Superstructured NiMoO4@CoMoO4 core-shell nanofibers for supercapacitors with ultrahigh areal capacitance.

High areal capacitance for a practical supercapacitor electrode requires both large mass loading and high utilization efficiency of electroactive materials, which presents a great challenge. Herein, we demonstrated the unprecedented synthesis of superstructured NiMoO4@CoMoO4 core-shell nanofiber arrays (NFAs) on a Mo-transition-layer-modified nickel foam (NF) current collector as a new material, achieving the synergistic combination of highly conductive CoMoO4 and electrochemical active NiMoO4. Moreover, this superstructured material exhibited a large gravimetric capacitance of 1,282.2 F/g in 2 M KOH with a mass loading of 7.8 mg/cm2, leading to an ultrahigh areal capacitance of 10.0 F/cm2 that is larger than any reported values of CoMoO4 and NiMoO4 electrodes. This work provides a strategic insight for rational design of electrodes with high areal capacitances for supercapacitors.

Designing Dense, Robust, and Ion-Diffusion-Effective Electrodes from Natural Wood Material toward High-Volumetric-Performance Supercapacitors.

Assembling active materials into dense electrodes is a promising way to obtain high-volumetric-capacitance supercapacitors, but insufficient ion channels in the dense structure lead to a low rate capability. Herein, a dense and robust wood electrode with a large MXene volumetric mass loading (1.25 g cm-3) and abundant ion diffusion channels is designed via a facile capillary-force-driven self-densification strategy. Specifically, MXene is assembled onto a wood cell wall, endowing the wood electrode with good electrical conductivity (86 S cm-1) and high electrochemical activity (5.9 F cm-2 at 1 mA cm-2). Notably, the oriented channels along with spaces between adjacent microfibrils recast after densification ensure efficient ion transport for the wood electrode, achieving an excellent rate capability with a high capacitance retention of 77% from 1 to 20 mA cm-2. Meanwhile, the capillary force induces self-densification on the softened wood cell wall, resulting in a highly compact and robust structure for the wood electrode.

Laser Additive Manufacturing of Three-Dimensional Ti/TiN Nanotube Arrays with Hierarchical Pore Structures and Promoted Supercapacitor Performances.

Titanium-based composites hold great promise in versatile functional application fields, including supercapacitors. However, conventional subtractive methods for preparing complex-shaped titanium-based composites generally suffer from several significant shortcomings, including low efficiency, strictly simple geometry, low specific surface area, and poor electrochemical performance of the products. Herein, three-dimensional composites of Ti/TiN nanotube arrays with hierarchically porous structures were prepared using the additive manufacturing method of selective laser melting combined with anodic oxidation and nitridation. The resultant Ti/TiN nanotube array composites exhibit good electrical conductivity, ultrahigh specific surface areas, and outstanding supercapacitor performances featuring the unique combination of a large specific capacitance of 134.4 mF/cm2 and a high power density of 4.1 mW/cm2, which was remarkably superior to that of their counterparts. This work is anticipated to provide new insights into the facile and efficient preparation of high-performance structural and functional devices with arbitrarily complex geometries and good overall performances.

Li Salt Assisted Highly Flexible Carbonaceous Ni3N@polyimide Electrode for an Efficient Asymmetric Supercapacitor.

This work used a highly flexible, sustainable polyimide tape as a substrate to deposit ductile-natured carbonaceous Ni3N (C/Ni3N@polyimide) material for supercapacitor application. C/Ni3N was prepared using a co-sputtering technique, and this method also provided better adhesion of the electrode material over the substrate, which is helpful in improving bending performance. The ductile behavior of the sputter-grown electrode and the high flexibility of the polyimide tape provide ultimate flexibility to the C/Ni3N@polyimide-based supercapacitor. To achieve optimum electrochemical performance, a series of electrochemical tests were done in the presence of various electrolytes. Further, a flexible asymmetric supercapacitor (NC-FSC) (C/Ni3N//carbon@polyimide) was assembled by using C/Ni3N as a cathode and a carbon thin film as an anode, separated by a GF/C-glass microfiber soaked in optimized 1 M Li2SO4 aqueous electrolyte. The NC-FSC offers a capacitance of 324 mF cm-2 with a high areal energy density of 115.26 µWh cm-2 and a power density of 811 µW cm-2, with ideal bending performance.

