Controllable Synthesis of Functional Hollow Carbon Nanostructures with Dopamine As Precursor for Supercapacitors

Efficient and Stable pH-Universal Water Electrolysis Catalyzed by N-Doped Hollow Carbon Confined RuIrOx Nanocrystals

A facile strategy is developed to fabricate 3 nm RuIrOx nanocrystals anchored onto N-doped hollow carbon for highly efficient and pH-universal overall water splitting and alkaline seawater electrolysis. The designed catalyst exhibits much lower overpotential and superior stability than most previously reported Ru- and Ir-based electrocatalysts for hydrogen/oxygen evolution reactions. It also manifests excellent overall water splitting activities and maintains ≈100% Faradic efficiency with a cell voltage of 1.53, 1.51, and 1.54 V at 10 mA cm-2 for 140, 255, and 200 h in acid, alkaline, and alkaline seawater electrolytes, respectively. The excellent electrocatalytic performance can be attributed to solid bonding between RuIrOx and the hollow carbon skeleton, and effective electronic coupling between Ru and Ir, thus inducing its remarkable electrocatalytic activities and long-lasting stability.

Bimetal Metal-Organic Framework-Derived Ni-Mn@Carbon/Reduced Graphene Oxide as a Cathode for an Asymmetric Supercapacitor with High Energy Density

As is known, metal-organic frameworks (MOFs) are a versatile class of materials in energy storage applications including supercapacitors. However, the individual kind of metal nodes connected by organic ligands to form a topological structure still limits the potential storage capacity of MOFs. Herein, a bimetal-based Ni-Mn MOF composite is configured with a one-pot hydrothermal method to derive a composite with a synergic effect to maximize the properties. Moreover, reduced graphene oxide (rGO) sheets are added as a conductive network to anchor the MOF-derived composite of Ni-Mn@C/rGO, which is expected to increase the conductivity of the materials system. The resulting composite exhibited a high specific capacitance of 1674 F g-1 at a current density of 0.3 A g-1, suggesting excellent energy storage performance. The composite was then integrated as the cathode in an asymmetrical supercapacitor with a 3D rGO aerogel anode, resulting in energy densities of 24.1 and 17.5 W h kg-1 at power densities of 88.9 and 444.4 W kg-1, respectively. Additionally, the device demonstrated remarkable long-term stability, with 90% capacitance retention after 10 000 charge-discharge cycles at 10 A g-1.

Carbon nanosphere synthesis and applications for rechargeable batteries

Carbon nanospheres (CNSs) have attracted great interest in energy conversion and storage technologies due to their excellent chemical and thermal stability, high electrical conductivity and controllable size structure characteristics. In order to further improve the energy storage properties, many efforts have been made to design suitable nanocarbon spherical materials to improve electrochemical performance. In this overview, we summarize the recent research progress on CNSs, mainly focusing on the synthesis methods and their application as high-performance electrode materials in rechargeable batteries. As for the synthesis methods, hard template methods, soft template methods, the extension of the Stöber method, hydrothermal carbonization, aerosol-assisted synthesis are described in detail. In addition, the use of CNSs as electrodes in energy storage devices (mainly concentrated on lithium-ion batteries (LIBs)), sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are also discussed in detail in this article. Finally, some perspectives on the future research and development of CNSs are provided.

Designing of 3D MnO2-graphene catalyst on sponge for abatement temperature removal of formaldehyde

The Mn-based catalysts, with low cost and high activity, are believed to be the effective composites for eliminating in-door formaldehyde (HCHO), while the powdered form nanosized catalysts are hardly to apply for practical application. Herein, hetero-structure of nanosheets manganese oxide (MnO₂) encapsulating N-doping graphene sphere (GS) were deposited in network-like sponge for constructing 3D catalyst. The prepared MnO₂-GS-Sponge composite catalyst exhibited excellent performance for removing HCHO at room temperature compared with GS and commercial MnO₂. The MnO₂-GS with larger specific surface area (209.1 m²·g^-1) was dispersed evenly in 3D network of sponge, which facilitated exposing more activate sites and achieving fast transport kinetics accelerating catalytic reaction for converting 97.1 % of 100 ppm of HCHO continuously to CO₂ for 120 h. Moreover, rely on the chemisorption of amino groups on N-doping GS surface, HCHO could be enriched even at low concentrations and efficient elimination (from 1000 ppb to12 ppb, at 35 ℃ in 48 h). The average oxidation state and infrared spectra analysis suggested that abundant oxygen vacancies on MnO₂-GS-Sponge could be identified as surface-active sites of converting HCHO into the intermediates of dioxymethylene and formate. This work might inspire the designing 3D composite material for potential application in other fields of environmental engineering or energy industrial.

