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

Large-Area Fabrication of Porous Graphene Networks on Carbon Fabric via Millisecond Photothermal Processing of Polyaniline for Supercapacitors

Supercapacitors demonstrate promising potential for flexible, multi-functional energy storage devices; however, their widespread adoption is confronted by fabrication challenges. To access a combination of desirable device qualities such as flexibility, lightweight, structural stability, and enhanced electrochemical performance, carbon fiber (CF) can be utilized as a current collector, alongside graphene as an electrochemically active material. Yet achieving a cost-effective, large-scale graphene production, particularly on CF, remains challenging. Here, a rapid (<1 min) photothermal approach is developed for the large-scale production of graphene directly onto CF, utilizing polyaniline (PANI) as a polymer precursor. The in situ electropolymerization of PANI on CF facilitates its rapid synthesis on large areas, followed by conversion into graphene networks, enabling the binder-free fabrication of supercapacitor devices. These devices exhibit an areal capacitance of 180 mF cm-2 (at 2 mA cm-2 in 1 m H2SO4), an order of magnitude higher than other fabric-based devices. Moreover, the devised photothermal strategy allows for one-step preparation of supercapacitor devices on areas exceeding 100 cm-2, yielding an absolute areal capacitance of 4.5 F. The proportional increase in capacitance with device area facilitates scaling and indicates the commercial viability of this approach for low-cost, energy-efficient, and high-throughput production of lightweight, high-performance graphene-based multi-functional supercapacitor devices.

Hierarchical Hollow Carbon Particles with Encapsulation of Carbon Nanotubes for High Performance Supercapacitors

A novel and sustainable carbon-based material, referred to as hollow porous carbon particles encapsulating multi-wall carbon nanotubes (MWCNTs) (CNTs@HPC), is synthesized for use in supercapacitors. The synthesis process involves utilizing LTA zeolite as a rigid template and dopamine hydrochloride (DA) as the carbon source, along with catalytic decomposition of methane (CDM) to simultaneously produce MWCNTs and COx -free H2 . The findings reveal a distinctive hierarchical porous structure, comprising macropores, mesopores, and micropores, resulting in a total specific surface area (SSA) of 913 m2  g-1 . The optimal CNTs@HPC demonstrates a specific capacitance of 306 F g-1 at a current density of 1 A g-1 . Moreover, this material demonstrates an electric double-layer capacitor (EDLC) that surpasses conventional capabilities by exhibiting additional pseudocapacitance characteristics. These properties are attributed to redox reactions facilitated by the increased charge density resulting from the attraction of ions to nickel oxides, which is made possible by the material's enhanced hydrophilicity. The heightened hydrophilicity can be attributed to the presence of residual silicon-aluminum elements in CNTs@HPC, a direct outcome of the unique synthesis approach involving nickel phyllosilicate in CDM. As a result of this synthesis strategy, the material possesses excellent conductivity, enabling rapid transportation of electrolyte ions and delivering outstanding capacitive performance.

High-Performance Flexible Energy Storage Devices Based on Graphene Decorated with Flower-Shaped MoS2 Heterostructures

MoS₂, owing to its advantages of having a sheet-like structure, high electrical conductivity, and benign environmental nature, has emerged as a candidate of choice for electrodes of next-generation supercapacitors. Its widespread use is offset, however, by its low energy density and poor durability. In this study, to overcome these limitations, flower-shaped MoS₂/graphene heterostructures have been deployed as electrode materials on flexible substrates. Three-electrode measurements yielded an exceptional capacitance of 853 F g^-1 at 1.0 A g^-1, while device measurements on an asymmetric supercapacitor yielded 208 F g^-1 at 0.5 A g^-1 and long-term cyclic durability. Nearly 86.5% of the electrochemical capacitance was retained after 10,000 cycles at 0.5 A g^-1. Moreover, a remarkable energy density of 65 Wh kg^-1 at a power density of 0.33 kW kg^-1 was obtained. Our MoS₂/Gr heterostructure composites have great potential for the development of advanced energy storage devices.

