Recent Advancement of Nanostructured Carbon for Energy Applications

Electrocatalytic Isoxazoline-Nanocarbon Metal Complexes

We report the synthesis of new carbon-nanomaterial-based metal chelates that enable effective electronic coupling to electrocatalytic transition metals. In particular, multiwalled carbon nanotubes (MWCNTs) and few-layered graphene (FLG) were covalently functionalized by a microwave-assisted cycloaddition with nitrile oxides to form metal-binding isoxazoline functional groups with high densities. The covalent attachment was evidenced by Raman spectroscopy, and the chemical identity of the surface functional groups was confirmed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The functional carbon nanomaterials effectively chelate precious metals Ir(III), Pt(II), and Ru(III), as well as earth-abundant metals such as Ni(II), to afford materials with metal contents as high as 3.0 atom %. The molecularly dispersed nature of the catalysts was confirmed by X-ray absorption spectroscopy (XAS) and energy-dispersive X-ray spectroscopy (STEM-EDS) elemental mapping. The interplay between the chelate structure on the graphene surface and its metal binding ability has also been investigated by a combination of experimental and computational studies. The defined ligands on the graphene surfaces enable the formation of structurally precise heterogeneous molecular catalysts. The direct attachment of the isoxazoline functional group on the graphene surfaces provides strong electronic coupling between the chelated metal species and the conductive carbon nanomaterial support. We demonstrate that the metal-chelated carbon nanomaterials are effective heterogeneous catalysts in the oxygen evolution reaction with low overpotentials and tunable catalytic activity.

An Ultra-Long-Lived Triplet Excited State in Water at Room Temperature: Insights on the Molecular Design of Tridecafullerenes

Suitably engineered molecular systems exhibiting triplet excited states with very long lifetimes are important for high-end applications in nonlinear optics, photocatalysis, or biomedicine. We report the finding of an ultra-long-lived triplet state with a mean lifetime of 93 ms in an aqueous phase at room temperature, measured for a globular tridecafullerene with a highly compact glycodendrimeric structure. A series of three tridecafullerenes bearing different glycodendrons and spacers to the C60 units have been synthesized and characterized. UV/Vis spectra and DLS experiments confirm their aggregation in water. Steady-state and time-resolved fluorescence experiments suggest a different degree of inner solvation of the multifullerenes depending on their molecular design. Efficient quenching of the triplet states by O2 but not by waterborne azide anions has been observed. Molecular modelling reveals dissimilar access of the aqueous phase to the internal structure of the tridecafullerenes, differently shielded by the glycodendrimeric shell.

Self-Template Synthesis of Nitrogen-Doped Hollow Carbon Nanospheres with Rational Mesoporosity for Efficient Supercapacitors

Rational design and economic fabrication are essential to develop carbonic electrode materials with optimized porosity for high-performance supercapacitors. Herein, nitrogen-doped hollow carbon nanospheres (NHCSs) derived from resorcinol and formaldehyde resin are successfully prepared via a self-template strategy. The porosity and heteroatoms in the carbon shell can be adjusted by purposefully introducing various dosages of ammonium ferric citrate (AFC). Under the optimum AFC dosage (30 mg), the as-prepared NHCS-30 possesses hierarchical architecture, high specific surface area up to 1987 m²·g^-1, an ultrahigh mesopore proportion of 98%, and moderate contents of heteroatoms, and these features endow it with a high specific capacitance of 206.5 F·g^-1 at 0.2 A·g^-1, with a good rate capability of 125 F·g^-1 at 20 A·g^-1 as well as outstanding electrochemical stability after 5000 cycles in a 6 M KOH electrolyte. Furthermore, the assembled NHCS-30 based symmetric supercapacitor delivers an energy density of 14.1 W·h·kg^-1 at a power density of 200 W·kg^-1 in a 6 M KOH electrolyte. This work provides not only an appealing model to study the effect of structural and component change on capacitance, but also general guidance to expand functionality electrode materials by the self-template method.

