (~80% retention after 100 cycles), indicating their potential application as energy storage devices.

Influence of Fe Doping on the Electrochemical Performance of a ZnO-Nanostructure-Based Electrode for Supercapacitors

ZnO is a potential candidate for providing an economic and environmentally friendly substitute for energy storage materials. Therefore, in this work, Fe-doped ZnO nanostructures prepared using the microwave irradiation procedure were investigated for structural, morphological, magnetic, electronic structural, specific surface area and electrochemical properties to be used as electrodes for supercapacitors. The X-ray diffraction, high-resolution transmission electron microscopy images, and selective-area electron diffraction pattern indicated that the nanocrystalline structures of Fe-doped ZnO were found to possess a hexagonal wurtzite structure. The effect of Fe doping in the ZnO matrix was observed on the lattice parameters, which were found to increase with the dopant concentration. Rods and a nanosheet-like morphology were observed via FESEM images. The ferromagnetic nature of samples is associated with the presence of bound magnetic polarons. The enhancement of saturation magnetization was observed due to Fe doping up to 3% in correspondence with the increase in the number of bound magnetic polarons with an Fe content of up to 3%. This behavior is observed as a result of the change in the oxidation state from +2 to +3, which was a consequence of Fe doping ranging from 3% to 5%. The electrode performance of Fe-doped ZnO nanostructures was studied using electrochemical measurements. The cyclic voltammetry (CV) results inferred that the specific capacitance increased with Fe doping and displayed a high specific capacitance of 286 F·g-1 at 10 mV/s for 3% Fe-doped ZnO nanostructures and decreased beyond that. Furthermore, the stability of the Zn0.97Fe0.03O electrode, which was examined by performing 2000 cycles, showed excellent cyclic stability (85.0% of value retained up to 2000 cycles) with the highest specific capacitance of 276.4 F·g-1, signifying its appropriateness as an electrode for energy storage applications.

Investigating the Correlation between Electrolyte Concentration and Electrochemical Properties of Ionogels

Ionogels are hybrid materials comprising an ionic liquid confined within a polymer matrix. They have garnered significant interest due to their unique properties, such as high ionic conductivity, mechanical stability, and wide electrochemical stability. These properties make ionogels suitable for various applications, including energy storage devices, sensors, and solar cells. However, optimizing the electrochemical performance of ionogels remains a challenge, as the relationship between specific capacitance, ionic conductivity, and electrolyte solution concentration is yet to be fully understood. In this study, we investigate the impact of electrolyte solution concentration on the electrochemical properties of ionogels to identify the correlation for enhanced performance. Our findings demonstrate a clear relationship between the specific capacitance and ionic conductivity of ionogels, which depends on the availability of mobile ions. The reduced number of ions at low electrolyte solution concentrations leads to decreased ionic conductivity and specific capacitance due to the scarcity of a double layer, constraining charge storage capacity. However, at a 31 vol% electrolyte solution concentration, an ample quantity of ions becomes accessible, resulting in increased ionic conductivity and specific capacitance, reaching maximum values of 58 ± 1.48 μS/cm and 45.74 F/g, respectively. Furthermore, the synthesized ionogel demonstrates a wide electrochemical stability of 3.5 V, enabling diverse practical applications. This study provides valuable insights into determining the optimal electrolyte solution concentration for enhancing ionogel electrochemical performance for energy applications. It highlights the impact of ion pairs and aggregates on ion mobility within ionogels, subsequently affecting their resultant electrochemical properties.

Investigating the Supercapacitive Performance of Cobalt Sulfide Nanostructures Prepared Using a Hydrothermal Method

In this study, we synthesized cobalt sulfide (CoS) nanostructures for supercapacitor applications via a one-step hydrothermal method. The effect of hydrothermal temperature on the synthesis process was investigated at temperatures ranging from 160 °C to 220 °C. The structural, morphological, and elemental analyses were performed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The XRD patterns show the hexagonal phase of CoS, and the samples prepared at 200 °C have high crystallinity. The samples prepared at other temperatures show amorphousness at lower 2-theta angles. EDX indicated that the sample was of high purity, except that the sample prepared at 220 °C had an additional oxygen peak, indicating that sulfur is not stable at high temperatures. In addition, a cobalt oxide (CoO) peak is also observed in the XRD data of the sample prepared at 220 °C. SEM images show that the particles in the samples prepared at 160 °C and 180 °C are agglomerated due to the high surface energy, whereas the samples prepared at 200 °C and 220 °C have a distinct morphology. Electrochemical analyses such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD) were performed on all samples. The CoS sample prepared at 200 °C exhibited a high specific capacitance (C_sp) of 1583 F/g at a current density of 1 A/g, with low resistivity and high cycling stability.

Core-Shell Structured Carbon Nanofiber-Based Electrodes for High-Performance Supercapacitors

The combination of multiple electrode materials and their reasonable structural design are conducive to the preparation of composite electrodes with excellent performance. In this study, based on carbon nanofibers grown with Ni(OH)₂ and NiO (CHO) prepared by electrospinning, hydrothermal growth, and low-temperature carbonization, five transition metal sulfides (MnS, CoS, FeS, CuS, and NiS) were hydrothermally grown on their surfaces, exhibiting that CHO/NiS had the optimal electrochemical properties. Subsequently, the effect of hydrothermal growth time on CHO/NiS revealed that the electrochemical performance of CHO/NiS-3h was optimal, with a specific capacitance of up to 1717 F g^-1 (1 A g^-1), due to its multistage core-shell structure. Moreover, the diffusion-controlled process of CHO/NiS-3h dominated its charge energy storage mechanism. Finally, the asymmetric supercapacitor assembled with CHO/NiS-3h as the positive electrode demonstrated an energy density of 27.76 Wh kg^-1 at a maximum power density of 4000 W kg^-1, and it still maintained a power density of 800 W kg^-1 at a maximum energy density of 37.97 Wh kg^-1, exhibiting the potential application of multistage core-shell composite materials in high-performance supercapacitors.

Asymmetric supercapacitors based on SnNiCoS ternary metal sulfide electrodes

While metal sulfides have extensively investigated as electrode materials for supercapacitors, the further optimization of their material system is still necessary to achieve satisfied performance. In this work, we reported the synthesis of ternary metal sulfide SnNiCoS and its application as electrode material of asymmetric supercapacitors, in which active carbon is used as the other electrode. For control experiments, asymmetric supercapacitors based on single metal sulfide CoS and binary metal sulfide NiCoS are also fabricated and investigated. The results show that the nanospherical SnNiCoS achieves the best performance. Ternary sulphide materials offer more redox than corresponding single-metal sulphides due to the synergy among various transition metal elements. The specific capacitance is 18.6 F cm^-2at current density of 5 mA·cm^-2. An energy density of 937.2μWh cm^-2is achieved at a power density of 4000μW·cm^-2. After 8000 cycles, the capacity retention rate is 82.9%. Present work indicates that SnNiCoS ternary metal sulfide could be a promising composite for high performance supercapacitors.