Construction of core-in-shell Au@N-HCNs nanozymes for tumor therapy

Noble metals act as nanozymes that can generate reactive oxygen species (ROS) by catalysis to induce apoptosis of tumor cells for cancer therapy. But they are easy to aggregate, which will affect their further application. Carbon materials are often used as the carrier of noble metals to improve their catalytic performance. However, designing a composite structure to build an efficient carbon/noble metal hybrid nanozyme with high catalytic performance for tumor therapy is still a significant challenge. In this work, a core-in-shell structure nanozyme composed of gold nanoparticles (AuNPs) embedded in nitrogen-doped hollow carbon nanoshells (AuNPs@N-HCNs) were fabricated, which exhibited peroxidase-like (POD-like) and oxidase-like (OXD-like) activity. Compared with core-out-of-shell structure composite, the AuNPs@N-HCNs showed a better ability to generate ROS to kill tumor cells. Furthermore, AuNPs@N-HCNs also exhibited satisfactory photothermal conversion properties, which helped build a platform for photothermal therapy. Meanwhile, the enzyme activity produced by AuNPs@N-HCNs increased significantly under light irradiation. Comparing the size of AuNPs in carbon shell, 15 nm AuNPs were better than 2 nm in both enzyme-like activities and in vivo therapeutic effect. In vitro and in vivo studies demonstrated that under the synergistic effect of light-enhancing nanozyme catalysis and photothermal therapy, AuNPs@N-HCNs could induce cancer cell apoptosis and destroy tumors effectively, which provided evidence for the feasibility of tumor catalytic-photothermal treatment.

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.

Micropore-Rich Yolk-Shell N-doped Carbon Spheres: An Ideal Electrode Material for High-Energy Capacitive Energy Storage

Increasing the energy density of electrochemical double layer capacitors (EDLCs) can broaden their applications in energy storage but remains a formidable challenge. Herein, micropore-rich yolk-shell structured N-doped carbon spheres (YSNCSs) were constructed by a one-pot surfactant-free self-assembly method in aqueous solution. The resultant YSNCSs after activation possessed an ultrahigh surface area of 2536 m²  g^-1 , among which 80 % was contributed from micropores. When applied in EDLCs, the activated YSNCSs demonstrated an unprecedentedly high capacitance (270 F g^-1 at 1 A g^-1 ) in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄ ]) ionic liquid, affording an ultrahigh energy density (133 Wh kg^-1 at 943 W kg^-1 ). The present contribution provides insight into engineering porous carbons for capacitive energy storage.

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.

Ultrasensitive simultaneous detection of ascorbic acid, dopamine, uric acid and acetaminophen on a graphitized porous carbon-modified electrode

NHCS-1000/GCE produces a noticeable electrocatalytic response towards the anodic oxidation for the multiple sensing of AA, DA, UA and AC.

Tailoring Polymer Colloids Derived Porous Carbon Spheres Based on Specific Chemical Reactions

Porous carbon spheres derived from polymer colloids with regular geometry, monodispersed morphology, well-controlled contents and structures play important roles in many areas of application, such as energy storage/conversion, gas adsorption/separation, catalysis, and chemo-photothermal therapy. Suitable polymerization reaction and synthetic strategy are both critical for the obtainment of stable polymer colloids as carbon precursors. Basic polymerization reactions are the cornerstones of synthetic strategies, which directly provides the direct molecular-based design of functionalized polymer/carbon spheres. Thus, this progress report mainly focuses on the summary of suitable polymerization reactions for colloidal polymer derived porous carbon spheres. Recent advances in the synthetic strategies and applications are also discussed, including their corresponding polymerization reactions. Finally, the perspectives for the development of polymer derived porous carbon spheres are provided based on the controlled synthesis of polymer colloids and optimization over the carbonization process to achieve highly functionalized carbon spheres for practical applications.

Renaissance of Stöber method for synthesis of colloidal particles: New developments and opportunities

Colloidal silica particles have received a widespread interest because of their potential applications in adsorption, ceramics, catalysis, drug delivery and more. Among many approaches towards fabrication of these colloidal particles, Stöber, Fink and Bohn (SFB) method, known as Stöber synthesis is an effective sol-gel strategy for production of uniform, monodispersed silica particles with highly tailorable size and surface properties. This review, after a brief introduction showing the importance of colloidal chemistry, is focused on the Stöber synthesis of silica spheres including discussion of the key factors affecting their particle size, porosity and surface properties. Next, further developments of this method are presented toward fabrication of polymer, carbon, and composite spheres.

