Direct Solvent‐Derived Polymer‐Coated Nitrogen‐Doped Carbon Nanodots with High Water Solubility for Targeted Fluorescence Imaging of Glioma

Cancer imaging requires biocompatible and bright contrast‐agents with selective and high accumulation in the tumor region but low uptake in normal tissues. Herein, 1‐methyl‐2‐pyrrolidinone (NMP)‐derived polymer‐coated nitrogen‐doped carbon nanodots (pN‐CNDs) with a particle size in the range of 5–15 nm are prepared by a facile direct solvothermal reaction. The as‐prepared pN‐CNDs exhibit stable and adjustable fluorescence and excellent water solubility. Results of a cell viability test (CCK‐8) and histology analysis both demonstrate that the pN‐CNDs have no obvious cytotoxicity. Most importantly, the pN‐CNDs can expediently enter glioma cells in vitro and also mediate glioma fluorescence imaging in vivo with good contrast via elevated passive targeting.     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

N‐Doped Carbon Nanofibers with Interweaved Nanochannels for High‐Performance Sodium‐Ion Storage

Although graphite materials have been applied as commercial anodes in lithium‐ion batteries (LIBs), there still remain abundant spaces in the development of carbon‐based anode materials for sodium‐ion batteries (SIBs). Herein, an electrospinning route is reported to fabricate nitrogen‐doped carbon nanofibers with interweaved nanochannels (NCNFs‐IWNC) that contain robust interconnected 1D porous channels, produced by removal of a Te nanowire template that is coelectrospun within carbon nanofibers during the electrospinning process. The NCNFs‐IWNC features favorable properties, including a conductive 1D interconnected porous structure, a large specific surface area, expanded interlayer graphite‐like spacing, enriched N‐doped defects and active sites, toward rapid access and transport of electrolyte and electron/sodium ions. Systematic electrochemical studies indicate that the NCNFs‐IWNC exhibits an impressively high rate capability, delivering a capacity of 148 mA h g^?1 at current density of as high as 10 A g^?1, and has an attractively stable performance over 5000 cycles. The practical application of the as‐designed NCNFs‐IWNC for a full SIBs cell is further verified by coupling the NCNFs‐IWNC anode with a FeFe(CN)₆ cathode, which displays a desirable cycle performance, maintaining acapacity of 97 mA h g^?1 over 100 cycles.     

High‐Performance Asymmetric Supercapacitors Based on Multilayer MnO2/Graphene Oxide Nanoflakes and Hierarchical Porous Carbon with Enhanced Cycling Stability

In this work, MnO₂/GO (graphene oxide) composites with novel multilayer nanoflake structure, and a carbon material derived from Artemia cyst shell with genetic 3D hierarchical porous structure (HPC), are prepared. An asymmetric supercapacitor has been fabricated using MnO₂/GO as positive electrode and HPC as negative electrode material. Because of their unique structures, both MnO₂/GO composites and HPC exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high voltage range of 0–2 V in aqueous electrolyte, which exhibits maximum energy density of 46.7 Wh kg^?1 at a power density of 100 W kg^?1 and remains 18.9 Wh kg^?1 at 2000 W kg^?1. Additionally, such device also shows superior long cycle life along with ～100% capacitance retention after 1000 cycles and ～93% after 4000 cycles.     

A Dual‐Function Na2SO4 Template Directed Formation of Cathode Materials with a High Content of Sulfur Nanodots for Lithium–Sulfur Batteries

The sulfur content in carbon–sulfur hybrid using the melt‐diffusion method is normally lower than 70 wt%, which greatly decreases the energy density of the cathode in lithium–sulfur (Li‐S) batteries. Here, a scalable method inspired by the commercialized production of Na₂S is used to prepare a hierarchical porous carbon–sulfur hybrid (denoted HPC‐S) with high sulfur content (≈85 wt%). The HPC‐S is characterized by the structure of sulfur nanodots naturally embedded in a 3D carbon network. The strategy uses Na₂SO₄ as the starting material, which serves not only as the sulfur precursor but also as a salt template for the formation of the 3D carbon network. The HPC‐S cathode with such a high sulfur content shows excellent rate performance and cycling stability in Li–S batteries because of the sulfur nanoparticles, the unique carbon framework, and the strong interaction between them. The production method can also be readily scaled up and used in practical Li–S battery applications.     

Aligning Solution‐Derived Carbon Nanotube Film with Full Surface Coverage for High‐Performance Electronics Applications

The main challenge for application of solution‐derived carbon nanotubes (CNTs) in high performance field‐effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution‐derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on‐state current I_on of 290 µA µm^?1 (V_ds = ?1.5 V and V_gs = ?2 V) and peak transconductance g_m of 150 µS µm^?1, which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT‐based electronics.     

