Symmetric Supercapacitor Device Research Articles

Boosting supercapacitor performance: Sb2O3 nano-blocks on rGO sheets for enhanced energy storage

In this work, the synthesis of antimony(III) oxide (Sb2O3) nanoblocks/reduced graphene oxide (rGO) sheets was obtained by a straightforward hydrothermal method. Sb2O3/rGO composites were prepared with various ratios of rGO. The results indicated that the Sb2O3/15 mg rGO composite had remarkable electrochemical performance. It displayed a good electrochemical efficiency, with a high specific capacitance of 151.89 F g−1 at 1 A g−1. Furthermore, it demonstrated a significant cycling stability, retaining 80 % of its initial capacitance after 5 K charge/discharge cycles. A symmetric supercapacitor device was prepared using Sb2O3/15 mg rGO composite as the electrodes for both positive and negative ends. The device exhibited a high specific energy of 44.36 Wh kg−1 and a significant specific power of 850.76 W kg−1. Moreover, it maintained 5.025 Wh kg−1 at a specific power of 7.25 kW kg−1. These results indicated that the Sb2O3/15 mg rGO composite has the potential promising application as an energy-storage electrode material, as no investigations have been conducted on using Sb2O3/rGO as a supercapacitor electrode.

Fabrication of solid-state symmetrical supercapacitor device based on constructed novel Gr-Cu-MoO2 disk electrodes based on Co-replacement reactions

The use of graphite-based substrates has attracted the attention of many researchers due to their high-performance capacitive behavior. Graphite Disk (GD) electrodes due to being more robust and capacity than graphite sheets can be used on an industrial scale. In this research, for the first time, by using the co-replacement method as a straightforward and without wasting energy method, MoO2 and Cu nanostructures with particular morphology were in-situ co-replaced on GD substrates based on commercial graphite and Zn-metal powder. The results of the scanning electron microscopy analysis clearly showed the MoO2–Cu nanosheet formed on the porous GD (PGC) electrode, which has caused a tremendous increase in the capacitance and cyclic stability due to the augment in the surface area and synergistic effect of MoO2–Cu nanostructure. Also, different characterization analysis results confirmed the co-replacement of MoO2 and Cu nanostructures onto the PGD electrode. Electrochemical investigation exhibited that this electrode has an extraordinary capacity of 28526 mF/cm2 at 2 mA/cm2 in 1M H2SO4. The investigation of the capacitive behavior of the MoO2–Cu/PGD supercapacitor device showed that the fabricated supercapacitor device has an astonished capacitance of 4916.98 mF/cm2 (145.27 F/g), power of 18017.34 mW/cm2, and energy density of 4154.84 mWh/cm2 at 1 mA/cm2.

Nanoscale synergy: Optimizing energy storage with SnO2 quantum dots on ZnO hexagonal prisms for advanced supercapacitors

Abstract Electrode materials comprising SnO2 quantum dots embedded within ZnO hexagonal prisms were successfully synthesized for building cost-effective energy-storage devices. Extensive structural and functional characterizations were performed to assess the electrochemical performance of the electrodes. SEM–EDS results confirm a uniform distribution of SnO2 quantum dots across ZnO. The integration of SnO2 quantum dots with ZnO hexagonal prisms markedly improved the electrochemical behavior. The analysis of electrode functionality conducted in a 3 M KOH electrolyte revealed specific capacitances of 949.26 and 700.68 F g⁻1 for SnO2@ZnO and ZnO electrodes, respectively, under a current density of 2 A g⁻1. After undergoing 5,000 cycles at a current density of 15 A g⁻1, the SnO2@ZnO and ZnO electrodes displayed impressive cycling stability, maintaining specific capacitance retention rates of 89.9 and 92.2%, respectively. Additionally, a symmetric supercapacitor (SSC) device constructed using the SnO2@ZnO electrode showcased exceptional performance, exhibiting a specific capacitance of 83 F g⁻1 at 1.2 A g⁻1. Impressive power and energy densities were achieved by the device, with values reaching 2,808 and 70.2 W kg⁻1, respectively. Notably, the SnO2@ZnO SSC device maintained a capacity preservation of 75% throughout 5,000 galvanostatic charge–discharge sequences. The outcomes highlight the potential of SnO2@ZnO hexagonal prisms as candidates for energy-storage applications, offering scalability and cost-effectiveness. The proposed approach enhances the electrochemical performance while ensuring affordability, facilitating the creation of effective and financially feasible energy storage solutions.

