Specific Area Capacity Research Articles

Facile preparation of nanocellulose/multi-walled carbon nanotube/polyaniline composite aerogel electrodes with high area-specific capacitance for supercapacitors

As a natural biological macromolecule, nanocellulose is a promising substrate for high-performance supercapacitor electrodes. However, it shows that a low area-specific capacitance can limit its use. To strengthen the area-specific capacitance of nanocellulose-based composite aerogel electrodes to obtain high-performance supercapacitors, we combined the addition of conductive materials and physical cross-linking. After physical cross-linking and polyaniline embedding in the original conductive framework, a nanocellulose-based composite aerogel with a conductive network and outstanding electrochemical performance was obtained. The good electrochemical performance of the composite aerogel film electrode can be attributed to the high specific surface area of 46.32 m2·g−1, mesoporous structure, and uniform growth of polyaniline. The electrode exhibited the highest area-specific capacitance of 2176.3 mF·cm−2 at a current density of 1 mA·cm−2. Even at a current density of 10 mA·cm−2, the capacitance was retained at 1071.67 mF·cm−2, thereby showing good rate performance. Furthermore, the as-prepared aerogel film electrode exhibited electrochemical stability with a capacitance retention of 64 % at a current density of 10 mA·cm−2 after 1050 cycles. The as-assembled all-solid-state supercapacitor showed the highest area-specific capacitance of 968.94 mF·cm−2 at a current density of 0.5 mA·cm−2 and considerable energy and power density of 86.1 μWh·cm−2 and 200 μW·cm−2, respectively. In this study, we demonstrated that the proper construction of conductive networks by conductive polymers could maximize electrochemical performance.

Hydrothermal synthesis of GO/ZnO composites and their micromorphology and electrochemical performance

In this study, a graphene oxide/zinc oxide (GO/ZnO) composite was synthesized by the one-pot hydrothermal technique using various GO/ZnO ratio compositions. These were characterised by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and Raman spectroscopy. The findings reveal that the GO/ZnO composite has three different micromorphologies: ZnO-nanorods (ZnO-NRs) were embedded and agglomerated over the GO surface; ZnO-microrods (ZnO-uRs) adhered to and separated on the GO surface; and GO was coated by ZnO at 1:1, 1:2 and 1:8 ratios. In addition, the electrochemical performance of the synthesized GO/ZnO composites was investigated using cyclic voltammetry (CV). The results show that the embedded and agglomerate of ZnO-NRs over the GO surface have the best performance, indicated by a larger CV curve area and higher specific capacitance than the GO and other GO/ZnO composites. The results indicate that the incorporation and insertion of GO and ZnO NRs have an effective reversible nature and are promising electrode materials for supercapacitor applications.

Fabrication of Hybrid Supercapacitor by MoCl5 Precursor‐Assisted Carbonization with Ultrafast Laser for Improved Capacitance Performance

AbstractHybrid supercapacitors use electric double‐layer capacitance and Faradaic pseudocapacitance as energy storage mechanisms. This type of supercapacitor is becoming a prime candidate for next‐generation energy storage devices, with advantages in terms of energy density, specific capacitance, and life cycle. However, reducing the electrode area and increasing the specific capacitance of hybrid supercapacitors remain challenging. In this study, a MoCl5 Precursor‐assisted Ultrafast Laser Carbonization (MPAULC) method to fabricate symmetric hybrid supercapacitors with improved capacitance and reduced size is proposed. The method uses an ultrafast laser to induce the formation of carbon/MoO3 composite with the assistance of the MoCl5 precursor. This ultrafast laser carbonization method exhibited high processing precision. The role of the precursor in laser processing is studied using time‐resolved imaging and temperature calculations. The specific area capacitance of the C/MoO3 hybrid supercapacitor is 11.85 mF cm−2, 9.2 times higher than that of the laser‐induced carbon supercapacitor without precursor. The MPAULC method provides a reliable pathway for fabricating miniaturized hybrid supercapacitors with carbon/metal oxide composite electrodes on polymer substrates.