Facile preparation of hierarchical porous polydopamine microspheres for rapid removal of chromate from the wastewater

Abstract

Cr(VI) containing industrial wastewaters are highly toxic and carcinogenic, and severely threats living creatures and the environment. Therefore, it is highly desired yet challenging to develop an available and economical adsorbent for simultaneously detoxifying Cr(VI) anions to Cr(III) ions and removing them from the wastewater. Here we propose a facile method for rapid removal of Cr(VI) ions from the wastewater by using a synthetic polydopamine microsphere (PPM) adsorbent with hierarchical porosity. The as-prepared PPM exhibits high Cr(VI) removal capacity of 307.7 mg/g and an outstanding removal efficiency. They can effectively decrease the Cr(VI) concentration to lower than 0.05 mg/L well below the limits for drinking water standard of WHO regulations in 60 s at pH 2. More importantly, PPMs can reduce the lethal Cr(VI) anions to Cr(III) ions with low toxicity, and simultaneously immobilize them on the matrices of PPMs.

Graphical abstract

Progress in supercapacitors: roles of two dimensional nanotubular materials

Overcoming the global energy crisis due to vast economic expansion with the advent of human reliance on energy-consuming labor-saving devices necessitates the demand for next-generation technologies in the form of cleaner energy storage devices. The technology accelerates with the pace of developing energy storage devices to meet the requirements wherever an unanticipated burst of power is indeed needed in a very short time. Supercapacitors are predicted to be future power vehicles because they promise faster charging times and do not rely on rare elements such as lithium. At the same time, they are key nanoscale device elements for high-frequency noise filtering with the capability of storing and releasing energy by electrostatic interactions between the ions in the electrolyte and the charge accumulated at the active electrode during the charge/discharge process. There have been several developments to increase the functionality of electrodes or finding a new electrolyte for higher energy density, but this field is still open to witness the developments in reliable materials-based energy technologies. Nanoscale materials have emerged as promising candidates for the electrode choice, especially in 2D sheet and folded tubular network forms. Due to their unique hierarchical architecture, excellent electrical and mechanical properties, and high specific surface area, nanotubular networks have been widely investigated as efficient electrode materials in supercapacitors, while maintaining their inherent characteristics of high power and long cycling life. In this review, we briefly present the evolution, classification, functionality, and application of supercapacitors from the viewpoint of nanostructured materials to apprehend the mechanism and construction of advanced supercapacitors for next-generation storage devices.

Fabrication of uniform urchin-like N-doped NiCo2O4@C hollow nanostructures for high performance supercapacitors

Transition metal oxides are commonly used in electrochemical energy storage materials, but there are still many drawbacks that impede a wide range of applications. Heteroatom doping can significantly improve its performance. Herein, we have successfully prepared highly uniform N-doped NiCo₂O₄@C hollow nanostructures for supercapacitors by a two-step hydrothermal treatment associated with successive annealing process. Prepared N-doped NiCo₂O₄@C materials exhibited an admirable specific capacitance of 1028 F g^-1 at a current density of 3 A g^-1, with 625 F g^-1 remaining even at high current density of 20 A g^-1. Besides, this composite showed good electrochemical stability with capacity retention of 84% after 5000 cycles repetitive galvanostatic charge-discharge test at 10 A g^-1. An asymmetric supercapacitor was assembled by the N-doped NiCo₂O₄@C electrode, attached activate carbon (AC) as a counter electrode, exhibiting a high energy density of 26.67 W h kg^-1 at a power density of 402 W kg^-1. The improvement of electrochemical performance is ascribed to the co-doping of nitrogen and carbon atoms. These results indicate that N-doped NiCo₂O₄@C can be employed as an ideal electrode material for electrochemical energy storage.

Catalytic Ozonation of Ketoprofen with In Situ N-Doped Carbon: A Novel Synergetic Mechanism of Hydroxyl Radical Oxidation and an Intra-Electron-Transfer Nonradical Reaction