Chitins from Seafood Waste as Sustainable Porous Carbon Precursors for the Development of Eco-Friendly Supercapacitors

Carbon materials derived from marine waste have been drawing attention for supercapacitor applications. In this work, chitins from squid and prawn marine wastes were used as carbon precursors for further application as electrodes for energy storage devices. Chitins were obtained through a deproteinization method based on enzymatic hydrolysis as an alternative to chemical hydrolysis as commonly presented in the literature. The obtained porous carbons were characterized using a BET surface area analyzer to determine the specific surface area and pore size, as well as scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), Raman spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), to characterize their morphology, composition, and structure. The electrochemical characterization was performed using a glassy carbon (GC) electrode modified with marine waste-based porous carbons as the working electrode through cyclic voltammetry and galvanostatic charge/discharge using ethaline, a choline chloride-based deep eutectic solvent (DES), as an eco-friendly and sustainable electrolyte. Squid and prawn chitin-based carbons presented a surface area of 149.3 m² g^-1 and 85.0 m² g^-1, pore volume of 0.053 cm³ g^-1 and 0.029 cm³ g^-1, and an associated specific capacitance of 20 and 15 F g^-1 at 1 A g^-1, respectively. Preliminary studies were performed to understand the effect of -OH groups on the chitin-based carbon surface with DES as an electrolyte, as well as the effect of aqueous electrolytes (1 mol L^-1 sulphuric acid (H₂SO₄) and 1 mol L^-1 potassium hydroxide (KOH)) on the capacitance and retention of the half-cell set up. It is provided, for the first time, the use of chitin-based carbon materials obtained through a one-step carbonization process combined with an eco-friendly DES electrolyte for potential application in energy storage devices.

Laser-Induced Graphene Microsupercapacitors: Structure, Quality, and Performance

Laser-induced graphene (LIG) is a graphenic material synthesized from a polymeric substrate through point-by-point laser pyrolysis. It is a fast and cost-effective technique, and it is ideal for flexible electronics and energy storage devices, such as supercapacitors. However, the miniaturization of the thicknesses of the devices, which is important for these applications, has still not been fully explored. Therefore, this work presents an optimized set of laser conditions to fabricate high-quality LIG microsupercapacitors (MSC) from 60 µm thick polyimide substrates. This is achieved by correlating their structural morphology, material quality, and electrochemical performance. The fabricated devices show a high capacitance of 22.2 mF/cm² at 0.05 mA/cm², as well as energy and power densities comparable to those of similar devices that are hybridized with pseudocapacitive elements. The performed structural characterization confirms that the LIG material is composed of high-quality multilayer graphene nanoflakes with good structural continuity and an optimal porosity.

In Situ Grown Mesoporous Structure of Fe-Dopant@NiCoOX@NF Nanoneedles as an Efficient Supercapacitor Electrode Material

In this study, we designed mixed metal oxides with doping compound nano-constructions as efficient electrode materials for supercapacitors (SCs). We successfully prepared the Fe-dopant with NiCoOx grown on nickel foam (Fe-dopant@NiCoOx@NF) through a simple hydrothermal route with annealing procedures. This method provides an easy route for the preparation of high activity SCs for energy storage. Obtained results revealed that the Fe dopant has successfully assisted NiCoOx lattices. The electrochemical properties were investigated in a three-electrode configuration. As a composite electrode for SC characteristics, the Fe-dopant@NiCoOx@NF exhibits notable electrochemical performances with very high specific capacitances of 1965 F g−1 at the current density of 0.5 A g−1, and even higher at 1296 F g−1 and 30 A g−1, respectively, which indicate eminent and greater potential for SCs. Moreover, the Fe-dopant@NiCoOx@NF nanoneedle composite obtains outstanding cycling performances of 95.9% retention over 4500 long cycles. The improved SC activities of Fe-dopant@NiCoOx@NF nanoneedles might be ascribed to the synergistic reactions of the ternary mixed metals, Fe-dopant, and the ordered nanosheets grown on NF. Thus, the Fe-dopant@NiCoOx@NF nanoneedle composite with unique properties could lead to promising SC performance.

Silicon Carbide Nanostructures as Potential Carbide Material for Electrochemical Supercapacitors: A Review

Silicon carbide (SiC) is a very promising carbide material with various applications such as electrochemical supercapacitors, photocatalysis, microwave absorption, field-effect transistors, and sensors. Due to its enticing advantages of high thermal stability, outstanding chemical stability, high thermal conductivity, and excellent mechanical behavior, it is used as a potential candidate in various fields such as supercapacitors, water-splitting, photocatalysis, biomedical, sensors, and so on. This review mainly describes the various synthesis techniques of nanostructured SiC (0D, 1D, 2D, and 3D) and its properties. Thereafter, the ongoing research trends in electrochemical supercapacitor electrodes are fully excavated. Finally, the outlook of future research directions, key obstacles, and possible solutions are emphasized.

Petal-like NiS-NiO/G-C3N4 Nanocomposite for High-Performance Symmetric Supercapacitor

Graphitic carbon nitride (G-C3N4) and NiS-NiO/G-C3N4 nanocomposite have been synthesized via combustion and hydrothermal techniques, respectively. The chemical and morphological properties of these materials were confirmed using different analytical methods. SEM confirms the formation of G-C3N4 sheets containing additional petal-like shapes of NiS-NiO nanoparticles. The electrochemical testing of NiS-NiO/G-C3N4 symmetric supercapacitors is carried out from 0.6 M HCl electrolyte. Such testing includes charge/discharge, cyclic voltammetry, impedance, and supercapacitor stability. The charge/discharge time reaches 790 s at 0.3 A/g, while the cyclic voltammetry curve forms under a high surface area. The produced specific capacitance (C_S) and energy density values are 766 F/g and 23.55 W.h.kg^-1, correspondingly.

Preparation of Three-Dimensional Porous Graphene by Hydrothermal and Chemical Reduction with Ascorbic Acid and its Electrochemical Properties

Three-dimensional porous graphene (3D-PG) has attracted much attention due to its excellent electrochemical performance. Chemical reduction is one of common methods for preparing porous graphene. In order to develop a green and facile method for preparing three-dimensional porous graphene, in this paper, 3D-PG was fabricated by reduction of graphene oxide (GO) with ascorbic acid (AA) as reductant in hydrothermal condition based on non-toxic, non-flammable and mild reducing performance of ascorbic acid. It was found that the size and distribution of pores could be controlled by the reduction time and the concentration of AA in the solution. The pore sizes in R0, R1 and R2 were in the range of 0.5-1 μm, 1-1.5 μm, and 1.5-3 μm, respectively. It was found that the average pore size and volume increased along with the amount of reductants. Under optimal conditions - a reaction time of 20 h and a ratio of GO to AA=1 : 1 - the CV area of the so-obtained sample R1-20 at 100 mV was 0.06 and the specific capacitance of the 3D-PG electrode reaches 153.5 F ⋅ g^-1 , which is suitable for use in supercapacitors.

Spinel CoFe2O4 Nanoflakes: A Path to Enhance Energy Generation and Environmental Remediation Potential of Waste-Derived rGO

Carbon nanomaterials derived from agricultural waste streams present an exciting material platform that hits multiple sustainability targets by reducing waste entering landfill, and enabling clean energy and environmental remediation technologies. In this work, the energy and photocatalytic properties of reduced graphene oxide fabricated from coconut coir using a simple reduction method using ferrocene are substantially improved by introducing metallic oxides flakes. A series of cobalt ferrite rGO/CoFe₂O₄ nanocomposites were assembled using a simple soft bubble self-templating assembly, and their potential for clean energy applications confirmed. The transmission electron microscopy images revealed the uniform dispersion of the metal oxide on the rGO sheets. The functional group of the as synthesized metal oxide and the rGO nanocomposites, and its individual constituents, were identified through the FTIR and XPS studies, respectively. The composite materials showed higher specific capacitance then the pure materials, with rGO spinal metal oxide nanocomposites showing maximum specific capacitance of 396 F/g at 1 A/g. Furthermore, the hybrid super capacitor exhibits the excellent cyclic stability 2000 cycles with 95.6% retention. The photocatalytic properties of the synthesized rGO nanocomposites were analyzed with the help of malachite green dye. For pure metal oxide, the degradation rate was only around 65% within 120 min, while for rGO metal oxide nanocomposites, more than 80% of MG were degraded.