Stretchable all-in-one supercapacitor enabled by poly(ethylene glycol)-based hydrogel electrolyte with low-temperature tolerance

Hydrogel electrolytes are crucial components of stretchable energy storage devices due to their flexibility and excellent ion transport ability. However, most hydrogels lose their stretchability in subzero-temperature environments. Herein, a stretchable all-in-one supercapacitor that can work at low temperatures was developed by designing an anti-freezing polyacrylic acid (PAA) hydrogel incorporated with polyethylene glycol (PEG)/H2O solvent. PEG endowed the hydrogel with anti-freezing property while avoiding the instability of low-molecular organic solvents. The all-in-one supercapacitor was prepared through the in-situ polymerization and deposition of polyaniline on the faces of the anti-freezing hydrogel electrolyte. The obtained supercapacitor exhibited high capacitive performance, good stretchable capacity, and excellent cycling stability. Moreover, benefiting from the outstanding low-temperature tolerance capacity, the all-in-one supercapacitor can maintain an area specific capacitance of over 63.1% even at −25 °C. This work presents an innovative polymer-solvent system for developing an anti-freezing stretchable all-in-one configured supercapacitor for use as a portable energy storage device in wearable electronics.

Three dimensional FeCo2O4@MnO2 core-shell nanocomposites for integrated solid-state asymmetric supercapacitors

Three dimensional FeCo2O4@MnO2 core-shell nanocomposites with a unique spherical structure were prepared on nickel foam by a two-step hydrothermal + annealing method and they show the specific area capacitance 4.2 F/cm2 at a current density of 2 mA/cm2, which is nearly four times higher than that of a single FeCo2O4 electrode (1.1 F/cm2). The assembled FeCo2O4@MnO2//active carbon solid-state asymmetric supercapacitor (ASC) has a specific area capacitance of 1.81 F/cm2, an energy density of 54.3 Wh/kg and a power density of 769.6 W/kg at 10 mA/cm2. The solid-state ASC exhibited an initial capacitance retention of 62.4% after 7000 cycles, demonstrating good cycling stability. Especially, the integrated solid-state asymmetric supercapacitors based on FeCo2O4@MnO2 electrode material were constructed in different connected manners. The series supercapacitor devices demonstrated the typical enhancement of the operating voltage window and the parallel devices significantly improved the capacitance. Therefore, the FeCo2O4@MnO2 electrode material exhibited the outstanding electrochemical performances in solid-state supercapacitors and promising practical application prospects in integrated circuits for energy storage.

Heteroatoms co-doped carbon from biowaste for capacitive energy storage: Dependence of physicochemical properties and electrochemical performances on precursor grain sizes

Biomass wastes are widely used as precursors for synthesizing heteroatoms doped carbons for capacitive energy storage. Based on one step of carbonization and chemical etching strategy, the effect of precursor grain sizes on physicochemical properties and electrochemical performances of resulting carbons is not paid enough attention. A biowaste of macadamia nutshell with different grain sizes is employed for the synthesis of heteroatom-doped porous carbons by chemical etching in the present study. Benefiting from more pore-forming agents loaded on the precursor with smaller grain sizes, the specific surface area and specific capacitance of carbons are significantly controlled by the grain size. As the nutshell decreased from 200 to 75 μm and was treated at 700 °C, the specific surface area enlarged from 717 to 1989 m2 g−1, while the total content of heteroatoms including oxygen, nitrogen, sulfur, and phosphorus decreased from 12.4 to 9.8 at.%. In a three-electrode system, the specific capacitance of the corresponding carbon increased from 231 to 291 F g−1 at 1 A g−1. The assembled analog supercapacitor achieves a maximum specific energy of 7.8 Wh kg−1 at the specific power of 239 W kg−1 in an aqueous electrolyte. Results demonstrate smaller precursor grain sizes lead to a higher specific surface area of carbons via one step of carbonization and chemical etching, thus achieving a stronger capacitance storage capacity of supercapacitors.