Molecular Modification of Lignin-Based Carbon Materials: Influence of Supramolecular Bonds on the Properties

For the application of lignin-based materials, it is necessary to develop simple and efficient chemical modification strategies for lignin. In this work, the iodization modification strategy is selected to improve the specific surface area and graphitization degree of lignin-based carbon fibers. The introduction of an iodine atom can effectively increase the π electron cloud density of the lignin aromatic hydrocarbon structure. High π electron cloud density can effectively enhance the π-π interaction force between lignin molecules (the supramolecular bonds). The biomass precursors with this intermolecular microstructure exhibit good thermal stability and can maintain the original fibrous morphology during high-temperature treatment, which is beneficial for increasing the specific surface area of biomass-based carbon materials. Furthermore, this intermolecular microstructure also contributes to the graphitization of biomass precursor materials and reduces the spacing of graphite micro-lamellae. The obtained lignin-based carbon fibers with iodization modification exhibit a specific capacitance of 333 F/g at a current density of 1 A/g in the three-electrode tests in 6 M KOH solution. As the assembled supercapacitor, the specific capacitance of lignin-based carbon fibers reaches 87 F/g in 1 M Na₂SO₄ solution. Compared to other modification processes for raw materials, this strategy is simple and efficient and has reference value for the synthesis of other high-performance biomass-based materials.

Janus-like Bx C/C Quantum Sheets with Z-Scheme Mechanism Strengthen Tumor Photothermal-Immunotherapy in NIR-II Biowindow

Carbon dots (CDs) are one of the most popular photothermal agents (PTAs) as a noninvasive strategy for tumor treatment. However, because of the inherent dominant fluorescent emission, the CDs-based PTAs hardly achieve a single photothermal conversion, which causes low photothermal conversion efficiency and poor photothermal performance. In this regard, finding a new CDs-based material system to greatly restrain its fluorescence to enhance its photothermal conversion efficiency is highly required, however, it is still a grand challenge. Herein, a kind of Z-scheme CDs-based PTAs consisting of 2D ultrathin nonmetallic B_x C/C Janus quantum sheets (B_x C/C JQSs) is reported to greatly enhance the photothermal conversion efficiency. It is demonstrated that the heterogeneous growth of Z-scheme B_x C/C JQSs enables the NIR-driven quick injection of hot electrons from C into the conjugated B_x C, realizing a single conversion of light to heat, and resulting in a high photothermal conversion of 60.0% in NIR-II. Furthermore, these new Z-scheme B_x C/C-polyethylene glycol JQSs display outstanding biocompatibility and show effective tumor elimination outcome both in vitro and in vivo through the synergistic photothermal-immunotherapy in the NIR-II biowindow with undetectable harm to normal tissues.

An ultralight, elastic carbon nanofiber aerogel with efficient energy storage and sorption properties

The fabrication of ultralight strong carbon nanofiber aerogels with excellent elasticity is still a challenge. Herein, 3D mesoporous graphene/carbon nanofibers (G/CNF) were prepared for the first time from polyacrylonitrile/poly(4-vinyl phenol) (PAN/PVPh) electrospun fibers. Through hydrogen bonding interactions between PAN and PVPh polymer chains, traditional soft carbon nanofibers can be converted to form hard nanofiber aerogels with excellent mechanical, electrical, and sorption properties. The specific interactions among PAN/PVPh led to the formation of porous features on carbonized nanofiber foams. The 3D carbon foams are extremely elastic, strong, and light in weight, and they exhibited super oleophilic and fire-resistance properties. Electrochemical studies indicate that the G/CNF foam achieves a capacitance of up to 267 F g^-1 (at a scan rate of 1 mV s^-1), with an energy density of 37.04 W h kg^-1, exhibiting better electrochemical performance than other reported porous carbon devices. In addition, the G/CNF foam also exhibits sorption capacity towards various organic solvents and oils. This study paves the way toward a new class of lightweight and robust porous carbon nanocomposites for application in electrochemical energy storage systems and oil sorption devices.