Recent Progress of Electrode Architecture for MXene/MoS2 Supercapacitor: Preparation Methods and Characterizations

Since their discovery, MXenes have conferred various intriguing features because of their distinctive structures. Focus has been placed on using MXenes in electrochemical energy storage including a supercapacitor showing significant and promising development. However, like other 2D materials, MXene layers unavoidably experience stacking agglomeration because of its great van der Waals forces, which causes a significant loss of electrochemically active sites. With the help of MoS₂, a better MXene-based electrodecan is planned to fabricate supercapacitors with the remarkable electrochemical performance. The synthesis of MXene/MoS₂ and the ground effects of supercapacitors are currently being analysed by many researchers internationally. The performance of commercial supercapacitors might be improved via electrode architecture. This analysis will support the design of MXene and MoS₂ hybrid electrodes for highly effective supercapacitors. Improved electrode capacitance, voltage window and energy density are discussed in this literature study. With a focus on the most recent electrochemical performance of both MXene and MoS₂-based electrodes and devices, this review summarises recent developments in materials synthesis and its characterisation. It also helps to identify the difficulties and fresh possibilities MXenes MoS₂ and its hybrid heterostructure in this developing field of energy storage. Future choices for constructing supercapacitors will benefit from this review. This review examines the newest developments in MXene/MoS₂ supercapacitors, primarily focusing on compiling literature from 2017 through 2022. This review also presents an overview of the design (structures), recent developments, and challenges of the emerging electrode materials, with thoughts on how well such materials function electrochemically in supercapacitors.

Rational Design of Porous Nanowall Arrays of Ultrafine Co4N Nanoparticles Confined in a La2O2CN2 Matrix on Carbon Cloth for a High-Performing Supercapacitor Electrode

Transition metal nitrides (TMNs) have received special concern as important energy storage materials, owing to their high conductibility, good mechanical strength, and superior corrosion resistance. However, their insufficient capacitance and poor cycling stability limit their practical applications for supercapacitors. Here, a novel three-dimensional (3D) self-supported integrated electrode consisted of porous nanowall arrays of ultrafine cobalt nitride (Co₄N) nanoparticles encapsulated in a lanthanum oxycyanamide (LOC) matrix on carbon cloth (Co₄N@LOC/CC) for outstanding electrochemical energy storage is rationally designed and fabricated. The 3D monolithic configuration of porous nanowall arrays facilitates the mass/charge transfer, the exposure of electroactive sites, and the enhancement of electrical conductivity. Meanwhile, the unique core-shell structure of Co₄N@LOC can prevent ultrafine Co₄N nanoparticles from sintering, agglomeration, and oxidation and promotes electron transfer dynamics during the redox reaction, meanwhile enhancing the stability of the electrode. Additionally, the synergy of Co₄N and LOC can result in an efficient electron/ion transport in the process of the charge-discharge. Because of these features, the Co₄N@LOC/CC electrode displays superior specific capacitance (895.6 mF cm^-2 or 613.4 F g^-1 at 1 mA cm^-2) and admirable cycling durability (87.9% capacitance reservation after 10 000 cycles), surpassing the majority of nitride-based electrodes reported thus far. Furthermore, after being assembled into an asymmetric supercapacitor using active carbon (AC) as an anode, the obtained Co₄N@LOC/CC//AC/CC device displays a high energy density of 41.7 Wh kg^-1 at the power density of 875.8 W kg^-1 with a high capacitance reservation of 87.6% after 5000 cycles at 2 mA cm^-2. This work offers an efficient approach of combining TMNs with rare earth compounds to enhance the capacitance and stability of TMNs for supercapacitor electrodes.

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn₂O₄/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn₂O₄/MWCNTs preparation involved initial synthesis of Mn₃O₄ and CuMn₂O₄ precursors followed by an energy efficient reflux growth method for the CuMn₂O₄/MWCNTs. The CuMn₂O₄/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g^-1 at 0.5 A g^-1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g^-1 at 0.5 A g^-1 current load. Stability studies showed that after 6000 cycles, the CuMn₂O₄/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte.

Sodium Pre-Intercalation-Based Na3-δ-MnO2@CC for High-Performance Aqueous Asymmetric Supercapacitor: Joint Experimental and DFT Study

Electrochemical energy storage devices are ubiquitous for personal electronics, electric vehicles, smart grids, and future clean energy demand. SCs are EES devices with excellent power density and superior cycling ability. Herein, we focused on the fabrication and DFT calculations of Na₃-δ-MnO₂ nanocomposite, which has layered MnO₂ redox-active sites, supported on carbon cloth. MnO₂ has two-dimensional diffusion channels and is not labile to structural changes during intercalation; therefore, it is considered the best substrate for intercalation. Cation pre-intercalation has proven to be an effective way of increasing inter-layered spacing, optimizing the crystal structure, and improving the relevant electrochemical behavior of asymmetric aqueous supercapacitors. We successfully established Na⁺ pre-intercalated δ-MnO₂ nanosheets on carbon cloth via one-pot hydrothermal synthesis. As a cathode, our prepared material exhibited an extended potential window of 0-1.4 V with a remarkable specific capacitance of 546 F g^-1(300 F g^-1 at 50 A g^-1). Moreover, when this cathode was accompanied by an N-AC anode in an asymmetric aqueous supercapacitor, it illustrated exceptional performance (64 Wh kg^-1 at a power density of 1225 W kg^-1) and incomparable potential window of 2.4 V and 83% capacitance retention over 10,000 cycles with a great Columbic efficiency.

Porous polyvinyl alcohol/graphene oxide composite film for strain sensing and energy-storage applications

In this study, a flexible porous polyvinyl alcohol (PVA)/graphene oxide (GO) composite film was developed and tested for flexible strain sensing and energy-storage applications. Morphology and mechanical properties were studied; tensile strength and Young's modulus increased by 225% and 86.88%, respectively, at 0.5 wt% GO. The PVA/GO film possesses exceptional sensing ability to various mechanical strains, such as tension, compression, bending, and torsion. For example, the gauge factor of the PVA/GO film as a tensile-strain sensor was measured as 2.46 (246%). Under compression loads, the PVA/GO composite film showed piezoresistive and capacitive strain-sensing characteristics. Under 5 kPa of compression load, the relative resistance increased by 81% with a 100 msec response time; the relative capacitance increased by 160% with a 120 msec response time. The PVA/GO strain sensor exhibited high durability and reliability over 20 × 10³cycles of tensile strain and bending at 3.33 Hz. Moreover, the PVA/GO composite film showed good electrochemical properties due to its porous structure; the maximum capacitance was 124.7 F g^-1at 0.5 wt% GO. After 20 × 10³charging-discharging cycles, the capacitance retention rate was 94.45%, representing high stable capacitance performance. The results show that electrically conductive porous PVA nanocomposite films are promising candidates for strain sensing and energy-storage devices.