Recyclable Fe3O4/MWCNT/CNF composite nanopaper as an advanced negative electrode for flexible asymmetric supercapacitors

This work constructed recyclable Fe3O4/MWCNT/CNF composite nanopaper, exhibiting exceptional flexibility, high electrical conductivity, and extraordinary mass- and area-specific capacitances as the negative electrode.

Fabrication of a flexible porous polypyrrole film with a 3D micro-nanostructure and its electrochemical properties.

Flexible energy storage systems have become attractive alternatives for applications in wearable energy storage and sensor devices. This study reports a simple electro-polymerization method for the fabrication of PPy films coated on PPy nanotubes (PPy NTs), which are binding-free, self-standing, and could be used as a flexible electrode for supercapacitors. With optimized kinetics for ion transportation, the mass specific capacitance of the flexible porous PPy films can be elevated to 1.36 F cm-2 at a charging/discharging rate of 2 mA cm-2 (0.45 A g-1). The mass specific capacitance of the flexible porous PPy films reaches 6.5 times as large as that of compact PPy films at a scan rate of 20 mV s-1. Furthermore, due to the large free space for volume change, the capacitance fading of the flexible porous PPy films is less than 3% after 10 000 cycles. This novel design provides an efficient method to synthesize high-performance, flexible and low-cost materials used in supercapacitors.

A crosslinked network polypyrrole coated cobalt doped Fe2O3@carbon cloth flexible anode material for quasi-solid asymmetric supercapacitors.

Iron(III) oxide (Fe2O3) exhibits a substantial theoretical specific capacitance and a broad operational voltage window, making it a prospective anode material. The crystal structure of Fe2O3 was altered through cobalt doping, and its electronic conductivity was improved by supporting it with carbon cloth (Co-Fe2O3@CC). Subsequently, a crosslinked network of polypyrrole (PPy) was synthesized onto Co-Fe2O3@CC via an ice-water bath, resulting in the formation of PPy/Co-Fe2O3@CC. This PPy nano-crosslinked network not only established three-dimensional electron transport pathways on the Fe2O3 surface but also amplified the composite material's specific surface area to 45.229 m2 g-1, thereby promoting its electrochemical performance. At a current density of 2 mA cm-2, PPy/Co-Fe2O3@CC displayed an area specific capacitance of 704 mF cm-2, a value 2.2 times higher than that of Co-Fe2O3@CC. The assembled PPy/Co-Fe2O3@CC//Ni-MnO2@CC asymmetric supercapacitor demonstrated an energy density of 1.41 mW h cm-3 at a power density of 54 mW cm-3, making the synthesized electrode material a promising candidate for flexible supercapacitors.

Semi-Embedding Zn-Co3O4 Derived from Hybrid ZIFs into Wood-Derived Carbon for High-Performance Supercapacitors.

Transition metal oxides (TMOs) can provide high theoretical capacitance due to the change of multiple valence states of transition metals. However, their intrinsic drawbacks, including poor electrical conductivity, lower energy density, and huge volume expansion, will result in the pulverization of electrode materials and restricted electrochemical kinetics, thus leading to poor rate capability and rapid capacity fading. Composite electrodes based on transition metal oxides and carbon-based materials are considered to be promising candidates for overcoming these limitations. Herein, we reported a preparation method of hybrid ZIFs derived Zn-doped Co3O4/carbon (Zn-Co3O4/C-230) particles semi-embedded in wood-derived carbon skeleton for integrated electrodes. A large specific surface area, excellent conductivity, and electrochemical stability provide a larger electrochemical activity and potential window for the electrode. Prepared Zn-Co3O4@CW-230 electrode (0.6 mm thick) displays ultrahigh area specific capacitances of 7.83 and 6.46 F cm-2 at the current densities of 5 and 30 mA cm-2, respectively. Moreover, a symmetric supercapacitor assembled by two identical Zn-Co3O4@CW-230 electrodes delivers a superior area-specific capacitance of 2.61 F cm-2 at the current densities of 5 mA cm-2 and great energy densities of 0.36 mWh cm-2 (6.0 mWh cm-3) at 2.5 mW cm-2, while maintaining 97.3% of initial capacitance over 10,000 cycles. It notably outperforms those of most carbon-based metal oxides, endowing the Zn-Co3O4@CW-230 with extensive prospects for practical application.

