Mass Production of Monodisperse Carbon Microspheres with Size-Dependent Supercapacitor Performance via Aqueous Self-Catalyzed Polymerization

Molecular Engineering to Regulate the Pseudo-Graphitic Structure of Hard Carbon for Superior Sodium Energy Storage

Resin-derived hard carbons have shown great advantages in serving as promising anode materials for sodium-ion batteries due to their flexible microstructure tunability. However, it remains a daunting challenge to rationally regulate the pseudo-graphitic crystallite and defect of hard carbon toward advanced sodium storage performance. Herein, a molecular engineering strategy is demonstrated to modulate the cross-linking degree of phenolic resin and thus optimize the microstructure of hard carbon. Remarkably, the resorcinol endows resin with a moderate cross-linking degree, which can finely tune the pseudo-graphitic structure with enlarged interlayer spacing and restricted surface defects. As a consequence, the optimal hard carbon delivers a notable reversible capacity of 334.3 mAh g-1 at 0.02 A g-1, a high initial Coulombic efficiency of 82.1%, superior rate performance of 103.7 mAh g-1 at 2 A g-1, and excellent cycling durability over 5000 cycles. Furthermore, kinetic analysis and in situ Raman spectroscopy are performed to reveal the electrochemical advantage and sodium storage mechanism. This study fundamentally sheds light on the molecular design of resin-based hard carbons to advance sodium energy for scale-up applications.

Anisotropic hat-like carbon nanoparticles with tunable inner hollow architectures by growth and dissolution kinetics control

The synthesis of nanoparticles with a hollow and anisotropic structure have attracted considerable interest in synthetic methodology and diverse potential applications, but endowing them with delicate control of the hollow structure and outer anisotropic morphology remains a significant challenge. In this study, anisotropic nanoparticles with hat-like morphology are prepared via a kinetics-controlled growth and dissolution strategy. Starting from forming solid polymer nanospheres with location-specific compositional chemistry distribution based on the distinct reactivity and growth kinetics of two reactants. After etching by acetone, the inhomogeneity nanospheres transformed to hat-like nanoparticles through the kinetics-controlled dissolution of two kinds of precursors. Due to chemical etching and repolymerization reactions occurring within a single nanospheres, an autonomous asymmetrical repolymerization and concave process are observed, which is novel at the nanoscale. Moreover, regulating the amount of ammonia significantly impacts the growth kinetics of precursors, primarily affecting the composition and subsequent dissolution process of solid polymer nanospheres, which play an important role in constructing polymer nanoparticles with varying morphologies and internal structures. The as-synthesized hat-like carbon nanoparticles with an open carbon structure, highly porous shell, and favorable N-doped functionalities demonstrate a potential candidate for lithium-sulfur batteries.

Towards Industrially Important Applications of Enhanced Organic Reactions by Microfluidic Systems

This review presents a comprehensive evaluation for the manufacture of organic molecules via efficient microfluidic synthesis. Microfluidic systems provide considerably higher control over the growth, nucleation, and reaction conditions compared with traditional large-scale synthetic methods. Microfluidic synthesis has become a crucial technique for the quick, affordable, and efficient manufacture of organic and organometallic compounds with complicated characteristics and functions. Therefore, a unique, straightforward flow synthetic methodology can be developed to conduct organic syntheses and improve their efficiency.

CO2 Adsorption Study of Potassium-Based Activation of Carbon Spheres

The adsorption properties of microporous spherical carbon materials obtained from the resorcinol-formaldehyde resin, treated in a solvothermal reactor heated with microwaves and then subjected to carbonization, are presented. The potassium-based activation of carbon spheres was carried out in two ways: solution-based and solid-based methods. The effect of various factors, such as chemical agent selection, chemical activating agent content, and the temperature or time of activation, was investigated. The influence of microwave treatment on the adsorption properties was also investigated and described. The adsorption performance of carbon spheres was evaluated in detail by examining CO₂ adsorption from the gas phase.

Controllable synthesis of porous tubular carbon by a Ag+-ligand-assisted Stöber-silica/carbon assembly process

Herein, in this study, we utilized Ag+-ligand interactions for critically regulating the morphology of carbon by the Stöber-silica/carbon co-assembly method for the first time. Tetraethyl orthosilicate (TEOS) and resorcinol/formaldehyde (RF) assemble upon dictation by Ag+ and pyridyl-functionalized surfactants, producing porous carbon tubes (RF1) with a high surface area of 696 m2 g-1 and accessible mesopores ∼15 nm in size. Furthermore, when using tetrapropyl orthosilicate (TPOS) with a slower hydrolysis rate than that of TEOS, carbon tubes (RF2) with enhanced uniformity and a surface area as high as 2112 m2 g-1 are generated. Additionally, when using dopamine hydrochloride instead of RF as a carbon precursor, tubular polydopamine (TDA) with lengths of tens of microns is fabricated, which exhibits excellent catalytic activity toward oxygen reduction reactions in alkaline solutions due to its unique structural feature, a high surface area of 1350 m2 g-1, metallic silver remains of 8.3 wt%, and a rich nitrogen content of 3.6 wt%. This work sheds light on the engineering of a micellar soft template and synthesizing novel nanostructures by the extension of the Stöber method.