Scalable synthesis of 2D-layered Ti3C2 MXene by HF etching method; electrochemical investigations and device fabrication to enhancing capacitive nature

The goal of the current effort is aimed to synthesise the uniform exfoliated titanium carbide (Ti3C2) MXene sheets by utilising hydrofluoric (HF) acid to remove/etch “aluminium” from the parental Ti3AlC2 MAX phase. The Ti3C2 MXene was investigated by structural analysis using X-ray diffraction (XRD), Higher Resolution Transmission Electron Microscope (HRTEM), Scanning electron microscope (SEM), and EDS with mapping for morphological and elemental analysis, Moreover, the Ti3C2 MXene was studied its electrochemical properties to electrochemical energy storage application using cyclic voltammetry (CV), Galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. Since the GCD analysis of Ti3C2 MXene, a great specific capacitance (Csp) of 318F/g was attained with current density of 1 A/g and up to 90 % retentivity was attained after 7500 cycles. Besides, fabricated Ti3C2 MXene||Ti3C2-MXene symmetric supercapacitor device (SSD) has described the energy density (ED) of 27.78 Wh/kg at a power density (PD) of 400 W/kg and the capacitive retention existed attained 92.1 % after 7500 cycles with 5 A/g.

Enhancing charge storage capacity of cellulose-sweat-based electrolyte flexible supercapacitors with electrochemically exfoliated free-standing carbon yarn electrodes

The Internet of Things (IoT) provides an interface between different electronic devices such as flexible electronics, and e-textiles to capture and receive real-time data and help humans to devise systems that will adequately respond to these environmental stimuli. The main limitations of these devices to work 24/7 are the lack of continuous power supply and easy integration into textiles to perform their functions. The other issues are poor adhesion of active materials with substrates and peeling-off of active material from the electrode substrates and consequently, degradation of electrochemical performance. A potential and evolving strategy is fabricating a current collector-less and integrable carbon yarn-based energy storage device. Herein, we are presenting a facile and novel technique to exfoliate carbon yarn fibers to enhance their electrochemical performance by 3 orders of magnitude. Activated carbon yarn wires acting as current collector-less electrodes along with cellulose acetate-based composite separators offer a large surface area to simulated sweat electrolyte ions and show a gravimetric capacitance of 11.28 Fg−1 at the scan rate of 5 mVs−1. Activated carbon yarn-based symmetric supercapacitor device in a simulated sweat solution electrolyte offers excellent cyclic and bending stability with over 95 % capacitance retention in both tests. Theoretical insightSupercapacitors (SCs) comprise many active and passive elements. The most passive and vital elements are current collectors, separators, binders, electrolytes, and packaging. Two key elements, current collector and binders can be eliminated by developing current collector-free or free-standing electrodes. Carbonaceous materials such as graphene [1,2], carbon nanotubes (CNT) [3], porous carbon [2], and carbon onions[4,5] are common alternatives of active materials for SCs electrodes owing to their low cost, chemical stability, large surface area, and high electrical conductivity. These active materials show exceptional attributes such as long cyclic life, and high-rate capability owing to their intrinsic operation mechanism e.g., surface charge storage due to large surface area. However, they also suffer from low specific capacitance ascribed to low surface area exposed to electrolyte ions and low charge storage due to poor wettability. The most efficient technique to address this problem is to incorporate doped heteroatoms or surface functional groups such as surface oxygen groups present on the surface of carbon yarn. The inclusion of these doped heteroatoms and functional groups boosts the intrinsic properties, such as electrical conductivity, and wettability. The increased electro-active surface area offers more active sites for electrolyte ions, resulting in more charge storage and higher pseudocapacitance [6–8].Carbon yarn comprised of long-chain carbon filaments of 2.5–5 µm in radius, excellent conductivity, high chemical and mechanical stability, and light weightiness make it a potential candidate as an active material or a free-standing electrode for SCs. However, due to its low specific capacitance, limited surface area, and low porosity, carbon yarn failed to be directly exploited as a free-standing or current collector-less electrode for flexible supercapacitor applications.