Role of Polyoxometalate Contents in Polypyrrole: Linear Actuation and Energy Storage

A combination of polyoxometalates with polypyrrole is introduced in this work. Our goal was to include phosphotungstic acid (PTA) in different molar concentrations (0.005, 0.01, and 0.05 M) in the electropolymerization of pyrrole doped with dodecylbenzene sulfonate (DBS) and phosphotungstinates (PT), forming PPy/DBS-PT films. Scanning electron microscopy (SEM) revealed that the PPy/DBS-PT films became denser and more compact with increasing PTA concentrations. The incorporation of PT in PPy/DBS was analyzed using Fourier-transform infrared (FTIR) and energy dispersive X-ray (EDX) spectroscopy. The linear actuation in cyclic voltammetry and potential square wave steps in an organic electrolyte revealed increasing mixed actuation, with major expansion upon oxidation found for PPy/DBS-PT films with a PTA concentration of 0.005 M. Best results of a strain of 12.8% and stress at 0.68 MPa were obtained for PPy/DBS-PT (0.01 M). The PPy/DBS-PT films polymerized in the presence of 0.05 M of PTA and showed main expansion upon reduction, changing the actuation direction. Chronopotentiometric measurements of PPy/DBS-PT samples were conducted to determine the specific capacitance optimal for a 0.01 M PTA concentration in the range of 80 F g⁻¹ (±0.22 A g⁻¹).

Ordered Mesoporous Boron Carbon Nitrides with Tunable Mesopore Nanoarchitectonics for Energy Storage and CO2 Adsorption Properties

Porous boron carbon nitride (BCN) is one of the exciting systems with unique electrochemical and adsorption properties. However, the synthesis of low-cost and porous BCN with tunable porosity is challenging, limiting its full potential in a variety of applications. Herein, the preparation of well-defined mesoporous boron carbon nitride (MBCN) with high specific surface area, tunable pores, and nitrogen contents is demonstrated through a simple integration of chemical polymerization of readily available sucrose and borane ammonia complex (BAC) through the nano-hard-templating approach. The bimodal pores are introduced in MBCN by controlling the self-organization of BAC and sucrose molecules within the nanochannels of the template. It is found that the optimized sample shows a high specific capacitance (296 F g^-1 at 0.5 A g^-1 ), large specific capacity for sodium-ion battery (349 mAg h^-1 at 50 mAh g^-1 ), and excellent CO₂ adsorption capacity (27.14 mmol g^-1 at 30 bar). Density functional theory calculations demonstrate that different adsorption sites (BC, BN, CN, and CC) and the large specific surface area strongly support the high adsorption capacity. This finding offers an innovative breakthrough in the design and development of MBCN nanostructures for energy storage and carbon capture applications.

Cellulose-Derived Nanostructures as Sustainable Biomass for Supercapacitors: A Review

Sustainable biomass has attracted a great attention in developing green renewable energy storage devices (e.g., supercapacitors) with low-cost, flexible and lightweight characteristics. Therefore, cellulose has been considered as a suitable candidate to meet the requirements of sustainable energy storage devices due to their most abundant nature, renewability, hydrophilicity, and biodegradability. Particularly, cellulose-derived nanostructures (CNS) are more promising due to their low-density, high surface area, high aspect ratio, and excellent mechanical properties. Recently, various research activities based on CNS and/or various conductive materials have been performed for supercapacitors. In addition, CNS-derived carbon nanofibers prepared by carbonization have also drawn considerable scientific interest because of their high conductivity and rational electrochemical properties. Therefore, CNS or carbonized-CNS based functional materials provide ample opportunities in structure and design engineering approaches for sustainable energy storage devices. In this review, we first provide the introduction and then discuss the fundamentals and technologies of supercapacitors and utilized materials (including cellulose). Next, the efficacy of CNS or carbonized-CNS based materials is discussed. Further, various types of CNS are described and compared. Then, the efficacy of these CNS or carbonized-CNS based materials in developing sustainable energy storage devices is highlighted. Finally, the conclusion and future perspectives are briefly conferred.

Structural and Electrochemical Properties of Physically and Chemically Activated Carbon Nanoparticles for Supercapacitors

The demand for supercapacitors has been high during the integration of renewable energy devices into the electrical grid. Although activated carbon materials have been widely utilized as supercapacitor electrodes, the need for economic and sustainable processes to extract and activate carbon nanomaterials is still crucial. In this work, the biomass waste of date palm fronds is converted to a hierarchical porous nanostructure of activated carbon using simple ball-milling and sonication methods. Chemical and physical activation agents of NaOH and CO2, receptively, were applied on two samples separately. Compared with the specific surface area of 603.5 m2/g for the CO2-activated carbon, the NaOH-activated carbon shows a higher specific surface area of 1011 m2/g with a finer nanostructure. Their structural and electrochemical properties are functionalized to enhance electrode-electrolyte contact, ion diffusion, charge accumulation, and redox reactions. Consequently, when used as electrodes in an H2SO4 electrolyte for supercapacitors, the NaOH-activated carbon exhibits an almost two-fold higher specific capacitance (125.9 vs. 56.8 F/g) than that of the CO2-activated carbon at the same current density of 1 A/g. Moreover, using carbon cloth as a current collector provides mechanical flexibility to our electrodes. Our practical approach produces cost-effective, eco-friendly, and flexible activated carbon electrodes with a hierarchical porous nanostructure for supercapacitor applications.

A comparative study on the electrochemical capacitor performance of 1T/2H hybridized phase and 2H pure phase of MoS2nanoflowers

The 1T/2H hybridized and 2H pure phases of MoS₂nanoflowers were synthesized in a one-step hydrothermal process with the molybdenum source as sodium molybdate dihydrate and the sulfur source as thiourea. The as-prepared 1T/2H hybridized and 2H pure phases of MoS₂were investigated using a thermogravimetry\differential thermal analysis, powder x-ray diffraction, field emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy. The obtained 1T/2H hybridized phases of MoS₂were confirmed by the Raman spectroscopy. The electrochemical characteristics of MoS₂electrodes were examined using cycle voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The electrodes are based on the 1T/2H hybridized phases MoS₂with specific capacitance (C_p) of 555.4 F g^-1at current densities (C_d) of 0.5 A g^-1, capacity retention ratio of 85% after 10 000 cycles were observed that could be a strong potential electrode material for supercapacitors application.

Bamboo-Based Mesoporous Activated Carbon for High-Power-Density Electric Double-Layer Capacitors

Demand for hybrid energy storage systems is growing, but electric double-layer capacitors (EDLCs) have insufficient output characteristics because of the microporous structure of the activated carbon electrode material. Commercially, activated carbon is prepared from coconut shells, which yield an activated carbon material (YP-50F) rich in micropores, whereas mesopores are desired in EDLCs. In this study, we prepared mesoporous activated carbon (PB-AC) using a readily available, environmentally friendly resource: bamboo. Crucially, modification using phosphoric acid and steam activation was carried out, which enabled the tuning of the crystal structure and the pore characteristics of the product. The structural characteristics and textural properties of the PB-AC were determined, and the specific surface area and mesopore volume ratio of the PB-AC product were 960–2700 m²/g and 7.5–44.5%, respectively. The high specific surface area and mesopore-rich nature originate from the phosphoric acid treatment. Finally, PB-AC was used as the electrode material in EDLCs, and the specific capacitance was found to be 86.7 F/g for the phosphoric-acid-treated sample steam activated at 900 °C for 60 min; this capacitance is 35% better than that of the commercial YP-50F (64.2 F/g), indicating that bamboo is a suitable material for the production of activated carbon.