One-Step Wet-Spinning of High-Energy Density Coaxial Fibrous Supercapacitors Based on In Situ Carbon-Modified Nitrogen-Doped MXene Nanosheets.

Fibrous supercapacitors (SCs) are emerging promising power sources for flexible/wearable electronics and have attracted an extensive amount of attention from researchers. However, the low energy density has always hindered their further development. Here, a coaxial fibrous SC (CFSC) was fabricated by one-step wet-spinning combined with an electrodeposition strategy. Benefiting from the large surface area and abundant pore structure of carbon-modified nitrogen-doped MXene nanosheets (NS), as well as the high conductivity of silver (Ag) NS, the electrolyte ion/electron transport paths are significantly improved. Furthermore, the distributed GO in the P(VDF-HFP) separator could form a high-speed continuous ion transport channel, thus enhancing the ionic conductivity. At a power density of 40-200 µW cm-2, the CFSC shows a high energy density of 0.7-3.39 µWh cm-2. The as-prepared CFSC also maintains an excellent capacitance retention rate of 90.3% even after 15 000 charge-discharge cycles. This work provides a general strategy for manufacturing high-performance, flexible, and wearable SCs.

Interfacial Modulation of Ti3C2Tx MXene by Cellulose Nanofibrils to Construct Hybrid Fibers with High Volumetric Specific Capacitance.

The intrinsic poor rheological properties of MXene inks result in the MXene nanosheets in dried MXene microfibers prone to self-stacking, which is not conducive to ion transport and diffusion, thus affecting the electrochemical performance of fiber-based supercapacitors. Herein, robust cellulose nanofibrils (CNF)/MXene hybrid fibers with high electrical conductivity (916.0 S cm-1) and narrowly distributed mesopores are developed by wet spinning. The interfacial interaction between CNF and MXene can be enhanced by hydrogen bonding and electrostatic interaction due to their rich surface functional groups. The interfacial modulation of MXene by CNF can not only regulate the rheology of MXene spinning dispersion, but also enhance the mechanical strength. Furthermore, the interlayer distance and self-stacking effect of MXene nanosheets are also regulated. Thus, the ion transport path within the fiber material is optimized and ion transport is accelerated. In H2SO4 electrolyte, a volumetric specific capacitance of up to 1457.0 F cm-3 (1.5 A cm-3) and reversible charge/discharge stability are demonstrated. Intriguingly, the assembled supercapacitors exhibit a high-volume energy density of 30.1 mWh cm-3 at 40.0 mW cm-3. Moreover, the device shows excellent flexibility and cycling stability, maintaining 83% of its initial capacitance after 10 000 charge/discharge cycles. Practical energy supply applications (Power for LED and electronic watch) can be realized.

Highly Ionic Conductive, Stretchable, and Tough Ionogel for Flexible Solid-State Supercapacitor.

The increasing demand for wearable electronics calls for advanced energy storage solutions that integrate high  electrochemical performances and mechanical robustness. Ionogel is a promising candidate due to its stretchability combined with high ionic conductivity. However, simultaneously optimizing both the electrochemical and mechanical performance of ionogels remains a challenge. This paper reports a tough and highly ion-conductive ionogel through ion impregnation and solvent exchange. The fabricated ionogel consists of double interpenetrating networks of long polymer chains that provide high stretchability. The polymer chains are crosslinked by hydrogen bonds that induce large energy dissipation for enhanced toughness. The resultant ionogel possesses mechanical stretchability of 26, tensile strength of 1.34 MPa, and fracture toughness of 4175 J m-2. Meanwhile, due to the high ion concentrations and ion mobility in the gel, a high ionic conductivity of 3.18 S m-1 at room temperature is achieved. A supercapacitor of this ionogel sandwiched with porous fiber electrodes provides remarkable areal capacitance (615 mF cm-2 at 1 mA cm-2), energy density (341.7 µWh cm-2 at 1 mA cm-2), and power density (20 mW cm-2 at 10 mA cm-2), offering significant advantages in applications where high efficiency, compact size, and rapid energy delivery are crucial, such as flexible and wearable electronics.