Renewable symmetric supercapacitors assembled with lignin nanoparticles-based thin film electrolyte and carbon aerogel electrodes

Lignin as a natural biopolymer is becoming increasingly in demand due to its eco-friendly properties, while lignin-based electrolyte with high conductivity and reliable durability for applications in supercapacitors is still challenging. Herein, a facile method to prepare lignin nanoparticles (LNPs)-based solid electrolyte thin film (LF) was proposed through chemical cross-linking reaction. The fabricated LF exhibited a distinctive spongy porous structure with the ionic conductivity of 3.26 mS cm−1, demonstrating the exceptional flexibility and favorable mechanical properties. Moreover, the assembly of all-LNPs-based symmetric supercapacitor (SSC) devices was achieved using LF electrolyte and LCA electrodes for the first time, confirming the LF3 electrolyte superior to commercial cellulose separator in capacitive behaviour. This SSC device exhibited a specific capacitance of 122.7 F g−1 at 0.5 A g−1 and the maximum energy density of 17.04 W h kg−1. Furthermore, the incorporation of sodium alginate (SA) significantly enhanced the ionic conductivity of SA/LF3 electrolyte, and the resulting SSC device delivered a higher specific capacitance of 174.5 F g−1 at 0.5 A g−1 and the maximum energy and power densities of 24.24 W h kg−1 and 5023 W kg−1, respectively. This study proposes a promising approach for sustainable utilization of lignin in energy storage applications.

PEDOT-Doped Mesoporous Nanocarbon Electrodes for High Capacitive Aqueous Symmetric Supercapacitors.

Poly(3,4-ethylenedioxythiophene) (PEDOT) and PEDOT-functionalized carbon nanoparticles (f-CNPs) were synthesized by in situ chemical oxidative polymerization and pyrolysis methods. f-CNP-PEDOT nanocomposites were prepared by varying the concentration of PEDOT from 1 to 20% by weight (i.e., 1, 2.5, 5, 10, and 20 wt%). Several characterization techniques, such as field-emission scanning electron microscopy (FESEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), N2 Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses, as well as cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS), were applied to investigate the morphology, the crystalline structure, the N2 adsorption/desorption capability, as well as the electrochemical properties of these new synthesized nanocomposite materials. FESEM analysis showed that these nanocomposites have defined porous structures, and BET surface area analysis showed that the standalone f-CNP exhibited the largest surface area of 801.6 m2/g, whereas the f-CNP-PEDOT with 20 wt% exhibited the smallest surface area of 116 m2/g. The BJH method showed that the nanocomposites were predominantly mesoporous. CV, GCD, and EIS measurements showed that f-CNP functionalized with 5 wt% PEDOT had a higher capacitive performance compared to the individual f-CNPs and PEDOT constituents, exhibiting an extraordinary specific capacitance of 258.7 F/g, at a current density of 0.25 A/g, due to the combined advantage of enhanced electrochemical activity induced by PEDOT doping, and highly developed porosity of f-CNPs. Symmetric aqueous supercapacitor devices were fabricated using the optimized f-CNP-PEDOT doped with 5 wt% of PEDOT as active material, exhibiting a high capacitance of 96.7 F/g at 1.4 V, holding practically their full charge, after 10,000 charge-discharge cycles at 2 A/g, thus providing the highest electrical electrodes performance. Hereafter, this work paves the way for the potential use of f-CNP-PEDOT nanocomposites in the development of high-energy-density supercapacitors.