Dictyophora-derived N-doped porous carbon microspheres for high-performance supercapacitors

PCMS-T hierarchical porous structures were prepared from biomass dictyophora as electrodes for high-performance supercapacitors.

Macroscopic synthesis of ultrafine N-doped carbon nanofibers for superior capacitive energy storage

Carbon nanofibers (CNFs) with excellent electric conductivity and high surface area have attracted immense research interests in supercapacitors. However, the macroscopic production of CNFs still remains a great challenge. Herein, ultrafine N-doped CNFs (N-CNFs) with a diameter of ∼20 nm are synthesized through a simple and scalable sol-gel method based on the self-assembly of phenolic resin and cetyltrimethylammonium bromide. When employed in aqueous supercapacitors, the obtained activated N-CNFs manifest a high gravimetric/areal capacitance (380 F g^-1/1.7 F cm^-2) as well as outstanding rate capability and cycling stability. Besides, the activated N-CNFs also demonstrate excellent capacitive performance (330 F g^-1) in flexible quasi-solid-state supercapacitors. The remarkable electrochemical performance as well as the easy and scalable synthesis makes the N-CNFs a highly promising electrode material for supercapacitors.

Formation of Monodisperse Carbon Spheres with Tunable Size via Triblock Copolymer-Assisted Synthesis and Their Capacitor Properties

A facile hydrothermal polymerization method has been developed for the preparation of monodisperse carbon spheres (MCSs) using the triblock copolymer F108 as surfactant. The synthesis is based on the ammonia-catalyzed polymerization reaction between phenol and formaldehyde (PF). The resultant MCSs have a perfect spherical morphology, smooth surface, and high dispersity. The particle sizes can be tuned in a wide range of 500~2400 nm by adjusting the dosage of the PF precursor. The activated MCSs with suitable heteroatoms (N and O) doped and a large specific surface area (960 m2 g-1) were obtained. A high-performance electrode of electrical double-layer capacitors fabricated by those active material have an excellent specific capacitance (310 F g-1 at 0.5 A g-1) and outstanding cycling stability (92% capacitance retention after 10,000 cycles). This work provides a new opportunity for the fabrication of MCSs with potential applications.

Monodisperse Carbon Sphere-Constructed Pomegranate-Like Structures for High-Volumetric-Capacitance Supercapacitors

Porous carbons have been extensively studied in supercapacitors. However, it remains a grand challenge for porous carbons to achieve a volumetric capacitance ( C_v) of over 200 F cm^-3 because of the low intrinsic density and limited capacitance. Herein, we propose a pomegranate-like carbon microsphere (PCS) constructed by monodisperse, submicron, N-doped microporous carbon spheres for high-volumetric-capacitance supercapacitors. The assembly of submicron carbon spheres into pomegranate-like structures significantly reduces the required binder amount (2.0 wt %) for electrode preparation, diminishes the interparticle resistance, and most importantly, endows the PCS with a high packing density (0.75 g cm^-3). Benefited from the high surface area (1477 m² g^-1), N-doping (3.0 wt %), and high packing density, the PCS demonstrates a high C_v (254 F cm^-3), four times that of unassembled monodisperse carbon spheres. This work opens a new avenue to enhance the C_v of porous carbons without compromising the rate capability or cyclability.

Tailoring porous carbon spheres for supercapacitors

The last decade has witnessed significant breakthroughs in the synthesis of porous carbon spheres (PCSs). This Review provides an updated summarization on the controlled synthesis of PCSs for supercapacitors. The synthetic methodologies can be generally categorized into (i) hard templating, (ii) soft templating, (iii) the modified Stöber method, (iv) hydrothermal carbonization (HTC), and (v) aerosol-assisted methods. The obtained PCSs include microporous/mesoporous/macroporous carbon spheres, single-/multi-shelled hollow carbon spheres, and yolk@shell carbon spheres. The structure-electrochemical performance correlation is discussed. Finally, the future research directions on the rational design of PCSs for supercapacitors are predicted.

