Solution‐Processing of High‐Purity Semiconducting Single‐Walled Carbon Nanotubes for Electronics Devices

High‐purity semiconducting single‐walled carbon nanotubes (s‐SWCNTs) are of paramount significance for the construction of next‐generation electronics. Until now, a number of elaborate sorting and purification techniques for s‐SWCNTs have been developed, among which solution‐based sorting methods show unique merits in the scale production, high purity, and large‐area film formation. Here, the recent progress in the solution processing of s‐SWCNTs and their application in electronic devices is systematically reviewed. First, the solution‐based sorting and purification of s‐SWCNTs are described, and particular attention is paid to the recent advance in the conjugated polymer‐based sorting strategy. Subsequently, the solution‐based deposition and morphology control of a s‐SWCNT thin film on a surface are introduced, which focus on the strategies for network formation and alignment of SWCNTs. Then, the recent advances in electronic devices based on s‐SWCNTs are reviewed with emphasis on nanoscale s‐SWCNTs' high‐performance integrated circuits and s‐SWCNT‐based thin‐film transistors (TFT) array and circuits. Lastly, the existing challenges and development trends for the s‐SWCNTs and electronic devices are briefly discussed. The aim is to provide some useful information and inspiration for the sorting and purification of s‐SWCNTs, as well as the construction of electronic devices with s‐SWCNTs.     

Aerosol‐Assisted Heteroassembly of Oxide Nanocrystals and Carbon Nanotubes into 3D Mesoporous Composites for High‐Rate Electrochemical Energy Storage

Nanostructured composites built from ordinary building units have attracted much attention because of their collective properties for critical applications. Herein, we have demonstrated the heteroassembly of carbon nanotubes and oxide nanocrystals using an aerosol spray method to prepare nanostructured mesoporous composites for electrochemical energy storage. The designed composite architectures show high conductivity and hierarchically structured mesopores, which achieve rapid electron and ion transport in electrodes. Therefore, as‐synthesized carbon nanotube/TiO₂ electrodes exhibit high rate performance through rapid Li⁺ intercalation, making them suitable for ultrafast energy storage devices. Moreover, the synthesis process provides a broadly applicable method to achieve the heteroassembly of vast low‐dimensional building blocks for many important applications.     

Carbon‐Based Functional Materials Derived from Waste for Water Remediation and Energy Storage

Carbon‐based functional materials hold the key for solving global challenges in the areas of water scarcity and the energy crisis. Although carbon nanotubes (CNTs) and graphene have shown promising results in various fields of application, their high preparation cost and low production yield still dramatically hinder their wide practical applications. Therefore, there is an urgent call for preparing carbon‐based functional materials from low‐cost, abundant, and sustainable sources. Recent innovative strategies have been developed to convert various waste materials into valuable carbon‐based functional materials. These waste‐derived carbon‐based functional materials have shown great potential in many applications, especially as sorbents for water remediation and electrodes for energy storage. Here, the research progress in the preparation of waste‐derived carbon‐based functional materials is summarized, along with their applications in water remediation and energy storage; challenges and future research directions in this emerging research field are also discussed.     

Selective Growth of Metal‐Free Metallic and Semiconducting Single‐Wall Carbon Nanotubes

A major obstacle for the use of single‐wall carbon nanotubes (SWCNTs) in electronic devices is their mixture of different types of electrical conductivity that strongly depends on their helical structure. The existence of metal impurities as a residue of a metallic growth catalyst may also lower the performance of SWCNT‐based devices. Here, it is shown that by using silicon oxide (SiO_x) nanoparticles as a catalyst, metal‐free semiconducting and metallic SWCNTs can be selectively synthesized by the chemical vapor deposition of ethanol. It is found that control over the nanoparticle size and the content of oxygen in the SiO_x catalyst plays a key role in the selective growth of SWCNTs. Furthermore, by using the as‐grown semiconducting and metallic SWCNTs as the channel material and source/drain electrodes, respectively, all‐SWCNT thin‐film transistors are fabricated to demonstrate the remarkable potential of these SWCNTs for electronic devices.     