Direct pyrolysis fabrication of N/O/S self-doping hierarchical porous carbon from Platycladus Orientali leaves for supercapacitor

To meet the growing market requirement for low-cost supercapacitor electrode materials, N/O/S self-doping hierarchical porous carbon is successfully fabricated by direct pyrolysis of platycladus orientalLeaves (POL). The obtained carbon material exhibits wide application prospects, because of simple and green-environmental technology, low-cost and satisfactory electrochemical properties, which avoided complex preparation routes and consumption of expensive chemical reagents in the traditional activation process. Under the optimum pyrolysis temperature (850 °C), the obtained POL-derived carbon (POL-850) possesses a high specific surface area (1140.2 m2g−1), sheet-like hierarchical porous microstructure, and uniform ternary heteroatoms co-doping (O: 6.79 at.%; N: 3.45 at.% and S: 2.20 at.%). As an electrode material for supercapacitor, the specific capacitance of the POL-850 reaches 224.4 Fg−1 of 0.5 Ag−1and 156.0 Fg−1 at 30 Ag−1, revealing excellent rate performance. The capacitance retention maintains 96.3 % after 10,000 consecutive charge-discharge cycles at 20 Ag−1, demonstrating superior cycling stability. Additionally, the assembled carbon-based symmetric supercapacitor device delivers a satisfied energy density of 11.0 Wh kg−1 with the power density of 65 W kg−1 and ultralong cycle-lifetime with 95.65 % capacitance retention after 10,000 charge/discharge cycles, while the Coulombic efficiency is retaining up to approximately 100 %. This work provides an easy and cost-effective way to rapidly prepare N/O/S co-doping hierarchical porous carbon for supercapacitors, which is very suitable for large-scale production.

Room temperature and rapid synthesis of ZnMn2O4 nanostructured spinel using deep eutectic solvent for high energy asymmetric supercapacitors

Recently, binary metal oxides have drawn significant attention due to their interesting physico-chemical characteristics, makes them suitable for supercapacitor application. In the present work, high surface area spinel ZnMn2O4 is prepared using a reaction of deep eutectic solvent (DES) containing zinc chloride, choline chloride and glycerol with manganese precursor (KMnO4). The DES serves as both precursor and template for the growth of ZnMn2O4. Interestingly, the spinel structure of ZnMn2O4 is prepared within one-minute time at room temperature using DES route makes this process cost-effective. The reaction between DES and manganese precursors can be halted at any stage with the addition of water to the reaction mixture as it reduces existing bonding interaction between the reactants. With this advantage, we have varied reaction time between DES and KMnO4 and further studied the effect of reaction time on surface area and electrochemical properties of the obtained ZnMn2O4. The ZnMn2O4 sample, where DES and KMnO4 reacted for 10 min (ZnMnO-10) showed highest surface area of 118.5 m2/g with a pore volume of 0.19 cm3/g. Further, the ZnMnO-10 sample showed a good specific capacitance of 499.58 F/g at 0.1 A/g in a neutral electrolyte (1 M Na2SO4). The symmetric supercapacitor device fabricated using ZnMnO-10//ZnMnO-10 with energy and power density of 39.40 Wh/kg and 7.06 kW/kg, respectively. Further, the asymmetric supercapacitor device is also assembled using ZnMn2O4 and agro waste-derived carbon (HBC-800) showed an excellent Csp of 331.24 F/g at 0.2 A/g with energy density and power density of 74.50 Wh/kg and 5.4 kW/kg, respectively. The current work proposes the rapid and facile synthesis of spinel ZnMn2O4 utilizing green DES and the obtained ZnMn2O4 showed good specific capacitance and energy density for both symmetric and asymmetric supercapacitor devices.