Enhanced Stability and Mechanical Properties of a Graphene–Protein Nanocomposite Film by a Facile Non-Covalent Self-Assembly Approach

Graphene-based nanocomposite films (NCFs) are in high demand due to their superior photoelectric and thermal properties, but their stability and mechanical properties form a bottleneck. Herein, a facile approach was used to prepare nacre-mimetic NCFs through the non-covalent self-assembly of graphene oxide (GO) and biocompatible proteins. Various characterization techniques were employed to characterize the as-prepared NCFs and to track the interactions between GO and proteins. The conformational changes of various proteins induced by GO determined the film-forming ability of NCFs, and the binding of bull serum albumin (BSA)/hemoglobin (HB) on GO’s surface was beneficial for improving the stability of as-prepared NCFs. Compared with the GO film without any additive, the indentation hardness and equivalent elastic modulus could be improved by 50.0% and 68.6% for GO–BSA NCF; and 100% and 87.5% for GO–HB NCF. Our strategy should be facile and effective for fabricating well-designed bio-nanocomposites for universal functional applications.

Energized Composites for Electric Vehicles: A Dual Function Energy-Storing Supercapacitor-Based Carbon Fiber Composite for the Body Panels

The current electric vehicles (EVs) face many challenges like limited charge capacity, low miles/charge, and long charging times. Herein, these issues are addressed by developing a dual-function supercapacitor-based energy-storing carbon fiber reinforced polymer (e-CFRP) that can store electrical energy and function as the structural component for the EV's body shell. This is achieved by developing a unique design, vertically aligned graphene sheets attached to carbon fiber electrodes on which different metal oxides are deposited to obtain high-energy density electrodes. A high-strength multilayer e-CFRP assembly is fabricated using an alternate layer patterning configuration of epoxy and polyacrylamide gel electrolyte. The e-CFRP so developed delivers a high areal energy density of 0.31 mWh cm^-2 at 0.3 mm thickness and a high tensile strength of 518 MPa, bending strength of 477 MPa, and impact strength of 2666 J m^-1 . To show its application in EVs, a toy car's body panel is fabricated with e-CFRP and the toy car is able to operate using the energy stored in its frame. Moreover, when integrated with a solar cell, this composite powers an Internet of Things device, showing its feasibility in communication satellites.

Aligned Carbon-Based Electrodes for Fast-Charging Batteries: A Review

Fast-charging batteries have attracted great attention, and are anticipated to charge electrical vehicles and consumer electronics to full-capacity in several minutes. However, commercial electrode materials in batteries generally have a limited rate performance and are difficult to be used in fast-charging batteries. Designing electrodes with an aligned structure is an effective way to shorten the ion transport path and improve the rate performance of a battery. The excellent electronic conductivity of carbon-based electrodes is another key factor for increasing the rate capability of rechargeable batteries. Therefore, aligned carbon-based electrodes (ACBEs) can significantly improve the power density by combining the advantages of an aligned structure and carbon-based materials. In this review, the mechanism, advantages, and challenges of ACBEs for fast-charging batteries are evaluated, and then the design and preparation methods of ACBEs based on their different dimensions are summarized, and their applications in different batteries are illustrated. Finally, the future development of ACBEs for fast-charging batteries is considered.