Microwave discharge for rapid introduction of bimetallic-synergistic configuration to conductive catecholate toward long-term supercapacitor

Bimetallic synergies have been commonly used to boost the intrinsic activity of metal–organic frameworks (MOFs), specifically accelerating the charge transfer in supercapacitor and improving the catalytic activity in electrocatalysis. Presently, most bimetallic synergistic MOFs are prepared by solvothermal method. However, the solvothermal process has several disadvantages such as time-consuming synthesis, acid and alkali corrosion, poor universality and controllability. Here, we present a novel vapor-phase microwave pulse discharge strategy for the rapid (20 s) introduction of bimetallic-synergistic configuration into MOFs. A high-performance and stable bimetallic Zn,Ni-catecholate (Zn,Ni-CAT) can be rapidly and controllably obtained by sputtering high-energy zinc particles onto conductive Ni-CAT utilizing microwave pulse-induced plasma and arc. Based on the high tunability of the microwave pulse discharge to the bimetallic lattice size, the Zn,Ni-CAT can exhibit extremely high area specific capacitance (422.54 mF cm−2), as well as robust long cycle stability (91.53 % retention of the original capacitance after 30,000 cycles). This rapid, acid/base-free and generic strategy is anticipated to provide a new route for atomic engineering of high-performance conductive functional materials for various applications.

Sustainable development of porous activated carbon from Sargassum wightii seaweed for electrode material in symmetric supercapacitors

• Sw-800 was prepared from Sargassum wightii seaweed by chemical activation method. • Sw-800 sample shows a high surface area of about 801.73 m 2 /g. • The Sw-800 electrode delivered 474 F/g at 1 A/g in three electrode system. • The Sw-800 | | Sw-800 device showed an energy density of 13.81 Wh/kg at a power density of 249.82 W/kg. In the present study, a simple, cost-effective preparation of the highly porous Activated Carbon from the Sargassum wightii macroalgae (Sw AC) using a chemical activation approach with KOH. The Sw-AC samples were prepared at different activation temperatures (600 °C, 700 °C and 800 °C). The samples were labelled based on the activation temperature, such as Sw-600, Sw-700 and Sw-800. Further, the as-prepared Sw-ACs were utilized in supercapacitors (SCs) as electrode materials to evaluate the effect of activation temperature and surface area on the energy storage performance of the Sw-AC electrodes. The successful conversion of seaweed into AC was confirmed by various spectral as well as analytical studies. Among the Sw-AC electrodes, the Sw-800 sample showed a high surface area (801.73 m 2 /g) and high specific capacitance in three-electrode measurements (474 F/g at the current density of 1 A/g). Also, the cyclic stability of the electrode was demonstrated to be 93 % up to 8000 GCD cycles. Owing to the improved performance rendered by Sw-800 electrode, which is used for the fabrication of symmetric device (Sw-800 | | Sw-800). The as-fabricated electrode delivered an energy density as well as a power density value of 13.81 Wh/kg and 249.82 W/kg respectively. All these findings proved that the as-prepared Sw-800 from Sargassum wightii seaweed could make a good impact on the creation of low-cost and sustainable electrode materials for SCs.

Beyond Polypyrrole: Pencil-Drawn Paper-Based Supercapacitors with High Energy Density

The construction of conductive graphite channels on paper using the pencil drawing method for supercapacitors and sensors has been reported, but its performance needs to be improved to meet practical applications. In this, we develop green and efficient method to prepare high-performance supercapacitor electrodes. After pencil drawing, the polypyrrole graphite active material (PPy-G) is prepared via interfacial polymerization. The graphite layer not only provides an efficient electron transport path but also greatly increases the electrical capacity of electrodes with a good combination of PPy. The prepared electrodes exhibit an excellent area specific capacitance (1654 mF cm−2) and good cycling stability (at 95.3% after 10,000 cycles). Furthermore, the symmetric supercapacitor is prepared using the dual electrodes exhibit a good energy density of 159.6 μWh cm−2 at a power density of 0.8 mW cm−2. The kinetic processes for the electrodes are also further investigated.