Fusarium oxysporum mediated synthesis of nitrogen-doped carbon supported platinum nanoparticles for supercapacitor device and dielectric applications

A scalable method has been developed for synthesizing nitrogen-doped carbon-supported platinum nanoparticles. Fusarium oxysporum was utilized as reducing and stabilizing agent, and calcination was employed to produce the carbon support. The unique properties of Fusarium oxysporum facilitate the reduction of metal ions while preventing agglomeration and maintaining nanoparticle stability. An extensive investigation of the electrochemical supercapacitor and temperature-dependent dielectric properties of the nanoparticles demonstrates their suitability for supercapacitor applications. Electrochemical analysis showed N-doped C/Pt NPs with high specific capacitance, 482.77F/g at 2.0 A/g, retaining 94 % capacitance even under 20 A/g after 10,000 cycles. The symmetric supercapacitor device displayed 275F/g at 2 A/g, maintaining 61.10 Wh/kg energy density at 1000 W/kg power density, with ∼ 92 % capacitance retention after 10,000 cycles. Dielectric properties of N-doped C/Pt NPs were analyzed at both ambient (300 K) and elevated (450 K) temperatures, revealing temperature-dependent characteristics and alternating current conductivity. At 0.75 MHz, the dielectric permittivity (ɛ’) was measured at 31, with tangent loss at 2.01 and a.c. conductivity at 2.597 × 10-3 O−1 m−1. Increasing the frequency to 6.0 MHz resulted in a 2.38-fold rise in dielectric permittivity and a decrease in tangent loss to 0.77, demonstrating the temperature-sensitive nature of dielectric relaxation.

Unveiling the marine Sargassum horneri material for energy and active sensor devices: Towards multitasking approaches

The quest for a future with greater environmental sustainability has led to a rising focus on investigating innovative methods for energy production and storage. However, marine invasions have steadily increased over the past two centuries, necessitating innovative approaches for the remediation and preservation of oceanic environments. Especially, Sargassum horneri (S. horneri) is a brown algae that causes massive floating macroalgal blooms along the coasts of East Asia. Given these facts, this paper develops high-performance triboelectric nanogenerator (TENG), and electrode material for both supercapacitor and water-splitting devices based on S. horneri. The TENG device, constructed using S. horneri coastal bio-waste collected from Jeju Island, yields impressive results. The output current, voltage and power generated by the S. horneri-based triboelectric nanogenerator (SH-TENG) is around 47 µA, 775 V, and 2880 µW, respectively. The electrochemical analysis of carbon derived from S. horneri reveals an excellent electrode capacitance of 225 F/g at 2.5 mA. Constructing the symmetric supercapacitor device using S. horneri-derived carbon, which shows excellent energy and power densities around 14.85 Wh/kg and 972.22 W/kg, with remarkable cyclic stability of 81.3 % for 5000 GCD cycles at 7 mA. On the other hand, the developed S. horneri electrode demonstrated much-improved activity towards water splitting application, exhibiting overpotentials of 0.101 V and 0.198 V for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at an applied current density of 20 mA/cm2, respectively. The fabricated sample also demonstrated the lowest Tafel values towards HER (119 mv/dec) and for OER (109 mv/dec). Finally, the time series analysis (TSA) technique was employed for modeling and prediction of capacity retention of the SH//SH supercapacitor and electrochemical potential (E) of SH/NF║SH/NF cell. In both cases, the mean squared error between experimental and predicted data was very small, suggesting the TSA is a powerful statistical technique to model and predict the vial features of the electrochemical devices. Overall, these results suggest that S. horneri-derived carbon presents a viable alternative in the realm of energy storage and harvesting, promising sustainable technological advancements.

Utilization of shea butter waste-derived hierarchical activated carbon for high-performance supercapacitor applications

In this work, carbonization and subsequent activation procedures were adopted to synthesize waste shea butter shells into oxygen-rich interconnected porous activated carbon (SAC_x, x is the mass ratio of KOH used for activation). The SAC_1.5 electrode material showed outstanding electrochemical performance with high specific capacitance (286.6 F/g) and improved rate capability, owing to various synergistic effects originating from a high specific surface area (1233.5 m2/g) and O-rich content. The SAC_1.5-based symmetric device delivered an impressive specific capacitance of 91.6 F/g with a high energy density of 12.7 Wh/kg at 0.5 A/g. The device recorded 99.9 % capacitance retention after 10,000 charge-discharge cycles. The symmetric supercapacitor device successfully lit an LED bulb for more than 1 h, signifying the potential of bio-waste as an efficient carbon precursor for electrode material in practical supercapacitors. This work offers an efficient, affordable, and environmentally friendly strategy for potential renewable energy storage devices.