Tailoring Hierarchically Porous Nitrogen‐, Sulfur‐Codoped Carbon for High‐Performance Supercapacitors and Oxygen Reduction

Heteroatom‐doped carbon materials are intensively studied in supercapacitors and fuel cells, because of their great potential for sustainably bearing on the energy crisis and environmental pollution. Although enormous efforts are put in material perfection with a hierarchically porous microstructure, the simultaneous optimization of both porous structures and surface functionalities is hard to achieve due to inevitable concurrent dopant leaching effect and structural collapse under required high pyrolysis temperature. In this study, an in situ dehalogenation polymerization and activation protocol is introduced to synthesize nitrogen‐ and sulfur‐codoped carbon materials (NS‐PCMs) with hierarchical pore distribution and abundant surface doping, which endows them with good conductivity, abundant accessible active sites, and efficient mass transport. As a result, the as‐prepared carbon materials (NS‐a‐PCM‐1000) show an excellent mass specific capacitance of 461.5 F g^?1 at a current density of 0.1 A g^?1, long cycle life (>23 k, 10 A g^?1), and high device energy and power density (17.3 Wh kg^?1, 250 W kg^?1). Significantly, NS‐a‐PCM‐1000 also exhibits one of the highest oxygen reduction reaction activities (onset potential of 1.0 V vs reversible hydrogen electrode) in alkaline media among all reported metal‐free catalysts.     

Hollow Carbon Nanobelts Codoped with Nitrogen and Sulfur via a Self‐Templated Method for a High‐Performance Sodium‐Ion Capacitor

Sodium‐ion capacitors (SICs) have attracted enormous attention due to their high energy density and high power density. In this work, N and S codoped hollow carbon nanobelts (N/S‐HCNs) are synthesized by a self‐templated method. The as‐synthesized carbon nanobelts exhibit excellent performance in pseudocapacitance and electric double layer anions adsorption. After pairing the N/S‐HCNs cathode with a tin foil anode in a carbonate electrolyte, the obtained SIC achieves a high specific capacity of 400 mAh g^?1 at 1 A g^?1 (based on the mass of cathode material) and energy density of 250.35 Wh kg^?1 at 676 W kg^?1 (based on the total mass of cathode and anode materials). Besides, the presented SIC also demonstrates high cycling stability with almost 100% capacity retention after 10 000 cycles, which is among the best results of the reported SICs, suggesting the potential for high‐performance energy storage applications.     

Confined Assembly of Hollow Carbon Spheres in Carbonaceous Nanotube: A Spheres‐in‐Tube Carbon Nanostructure with Hierarchical Porosity for High‐Performance Supercapacitor

Carbonaceous nanotubes (CTs) represent one of the most popular and effective carbon electrode materials for supercapacitors, but the electrochemistry performance of CTs is largely limited by their relatively low specific surface area, insufficient usage of intratube cavity, low content of heteroatom, and poor porosity. An emerging strategy for circumventing these issues is to design novel porous CT‐based nanostructures. Herein, a spheres‐in‐tube nanostructure with hierarchical porosity is successfully engineered, by encapsulating heteroatom‐doping hollow carbon spheres into one carbonaceous nanotube (HCSs@CT). This intriguing nanoarchitecture integrates the merits of large specific surface area, good porosity, and high content of heteroatoms, which synergistically facilitates the transportation and exchange of ions and electrons. Accordingly, the as‐prepared HCSs@CTs possess outstanding performances as electrode materials of supercapacitors, including superior capacitance to that of CTs, HCSs, and their mixtures, coupled with excellent cycling life, demonstrating great potential for applications in energy storage.     

In Situ Oxidation Synthesis of p‐Type Composite with Narrow‐Bandgap Small Organic Molecule Coating on Single‐Walled Carbon Nanotube: Flexible Film and Thermoelectric Performance

Although composites of organic polymers or n‐type small molecule/carbon nanotube (CNT) have achieved significant advances in thermoelectric (TE) applications, p‐type TE composites of small organic molecules as thick surface coating layers on the surfaces of inorganic nanoparticles still remain a great challenge. Taking advantage of in situ oxidation reaction of thieno[3,4‐b]pyrazine (TP) into TP di‐N‐oxide (TPNO) on single‐walled CNT (SWCNT) surface, a novel synthesis strategy is proposed to achieve flexible films of TE composites with narrow‐bandgap (1.19 eV) small molecule coating on SWCNT surface. The TE performance can be effectively enhanced and conveniently tuned by poly(sodium‐p‐styrenesulfonate) content, TPNO/SWCNT mass ratio, and posttreatment by various polar solvents. The maximum of the composite power factor at room temperature is 29.4 ± 1.0 µW m^?1 K^?2. The work presents a way to achieve flexible films of p‐type small organic molecule/inorganic composites with clear surface coating morphology for TE application.     

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.     

Ultrathin Hierarchical Porous Carbon Nanosheets for High‐Performance Supercapacitors and Redox Electrolyte Energy Storage

The design of advanced high‐energy‐density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape‐controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal–organic frameworks (MOFs) are developed. As a proof‐of‐concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon‐sheet‐based symmetric cell shows an ultrahigh Brunauer–Emmett–Teller (BET)‐area‐normalized capacitance of 21.4 µF cm^?2 (233 F g^?1), exceeding other carbon‐based supercapacitors. The addition of potassium iodide as redox‐active species in a sulfuric acid (supporting electrolyte) leads to the ground‐breaking enhancement in the energy density up to 90 Wh kg^?1, which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery‐level energy and capacitor‐level power density.