Leaping Supercapacitor Performance via a Flash-Enabled Graphene Photothermal Coating.

Elevating the working temperature delivers a simple and universal approach to enhance the energy storage performances of supercapacitors owing to the fundamental improvements in ion transportation kinetics. Among all heating methods, introducing green and sustainable photothermal heating on supercapacitors (SCs) is highly desired yet remains an open challenge, especially for developing an efficient and universal photothermal heating strategy that can be generally applied to arbitrary SC devices. Flash-enabled graphene (FG) absorbers are produced through a simple and facile flash reduction process, which can be coated on the surface of any SC devices to lift their working temperature via a photothermal effect, thus, improving their overall performance, including both power and energy densities. With the systematic temperature-dependent investigation and the in-depth numerical simulation of SC performances, an evident enhancement in capacitance up to 65% can be achieved in photothermally enhanced SC coin cell devices with FG photo-absorbers. This simple, practical, and universal enhancement strategy provides a novel insight into boosting SC performances without bringing complexity in electrode fabrication/optimization. Also, it sheds light on the highly efficient utilization of green and renewable photothermal energies for broad application scenarios, especially for energy storage devices.

Multilayer Core-Shell Fiber Device for Improved Strain Sensing and Supercapacitor Applications.

1D fiber devices, known for their exceptional flexibility and seamless integration capabilities, often face trade-offs between desired wearable application characteristics and actual performance. In this study, a multilayer device composed of carbon nanotube (CNT), transition metal carbides/nitrides (MXenes), and cotton fibers, fabricated using a dry spinning method is presented, which significantly enhances both strain sensing and supercapacitor functionality. This core-shell fiber design achieves a record-high sensitivity (GF ≈ 4500) and maintains robust durability under various environmental conditions. Furthermore, the design approach markedly influences capacitance, correlating with the percentage of active material used. Through systematic optimization, the fiber device exhibited a capacitance 26-fold greater than that of a standard neat CNT fiber, emphasizing the crucial role of innovative design and high active material loading in improving device performance.

MXene/Nitrogen-Doped Carbon Nanosheet Scaffold Electrode toward High-Performance Solid-State Zinc Ion Supercapacitor.

While MXene is widely used as an electrode material for supercapacitor, the intrinsic limitation of stacking caused by the interlayer van der Waals forces has yet to be overcome. In this work, a strategy is proposed to fabricate a composite scaffold electrode (MCN) by intercalating MXene with highly nitrogen-doped carbon nanosheets (CN). The 2D structured CN, thermally converted and pickling from Zn-hexamine (Zn-HMT), serves as a spacer that effectively prevents the stacking of MXene and contributes to a hierarchically scaffolded structure, which is conducive to ion movement; meanwhile, the high nitrogen-doping of CN tunes the electronic structure of MCN to facilitate charge transfer and providing additional pseudocapacitance. As a result, the MCN50 composite electrode achieves a high specific capacitance of 418.4 F g-1 at 1 A g-1. The assembled symmetric supercapacitor delivers a corresponding power density of 1658.9 W kg-1 and an energy density of 30.8 Wh kg-1. The all-solid-state zinc ion supercapacitor demonstrates a superior energy density of 68.4 Wh kg-1 and a power density of 403.5 W kg-1 and shows a high capacitance retention of 93% after 8000 charge-discharge cycles. This study sheds a new light on the design and development of novel MXene-based composite electrodes for high performance all-solid-state zinc ion supercapacitor.

Activating Ion Channels in Collapsed Hydrogel Derived Densified MXene Films with Cellulose Nanofibers to Overcome the Areal Versus Volumetric Capacitance Trade-Off.