Nitrogen-enriched nanoporous polytriazine as efficient electrode material for high-performance supercapacitor application in non-aqueous medium with high cyclic stability

Nitrogen-enriched nanoporous polytriazine (NENP) synthesized by conventional heating method possesses a high specific surface area (SABET) of 966 m2 g−1, controlled pore size distribution (1.6, 5, and 8.3 nm) and total pore volume of 2.73 cm3 g−1. The synthesized specimen was utilized as an electrode material for supercapacitor (SC) application in non-aqueous media. The electrodes of NENP were fabricated by two approaches viz., conventional binder-based method and a binder-free electrophoretic deposition (EPD) approach. In case of electrode fabrication by controlled EPD process, the mass of 0.58 mg was obtained as the optimized mass achieved at pH = 2, deposition voltage = 20 V and deposition time = 6 min. The optimized electrodes and tetraethylammonium tetrafluoroborate in adiponitrile (TEA-BF4/ADP) non-aqueous electrolyte were used to fabricate symmetric supercapacitor devices (SC). The SC device, with EPD- based binder-free electrodes, exhibited higher specific capacitance (Csp = 84 F g−1), energy density (Esp = 118.8 Wh kg−1) and power density (Psp = 17 kW kg−1) compared to SC device (49 F g−1, 68.8 Wh kg−1, and 11 kW kg−1 at 0.8 A g−1) fabricated using electrode made from the binder based method. To enhance the SC performance, KI was added as a redox additive to the non-aqueous electrolyte (TEA-BF4/ADP). The SC device, with NENP binder-free electrodes and redox-active nonaqueous electrolyte (TEA-BF4/ADP/KI), achieved the highest Csp, Esp, and Psp (112 F g−1, 150.5 Wh kg−1, and 27 kW kg−1) and demonstrated high cyclic stability (~80.2 % initial capacitance retention after 30,000 cycles, at 5 A g−1).

Unravelling the electrochemistry of Ni-MOF derived nickel phosphide/carbon composite electrode and redox additive electrolyte for high performance supercapacitors

The performance and operation of an energy storage device are significantly influenced by the electrolyte and electrode materials. Therefore, it is crucial to develop an electrode material with a rational design and achieve compatibility with the electrolyte. In this study, we prepare Ni-MOF derived nickel phosphides/carbon (NP@C) nanostructure as an electrode for supercapacitor application. The as synthesized material provides more redox-active sites, better spatial utilization, improved conductivity, and a high-polarized surface that will speed up ion migration at electrode/electrolyte. Also, the usage of redox additive electrolyte (0.2 M K3[Fe (CN)6] in 1 M Na2SO4) further complements the redox active sites and hence the improved charge transport. Therefore, NP@C electrode achieved a remarkable 2136.3 F/g of capacitance at 3 A/g with 90.6 % of capacitance retention after 5000 charge-discharge cycles. In addition, the surface-diffusion studies confirms that NP@C shows high diffusion contribution of 82.6 % in redox electrolyte than that of 25.1 % in 1 M Na2SO4. Furthermore, NP@C//NP@C symmetric supercapacitor device in redox additive electrolyte also delivered remarkable performance rendering high energy density of 52.5 Wh/kg at a power density of 750 W/kg. In addition, NP@C//NP@C also shows the long-term stability with attenuating only 7.2 % of initial capacitance value after 10000 charge-discharge cycles. In addition to this, the device performs extremely well when tested for self-discharge studies. Hence, this study demonstrates the perfect harmony of NP@C electrodes and redox additive electrolyte to fabricate a high-performance supercapacitor.