Cellulose‐Based Nanomaterials for Energy Applications

Cellulose is the most abundant natural polymer on earth, providing a sustainable green resource that is renewable, degradable, biocompatible, and cost effective. Recently, nanocellulose‐based mesoporous structures, flexible thin films, fibers, and networks are increasingly developed and used in photovoltaic devices, energy storage systems, mechanical energy harvesters, and catalysts components, showing tremendous materials science value and application potential in many energy‐related fields. In this Review, the most recent advancements of processing, integration, and application of cellulose nanomaterials in the areas of solar energy harvesting, energy storage, and mechanical energy harvesting are reviewed. For solar energy harvesting, promising applications of cellulose‐based nanostructures for both solar cells and photoelectrochemical electrodes development are reviewed, and their morphology‐related merits are discussed. For energy storage, the discussion is primarily focused on the applications of cellulose‐based nanomaterials in lithium‐ion batteries, including electrodes (e.g., active materials, binders, and structural support), electrolytes, and separators. Applications of cellulose nanomaterials in supercapacitors are also reviewed briefly. For mechanical energy harvesting, the most recent technology evolution in cellulose‐based triboelectric nanogenerators is reviewed, from fundamental property tuning to practical implementations. At last, the future research potential and opportunities of cellulose nanomaterials as a new energy material are discussed.     

Recent Progress in Iron‐Based Electrode Materials for Grid‐Scale Sodium‐Ion Batteries

Grid‐scale energy storage batteries with electrode materials made from low‐cost, earth‐abundant elements are needed to meet the requirements of sustainable energy systems. Sodium‐ion batteries (SIBs) with iron‐based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid‐scale energy storage systems. Although various iron‐based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron‐based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure–composition–performance relationships, merits and drawbacks of iron‐based electrode materials for SIBs are discussed. Such iron‐based electrode materials will be competitive and attractive electrodes for next‐generation energy storage devices.     

Thread‐like Supercapacitors Based on One‐Step Spun Nanocomposite Yarns

Thread‐like electronic devices have attracted great interest because of their potential applications in wearable electronics. To produce high‐performance, thread‐like supercapacitors, a mixture of stable dispersions of single‐walled carbon nanotubes and conducting polyaniline nanowires are prepared. Then, the mixture is spun into flexible yarns with a polyvinyl alcohol outer sheath by a one‐step spinning process. The composite yarns show excellent mechanical properties and high electrical conductivities after sufficient washing to remove surfactants. After applying a further coating layer of gel electrolyte, two flexible yarns are twisted together to form a thread‐like supercapacitor. The supercapacitor based on these two yarns (SWCNTs and PAniNWs) possesses a much higher specific capacitance than that based only on pure SWCNTs yarns, making it an ideal energy‐storage device for wearable electronics.     

Toward Wearable Self‐Charging Power Systems: The Integration of Energy‐Harvesting and Storage Devices

One major challenge for wearable electronics is that the state‐of‐the‐art batteries are inadequate to provide sufficient energy for long‐term operations, leading to inconvenient battery replacement or frequent recharging. Other than the pursuit of high energy density of secondary batteries, an alternative approach recently drawing intensive attention from the research community, is to integrate energy‐generation and energy‐storage devices into self‐charging power systems (SCPSs), so that the scavenged energy can be simultaneously stored for sustainable power supply. This paper reviews recent developments in SCPSs with the integration of various energy‐harvesting devices (including piezoelectric nanogenerators, triboelectric nanogenerators, solar cells, and thermoelectric nanogenerators) and energy‐storage devices, such as batteries and supercapacitors. SCPSs with multiple energy‐harvesting devices are also included. Emphasis is placed on integrated flexible or wearable SCPSs. Remaining challenges and perspectives are also examined to suggest how to bring the appealing SCPSs into practical applications in the near future.     