Bio-nanocomposites of graphene with biopolymers; fabrication, properties, and applications

The unique properties of graphene and graphene oxide (GO) nanocomposites make them suitable for a wide range of medical, industrial, and agricultural applications. The addition of graphene or GO to a polymeric matrix can ameliorate its thermo-mechanical, electrical, and barrier characteristics. The present paper reviews the literature on graphene/GO-based bio-nanocomposites and examines the various fabrication methods, such as chemical vapor deposition, chemical synthesis, microwave synthesis, the solvothermal method, molecular beam epitaxy, and colloidal suspension. Each procedure potentially has its disadvantages, especially for mass production. Therefore, introducing an effective method for fabricating graphene on a large scale with high quality is essential. Recent studies have shown that graphene-based bio-nanocomposites are promising materials given their excellent performance in the development of biosensors, drug delivery systems, antimicrobials, modified electrodes, and energy storage systems among other applications. In this review, we evaluate the various procedures used for developing graphene/GO-based bio-nanocomposites and examine the features and applications of the related products. Furthermore, the toxicity of these compounds and attempts to uncover the optimal combinations of biopolymers and carbon nanomaterials for industrial applications will be discussed.

One-Dimensional (1D) Nanostructured Materials for Energy Applications

At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal, and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized, which undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes, and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface-volume relationship, tunable thermal and transport properties, and its high surface area, these 1D nanostructures have become fundamental elements for the development of energy processes. The most relevant 1D nanomaterials, their different synthesis procedures, and useful methods for assembling 1D nanostructures in functional devices will be presented. Applications in relevant topics such as optoelectronic and photochemical devices, hydrogen production, or energy storage, among others, will be discussed. The present review concludes with a forecast on the directions towards which future research could be directed on this class of nanostructured materials.

Hazardous Petroleum Sludge-Derived Nitrogen and Oxygen Co-Doped Carbon Material with Hierarchical Porous Structure for High-Performance All-Solid-State Supercapacitors

Rational design and sustainable preparation of high-performance carbonaceous electrode materials are important to the practical application of supercapacitors. In this work, a cost-effective synthesis strategy for nitrogen and oxygen co-doped porous carbon (NOC) from petroleum sludge waste was developed. The hierarchical porous structure and ultra-high surface area (2514.7 m² g⁻¹) of NOC electrode materials could provide an efficient transport path and capacitance active site for electrolyte ions. The uniform co-doping of N and O heteroatoms brought enhanced wettability, electrical conductivity and probably additional pseudo-capacitance. The as-obtained NOC electrodes exhibited a high specific capacitance (441.2 F g⁻¹ at 0.5 A g⁻¹), outstanding rate capability, and cycling performance with inconspicuous capacitance loss after 10,000 cycles. Further, the assembled all-solid-state MnO₂/NOC asymmetrical supercapacitor device (ASC) could deliver an excellent capacitance of 119.3 F g⁻¹ at 0.2 A g⁻¹ under a wide potential operation window of 0–1.8 V with flexible mechanical stability. This ASC device yielded a superior energy density of 53.7 W h kg⁻¹ at a power density of 180 W kg⁻¹ and a reasonable cycling life. Overall, this sustainable, low-cost and waste-derived porous carbon electrode material might be widely used in the field of energy storage, now and into the foreseeable future.

A robust magnesiothermic reduction combined self-activation strategy towards highly-curved carbon nanosheets for advanced zinc-ion hybrid supercapacitors applications

Aqueous zinc-ion hybrid supercapacitors are considered to be a newly emerging electrochemical energy storage devices. However, the exploration and design of advanced cathode materials remain a huge challenge. Herein, we developed a versatile one-step magnesiothermic reduction and self-activation process for the synthesis of highly-curved carbon nanosheets (HCCNs) with hierarchical pore structures. In this process, low-molecular weight organic potassium salts (e.g. potassium bitartrate, potassium acetate, potassium oxalate, potassium formate, potassium oleate, potassium sorbate), which usually used as the chemical activating reagents, serve as the carbon source whereas the Mg power acts as the reducing agent. The resulting HCCNs possess hierarchical porosity and unique HCCN geometry which can afford abundant active sites for charge accumulation as well as the highly efficient ions diffusion kinetics. Because of the high ratio of surface-controlled capacitive contribution and high ions diffusion coefficient, the optimized sample can exhibit excellent charge storage performance with an impressive reversible capacity (200.2 mAh g^-1), excellent rate capability, and good cyclic stability. The excellent capacitive behaviors combined with the feasible synthetic procedure make the present synthetic protocol a promising choice towards well-designed nanocarbons for electrochemical energy storage applications.