Tailoring the Hollow Structure within CoSn(OH)6 Nanocubes for Advanced Supercapacitors.

The enhanced application performance of hollow-structured materials is attributed to their large surface area with more active sites. In this work, the hollow CoSn(OH)6 nanocubes with increased surface area and mesopores were derived from dense CoSn(OH)6 nanocube precursors by alkaline etching. As a result, the hollow CoSn(OH)6 nanocubes-based cathode electrode exhibited a higher area-specific capacitance of 85.56 µF cm-2 at 0.5 mA cm-2 and a mass-specific capacitance of 5.35 mF g-1 at 0.5 mA cm-2, which was more extensive than that of the dense precursor. Meanwhile, the current density was increased 4-fold with good rate capability for hollow CoSn(OH)6 nanocubes.

Mn3P2O8/TiN on Titanium Substrate for Superapacitor Electrode with Long Cycle Stability in KOH and Na2SO4 Aqueous Eletrolytes

The limitation of low-cost and high-safety aqueous manganese-based materials for electrochemical energy storage is largely hampered by their poor cyclic stability, which is usually caused by the manganese dissolution and interfacial kinetics. Here we synthesize a composite electrode which possesses unique structural properties for aqueous supercapacitor application and exhibits higher area specific capacitance. The remarkable long cycle stability of Mn3P2O8/TiN on titanium (Mn3P2O8/TiN@Ti) outperforms that most manganese-based pseudocapacitive electrode materials. The designed unique structure is attractive for quick charge migration, which confirms that the appropriate anodizing of substrate, electrodeposition of active substances and their in situ loading, is an efficient strategy to improve kinetics for high power density pseudocapacitive supercapacitor energy storage application.

MXene/carboxymethylcellulose-polyaniline (Ti3C2Tx/CMC-PANI) film as flexible electrode for high-performance asymmetric supercapacitors

Two-dimensional (2D) MXene (Ti3C2Tx) materials have received widespread attention as potential electrodes for supercapacitors due to their solution processability, metallic conductivity and excellent energy storage properties. Unfortunately, the self-stacking and interlayer interactions of Ti3C2Tx flakes cause them to acquire poor electrochemical characteristics. Herein, the interwoven carboxymethylcellulose-polyaniline (CMC-PANI) composites were prepared by in-situ polymerization of aniline on the surface of CMC, which was subsequently used as the intercalators to expand the layer spacing of Ti3C2Tx nanosheets via a facile self-assembly process. The interwoven CMC-PANI bridges horizontal Ti3C2Tx nanosheets to construct interconnected conductive and ion channels, making the internal structure of the Ti3C2Tx/CMC-PANI (TCP) film more uniformly and orderly, thereby achieving a high mechanical strength (≈ 35.6 MPa). Meanwhile, the TCP film exhibits a maximum area specific capacitance of 1161.4 mF cm−2 (812.9 mC cm−2) at 1 mA cm−2, and a superior rate performance (maintains 58.4% of the initial value at 50 mA cm−2). Moreover, the fabricated asymmetric supercapacitor (ASC) device presents a high area energy density of 158.7 µW h cm−2 at a power density of 700.1 µW cm−2 and good cycle stability (retention of 89.6% after 15,000 charging/discharging cycles). This rational design balancing flexibility and electrochemical performance provides a broadened idea to solve the inherent defects of MXene and further develop high performance energy storage devices.