3D Cross-linked Ti3C2Tx-Ca-SA films with expanded Ti3C2Tx interlayer spacing as freestanding electrode for all-solid-state flexible pseudocapacitor

Ti₃C₂T_x, a member of the MXene, has attracted extensive interest because of its high conductivity, unique two-dimensional (2D) structure and intrinsic pseudocapacitance for supercapacitors. Flexible and freestanding Ti₃C₂T_x films are promising electrodes for functioned supercapacitors used in wearable and portable electronic devices. However, the severe self-restacking of 2D Ti₃C₂T_x nanosheets restraints their practical application. Herein, freestanding and flexible three-dimensional (3D) cross-linked Ti₃C₂T_x-Ca-SA (sodium alginate) films with expanded Ti₃C₂T_x interlayer spacing are reported. The expanded interlayer spacing allows more electrolyte ions to quickly intercalate providing more intercalation pseudocapacitance, while the 3D cross-linked microstructure ensures a continuous conductive network facilitating charges transport. Attributing to the unique structure, the Ti₃C₂T_x-Ca-SA film delivers an outstanding areal capacitance (633 mF cm^-2 at 5 mV s^-1). Meanwhile, the assembled all-solid-state pseudocapacitor shows good flexibility and capacity stability under various bending conditions. The device exhibits a high energy density up to 12.6 µWh cm^-2 at the power density of 375 µW cm^-2 and excellent cycling stability, which are much better than prior reported state-of-the-art supercapacitors. This research exploits a simple method to optimize the structure of MXene as state-of-the-art electrodes for high-performance flexible energy-storage devices.

Transparent Molecular Adhesive Enabling Mechanically Stable ITO Thin Films

With rapid advances in flexible electronics, transparent conductive electrodes (TCEs) have also been significantly developed as alternatives to the conventional indium tin oxide (ITO)-based material systems that exhibit low mechanical flexibility. Nanomaterial-based alternating materials, such as graphene, nanowire, and nanomesh, exhibit remarkable properties for TCE-based applications, such as high electrical conductivity, high optical transparency, and high mechanical stability. However, these nanomaterial-based systems lack scalability, which is a key requirement for practical applications, and exhibit a size-dependent property variation and inhomogeneous surface uniformity that limit reliable properties over a large area. Here, we exploited a conventional ITO-based material platform; however, we incorporated a transparent molecular adhesive, 4-aminopyridine (4-AP), to improve mechanical flexibility. While the presence of 4-AP barely affected optical transmittance and sheet resistance, it improved interfacial adhesion between the substrate and ITO as well as formed a wavy surface, which could improve the mechanical flexibility. Under various mechanical tests, ITO/4-AP/poly(ethylene terephthalate) (PET) exhibited remarkably improved mechanical flexibility as compared with that of ITO/PET. Furthermore, ITO/4-AP/PET was utilized for a flexible Joule heater application having spatial uniformity of heat generation, voltage-dependent temperature control, and mechanical flexibility under repeated bending tests. This molecular adhesive could overcome the current limitations of material systems for flexible electronics.

Reduced graphene oxide/g-C3N4 modified carbon fibers for high performance fiber supercapacitors

The increasing demand for high performance portable electronic devices has promoted the research of flexible energy storage devices, and various devices have been suggested and investigated.

Micropores within N,S co-doped mesoporous 3D graphene-aerogel enhance the supercapacitive performance

Micropores within N,S co-doped mesoporous 3D graphene-aerogel enhances supercapacitive performance.

High-performance flexible asymmetric supercapacitor based on rGO anode and WO3/WS2 core/shell nanowire cathode

Flexible smart electronics require their energy storage device to be flexible in nature. Developing high-performance flexible energy storage devices require direct integration of electrode active materials on current collectors to satisfy the high electronic/ionic conductivity and long-term durability requirements. Herein, we develop a flexible all-solid-state asymmetric supercapacitor comprised of reduced graphene oxide (rGO) and core/shell tungsten trioxide/tungsten disulfide (WO₃/WS₂) nanowire based electrodes. The electrodes synthesized via electrochemical deposition and chemical vapor deposition avoided the necessity to use non-conductive binders and offered excellent cyclic stability. The structural integrity provided by the rGO and WO₃/WS₂ electrodes facilitated excellent electrochemical stability with capacitance retention of 90% and 100% after 10 000 charge-discharge cycles, respectively. An all-solid-state device provides a voltage window of 1.5 V and more than 70% capacitance retention after 10 000 charge-discharge cycles. Providing 97% capacitance retention upon mechanical bending reveals its potential to be used as an energy storage devices in flexible electronics.