Nacre-inspired composite films with high mechanical strength constructed from MXenes and wood-inspired hydrothermal cellulose-based nanofibers for high performance flexible supercapacitors

Two dimensional MXenes with fascinating characteristics of high electrical conductivity, high density and electroactivity show promising applications in various fields. However, the direct applications of MXenes have been limited due to their inferior mechanical properties and easy restacking. Herein, a kind of nacre-like composite film constructed with Ti3C2Tx, cellulose nanofiber (HCNF) and sodium lignosulfonate (Lig) obtained through the hydrothermal process, named Ti3C2Tx/HCNF@Lig, has been successfully synthesized. The hydrothermal cellulose nanofiber (HCNF) film shows an enhanced mechanical strength (114 MPa) compared to that of the CNF film (95 MPa). Wood-inspired HCNF@Lig composite films present an enhanced mechanical tensile strength of up to 133 MPa. Nacre-like deformable Ti3C2Tx/HCNF@Lig(3@1) composite films exhibit high conductivity (up to 1.75 × 105 S m-1) and mechanical properties (up to 258 MPa). The electrodes of Ti3C2Tx/HCNF@Lig(3@1)97/3 composite film assembled flexible solid-state supercapacitors possess an excellent volumetric specific capacitance of 748.96 F cm-3. The corresponding deformable supercapacitors show an excellent energy density of 16.2 W h L-1 and outstanding electrochemical cycling stability. The as-prepared nacre-like Ti3C2Tx/HCNF@Lig composite films with high mechanical properties and electrochemical performance are expected to be practically applied in flexible/wearable energy storage devices.

A high-voltage quasi-solid-state flexible supercapacitor with a wide operational temperature range based on a low-cost "water-in-salt" hydrogel electrolyte

Recently, "water-in-salt" electrolytes have provided a huge boost to the realization of high energy density for water-based supercapacitors by broadening the electrochemical stability window. However, the high cost and low conductivity of high concentration LiTFSI greatly restrict the possibility of practical application. Herein, we adopt a new strategy to develop a low-cost and quasi-solid-state polyelectrolyte hydrogel accommodating a superhigh concentration of CH₃COOK through in situ polymerization, avoiding the problem that many conventional polymers cannot accommodate ultra-high ion concentration. The polyelectrolyte hydrogel with 24 M CH₃COOK exhibits a conductivity of up to 35.8 mS cm^-1 and a stretchability of 950%. With advanced N-doped graphene hydrogel electrodes, the assembled supercapacitor yields a voltage window of 2.1 V with an energy density of 33.0 W h kg^-1 and superior cyclability with 88.2% capacitance retention at 4 A g^-1 after 6000 cycles comparable to those supercapacitors using high-cost LiTFSI salts. Besides, the supercapacitor with excellent temperature stability in the range of -20 to 70 °C can light an LED for more than one minute. The assembled flexible device with the PAAK/CMC-24 M gel film sandwiched in between demonstrates excellent bendability from 0° to 180° and shows great potential for flexible/wearable electronic devices. Our feasible approach provides a new route for assembling quasi-solid-state flexible high-energy storage devices with "water-in-salt" electrolytes.

Recent advances in electroanalytical drug detection by porphyrin/phthalocyanine macrocycles: developments and future perspectives

Porphyrins and phthalocyanines used to construct sensors for electroanalytical drug detection.

Carbon materials for ion-intercalation involved rechargeable battery technologies

The development of carbon electrode materials for rechargeable batteries is reviewed from the perspective of structural features, electrochemistry, and devices.

Controllable synthesis of spherical carbon particles transition from dense to hollow structure derived from Kraft lignin

The tailored synthesis of carbon particles with controllable shapes and structures from biomass as a raw material would be highly beneficial to meet the demands of various applications of carbon materials from the viewpoint of sustainable development goals. In this work, the spherical carbon particles were successfully synthesized through a spray drying method followed by the carbonization process, using Kraft lignin as the carbon source and potassium hydroxide (KOH) as the activation agent. As the results, the proposed method successfully controlled the shape and structure of the carbon particles from dense to hollow by adjusting the KOH concentration. Especially, this study represents the first demonstration that KOH plays a crucial role in the formation of particles with good sphericity and dense structures. In addition, to obtain an in-depth understanding of the particle formation of carbon particles, a possible mechanism is also investigated in this article. The resulting spherical carbon particles exhibited dense structures with a specific surface area (1233 m²g^-1) and tap density (1.46 g cm^-3) superior to those of irregular shape carbon particles.