Preparation and Electrical Properties of Polyacrylonitrile Based Porous Carbon by Different Activation Methods

Polyacrylonitrile (PAN)-based porous carbon was prepared by different methods of activation with PAN polymer microsphere as precursor. The morphology, structure and electrical properties for supercapacitor of the porous carbon were investigated. It was found that the morphology of PAN nanospheres tended to be destroyed in the process of one-step activation (activation and carbonization were carried out simultaneously, and could only be retained when the amount of activating agent KOH was small). While the spherical morphology could be well reserved during the two-step activation method (carbonization and activation sequentially). The specific surface area and pore volume increased first and then decreased, with the increase in activation holding time for both one-step and two-step activation methods. The specific surface area reached the maximum value with 2430 m² g⁻¹ for the one-step activation method and 2830 m² g⁻¹ for the two-step activation method. Additionally, their mass-specific capacitances were 178.8 F g⁻¹ and 160.2 F g⁻¹, respectively, under the current density of 1 A g⁻¹. After 2000 cycles, the specific capacitance retentions were 92.9% and 91.3%.

High energy density and extremely stable supercapacitors based on carbon aerogels with 100% capacitance retention up to 65,000 cycles

In terms of ideal future energy storage systems, besides the always-pursued energy/power characteristics, long-term stability is crucial for their practical application. Here, we report a facile and sustainable strategy for the scalable fabrication of carbon aerogels with three-dimensional interconnected nanofiber networks and rationally designed hierarchical porous structures, which are based on the carbonization of bacterial cellulose assisted by the soft template of Zn-1,3,5-benzenetricarboxylic acid. As binder-free electrodes, they deliver a fundamentally enhanced specific capacitance of 352 F ⋅ g^-1 at 1 A ⋅ g^-1 in a wide potential window (1.2 V, 6 M KOH) in comparison with those of bacterial cellulose-derived carbons (178 F ⋅ g^-1) and most activated carbons (usually lower than 250 F ⋅ g^-1). The as-assembled supercapacitors exhibit an ultrahigh capacitance of 297 F ⋅ g^-1 at 1 A ⋅ g^-1, remarkable energy density (14.83 Wh ⋅ kg^-1 at 0.60 kW ⋅ kg^-1), and extremely high stability, with 100% capacitance retention for up to 65,000 cycles at 6 A ⋅ g^-1, representing their superior energy storage performance when compared with that of state-of-the-art supercapacitors of commercial activated carbons and biomass-derived analogs.

Bottom-up Approach for Designing Cobalt Tungstate Nanospheres through Sulfur Amendment for High-Performance Hybrid Supercapacitors

Nanofabrication of heteroatom-doped metal oxides into a well-defined architecture via a "bottom-up" approach is crucial to overcome the boundaries of the metal oxides for energy storage systems. In the present work, this issue was addressed by developing sulfur-doped bimetallic cobalt tungstate (CoWO₄ ) porous nanospheres for efficient hybrid supercapacitors via a single-step, ascendable bottom-up approach. The combined experimental and kinetics studies revealed enhanced electrical conductivity, porosity, and openness for ion migration after amendments of the CoWO₄ via sulfur doping. As a result, the sulfur-doped CoWO₄ nanospheres exhibited a specific capacity of 248.5 mA h g^-1 with outstanding rate capability and cycling stability. The assembled hybrid supercapacitor cell with sulfur-doped CoWO₄ nanospheres and activated carbon electrodes could be driven reversibly in a voltage of 1.6 V and exhibited a specific capacitance of 177.25 F g^-1 calculated at 1.33 A g^-1 with a specific energy of 63.41 Wh kg^-1 at 1000 W kg^-1 specific power. In addition, the hybrid supercapacitor delivered 94.85 % initial capacitance over 10000 charge-discharge cycles. The excellent supercapacitive performance of sulfur-doped CoWO₄ nanospheres may be credited to the sulfur doping and bottom-up fabrication of the electrode materials.

Nanoarchitectonics of Lotus Seed Derived Nanoporous Carbon Materials for Supercapacitor Applications

Of the available environmentally friendly energy storage devices, supercapacitors are the most promising because of their high energy density, ultra-fast charging-discharging rate, outstanding cycle life, cost-effectiveness, and safety. In this work, nanoporous carbon materials were prepared by applying zinc chloride activation of lotus seed powder from 600 °C to 1000 °C and the electrochemical energy storage (supercapacitance) of the resulting materials in aqueous electrolyte (1M H₂SO₄) are reported. Lotus seed-derived activated carbon materials display hierarchically porous structures comprised of micropore and mesopore architectures, and exhibited excellent supercapacitance performances. The specific surface areas and pore volumes were found in the ranges 1103.0–1316.7 m² g⁻¹ and 0.741–0.887 cm³ g⁻¹, respectively. The specific capacitance of the optimum sample was ca. 317.5 F g⁻¹ at 5 mV s⁻¹ and 272.9 F g⁻¹ at 1 A g⁻¹ accompanied by high capacitance retention of 70.49% at a high potential sweep rate of 500 mV s⁻¹. The electrode also showed good rate capability of 52.1% upon increasing current density from 1 to 50 A g⁻¹ with exceptional cyclic stability of 99.2% after 10,000 cycles demonstrating the excellent prospects for agricultural waste stuffs, such as lotus seed, in the production of the high performance porous carbon materials required for supercapacitor applications.

Modified Activation Process for Supercapacitor Electrode Materials from African Maize Cob

In this work, African maize cobs (AMC) were used as a rich biomass precursor to synthesize carbon material through a chemical activation process for application in electrochemical energy storage devices. The carbonization and activation were carried out with concentrated Sulphuric acid at three different temperatures of 600, 700 and 800 °C, respectively. The activated carbon exhibited excellent microporous and mesoporous structure with a specific surface area that ranges between 30 and 254 m²·g^-1 as measured by BET analysis. The morphology and structure of the produced materials are analyzed through Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Boehm titration, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. X-ray photoelectron spectroscopy indicates that a considerable amount of oxygen is present in the materials. The functional groups in the activated carbon enhanced the electrochemical performance and improved the material's double-layer capacitance. The carbonized composite activated at 700 °C exhibited excellent capacitance of 456 F g^-1 at a specific current of 0.25 A g^-1 in 6 M KOH electrolyte and showed excellent stability after 10,000 cycles. Besides being a low cost, the produced materials offer good stability and electrochemical properties, making them suitable for supercapacitor applications.

Single Alkali Metal Ion-Activated Porous Carbon With Heteroatom Doping for Supercapacitor Electrode

A single alkali metal ion activation method was used to prepare sulfur-doped microporous carbons. A series of alkali metal ions such as Li⁺, Na⁺, K⁺, and Cs⁺ was used in the polymerization process of 3-hydroxythiophenol and formaldehyde to obtain metal ion anchored in the sulfur-containing resin, which was further treated to obtain xerogel and carbonized to obtain microporous carbon with sulfur doping. In this case, the monodispersed alkali metal ions could realize highly effective activation with low activating agent dosage. Intensive material characterizations show that the alkali metal ions determine the pore structure and surface properties of as-prepared carbons. C-Cs prepared by Cs⁺ ion possesses a high Brunauer-Emmett-Teller specific surface area of 1,037 m² g^-1 with interconnected microporosity and sulfur doping. The specific capacitance of C-Cs can reach up to 270.9 F g^-1 in a two-cell electrode measurement system, whereas C-Cs-based supercapacitors can deliver an energy density of 7.6 Wh kg^-1, which is much larger than that of other samples due to its surface functionalities and well-interconnected porosities.