(Excellent Student Presentation Award) Activated Biomass Converted Carbon in High-Efficient Water Desalination By Capacitive Deionization

Porous carbon materials, utilized as electrodes in capacitive deionization (CDI), play an important role in water desalination. Currently, benefiting from the abundance, cheap, environmental-friendly, biomass converted carbon was selected as the carbon electrode. We study the salt adsorption properties of carbon materials prepared by biomass precursor such as wood, eggplant, etc. The as obtained biomass converted carbon was further processed with activation. Potassium hydroxide, as a chemical activation agent, was selected and reacted with biomass converted carbon at high temperature. The influence of activating agent-carbon ratio and activating temperature was investigated. Due to the natural porous morphology, the biomass converted carbon materials usually exhibit a large surface area and high electrical specific capacitance after carbonization. Taking advantage of these properties, biomass converted carbon materials own a good water desalination performance. Additionally, the salt adsorption property of activated biomass converted carbon usually has an obvious enhancement, which benefit from the creation of extra porous structure. Based on our experiment, the activated biomass converted carbon materials are excellent candidates to be utilized in further industrial water purification.

Preparation of cyclodextrin polymer-functionalized polyaniline/porous carbon composites for use in high-performance supercapacitors

• Pani can be polymerized on PC surface through host–guest interactions. • Ordered polymerization of Pani on PC is achieved by cyclodextrin polymer. • The products exhibit good specific surface area and high specific capacitance. Ordered polymerization of polyaniline (PANI) on porous carbon (PC) was achieved using cyclodextrin polymer (CDP)-functionalization (CDP/PC) on PC. PANI can be polymerized on PC surface through host–guest interactions between aniline monomers and the CDP to form the CDP-PANI/PC composite. CD modification induced the ordered polymerization of aniline monomers. So CDP-PANI/PC exhibited remarkable specific capacitance (739.2 F·g −1 at 1 A·g −1 ) and high rate capability (516 F·g −1 at 10 A·g −1 , retaining 69.8% of its original capacitance) in a three-electrode system. A symmetrical supercapacitor device assembled from CDP-PANI/PC electrodes retained over 81 % of its initial capacitance after 5000 cycles at 5 A·g −1 .

One-step preparation of flexible nanocellulose-based composite hydrogel supercapacitors with high specific capacitance

Supercapacitors (SCs) have ultra-high specific capacitance far exceeding traditional capacitors, and have become an important direction in the field of capacitor research. However, SCs devices based on carbon materials usually require a high temperature environment for N-doping or compounding of pseudocapacitive materials, which greatly increases the manufacturing cost and the difficulty of industrialized production. Herein, we fabricated cellulose-based flexible hydrogel supercapacitors by Fe3+ facilitated one-step ternary composite of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCN)/sulfonated carbon nanotubes (SCNT)/polyaniline (PANI). The combination of these three substances could form a porous and flexible three-dimensional conductive hydrogel just at room temperature. By comparing the performance of supercapacitors prepared with different ratios of three substances, it was found that the best supercapacitors exhibited a high area specific capacitance of 1786 mF/cm2 at a current density of 1 mA/cm2 and excellent flexibility. Therefore, these composite hydrogels are promising for high-performance flexible solid-state supercapacitors.

High-performance cobalt-doped carbon cloth supported porous Fe2O3 flexible electrode material in quasi-solid asymmetric supercapacitors

Iron oxide, as a promising anode material, has environmental friendliness, high theoretical capacitance, and a wide voltage window. Cobalt-doped iron oxide was loaded on flexible carbon cloth (Co-Fe2O3 @CC) via hydrothermal reaction. Cobalt doping changes the iron oxide’s crystal structure and improves the conductivity of the iron oxide. At the same time, it also increases the oxidation state of iron oxide and improves the pseudocapacitance of the electrode material. The reaction conditions were controlled to prepare iron oxide nano-spheres having porous morphology. The porous structure increases the area where the electrode material is reacted. The area-specific capacitance of the Co-Fe2O3 @CC electrode material is 315.6 mF cm−2, which is 137.2% higher than that of pure Fe2O3 @CC(133 mF cm−2). The capacitance is unchanged before and after 200 times of 90° bending. The voltage window of assembled Co-Fe2O3 @CC//Ni-MnO2 @CC asymmetric supercapacitors is 0–2 V. The energy density is 0.96 mWh cm−3 and the power density is 28.6 mW cm−3, which has excellent electrochemical performance. After 4000 cycles at a current density of 10 mA cm−2, the capacitance is maintained at 85%. Flexible asymmetric supercapacitors have potential applications in the field of flexible wearables.