Bioinspired Assembly of Double Honeycomb-Like Hierarchical Capsule Confined Encapsulation with Functional Micro/Nanocrystals

Inspired by "micro/nanoreactor" effect of cellular organelle on specific biochemical reactions, a double honeycomb-like hierarchical capsule confined encapsulation with functional micro/nanocrystals is designed. The bioinspired hierarchical capsules derived from polymeric composite microspheres are successfully fabricated through a combination of selective chemical etching and pyrolysis. In situ introduction of functional guests (including organometallic molecules, tetraethoxysilane, or metal-organic frameworks (MOFs)) into internal cellular structure of microspheres is first put forward by phase inversion method. The development of selective etching creates honeycomb-like structure on the outside surface of capsule and allows sulfur to homogeneously distribute into matrix. With the novel approach, the hierarchical channels (micro-meso-macropore) of composite capsule enhance transportation of reactants and dispersion of active sites, and thus exhibit superior photocatalytic oxidation and electromagnetic absorbing. The promising strategy will be applied more generally to encapsulate different species into hierarchical capsule with tailored properties and functionalities.

Waffle-Like Carbons Combined with Enriched Mesopores and Highly Heteroatom-Doped Derived from Sandwiched MOF/LDH/MOF for High-Rate Supercapacitor

Supercapacitors (SCs) are promising for powering mobile devices, electric vehicles and smart power grids due to their fast charge/discharge rate, high power capability and robust cycle stability. Nitrogen-doped porous carbons are great alternatives because they provide pseudocapacitance without losing their power rate. Nanoporous carbon derived from metal organic frameworks (MOFs) is an ideal precursor for preparing heteroatom-doped carbons due to their abundant nitrogen contents and incredible specific surface areas. However, severe aggregations and the leakage of nitrogen can occur during harsh carbonization. In this study, we used CoAl-LDH (cobalt aluminum layered double hydroxide) as an in-situ growth substrate, allowing Co-based MOF to uniformly grow onto the CoAl-LDH to form a sandwiched MOF/LDH/MOF structure. After acid etching, we obtained waffle-like nanoporous carbons (WNPC). WNPC exhibited high nitrogen and oxygen retention (7.5 wt% and 9.1 wt%) and a broad mesopores distribution with specific surface areas of 594 m²g⁻¹, which promoted a sieving effect. This renders a specific capacitance of 300.7 F·g⁻¹ at 1 A·g⁻¹ and the high retention (72%) of capacitance at 20 A·g⁻¹, ensuring its use at high-rate supercapacitor electrodes. Finally, the WNPC symmetric supercapacitor reaches a superior specific energy of 27 W·h·kg⁻¹ at a power of 500 W·kg⁻¹, and a good cycle stability (85% capacitance retention after 10,000 cycles).

"Water in salt/ionic liquid" electrolyte for 2.8 V aqueous lithium-ion capacitor

Development of high-voltage electrolytes with non-flammability is significantly important for future energy storage devices. Aqueous electrolytes are inherently non-flammable, easy to handle, and their electrochemical stability windows (ESWs) can be considerably expanded by increasing electrolyte concentrations. However, further breakthroughs of their ESWs encounter bottlenecks because of the limited salt solubility, leading to that most of the high-energy anode materials can hardly function reversibly in aqueous electrolytes. Here, by introducing a non-flammable ionic liquid as co-solvent in a lithium salt/water system, we develop a "water in salt/ionic liquid" (WiSIL) electrolyte with extremely low water content. In such WiSIL electrolyte, commercial niobium pentoxide (Nb₂O₅) material can operate at a low potential (-1.6 V versus Ag/AgCl) and contribute its full capacity. Consequently, the resultant Nb₂O₅-based aqueous lithium-ion capacitor is able to operate at a high voltage of 2.8 V along with long cycling stability over 3000 cycles, and displays comparable energy and power performance (51.9 Wh kg^-1 at 0.37 kW kg^-1 and 16.4 Wh kg^-1 at 4.9 kW kg^-1) to those using non-aqueous electrolytes but with improved safety performance and manufacturing efficiency.