Enhanced Activity of Hierarchical Nanostructural Birnessite-MnO2-Based Materials Deposited onto Nickel Foam for Efficient Supercapacitor Electrodes

Hierarchical porous birnessite-MnO₂-based nanostructure composite materials were prepared on a nickel foam substrate by a successive ionic layer adsorption and reaction method (SILAR). Following composition with reduced graphene oxide (rGO) and multiwall carbon nanotubes (MWCNTs), the as-obtained MnO₂, MnO₂/rGO and MnO₂/rGO-MWCNT materials exhibited pore size distributions of 2-8 nm, 5-15 nm and 2-75 nm, respectively. For the MnO₂/rGO-MWCNT material in particular, the addition of MWCNT and rGO enhanced the superb distribution of micropores, mesopores and macropores and greatly improved the electrochemical performance. The as-obtained MnO₂/rGO-MWCNT/NF electrode showed a specific capacitance that reached as high as 416 F·g^-1 at 1 A·g^-1 in 1 M Na₂SO₄ aqueous electrolyte and also an excellent rate capability and high cycling stability, with a capacitance retention of 85.6% after 10,000 cycles. Electrochemical impedance spectroscopy (EIS) analyses showed a low resistance charge transfer resistance for the as-prepared MnO₂/rGO-MWCNT/NF nanostructures. Therefore, MnO₂/rGO-MWCNT/NF composites were successfully synthesized and displayed enhanced electrochemical performance as potential electrode materials for supercapacitors.

Nitrogen, Phosphorus and Sulfur Co-Doped Pyrolyzed Bacterial Cellulose Nanofibers for Supercapacitors

Heteroatom doping is an effective way to raise the electrochemical properties of carbon materials. In this paper, a novel electrode material including nitrogen, phosphorus, and sulfur co-doped pyrolyzed bacterial cellulose (N/P/S-PBC) nanofibers was produced. The morphologies, structure characteristics and electrochemical performances of the materials were investigated by Scanning electron microscopy, Fourier transform infrared spectra, X-ray diffraction patterns, X-ray photoelectronic spectroscopy, N₂ sorption analysis and electrochemical measurements. When 3.9 atom% of nitrogen, 1.22 atom% of phosphorus and 0.6 atom% of sulfur co-doped into PBC, the specific capacitance of N/P/S-PBC at 1.0 A/g was 255 F/g and the N/P/S-PBC supercapacitors’ energy density at 1 A/g was 8.48 Wh/kg with a power density of 489.45 W/kg, which were better than those of the N/P-PBC and N/S-PBC supercapacitors. This material may be a very good candidate as the promising electrode materials for high-performance supercapacitors.

Facile Synthesis of Yolk-Shelled CuCo2Se4 Microspheres as a Novel Electrode Material for Supercapacitor Application

Recently, metal selenides have attracted much attention in the energy storage applications. This attention is due to the outstanding properties of metal selenides (lower cost, lower electronegativity, and environmental friendliness) compared to metal sulfides and oxides. In this work, novel yolk-shelled CuCo₂Se₄ (YS-CCS) microspheres are synthesized by a facile two-step hydrothermal method and used as an electrode material for high-performance supercapacitors (SCs) in alkaline media. The proposed YS-CCS electrode shows remarkable electrochemical performance, including fast kinetics, high reversibility, low internal resistance (0.45 Ω), excellent specific capacitance (512 F g^-1 at a current density of 1A g^-1), high rate capability (70.8% after increasing the current density six times), and good cycling stability (about 83.7% of the initial retention after 6000 successive charge-discharge cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by using the YS-CCS (as a cathode electrode material) and active carbon (as an anode electrode material). The assembled device delivers a maximum energy density of 9.45 W h kg^-1 and a power density up to 850 W kg^-1 in a wide potential window of 1.70 V. Meanwhile, the ASC device exhibits superb rate capability (∼84.67%) after increasing the current density five times and very good capacitance retention (∼88%) after 6000 cycles.

Study on Direct Synthesis of Energy Efficient Multifunctional Polyaniline-Graphene Oxide Nanocomposite and Its Application in Aqueous Symmetric Supercapacitor Devices

The synthesis of promising nanocomposite materials can always be tricky and depends a lot on the method of synthesis itself. Developing such synthesis routes, which are not only simple but also can effectively catch up the synergy of the compositing material, is definitely a worthy contribution towards nanomaterial science. Carbon-based materials, such as graphene oxide, and conjugative polymers, such as conductive polyaniline, are considered materials of the 21st century. This study involves a simple one pot synthesis route for obtaining a nanocomposite of polyaniline and graphene oxide with synergistic effects. The study was carried out in a systematic way by gradually changing the composition of the ingredients in the reaction bath until the formation of nanocomposite took place at some particular reaction parameters. These nanocomposites were then utilized for the fabrication of electrodes for aqueous symmetric supercapacitor devices utilizing gold or copper as current collectors. The device manifested a good capacitance value of 264 F/g at 1 A/g, magnificent rate performance, and capacitance retention of 84.09% at a high current density (10 A/g) when gold sheet electrodes were used as the current collectors. It also showed a capacitance retention of 79.83% and columbic efficiency of 99.83% after 2000 cycles.

CNTs Supercapacitor Based on the PVDF/PVA Gel Electrolytes

BACKGROUND

In this paper, the supercapacitor based on the carbon nanotubes (CNTs) electrodes has been fabricated.

OBJECTIVE

The Polyvinylidene Fluoride (PVDF) and Polyvinyl Alcohol (PVA) were used as a gel electrolyte.

METHODS

The electrodes and electrolytes thin films were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The specific Capacitance (Cs) of the CNTs-based supercapacitor has been measured using the cyclic voltammetry and galvanostatic methods. For the scan rate, 20 mV s-1 the Cs of the CNTs-based supercapacitor was 173 F g-1.

RESULTS

Using the electrochemical impedance spectroscopy the Nyquist curve has been plotted. The reactance capacitance and the equivalent series resistance of the CNTs-based supercapacitor with PVDF/PVA gel electrolytes were 90 Ω and 25 Ω respectively.

CONCLUSION

Also, few patents for the CNTs-based supercapacitor have been reviewed and cited. The CNTs-based supercapacitor proposed a new structure solid-state and flexible supercapacitor with high performance.

Facile Preparation of Ni-Co Bimetallic Oxide/Activated Carbon Composites Using the Plasma in Liquid Process for Supercapacitor Electrode Applications

In this study, a plasma in a liquid process (PiLP) was used to facilely precipitate bimetallic nanoparticles composed of Ni and Co elements on the surface of activated carbon. The physicochemical and electrochemical properties of the fabricated composites were evaluated to examine the potential of supercapacitors as electrode materials. Nickel and cobalt ions in the aqueous reactant solution were uniformly precipitated on the AC surface as spherical nanoparticles with a size of about 100 nm by PiLP reaction. The composition of nanoparticles was determined by the molar ratio of nickel and cobalt precursors and precipitated in the form of bimetallic oxide. The electrical conductivity and specific capacitance were increased by Ni-Co bimetallic oxide nanoparticles precipitated on the AC surface. In addition, the electrochemical performance was improved by stable cycling stability and resistance reduction and showed the best performance when the molar ratios of Ni and Co precursors were the same.