Novel ferrocene-based graphene oxide/Polypyrrole nanocomposites: Electro-capacitive properties study

In this research, we fabricated two novel ferrocene-modified graphene oxide (GO) nano-hybrids as electrode material for supercapacitors. Particularly, the physicochemical interaction of GO surface functional groups and as-synthesized ferrocenyl derivative, along with physical addition of polypyrrole (PPy) resulted in the preparation of high-performance battery-type capacitive materials. The GO-FBF1/PPy, and GO-FBF2/PPy, as final nanocomposites exhibited 229.43 and 269.57 mAhg−1 charge storage capacity, and capacity retention of 91 % and 93 % over 5000 CV cycles, respectively. Also, a symmetric supercapacitor (SSC) with GO-FBF2/PPy as both the anode and cathode exhibits exceptional cycling performance, with 95 % of its capacity remaining after 3000 cycles, and can be operated in a broad electrochemical window up to 1.6 V. Furthermore, our SSC device shows remarkable power and energy densities of 7859 W kg−1 and 123 Wh kg−1, respectively. For high-performance SCs, this research offers a way to improve the electrochemical characteristics of redox-active battery-type electrode materials.

Phenolic resin filled wood-derived hierarchically porous carbon monolith for high areal capacitance supercapacitors

Wood-based electrodes are widely used in supercapacitors due to their renewable and three-dimensional self-supported properties. Low space utilization of wood-based electrodes seriously restricts its practical applications. In this paper, a wood/phenolic resin composite was designed, which can effectively enhance the space utilization of wood and ensure a hierarchical porous structure. The prepared balsa wood/phenolic resin composite-derived electrode obtained a high areal capacitance (8169 mF cm–2), which is 954 % of pure balsa wood-based electrode. Moreover, the assembled symmetrical supercapacitor device exhibits outstanding electrochemical performance, displaying a high areal capacitance of 3.3 F cm–2, and a competitive volumetric energy density of 2.88 mWh cm–3. More importantly, this design has been successfully used to prepare various species wood-derived electrodes. Therefore, as a general strategy, which gives a novel idea for the design of wood-derived electrodes and may affect other fields using wood-based materials.

Iron Sulfide Microspheres Supported on Cellulose-Carbon Nanotube Conductive Flexible Film as an Electrode Material for Aqueous-Based Symmetric Supercapacitors with High Voltage.

Nanostructured iron disulfide (FeS2) was uniformly deposited on regenerated cellulose (RC) and oxidized carbon nanotube (CNT)-based composite films using a simple chemical bath deposition method to form RC/CNT/FeS2 composite films. The RC/CNT composite film served as an ideal substrate for the homogeneous deposition of FeS2 microspheres due to its unique porous architecture, large specific surface area, and high conductivity. Polypyrrole (PPy), a conductive polymer, was coated on the RC/CNT/FeS2 composite to improve its conductivity and cycling stability. Due to the synergistic effect of FeS2 with high redox activity and PPy with high stability and conductivity, the RC/CNT/FeS2/PPy composite electrode exhibited excellent electrochemical performance. The RC/CNT/0.3FeS2/PPy-60 composite electrode tested with Na2SO4 aqueous electrolyte could achieve an excellent areal capacitance of 6543.8 mF cm-2 at a current density of 1 mA cm-2. The electrode retained 91.1% of its original capacitance after 10,000 charge/discharge cycles. Scanning electron microscopy (SEM) images showed that the ion transfer channels with a pore diameter of 5-30 μm were formed in the RC/CNT/0.3FeS2/PPy-60 film after a 10,000 cycle test. A symmetrical supercapacitor device composed of two identical pieces of RC/CNT/0.3FeS2/PPy-60 composite electrodes provided a high areal capacitance of 1280 mF cm-2, a maximum energy density of 329 μWh cm-2, a maximum power density of 24.9 mW cm-2, and 86.2% of capacitance retention after 10,000 cycles at 40 mA cm-2 when tested at a wide voltage window of 1.4 V. These results demonstrate the greatest potential of RC/CNT/FeS2/PPy composite electrodes for the fabrication of high-performance symmetric supercapacitors with high operating voltages.