Free-Standing, Foldable V2 O3 /Multichannel Carbon Nanofibers Electrode for Flexible Li-Ion Batteries with Ultralong Lifespan

Free-standing electrodes with high energy density and long life are of critical importance to the development of lithium-ion batteries (LIBs) for flexible/wearable electronic devices. Herein, the free-standing and foldable V₂ O₃ /multichannel carbon nanofibers (V₂ O₃ /MCCNFs) composites are prepared via electrospinning and subsequent carbonization. Such V₂ O₃ /MCCNFs electrode delivers a superior capacity of 881.1 mAh g^-1 at 0.1 A g^-1 after 240 cycles. More importantly, the ultralong lifespan is achieved with a high capacity of 487.8 mAh g^-1 even after 5000 cycles at a high current density of 5 A g^-1 with only 0.00323% decay rate, which shows the best performance among the reported V₂ O₃ -based anodes and other metal oxides based free-standing anodes. Furthermore, this flexible electrode is further applied to the pouch cell, which exhibits prominent capacity of 348.3 mAh g^-1 after 500 cycles at 1 A g^-1 with 0.094% decay per cycle. The unprecedented performance can be ascribed to synergetic contributions of V₂ O₃ and multichannel carbon nanofibers, which not only promote the penetration of electrolyte and reduce the transport length of Li⁺ , but also increase active material/electrolyte contact area and buffer the volume change. This work paves the way to develop free-standing electrode for flexible/wearable electronic devices with ultralong lifespan.

Low-cost 3D porous sea-hedgehog-like NiCo2O4/C as anode for Li-ion battery

Carbon is effective additive to improve cyclic performances of transition metal oxides for lithium ion battery, while common graphene or carbon nanotube is expensive. In this study, waste of rice husk is used to prepare low cost carbon. A composite of NiCo₂O₄/carbon is synthesized via hydrothermal method plus calcination. At hydrothermal time of 6 h, the material displays 3-D sea hedgehog-like structure with radial corn cob-shaped nanorod. The NiCo₂O₄/carbon presents better rate performances, coulombic efficiency and cyclic stability than pristine NiCo₂O₄, showing stable capacity of 1018 mAhg^-1 (52.6% higher than NiCo₂O₄) after 100 cycles at 0.1 Ag^-1. For long-term cycling during 500 cycles at 0.5 Ag^-1, the composite anode exhibits a reversible capacity of ∼880 mAhg^-1, with high retention of 92.2%. The capacity is still retained ∼715 mAhg^-1 even after 1000 cycles at 1 Ag^-1.

Three-Dimensional Cathodes for Electrochemical Reduction of CO2: From Macro- to Nano-Engineering

Rising anthropogenic CO2 emissions and their climate warming effects have triggered a global response in research and development to reduce the emissions of this harmful greenhouse gas. The use of CO2 as a feedstock for the production of value-added fuels and chemicals is a promising pathway for development of renewable energy storage and reduction of carbon emissions. Electrochemical CO2 conversion offers a promising route for value-added products. Considerable challenges still remain, limiting this technology for industrial deployment. This work reviews the latest developments in experimental and modeling studies of three-dimensional cathodes towards high-performance electrochemical reduction of CO2. The fabrication-microstructure-performance relationships of electrodes are examined from the macro- to nanoscale. Furthermore, future challenges, perspectives and recommendations for high-performance cathodes are also presented.