Concomitant achievement of all three performance pillars of a supercapacitor device, namely gravimetric, areal, and volumetric capacitance is a grand challenge. Nevertheless, its fulfilment is indispensable for commercial usage. Although, high compactness is the fundamental requirement to achieve high volumetric performance, it severely affects ion transportation in thick electrodes. Such trade-off makes it extremely challenging to realize very high areal and volumetric performance simultaneously. Here, a collapsed hydrogel strategy is introduced to develop MXene/cellulose nanofiber (CNF) based densified electrodes that offer excellent ion transportation despite a massive increase in areal mass loading (>70 mg cm-2). Quasi-oriented MXene/CNF (MXCF) hydrogels are produced through an electric field-guided co-assembly technique. Ambient dehydration of these hydrogels incorporates numerous pores in the resultant compact electrodes due to crumpling of the MXene sheets, while CNF ensures connectivity among the locally blocked pores in different length scales. The resultant collapsed MXCF densified electrode shows a remarkably high areal capacitance of 16 F cm-2 while simultaneously displaying a high volumetric capacitance of 849.8 F cm-3 at an ultrahigh mass loading of up to 73.4 mg cm-2. The universality of strategy, including the co-assembly of hydrogel and its collapse, is further demonstrated to develop high-performance asymmetric and wearable devices.

Application Scopes of Miniaturized MXene-Functionalized Electrospun Nanofibers-Based Electrochemical Energy Devices.

Exploring combinatorial materials, as well as rational device configuration design, are assumed to be the key strategies for deploying versatile electrochemical devices. MXene sheets have revealed a high hydrophilic surface with proper mechanical and electrical characteristics, rendering them supreme additive candidates to integrate in electrospun electrochemical power tools. The synergetic effects of MXene 2D layers with the nanofibrous networks can boost actuator responsive ability, battery capacity retention, fuel cell stability, sensor sensitivity, and supercapacitor areal capacitance. Their superior mechanical features can be endowed to the electrospun layers through the embedding of the MXene additive. In this review, the preparation and inherent features of the MXene configurations are briefly evaluated. The fabrication and overall performance of the MXene-loaded nanofibers applicable in electrochemical actuators, batteries, fuel cells, sensors, and supercapacitors are comprehensively figured out. Eventually, an outlook on the future development of MXene-based electrospun composites is presented. A substantial focus has been devoted to date to engineering conjugated MXene and electrospun fibrous frames. The potential performance of the MXene-decorated nanofibers presents a bright future of nanoengineering toward technological growth. Meanwhile, a balance between the pros and cons of the synthesized MXene composite layers is worthwhile to consider in the future.

Recent Research Progress of Porous Graphene and Applications in Molecular Sieve, Sensor, and Supercapacitor.

Porous graphene, including 2D and 3D porous graphene, is widely researched recently. One of the most attractive features is the proper utilization of graphene defects, which combine the advantages of both graphene and porous materials, greatly enriching the applications of porous graphene in biology, chemistry, electronics, and other fields. In this review, the defects of graphene are first discussed to provide a comprehensive understanding of porous graphene. Then, the latest advancements in the preparation of 2D and 3D porous graphene are presented. The pros and cons of these preparation methods are discussed in detail, providing a direction for the fabrication of porous graphene. Moreover, various superior properties of porous graphene are described, laying the foundation for their promising applications. Owing to its abundant morphology, wide distribution of pore size, and remarkable properties benefited from porous structure, porous graphene can not only promote molecular diffusion and electron transfer but also expose more active sites. Consequently, a serious of applications containing gas sieving, liquid separation, sensors, and supercapacitors, are presented. Finally, the challenges confronted during preparation and characterization of porous graphene are discussed, offering guidance for the future development of porous graphene in fabrication, characterization, properties, and applications.

V-Doping Strategy Induces the Construction of the CoFe-LDHs/NF Electrodes with Higher Conductivity to Achieve Higher Energy Density for Advanced Energy Storage Devices.