Facile Synthesis of Nitrogen-Doped Microporous Carbon Spheres for High Performance Symmetric Supercapacitors

Nitrogen-doped microporous carbon spheres (NMCSs) are successfully prepared via carbonization and KOH activation of phenol-formaldehyde resin polymer spheres synthesized by a facile and time-saving one-step hydrothermal strategy using triblock copolymer Pluronic F108 as a soft template under the Stöber-like method condition. The influence of the ethanol/water volume ratios and carbonation temperatures on the morphologies, pore structures and electrochemical performances of the prepared NMCSs are investigated systematically. The optimal NMCSs have a large specific surface area of 1517 m2 g- 1 with a pore volume of 0.8 cm3 g- 1. The X-ray photo-electron spectroscopy analysis reveals a suitable nitrogen-doped content of 2.6 at.%. The as-prepared NMCSs used as supercapacitor electrode materials exhibit an outstanding specific capacitance of 416 F g- 1 at a current density of 0.2 A g- 1, also it shows an excellent charge/discharge cycling stability with 96.9% capacitance retention after 10,000 cycles. The constructed symmetric supercapacitors using PVA/KOH as the gel electrolyte can deliver a specific capacitance of 60.6 F g- 1 at current density of 1 A g- 1. A maximum energy density of 21.5 Wh kg- 1 can be achieved at a power density of 800 W kg- 1, and the energy density still maintains 13.3 Wh kg- 1 even at a high power density of 16 kW kg- 1. The results suggest that this work can open up a facile and effective way to synthesize the NMCSs for electrode materials of high performance energy storage devices.

Self-Generated Nanoporous Silver Framework for High-Performance Iron Oxide Pseudocapacitor Anodes

The rapid development of electric vehicles is increasing the demand for next-generation fast-charging energy storage devices with a high capacity and long-term stability. Metal oxide/hydroxide pseudocapacitors are the most promising technology because they show a theoretical capacitance that is 10-100 times higher than that of conventional supercapacitors and rate capability and long-term stability that are much higher than those of Li-ion batteries. However, the poor electrical conductivity of metal oxides/hydroxides is a serious obstacle for achieving the theoretical pseudocapacitor performance. Here, a nanoporous silver (np-Ag) structure with a tunable pore size and ligament is developed using a new silver halide electroreduction process. The structural characteristics of np-Ag (e.g., large specific surface area, electric conductivity, and porosity) are desirable for metal oxide-based pseudocapacitors. This work demonstrates an ultra-high-capacity, fast-charging, and long-term cycling pseudocapacitor anode via the development of an np-Ag framework and deposition of a thin layer of Fe₂O₃ on its surface (np-Ag@Fe₂O₃). The np-Ag@Fe₂O₃ anode shows a capacitance of ∼608 F g^-1 at 10 A g^-1, and ∼84.9% of the capacitance is retained after 6000 charge-discharge cycles. This stable and high-capacity anode, which can be charged within a few tens of seconds, is a promising candidate for next-generation energy storage devices.

Free-Standing Hybrid Graphene Paper Encapsulating Nanostructures for High Cycle-Life Supercapacitors

The incorporation of spacers between graphene sheets has been investigated as an effective method to improve the electrochemical performance of graphene papers (GPs) for supercapacitors. Here, we report the design of free-standing GP@NiO and GP@Ni hybrid GPs in which NiO nanoclusters and Ni nanoparticles are encapsulated into graphene sheets through electrostatic assembly and subsequent vacuum filtration. The encapsulated NiO nanoclusters and Ni nanoparticles can mitigate the restacking of graphene sheets, providing sufficient spaces for high-speed ion diffusion and electron transport. In addition, the spacers strongly bind to graphene sheets, which can efficiently improve the electrochemical stability. Therefore, at a current density of 0.5 A g^-1 , the GP@NiO and GP@Ni electrodes exhibit higher specific capacitances of 306.9 and 246.1 F g^-1 than the GP electrode (185.7 F g^-1 ). The GP@NiO and GP@Ni electrodes exhibit capacitance retention of 98.7 % and 95.6 % after 10000 cycles, demonstrating an outstanding cycling stability. Additionally, the GP@NiO∥GP@Ni delivers excellent cycling stability (93.7 % after 10 000 cycles) and high energy density. These free-standing encapsulated hybrid GPs have great potential as electrode for high-performance supercapacitors.

Disodium citrate-assisted hydrothermal synthesis of V2O5 nanowires for high performance supercapacitors

Orthorhombic vanadium pentoxide (V₂O₅) nanowires with uniform morphology were successfully fabricated via a facile hydrothermal process. The effect of disodium citrate dosage on the crystallinity, morphology and electrochemical properties of the products was analyzed. Experimental results indicate that orthorhombic V₂O₅ nanowires with high crystallinity and diameter of about 20 nm can be obtained at 180 °C for 24 h when the dosage of disodium citrate is 0.236 g. Furthermore, the prepared V₂O₅ nanowires demonstrate a high specific capacitance of 528.2 F g⁻¹ at 0.5 A g⁻¹ and capacitance retention of 85% after 1000 galvanostatic charge/discharge cycles at 1 A g⁻¹ when used as supercapacitors electrode in 0.5 M K₂SO₄.

Orthorhombic vanadium pentoxide (V₂O₅) nanowires with uniform morphology were successfully fabricated via a facile hydrothermal process.