Enhancing the Thermal Performance of a Stearate Phase Change Material with Graphene Nanoplatelets and MgO Nanoparticles

The effectiveness of dispersed nanomaterials to improve the thermal performance of phase change materials (PCMs) is well-proven in the literature. The proposal of new engineered nanoenhanced phase change materials (NePCMs) with customized characteristics may lead to more efficient thermal energy storage (TES) systems. This work is focused on the development of new NePCMs based on the dispersions of graphene nanoplatelets (GnPs) or MgO nanoparticles in a stearate PCM. The new proposed materials were synthesized using a two-step method, and acetic acid was selected as a surfactant to improve the stability of the dispersions. An extensive characterization of the constitutive materials and the developed dispersions using different spectroscopy techniques is reported. Also, the GnP nanopowder was explored by using the XPS technique with the aim to characterize the used carbon nanomaterial. The obtained spectra were investigated in terms of the chemical bonds related to the observed peaks. The thermophysical profile (density, thermal conductivity, isobaric heat capacity, and thermal diffusivity) was experimentally determined once the main components of the NePCMs were characterized and dispersions were designed and developed. This discussion focuses on the differentiated and distinguished effects of the dispersed GnPs and MgO on the properties of the NePCMs. A comprehensive analysis of the measurements to elucidate the mechanism that promoted higher improvements using GnPs instead of MgO was performed.

Three-dimensional hierarchical ZnCo2O4@C3N4-B nanoflowers as high-performance anode materials for lithium-ion batteries

ZnCo2O4 has become one of the most widely used anode materials due to its good specific capacity, cost-efficiency, high thermal stability and environmental benignity. However, its poor conductivity and cycle stability have limited its practical application in lithium-ion batteries. To overcome these issues, we constructed a 3D nanoflower composite material (ZnCo2O4@C3N4-B) by combining ZnCo2O4 as a framework and B-doped g-C3N4 (g-C3N4-B) as a new carbon source material via a simple hydrothermal method. ZnCo2O4@C3N4-B exhibited exceptional specific capacitance of 919.76 mA h g-1 after 500 cycles at 0.2 A g-1 and a long-term capacity retention of 97.8% after 1000 cycles at 2 A g-1. The high reversible capacity, long cycling life and good rate performance could be attributed to the 3D interconnected architecture and doping of g-C3N4-B. This work provides a simple and general strategy to design high-performance anode materials for lithium-ion batteries to meet the needs of practical applications.

Two-Dimensional Mesoporous Carbon Materials Derived from Fullerene Microsheets for Energy Applications

Porous carbon materials rich in defects are promising candidates in energy storage and conversion applications. Herein, a facile template-free approach is reported for the synthesis of a two-dimensional (2 D) mesoporous carbon material derived from fullerene (C₆₀ ) microsheets (FMSs) through simple heat treatment. The sample obtained at 1000 °C (FMS1000) shows a large surface area of 1507.6 m²  g^-1 owing to the presence of mesopores and rich defects, which promote electron and mass transfer in the electrocatalytic process of the oxygen reduction reaction (ORR), showing an excellent performance with an onset potential of 0.95 V, a half-wave potential of 0.85 V, and long-term durability of 2000 cycles, comparable to the performance of commercial Pt/C. Moreover, FMS1000 displays a remarkable supercapacitive property with a specific capacitance of 330.7 F g^-1 at 0.2 A g^-1 and good long-term stability with a capacitance retention of 97 % over 50 000 cycles. Thus, a practical strategy for the production of mesoporous carbon materials with different morphological structures and porous defects as high-performance energy materials is advanced.

Two-Dimensional Carbon-Rich Conjugated Frameworks for Electrochemical Energy Applications

Following a 15-year-long investigation on graphene, two-dimensional (2D) carbon-rich conjugated frameworks (CCFs) have attracted growing research interest as a new generation of multifunctional materials. Typical 2D CCFs include 2D π-conjugated polymers (also classified as 2D π-conjugated covalent organic frameworks) and 2D π-conjugated metal-organic frameworks, which are characterized by layer-stacked periodic frameworks with high in-plane π-conjugation. These unique structures endow 2D CCFs with regular porosities, large specific surface areas, and superior chemical stability. In addition, 2D CCFs exhibit certain notable properties (e.g., excellent electronic conductivity, designable topologies, and defined catalytic/redox-active sites), which have motivated increasing efforts to explore 2D CCFs for electrochemical energy applications. In this Perspective, the structural features and synthetic principles of 2D CCFs are briefly introduced. Moreover, we discuss recent achievements in 2D CCFs designed for various electrochemical energy conversion (electrocatalysis) and storage (supercapacitors and batteries) applications. Particular emphasis is placed on analyzing the precise structural regulation of 2D CCFs. Finally, we provide an outlook about the future development of synthetic 2D CCFs for electrochemical applications, which concerns novel monomer design, chemical methodology/strategy establishment, and a roadmap toward practical applications.