Chemical‐to‐Electricity Carbon: Water Device

The ability to release, as electrical energy, potential energy stored at the water:carbon interface is attractive, since water is abundant and available. However, many previous reports of such energy converters rely on either flowing water or specially designed ionic aqueous solutions. These requirements restrict practical application, particularly in environments with quiescent water. Here, a carbon‐based chemical‐to‐electricity device that transfers the chemical energy to electrical form when coming into contact with quiescent deionized water is reported. The device is built using carbon nanotube yarns, oxygen content of which is modulated using oxygen plasma‐treatment. When immersed in water, the device discharges electricity with a power density that exceeds 700 mW m^?2, one order of magnitude higher than the best previously published result. X‐ray absorption and density functional theory studies support a mechanism of operation that relies on the polarization of sp² hybridized carbon atoms. The devices are incorporated into a flexible fabric for powering personal electronic devices.     

Flexible Energy‐Storage Devices: Design Consideration and Recent Progress

Flexible energy‐storage devices are attracting increasing attention as they show unique promising advantages, such as flexibility, shape diversity, light weight, and so on; these properties enable applications in portable, flexible, and even wearable electronic devices, including soft electronic products, roll‐up displays, and wearable devices. Consequently, considerable effort has been made in recent years to fulfill the requirements of future flexible energy‐storage devices, and much progress has been witnessed. This review describes the most recent advances in flexible energy‐storage devices, including flexible lithium‐ion batteries and flexible supercapacitors. The latest successful examples in flexible lithium‐ion batteries and their technological innovations and challenges are reviewed first. This is followed by a detailed overview of the recent progress in flexible supercapacitors based on carbon materials and a number of composites and flexible micro‐supercapacitors. Some of the latest achievements regarding interesting integrated energy‐storage systems are also reviewed. Further research direction is also proposed to surpass existing technological bottle‐necks and realize idealized flexible energy‐storage devices.     

Photon‐Pair Generation with a 100 nm Thick Carbon Nanotube Film

Nonlinear optics based on bulk materials is the current technique of choice for quantum‐state generation and information processing. Scaling of nonlinear optical quantum devices is of significant interest to enable quantum devices with high performance. However, it is challenging to scale the nonlinear optical devices down to the nanoscale dimension due to relatively small nonlinear optical response of traditional bulk materials. Here, correlated photon pairs are generated in the nanometer scale using a nonlinear optical device for the first time. The approach uses spontaneous four‐wave mixing in a carbon nanotube film with extremely large Kerr‐nonlinearity (≈100 000 times larger than that of the widely used silica), which is achieved through careful control of the tube diameter during the carbon nanotube growth. Photon pairs with a coincidence to accidental ratio of 18 at the telecom wavelength of 1.5 µm are generated at room temperature in a ≈100 nm thick carbon nanotube film device, i.e., 1000 times thinner than the smallest existing devices. These results are promising for future integrated nonlinear quantum devices (e.g., quantum emission and processing devices).     

Microstructure Design of Carbonaceous Fibers: A Promising Strategy toward High‐Performance Weaveable/Wearable Supercapacitors

Fiber‐based supercapacitors (FSCs) possess great potential as an ideal type of power source for future weaveable/wearable electronics and electronic‐textiles. The performance of FSCs is, without doubt, primarily determined by the properties of fibrous electrodes. Carbonaceous fibers, e.g., commercial carbon fibers, newly developed graphene fibers, and carbon nanotube fibers, are deemed as promising materials for weaveable/wearable supercapacitors owing to their exotic properties including high tensile strength and robustness, excellent electrical conductivity, good flexibility, and environmental stability. Nevertheless, bare carbonaceous fiber normally exhibits low capacitance originating from electric double‐layer capacitance, which remains unsatisfactory for efficiently powering wearable and portable devices. Numerous efforts have been devoted to tailoring fiber properties by hybridizing pseudocapacitive materials, and impressive progress has been achieved thus far. Herein, the microstructures of pristine carbonaceous fibers are introduced in detail, and the recent advances in rational nano/microstructure design of their hybrids, which provides the feasibility to achieve the synergistic interaction between conductive agents and pseudocapacitive nanomaterials but are normally overlooked, are comprehensively reviewed. Besides, the challenges in developing high‐performance fibrous electrodes are also elaborately discussed.     