Doping of metal ions shows promising potential in optimizing and modulating the electrical conductivity of layered double hydroxides (LDHs). However, there is still much room for improvement in common metal ions and conventional doping methods. In contrast to previous methodologies, a hollow triangular nanoflower structure of CoFeV-LDHs is devised, which is enriched with a greater number of oxygen vacancies. This resulted in a significant enhancement in the conductivity of the LDHs, leading to an increase in energy density following the appropriate doping of V. To investigate the impact of V-doping on the energy density of the LDHs, in situ XPS and in situ X-ray spectroscopy is employed. Regarding electrochemical performance, the CoFeV-LDHs/NF electrode with optimal doping ratio exhibited a specific capacitance of 881 F g-1 at a current density of 1 A g-1. The capacitance remained at 90.53% after 3000 cycles. In addition, the constructed battery-type supercapacitor CoFeV-LDHs/NF-2//AC exhibited an impressive energy density of 124.7 Wh kg-1 at a power density of 850 W kg-1 and capacitance remained almost unchanged at 95.2% after 3000 cycles. All the above demonstrates the great potential of V-doped LDHs and brings a new way for the subsequent research of LDHs.

Advances In Borophene: Synthesis, Tunable Properties, and Energy Storage Applications.

Monolayer boron nanosheet, commonly known as borophene, has garnered significant attention in recent years due to its unique structural, electronic, mechanical, and thermal properties. This review paper provides a comprehensive overview of the advancements in the synthetic strategies, tunable properties, and prospective applications of borophene, specifically focusing on its potential in energy storage devices. The review begins by discussing the various synthesis techniques for borophene, including molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and chemical methods, such as ultrasonic exfoliation and thermal decomposition of boron-containing precursors. The tunable properties of borophene, including its electronic, mechanical, and thermal characteristics, are extensively reviewed, with discussions on its bandgap engineering, plasmonic behavior, and thermal conductivity. Moreover, the potential applications of borophene in energy storage devices, particularly as anode materials in metal-ion batteries and supercapacitors, along with its prospects in other energy storage systems, such as sodium-oxygen batteries, are succinctly, discussed. Hence, this review provides valuable insights into the synthesis, properties, and applications of borophene, offering much-desired guidance for further research and development in this promising area of nanomaterials science.

Direct Electrodeposition of Electrically Conducting Ni3(HITP)2 MOF Nanostructures for Micro-Supercapacitor Integration.

Micro-supercapacitors emerge as an important electrical energy storage technology expected to play a critical role in the large-scale deployment of autonomous microdevices for health, sensing, monitoring, and other IoT applications. Electrochemical double-layer capacitive storage requires a combination of high surface area and high electronic conductivity, with these being attained only in porous or nanostructured carbons, and recently found also in conducting metal-organic frameworks (MOFs). However, techniques for conformal deposition at micro- and nanoscale of these materials are complex, costly, and hard to upscale. Herein, the study reports direct, one step non-sacrificial anodic electrochemical deposition of Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 - Ni3(HITP)2, a porous and electrically conducting MOF. Employing this strategy enables the growth of Ni3(HITP)2 films on a variety of 2D substrates as well as on 3D nanostructured substrates to form Ni3(HITP)2 nanotubes and Pt@ Ni3(HITP)2 core-shell nanowires. Based on the optimal electrodeposition protocols, Ni3(HITP)2 films interdigitated micro-supercapacitors are fabricated and tested as a proof of concept.

Longevous Protic Hybrid Supercapacitors Using Bimetallic Prussian Blue Analogue/rGO-Based Nanocomposite Against MXene Anode.

MXenes exhibit a unique combination of properties-2D structure, high conductivity, exceptional capacity, and chemical resistance-making them promising candidates for hybrid supercapacitors (HSCs). However, the development of MXene-based HSCs is often hindered by the limited availability of cathode materials that deliver comparable electrochemical performance, especially in protic electrolytes. In this study, this challenge is addressed by introducing a durable protic HSC utilizing a bimetallic Prussian Blue Analogue (PBA) decorated on reduced graphene oxide (rGO) as a nanocomposite cathode paired with a single-layered Ti3C2Tx MXene (SL-MXene) anode. The bimetallic PBA, specifically nickel hexacyanocobaltate (NiHCC), is utilized by virtue of its open and stable structure that facilitates efficient charge storage, leading to enhanced stability and energy storage capabilities. The resulting NiHCC/rGO//SL-MXene cell demonstrates impressive performance, achieving a maximum specific energy of 38.03 Wh kg-1 and a power density of 20 666.67 W kg-1. Remarkably, the NiHCC/rGO//SL-MXene HSC cell also exhibits excellent cycling stability without any loss even after 15 000 cycles while retaining ≈100% coulombic efficiency. This work underscores the potential of bimetallic PBA materials with conductive rGO backbone for overcoming the limitations of current MXene-based protic HSCs, highlighting the significance of this work.