Soft Materials for Wearable/Flexible Electrochemical Energy Conversion, Storage, and Biosensor Devices

Next-generation wearable technology needs portable flexible energy storage, conversion, and biosensor devices that can be worn on soft and curved surfaces. The conformal integration of these devices requires the use of soft, flexible, light materials, and substrates with similar mechanical properties as well as high performances. In this review, we have collected and discussed the remarkable research contributions of recent years, focusing the attention on the development and arrangement of soft and flexible materials (electrodes, electrolytes, substrates) that allowed traditional power sources and sensors to become viable and compatible with wearable electronics, preserving or improving their conventional performances.

Review of the Design of Current Collectors for Improving the Battery Performance in Lithium-Ion and Post-Lithium-Ion Batteries

Current collectors (CCs) are an important and indispensable constituent of lithium-ion batteries (LIBs) and other batteries. CCs serve a vital bridge function in supporting active materials such as cathode and anode materials, binders, and conductive additives, as well as electrochemically connecting the overall structure of anodes and cathodes with an external circuit. Recently, various factors of CCs such as the thickness, hardness, compositions, coating layers, and structures have been modified to improve aspects of battery performance such as the charge/discharge cyclability, energy density, and the rate performance of a cell. In this paper, the details of interesting and useful attempts of preparing CCs for high battery performance in lithium-ion and post-lithium-ion batteries are reviewed. The advantages and disadvantages of these attempts are discussed.

Zeolitic imidazolate framework derived ZnCo2O4 hollow tubular nanofibers for long-life supercapacitors

Uniform one-dimensional metal oxide hollow tubular nanofibers (HTNs) have been controllably prepared using a calcination strategy using electrospun polymer nanofibers as soft templates and zeolitic imidazolate framework nanoparticles as precursors. Utilizing the general synthesis method, the ZnO HTNs, Co3O4 HTNs and ZnCo2O4 HTNs have been successfully prepared. The optimal ZnCo2O4 HTNs, as a representative substance applied in supercapacitors as the positive electrode, delivers a high specific capacity of 181 C g-1 at a current density of 0.5 A g-1, an excellent rate performance of 75.14% and a superior capacity retention of 97.42% after 10 000 cycles. Furthermore, an asymmetric supercapacitor assembled from ZnCo2O4 HTNs and active carbon also shows a stable and ultrahigh cycling stability with 95.38% of its original capacity after 20 000 cycle tests.

Flexible 3D carbon cloth as a high-performing electrode for energy storage and conversion

High-performance energy storage and conversion devices with high energy density, power density and long-term cycling life are of great importance in current consumer electronics, portable electronics and electric vehicles. Carbon materials have been widely investigated and utilized in various energy storage and conversion devices due to their excellent conductivity, mechanical and chemical stability, and low cost. Abundant excellent reviews have summarized the most recent progress and future outlooks for most of the current prime carbon materials used in energy storage and conversion devices, such as carbon nanotubes, fullerene, graphene, porous carbon and carbon fibers. However, the significance of three-dimensional (3D) commercial carbon cloth (CC), one of the key carbon materials with outstanding mechanical stability, high conductivity and flexibility, in the energy storage and conversion field, especially in wearable electronics and flexible devices, has not been systematically summarized yet. In this review article, we present a careful investigation of flexible CC in the energy storage and conversion field. We first give a general introduction to the common properties of CC and the roles it has played in energy storage and conversion systems. Then, we meticulously investigate the crucial role of CC in typical electrochemical energy storage systems, including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries and supercapacitors. Following a description of the wide application potential of CC in electrocatalytic hydrogen evolution, oxygen evolution/reduction, full-water splitting, etc., we will give a brief introduction to the application of CC in the areas of photocatalytically and photoelectrochemically induced solar energy conversion and storage. The review will end with a brief summary of the typical superiorities that CC has in current energy conversion and storage systems, as well as providing some perspectives and outlooks on its future applications in the field. Our main interest will be focused on CC-based flexible devices due to the inherent superiority of CC and the increasing demand for flexible and wearable electronics.