Electrochemical Properties of Carbon Aerogel Electrodes: Dependence on Synthesis Temperature

A series of carbon aerogels (C-AGs) were prepared by the pyrolysis of resorcinol-formaldehyde aerogels at 700-1100 °C as potential supercapacitor electrodes, and their texture and electrochemical properties were determined. The specific surface area of all C-AGs was in the range of 700-760 m2/g, their electron conductivity increased linearly from 0.4 to 4.46 S/cm with an increase of the pyrolysis temperature. The specific capacitance of electrode material based on C-AGs reached 100 F/g in sulfuric acid and could be realized at a 2 A/g charge-discharge current, which makes it possible to use carbon aerogels as electrode materials.

Achieving Ultrahigh Cycling Stability and Extended Potential Window for Supercapacitors through Asymmetric Combination of Conductive Polymer Nanocomposite and Activated Carbon

Conducting polymers and carbon-based materials such as graphene oxide (GO) and activated carbon (AC) are the most promising capacitive materials, though both offer charge storage through different mechanisms. However, their combination can lead to some unusual results, offering improvement in certain properties in comparison with the individual materials. Cycling stability of supercapacitors devices is often a matter of concern, and extensive research is underway to improve this phenomena of supercapacitive devices. Herein, a high-performance asymmetric supercapacitor device was fabricated using graphene oxide–polyaniline (GO@PANI) nanocomposite as positive electrode and activated carbon (AC) as negative electrode. The device showed 142 F g⁻¹ specific capacitance at 1 A g⁻¹ current density with capacitance retention of 73.94% at higher current density (10 A g⁻¹). Most importantly, the device exhibited very high electrochemical cycling stability. It retained 118.6% specific capacitance of the starting value after 10,000 cycles at 3 Ag⁻¹ and with coulombic efficiency of 98.06 %, indicating great potential for practical applications. Very small solution resistance (Rs, 0.640 Ω) and charge transfer resistance (Rct, 0.200 Ω) were observed hinting efficient charge transfer and fast ion diffusion. Due to asymmetric combination, potential window was extended to 1.2 V in aqueous electrolyte, as a result higher energy density (28.5 Wh kg⁻¹) and power density of 2503 W kg⁻¹ were achieved at the current density 1 Ag⁻¹. It also showed an aerial capacitance of 57 mF cm⁻² at current 3.2 mA cm⁻². At this current density, its energy density was maximum (0.92 mWh cm⁻²) with power density (10.47 W cm⁻²).

Vertically Aligned Graphene-Carbon Fiber Hybrid Electrodes with Superlong Cycling Stability for Flexible Supercapacitors

Graphene electrode-based supercapacitors are in high demand due to their superior electrochemical characteristics. A major bottleneck of using the supercapacitors for commercial applications lies in their inferior electrode cycle life. Herein, a simple and facile method to fabricate highly efficient supercapacitor electrodes using pristine graphene sheets vertically stacked and electrically connected to the carbon fibers which can result in vertically aligned graphene-carbon fiber nanostructure is developed. The vertically aligned graphene-carbon fiber electrode prepared by electrophoretic deposition possesses a mesoporous 3D architecture which enabled faster and efficient electrolyte-ion diffusion with a gravimetric capacitance of 333.3 F g^-1 and an areal capacitance of 166 mF cm^-2 . The electrodes displayed superlong electrochemical cycling stability of more than 100 000 cycles with 100% capacitance retention hence promising for long-lasting supercapacitors. Apart from the electrochemical double layer charge storage, the oxygen-containing surface moieties and α-Ni(OH)₂ present on the graphene sheets enhance the charge storage by faradaic reactions. This enables the assembled device to provide an excellent gravimetric energy density of 76 W h kg^-1 with a 100% capacitance retention even after 1000 bending cycles. This study opens the door for developing high-performing flexible graphene electrodes for wearable energy storage applications.

Development of ZIF-Derived Nanoporous Carbon and Cobalt Sulfide-Based Electrode Material for Supercapacitor

Zeolitic Imidazolate Framework (ZIF-67) was prepared in two different solvents—water and methanol. Nanoporous carbon was derived from ZIF-67 via pyrolysis in an inert atmosphere. Anion exchange step of sulfidation on the synthesized material has a great influence on the structure and properties. Structural morphology and thermal stability were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDS), Brunauer-Emmett-Teller (BET), and thermogravimetric (TG) analysis. The electrochemical analysis was evaluated by cyclic voltammetry, chronopotentiometry, and impedance analysis. The as-prepared nanoporous carbon and cobalt sulfide (NPC/CS) electrode material (water) in 2M KOH electrolyte solution exhibit high specific capacitance of 677 F/g. The excellent electrochemical performance of the NPC/CS was attributed to its hierarchical structure. This functionalized ZIF driven strategy paves the way to the preparation of various metal oxide and metal sulfide-based nanoheterostructures by varying the type of metal.

Fabrication of Eco-Friendly Solid-State Symmetric Ultracapacitor Device Based on Co-Doped PANI/GO Composite

An eco-friendly solid-state symmetric ultracapacitor (Uc) device was fabricated using a polyaniline graphene oxide composite co-doped with sulfuric acid (H₂SO₄) and dodecyl benzene sulfonic acid (DBSA) or camphor sulfonic acid (CSA), as electrode material utilizing gold sheets as current collectors. The device showed specific capacitance value of 150 F/g at 1 A/g current density, with a capacitance retention value of 93.33% at higher current density (10 A/g), indicating a high rate capability. An energy density of 15.30 Whkg⁻¹ with a power density of 1716 Wkg⁻¹ was obtained at the current density of 1 A/g. The values of areal capacitance, power density, and energy density, achieved at the current density of 5 mAcm⁻², were 97.38 mFcm⁻², 9.93 mWhcm⁻², and 1.1 Wcm⁻², respectively. Additionally, the device showed very low solution and charge transfer resistance (0.885 Ω and 0.475 Ω, respectively). A device was also fabricated utilizing copper as current collector; however, a lower value of specific capacitance (82 F/g) was observed in this case.

Three-Dimensional Hierarchically Porous Graphene Fiber-Shaped Supercapacitors with High Specific Capacitance and Rate Capability

Chemically converted graphene fiber-shaped supercapacitors (FSSCs) are highly promising flexible energy storage devices for wearable electronics. However, the ultralow specific capacitance and poor rate performance severely hamper their practical applications. They are caused by severe stacking of graphene nanosheets and tortuous ion diffusion path in graphene-based electrodes; thus, the ultralow utilization of graphene has been rarely carefully considered to date. Here, we address these issues by developing three-dimensional hierarchically porous graphene fiber with the incorporation of holey graphene for efficient utilization of graphene to achieve fast charge diffusion and good charge storage capability. Without deterioration in electrical but robust mechanical properties, the optimal graphene fiber shows ultrahigh specific capacitance of 220.1 F cm^-3 at current density of 0.1 A cm^-3 and boosted specific capacitance of 254.3 F cm^-3 at 0.1 A cm^-3 after nitrogen doping. Moreover, the nitrogen-doped 40% holey graphene hybrid fiber-assembled FSSC exhibits ultrahigh rate capability (96, 91, and 87% at current density of 0.5, 1.0, and 2.0 A cm^-3, respectively, and 67% even at ultrahigh current density of 10.0 A cm^-3) and excellent cycle stability (95.65% capacitance retention after 10 000 cycles). The contribution of three-dimensional interconnected hierarchically porous network to the enhanced electrochemical (EC) performance is semiquantitatively elucidated by Brunauer-Emmett-Teller and energy dispersive spectroscopy mapping. Our work gives insights into the importance of fully utilizing graphene and provides an efficient strategy for high EC performance in chemically converted graphene-based FSSCs.