Improving the Supercapacitor Performance by Dispersing SiO2 Microspheres in Electrodes

This paper describes a simple, reproducible, and scalable procedure for the preparation of a SiO₂-containing supercapacitor with high cycle stability. A carbon mesoporous material (CMM) with a high specific surface area, CMK-3, was adopted as an electric double-layer capacitor (EDLC) active material for the preparation of electrodes for the supercapacitor. The optimized SiO₂ content decreased as the microsphere diameter decreased, and the optimal specific capacitance was obtained with 6 wt % SiO₂ microspheres (100 nm size). The capacitance improved from 133 to 298 F/g. The corresponding capacitance retention rate after 1000 cycles increased from 68.04 to 91.53%. In addition, the energy density increased from 21.05 to 26.25 Wh/kg with a current density of 1 A/g. Finally, similar results based on active carbon, CeO₂/CMK-3, and graphene/CNT/MnO_v composite electrodes demonstrated that the proposed method exhibits wide compatibility with diverse electrode materials.

CuO nanorods grown vertically on graphene nanosheets as a battery-type material for high-performance supercapacitor electrodes

This work reports the preparation and characterization of the CuO nanorods grown vertically on graphene nanosheets, denoted as CuO/rGO@NF. Graphene is deposited by electrostatic attraction showing the morphology of folded nanosheets, which improves the electrical conductivity of the electrode, while CuO is modified by filtered cathodic vacuum arc technology and subsequent electrochemical oxidation presenting the morphology of nanorods, which increases the contact area of active sites and shortens the ion and electronic diffusion path. The results show that the CuO/rGO@NF electrode deliver an ultrahigh specific capacity (2.51 C cm⁻² at 2 mA cm⁻²), remarkable rate performance (64.6%) and improved conductivity. A symmetrical supercapacitor is assembled by two identical electrodes, presenting the maximum energy density of 38.35 W h kg⁻¹ at a power density of 187.5 W kg⁻¹. Therefore, the CuO/rGO@NF electrode can be used as a prospective electrode for energy storage devices. In addition, the whole electrode preparation process is short in time, safe and environmentally friendly, which provides a new idea for the preparation of other electrode materials.

The CuO/rGO@NF electrode is prepared by a simple and time-saving method, which has ultrahigh area capacity and excellent rate performance.

Bio-cleaning improves the mechanical properties of lignin-based carbon fibers

Production of carbon fibers (CF) using renewable precursors has gained importance particularly in the last decade to reduce the dependency on conventional petroleum-based precursors. However, pre-treatment of these renewable precursors is still similar to that of conventional ones. Little work is put into greener pre-treatments and their effects on the end products. This work focuses on the use of bio-cleaned lignin as a green precursor to produce CF by electrospinning. Bio-cleaned kraft lignin A (Bio-KLA) and uncleaned kraft lignin A (KLA) were used to explore the effect of bio-cleaning on the diameter and mechanical properties of lignin fibers and CF. The effect of electric field, lignin-to-poly(ethylene oxide) (PEO) ratio and PEO molecular weight (MW) were evaluated by 3³ factorial design using Design of Experiment (DOE). The electrospinning process parameters were optimized to obtain a balance between high elastic modulus and small fiber diameter. The model predicted optimized conditions were 50 kV m⁻¹ electric field, 95/5 lignin-to-PEO ratio and 1000 kDa MW of PEO. When compared to KLA, Bio-KLA CFs showed a 2.7-fold increase in elastic modulus, 2-fold increase in tensile strength and 30% decrease in fiber diameter under the same optimum conditions. The results clearly show that bio-cleaning improved the mechanical properties of lignin derived CF.

Waste lignin (KLA) and bio-cleaned lignin (Bio-KLA) precursors, used to produce parameter-optimized-electrospun carbon fibers showed improved mechanical properties for Bio-KLA.