Eco-friendly preparation of nitrogen-doped porous carbon materials for enhanced solid-state supercapacitor device

In the last years, researchers all over the world have been looking for biomass-derived porous carbon materials, due to the possibilities for large-scale synthesis, easy to control the pore structure, and high specific surface area. Activated heteroatom doped porous carbon (AHPC) with a high porosity was made by treating inexpensive waste Ficus elastica leaves with a base. The electrochemical performance of the produced activated carbon has been evaluated in various electrolytes, including basic, neutral, and acidic electrolytes. At a current density of 1 A/g in the acidic electrolyte, the specific capacitance of the activated carbon AHPC electrode is higher, 456 F/g, compared to other electrolytes. The symmetric supercapacitor device is built using PVA-H2SO4 gel electrolyte, and its electrochemical performance is evaluated. In addition, the energy density of the built symmetric supercapacitor device is higher than the existing commercial supercapacitors, achieving 62 Wh/kg at a power density of 15.2 kW/kg. This is because the porous carbon has a hierarchical pore distribution and a heteroatom-enriched structure, which allows for rapid charge/mass diffusion channels, and a vast ion-accessible network.

Efficient Electrochemical Performance of Sr(OH)2:MnO2 Binary Composites for Solid State Symmetric Supercapacitor

AbstractIn this study, we synthesized a binder‐free composite electrode based on Sr(OH)2/MnO2 material. The active electrode was prepared using the layer‐by‐layer (LBL) technique. The surface architecture of the sample was examined through scanning electron microscopy (SEM) and high‐resolution scanning electron microscopy (FE‐SEM). Further, the microstructural information of the electrode was revealed via transmission electron microscopy (TEM). The composite confirmation was ensured through X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), and energy‐dispersive X‐ray spectroscopy (EDX) spectra with mapping analysis. The electrode exhibited the maximum specific capacitance of 554.7 F g−1 at 5 mVs−1 in the 6 M KOH electrolyte. The electrode maintained ~65 % capacitance retention after 10,000 galvanostatic charge‐discharge (GCD) cycles. Furthermore, the assembled symmetric supercapacitor device exhibited the highest specific capacitance value of 124.7 F g−1 @ 5 mVs−1 within a potential span of 1.2 V. This device demonstrated the capability to illuminate light‐emitting diodes (LEDs) of different colors. The energy and power densities of the device were calculated as 26.66 Wh kg−1 and 9884.54 W kg−1 respectively. The stability performance of the device was ~57 % after 10,000 GCD cycles. These findings strongly suggest that the material and the device represent promising options for future energy storage applications.

Effect of air-annealing on the structure, surface morphology, and supercapacitive properties of the 2D-BiOCl nanosheets

Upright-standing nanosheets of bismuth oxychloride (BiOCl), synthesized via a facile chemical synthesis method and air-annealed from 50 to 600 ℃ temperatures (named BOC-50–600), are envisaged as electrochemical supercapacitor electrodes. These electrodes are initially screened for their surface morphology, elemental configuration, phase purity, and binding energy by various means. Due to changes in the surface morphology, phase, charge transfer resistance, and binding energy, the one annealed at 150 ℃ i.e., BOC-150 has offered targeted supercapacitive performance due to quasi-faradaic redox reactions in 6 M KOH electrolyte solution. The specific capacitance of the BOC-150 electrode, measured at 1.40–5.0 A/g current densities, varies from 264.6 to 95 F/g. The as-assembled BOC-150//BOC-150 symmetric supercapacitor device (SSD) demonstrates an efficient supercapacitive performance with a maximum 86.87 Wh/kg energy density and 3735 W/kg power density. Additionally, the as-designed SSD endows an admirable capacity retention of 81.6% for 5000 charge-discharge cycles, approving moderate chemical stability and considerable mechanical robustness for use in commercial electronic items.