C60(OH)12 and Its Nanocomposite for High-Performance Lithium Storage

Organic carbon materials, such as graphene and nanotubes, with a high specific capacity show promise in improving the energy density for lithium ion batteries (LiBs). Here, we report on the synthesis and characterization of C₆₀(OH)₁₂ and the C₆₀(OH)₁₂/graphene oxide (GO) composite and demonstrate their use as anode materials in LiBs. We find that the C₆₀(OH)₁₂/GO composite forms due to the chemical reactions between the carboxyl and epoxy groups of GO and the hydroxyl of C₆₀(OH)₁₂ nanoparticles and that C₆₀(OH)₁₂ uniformly grows on the surface of GO nanosheets. Using a suite of spectroscopy probes, we unequivocally show the mixing between C₆₀(OH)₁₂ and GO at the molecular level, which leads to superior battery performances. This composite has a reversible capacity of 1596 mAh g^-1 at 0.2 A g^-1, higher than the capacities of C₆₀(OH)₁₂ and GO. This composite has a superior cycling stability and excellent rate performance, making it a promising organic anode material for high-performance LiBs.

Recent Advances in Fiber Supercapacitors: Materials, Device Configurations, and Applications

Fiber supercapacitors (SCs), with their small size and weight, excellent flexibility and deformability, and high capacitance and power density, are recognized as one of the most robust power supplies available for wearable electronics. They can be woven into breathable textiles or integrated into different functional materials to fit curved surfaces for use in day-to-day life. A comprehensive review on recent important development and progress in fiber SCs is provided, with respect to the active electrode materials, device configurations, functions, integrations. Active electrode materials based on different electrochemical mechanisms and intended to improve performance including carbon-based materials, metal oxides, and hybrid composites, are first summarized. The three main types of fiber SCs, namely parallel, twist, and coaxial structures, are then discussed, followed by the exploration of some functions including stretchability and self-healing. Miniaturized integration of fiber SCs to obtain flexible energy fibers and integrated sensing systems is also discussed. Finally, a short conclusion is made, combining with comments on the current challenges and potential solutions in this field.

Recent Advances in 1D Stretchable Electrodes and Devices for Textile and Wearable Electronics: Materials, Fabrications, and Applications

Research on wearable electronic devices that can be directly integrated into daily textiles or clothes has been explosively grown holding great potential for various practical wearable applications. These wearable electronic devices strongly demand 1D electronic devices that are light-weight, weavable, highly flexible, stretchable, and adaptable to comport to frequent deformations during usage in daily life. To this end, the development of 1D electrodes with high stretchability and electrical performance is fundamentally essential. Herein, the recent process of 1D stretchable electrodes for wearable and textile electronics is described, focusing on representative conductive materials, fabrication techniques for 1D stretchable electrodes with high performance, and designs and applications of various 1D stretchable electronic devices. To conclude, discussions are presented regarding limitations and perspectives of current materials and devices in terms of performance and scientific understanding that should be considered for further advances.

A Review on Quantum Dots Modified g-C3N4-Based Photocatalysts with Improved Photocatalytic Activity

In the 21st century, the development of sustainable energy and advanced technologies to cope with energy shortages and environmental pollution has become vital. Semiconductor photocatalysis is a promising technology that can directly convert solar energy to chemical energy and is extensively used for its environmentally-friendly properties. In the field of photocatalysis, graphitic carbon nitride (g-C3N4) has obtained increasing interest due to its unique physicochemical properties. Therefore, numerous researchers have attempted to integrate quantum dots (QDs) with g-C3N4 to optimize the photocatalytic activity. In this review, recent progress in combining g-C3N4 with QDs for synthesizing new photocatalysts was introduced. The methods of QDs/g-C3N4-based photocatalysts synthesis are summarized. Recent studies assessing the application of photocatalytic performance and mechanism of modification of g-C3N4 with carbon quantum dots (CQDs), graphene quantum dots (GQDs), and g-C3N4 QDs are herein discussed. Lastly, challenges and future perspectives of QDs modified g-C3N4-based photocatalysts in photocatalytic applications are discussed. We hope that this review will provide a valuable overview and insight for the promotion of applications of QDs modified g-C3N4 based-photocatalysts.