Carbon‐Based Microbial‐Fuel‐Cell Electrodes: From Conductive Supports to Active Catalysts

Microbial fuel cells (MFCs) have attracted considerable interest due to their potential in renewable electrical power generation using the broad diversity of biomass and organic substrates. However, the difficulties in achieving high power densities and commercially affordable electrode materials have limited their industrial applications to date. Carbon materials, which can exhibit a wide range of different morphologies and structures, usually possess physiological activity to interact with microorganisms and are therefore fast‐emerging electrode materials. As the anode, carbon materials can significantly promote interfacial microbial colonization and accelerate the formation of extracellular biofilms, which eventually promotes the electrical power density by providing a conductive microenvironment for extracellular electron transfer. As the cathode, carbon‐based materials can function as catalysts for the oxygen‐reduction reaction, showing satisfying activities and efficiencies nowadays even reaching the performance of Pt catalysts. Here, first, recent advancements on the design of carbon materials for anodes in MFCs are summarized, and the influence of structure and surface functionalization of different types of carbon materials on microorganism immobilization and electrochemical performance is elucidated. Then, synthetic strategies and structures of typical carbon‐based cathodes in MFCs are briefly presented. Furthermore, future applications of carbon‐electrode‐based MFC devices in the energy, environmental, and biological fields are discussed, and the emerging challenges in transferring them from laboratory to industrial scale are described.     

The effect of Stone–Wales defect on the tensile behavior and fracture of single-walled carbon nanotubes

The effectiveness of carbon nanotubes as reinforcements in the next generation of composites is designated by their mechanical behavior as standalone units. One of the most commonly present topological defects, whose effect on the mechanical behavior of carbon nanotubes needs to be clarified, is the Stone–Wales (SW) defect. In this paper, the effect of SW defect on the tensile behavior and fracture of armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs) was studied using an atomistic-based progressive fracture model. The model uses the finite element method for analyzing the structure of SWCNTs and the modified Morse interatomic potential for describing the nonlinear force-field of the C–C bonds. In all cases examined, the SW defect serves as nucleation site for fracture. Its effect on the tensile behavior of the SWCNTs depends solely on nanotube chirality. In armchair SWCNTs, contrary to zigzag ones, a significant reduction in failure stress and failure strain was predicted; ranging from 18% to 25% and from 30% to 41%, respectively. In chiral SWCNTs, the effect of the defect is between those of the armchair and zigzag SWCNTs, depending on chiral angle. The stiffness of the nanotubes was not affected. The nanotube size was found to play a minimal role in the tensile behavior of SW-defected SWCNTs; only in cases of very small nanotube diameters, where the fraction of defect area to the nanotube area is high, was a larger decrease in the failure stress predicted.     

Carbon‐Based Photocathode Materials for Solar Hydrogen Production

Hydrogen is considered a promising environmentally friendly energy carrier for replacing traditional fossil fuels. In this context, photoelectrochemical cells effectively convert solar energy directly to H₂ fuel by water photoelectrolysis, thereby monolitically combining the functions of both light harvesting and electrolysis. In such devices, photocathodes and photoanodes carry out the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. Here, the focus is on photocathodes for HER, traditionally based on metal oxides, III–V group and II–VI group semiconductors, silicon, and copper‐based chalcogenides as photoactive material. Recently, carbon‐based materials have emerged as reliable alternatives to the aforementioned materials. A perspective on carbon‐based photocathodes is provided here, critically analyzing recent research progress and outlining the major guidelines for the development of efficient and stable photocathode architectures. In particular, the functional role of charge‐selective and protective layers, which enhance both the efficiency and the durability of the photocathodes, is discussed. An in‐depth evaluation of the state‐of‐the‐art fabrication of photocathodes through scalable, high‐troughput, cost‐effective methods is presented. The major aspects on the development of light‐trapping nanostructured architectures are also addressed. Finally, the key challenges on future research directions in terms of potential performance and manufacturability of photocathodes are analyzed.     