The Effect of an External Magnetic Field on the Electrochemical Capacitance of Nanoporous Nickel for Energy Storage

This work investigates the effect of a magnetic field on the electrochemical performance of nanoporous nickel (np-Ni). We first compare the electrochemical capacitance of np-Ni electrodes, which were prepared using the chemical dealloying strategy under different magnetic flux densities (B = 0, 500 mT). Our experimental data show that np-Ni₅₀₀ prepared under an external magnetic field of 500 mT exhibits a much better electrochemical performance, in comparison with that (np-Ni₀) prepared without applying a magnetic field. Furthermore, the specific capacitance of the np-Ni₀ electrode could be further enhanced when we increase the magnetic flux densities from 0 T to 500 mT, whereas the np-Ni₅₀₀ electrode exhibits a stable electrochemical performance under different magnetic flux densities (B = 0 mT, 300 mT, 500 mT). This could be attributed to the change in the electrochemical impedance of the np-Ni₀ electrode induced by an external magnetic field. Our work thus offers an alternative method to enhance the electrochemical energy storage of materials.

Mixed-Phase MnO₂/N-Containing Graphene Composites Applied as Electrode Active Materials for Flexible Asymmetric Solid-State Supercapacitors

MnO₂/N-containing graphene composites with various contents of Mn were fabricated and used as active materials for the electrodes of flexible solid-state asymmetric supercapacitors. By scanning electron microscopes (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectrometer (XPS), fourier-transform infrared spectroscopy (FTIR) and Raman spectra, the presence of MnO₂ and N-containing graphene was verified. The MnO₂ nanostructures decorated on the N-containing graphene were of α- and γ-mixed phases. N-containing graphene was found to reduce the charge transfer impedance in the high-frequency region at the electrode/electrolyte interface (R_CT) due to its good conductivity. The co-existence of MnO₂ and N-containing graphene led to a more reduced R_CT and improved charge transfer. Both the mass loading and content of Mn in an active material electrode were crucial. Excess Mn caused reduced contacts between the electrode and electrolyte ions, leading to increased R_CT, and suppressed ionic diffusion. When the optimized mass loading and Mn content were used, the 3-NGM1 electrode exhibiting the smallest R_CT and a lower ionic diffusion impedance was obtained. It also showed a high specific capacitance of 638 F·g^-1 by calculation from the cyclic voltammetry (CV) curves. The corresponding energy and power densities were 372.7 Wh·kg^-1 and 4731.1 W·kg^-1, respectively. The superior capacitance property arising from the synergistic effect of mixed-phase MnO₂ and N-containing graphene had permitted the composites promising active materials for flexible solid-state asymmetric supercapacitors. Moreover, the increase of specific capacitance was found to be more significant by the pseudocapacitive MnO₂ than N-containing graphene.

Bifunctional Photo-Supercapacitor with a New Architecture Converts and Stores Solar Energy as Charge

Photo-supercapacitors (PSCs) combine functions of energy harvesting and storage in a single device, and in this study, a new architecture for a PSC is designed and implemented. Cadmium sulfide (CdS) quantum dots/hibiscus (hb) dye co-sensitized TiO₂ is used as the solar cell. Poly(3,4-ethylenedioxypyrrole) (PEDOP)@manganese dioxide (MnO₂) is employed as the counter electrode (CE) for the solar cell and also as the electrodes for the symmetric supercapacitor. The two ends of a long flat current collector support two spatially separated PEDOP@MnO₂ coatings, which serve as the CEs for the TiO₂/hb/CdS photoanode and yet another PEDOP@MnO₂ electrode in sandwich configurations. In this cell, under 1 sun (100 mW cm^-2) illumination, the TiO₂/hb/CdS photoanode undergoes charge separation and by channeling the photocurrent to the PEDOP@MnO₂ electrodes, the symmetric cell part is charged to a voltage of 0.72 V. The PSC delivers a specific capacitance of 183 F g^-1, an energy density of 13.2 Wh kg^-1, and a power density of 360 W kg^-1 at a discharge current density of 1 A g^-1. During the self-discharge process, PEDOP@MnO₂-based PSC retains a voltage of 0.72 V up to 500 s and maintains a stable voltage of 0.5 V thereafter. The TiO₂/hb/CdS photoanode with the PEDOP@MnO₂ CE in an aqueous polysulfide-silica gel electrolyte delivers a power conversion efficiency of 6.11%. This demonstration of a novel PSC opens up opportunities to develop new architectures for efficiently combining energy conversion and storage.

Emerging Robust Heterostructure of MoS2-rGO for High-Performance Supercapacitors

The intermittent nature of renewable energy resources has led to a continuous mismatch between energy demand and supply. A possible solution to overcome this persistent problem is to design appropriate energy-storage materials. Supercapacitors based on different nanoelectrode materials have emerged as one of the promising storage devices. In this work, we investigate the supercapacitor properties of a molybdenum disulfide-reduced graphene oxide (rGO) heterostructure-based binder-free electrode, which delivered a high specific capacitance (387.6 F g^-1 at 1.2 A g^-1) and impressive cycling stability (virtually no loss up to 1000 cycles). In addition, the possible role of rGO in the composite toward synergistically enhanced supercapacitance has been highlighted. Moreover, an attempt has been made to correlate the electrochemical impedance spectroscopy studies with the voltammetric analyses. The performance exceeds that of the reported state-of-the-art structures.

In Situ Growth of Layered Bimetallic ZnCo Hydroxide Nanosheets for High-Performance All-Solid-State Pseudocapacitor

Two-dimensional (2D) hydroxide nanosheets can exhibit exceptional electrochemical performance owing to their shortened ion diffusion distances, abundant active sites, and various valence states. Herein, we report ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheets (thickness ∼30 nm) which crystallize in a layered structure and exhibit a high specific capacitance of 3946.5 F g^-1 at 3 A g^-1 for an electrochemical pseudocapacitor. ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O was synthesized by a homogeneous precipitation method and spontaneously crystallized into 2D nanosheets in well-defined hexagonal morphology with crystal structure revealed by synchrotron X-ray powder diffraction data analysis. In situ growth of ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheet arrays on conductive Ni foam substrate was successfully realized. Asymmetric supercapacitors based on ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheets @Ni foam// PVA, KOH//reduced graphene oxide exhibits a high energy density of 114.8 Wh kg^-1 at an average power density of 643.8 W kg^-1, which surpasses most of the reported all-solid-state supercapacitors based on carbonaceous materials, transition metal oxides/hydroxides, and MXenes. Furthermore, a supercapacitor constructed from ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheets@PET substrate shows excellent flexibility and mechanical stability. This study provides layered bimetallic hydroxide nanosheets as promising electroactive materials for flexible, solid-state energy storage devices, presenting the best reported performance to date.