Serial Nitrogen-Doped Metal/Carbon Composites Derived from Organic Salts for Superior Electromagnetic Wave Absorption and Supercapacitor Electrode.

The present study provides a facile one-pot pyrolysis strategy to prepare serial nitrogen-doped (N-doped) metal/carbon composites derived from six types of metal ethylenediaminetetraacetic acid (EDTA-M, M = Co, Cu, Mn, Fe, Mg, and Ca). N-doped Co/C composite integrated carbonaceous with magnetic components to attain dielectric-magnetic double loss mechanisms. The minimum reflection loss and effective absorption bandwidth reached -57.6 dB at 1.75 mm and 4.64 GHz at 1.52 mm, respectively. The electromagnetic simulation further confirms that the dissipation ability increases with the improvement of carbonization temperature. Results show that altering the metal species of precursors can significantly improve the electrochemical performance of the composites using the identical strategy. N-doped Cu/C composite performed a maximum specific capacitance of 2383.3 F g-1 at 0.5 A g-1 -1, and maintained 86.3% cycling stability at 20 A g-1 after 5000 cycles. The energy density of a symmetrical two-electrode configuration achieved 350.13 Wh kg-1 at a power density of 4000.04 W kg-1. Density functional theory calculations indicate that nitrogen dopants cause faster ion transport and stronger adsorption capacity. Moreover, the bifunctionality of other composites types are also systematically characterized.

Scaling Supercapacitive Swing Adsorption of CO2 Using Bipolar Electrode Stacks.

Supercapacitive swing adsorption (SSA) modules with bipolar stacks having 2, 4, 8, and 12 electrode pairs made from BPL 4 × 6 activated carbon are constructed and tested for carbon dioxide capture applications. Tests are performed with simulated flue gas (15%CO2 /85%N2) at 2, 4, 8, and 12 V, respectively. Reversible adsorption with sorption capacities (≈58 mmol kg-1) and adsorption rates (≈38 µmol kg-1 s-1) are measured for all stacks. The productivity scales with the number of cells in the module, and increases from 70 to 390 mmol h-1 m-2. The energy efficiency and energy consumption improve with increasing number of bipolar electrodes from 67% to 84%, and 142 to 60 kJ mol-1, respectively. Overall, the results show that SSA modules with bipolar electrodes can be scaled without reducing the adsorptive performance, and with improvement of energetic performance.

Stoichiometrically Optimized Electrochromic Complex [V2O2+ξ(OH)3-ξ] Based Electrode: Prototype Supercapacitor with Multicolor Indicator.

The systematic structure modification of metal oxides is becoming more attractive, and effective strategies for structural tunning are highly desirable for improving their practical color-modulating energy storage performances. Here, the ability of a stoichiometrically tuned oxide-hydroxide complex of porous vanadium oxide, namely [V2O2+ξ(OH)3-ξ]ξ = 0:3 for multifunctional electrochromic supercapacitor application is demonstrated. Theoretically, the pre-optimized oxide complex is synthesized using a simple wet chemical etching technique in its optimized stoichiometry [V2O2+ξ(OH)3-ξ] with ξ = 0, providing more electroactive surface sites. The multifunctional electrode shows a high charge storage property of 610 Fg-1 at 1A g-1, as well as good electrochromic properties with high color contrast of 70% and 50% at 428 and 640 nm wavelengths, faster switching, and high coloration efficiency. When assembled in a solid-state symmetric electrochromic supercapacitor device, it exhibits an ultrahigh power density of 1066 mWcm-2, high energy density of 246 mWhcm-2, and high specific capacitance of 290 mFcm-2 at 0.2 mAcm-2. A prepared prototype device displays red when fully charged, green when half charged, and blue when fully discharged. A clear evidence of optimizing the multifunctional performance of electrochromic supercapacitor by stoichiometrical tuning is presented along with demonstrating a device prototype of a 25 cm2 large device for real-life applications.