A Binder‐Free and Free‐Standing Cobalt Sulfide@Carbon Nanotube Cathode Material for Aluminum‐Ion Batteries

Rechargeable aluminum‐ion batteries (AIBs) are considered as a new generation of large‐scale energy‐storage devices due to their attractive features of abundant aluminum source, high specific capacity, and high energy density. However, AIBs suffer from a lack of suitable cathode materials with desirable capacity and long‐term stability, which severely restricts the practical application of AIBs. Herein, a binder‐free and self‐standing cobalt sulfide encapsulated in carbon nanotubes is reported as a novel cathode material for AIBs. The resultant new electrode material exhibits not only high discharge capacity (315 mA h g⁻¹ at 100 mA g⁻¹) and enhanced rate performance (154 mA h g⁻¹ at 1 A g⁻¹), but also extraordinary cycling stability (maintains 87 mA h g⁻¹ after 6000 cycles at 1 A g⁻¹). The free‐standing feature of the electrode also effectively suppresses the side reactions and material disintegrations in AIBs. The new findings reported here highlight the possibility for designing high‐performance cathode materials for scalable and flexible AIBs.     

Hybrid Films of Graphene and Carbon Nanotubes for High Performance Chemical and Temperature Sensing Applications

A hybrid composite material of graphene and carbon nanotube (CNT) for high performance chemical and temperature sensors is reported. Integration of 1D and 2D carbon materials into hybrid carbon composites is achieved by coupling graphene and CNT through poly(ionic liquid) (PIL) mediated‐hybridization. The resulting CNT/PIL/graphene hybrid materials are explored as active materials in chemical and temperature sensors. For chemical sensing application, the hybrid composite is integrated into a chemo‐resistive sensor to detect a general class of volatile organic compounds. Compared with the graphene‐only devices, the hybrid film device showed an improved performance with high sensitivity at ppm level, low detection limit, and fast signal response/recovery. To further demonstrate the potential of the hybrid films, a temperature sensor is fabricated. The CNT/PIL/graphene hybrid materials are highly responsive to small temperature gradient with fast response, high sensitivity, and stability, which may offer a new platform for the thermoelectric temperature sensors.     

Single Chirality (6,4) Single‐Walled Carbon Nanotubes for Fluorescence Imaging with Silicon Detectors

Postsynthetic single‐walled carbon nanotube (SWCNT) sorting methods such as density gradient ultracentrifugation, gel chromatography, and electrophoresis have all been inspired by established biochemistry separation techniques designed to separate subcellular components. Biochemistry separation techniques have been refined to the degree that parameters such as pH, salt concentration, and temperature are necessary for a successful separation, yet these conditions are only now being applied to SWCNT separation methodologies. Slight changes in pH produce radically different behaviors of SWCNTs inside a density gradient, allowing for the facile separation of ultrahigh purity (6,4) SWCNTs from as‐synthesized carbon nanotubes. The (6,4) SWCNTs are novel fluorophores emitting below ≈900 nm and can be easily detected with conventional silicon‐based charge‐coupled device detectors without the need for specialized InGaAs cameras. The (6,4) SWCNTs are used to demonstrate their potential as a clinically relevant NIR‐I fluorescence stain for the immunohistochemical staining of cells and cancer tissue sections displaying high endothelial growth factor receptor levels.     

Ink Processing for Thermoelectric Materials and Power‐Generating Devices

The growing concern over the depletion of hydrocarbon resources, and the adverse environmental effects associated with their use, has increased the demand for renewable energy sources. Thermoelectric (TE) power generation from waste heat has emerged as a renewable energy source that does not generate any pollutants. Recently, ink‐based processing for the preparation of TE materials has attracted tremendous attention because of the simplicity in design of power generators and the possibility of cost‐effective manufacturing. In this progress report, recent advances in the development of TE inks, processing techniques, and ink‐fabricated devices are reviewed. A summary of typical formulations of TE materials as inks is included, as well as a discussion on various ink‐based fabrication methods, with several examples of newly designed devices fabricated using these techniques. Finally, the prospects of this field with respect to the industrialization of TE power generation technology are presented.     

Rational Design of Carbon‐Rich Materials for Energy Storage and Conversion

Carbon‐rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom‐up constructed carbon‐rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon‐rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp² carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure–property relationships of the resultant carbon‐rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon‐rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon‐rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.