A novel synergetic mechanism of hydroxyl radical (^•OH) oxidation and an intra-electron-transfer nonradical reaction was found in the catalytic ozonation of ketoprofen (KTP) with the in situ N-doped hollow sphere carbon (NHC). Outperforming the conventional ^•OH-based catalytic ozonation process, O₃/NHC not only realized an enhancement of the pseudo-first-order rate constant of 11 times in comparison with that of O₃ alone, but was also endowed with a high stability over a wide pH (4-9) and temperature (15-35 °C) range for the degradation of KTP. The high graphitization degree (I_D/I_G = 0.78-0.88) and low unsaturated oxygen content (0.10-1.38%) of NHC highlighted the dominant role of N-heteroatoms in the O₃/NHC system. The specific effects of different N species were confirmed by a relationship study (N property vs catalytic activity) and X-ray photoelectron spectroscopy characterization. The graphitic N forming in the bulk of the graphitic structure served as the "electron-mobility" region to promote KTP degradation with the transfer of electrons from the KTP molecule to O₃ via a nonradical reaction process. The pyrrolic and pyridinic N located at defects of the graphitic structure acted as the "radical-generation" region to decompose O₃ into ^•OH for degrading KTP by a radical oxidation process. This finding provided a brand new insight into engineering N-doped carbonaceous catalysts precisely in the catalytic ozonation process for the efficient treatment of organic-contaminated water.

Design of Hollow Nanostructures for Energy Storage, Conversion and Production

Hollow nanostructures have shown great promise for energy storage, conversion, and production technologies. Significant efforts have been devoted to the design and synthesis of hollow nanostructures with diverse compositional and geometric characteristics in the past decade. However, the correlation between their structure and energy-related performance has not been reviewed thoroughly in the literature. Here, some representative examples of designing hollow nanostructure to effectively solve the problems of energy-related technologies are highlighted, such as lithium-ion batteries, lithium-metal anodes, lithium-sulfur batteries, supercapacitors, dye-sensitized solar cells, electrocatalysis, and photoelectrochemical cells. The great effect of structure engineering on the performance is discussed in depth, which will benefit the better design of hollow nanostructures to fulfill the requirements of specific applications and simultaneously enrich the diversity of the hollow nanostructure family. Finally, future directions of hollow nanostructure design to solve emerging challenges and further improve the performance of energy-related technologies are also provided.

Heterostructured CoO-Co3O4 nanoparticles anchored on nitrogen-doped hollow carbon spheres as cathode catalysts for Li-O2 batteries

Lithium-oxygen batteries have received extensive attention due to their high theoretical energy density and environmental friendliness. Herein, CoO-Co3O4 nanoparticles coated on nitrogen-doped hollow carbon spheres (N-HC@CoO-Co3O4) are prepared by a simple method, and N-HC@CoO-Co3O4 when used as the cathode material for a lithium-oxygen battery shows high catalytic performance. The nitrogen-doped hollow carbon spheres not only ensure an ultra-high specific surface area for the accommodation of the Li2O2 discharge products but also provide more reactive sites. CoO-Co3O4 nanoparticles supported on the surface of the nitrogen-doped hollow carbon spheres can effectively catalyze the formation and decomposition of worm-like Li2O2. The batteries assembled with N-HC@CoO-Co3O4 catalysts exhibit reduced overpotential, improved cycling performance, and high rate capability. Ultra-high discharge capacities of 24 265 mA h g-1 at a current density of 300 mA g-1 and 3622 mA h g-1 at a current density of 1000 mA g-1 are obtained. With a cutoff capacity of 500 mA h g-1, the battery with an N-HC@CoO-Co3O4 electrode can reach more than 112 cycles. This research offers new insights into the design of heterostructured oxide catalysts for Li-O2 batteries.

Multi-layered zeolitic imidazolate framework based self-templated synthesis of nitrogen-doped hollow porous carbon dodecahedrons as robust substrates for supercapacitors

N-Doped hierarchical hollow porous carbon dodecahedrons derived from multi-layered core–shell ZIFs exhibit superior performance as supercapacitor electrodes.

Nitrogen-doped hollow carbon spheres functionalized by 9,10-phenanthrenequinone molecules as a high-performance electrode for asymmetric supercapacitors

9,10-Phenanthrenequinone as a novel organic electrochemically active material for supercapacitors has been non-covalently functionalized onto N-doped hollow carbon spheres.

Facile Synthesis of Mesoporous Carbon Spheres Using 3D Cubic Fe-KIT-6 by CVD Technique for the Application of Active Electrode Materials in Supercapacitors

Mesoporous carbon spheres (MCS-750, MCS-800, MCS-850, MCS-900, and MCS-950) have been synthesized by a facile strategy with low temperature and rapid chemical vapor deposition technique. The synthesized MCS possess relatively large surface area (570-670 m² g^-1), good graphitization, remarkable porosity, and redox functionalities on the surface of the synthesized MCS. Combination of these structural and surface properties of the synthesized MCS as an electrode material (MCS-850) showed an excellent charge-storage capacity with a specific capacitance of 338 F/g at 1 mV/s, 217 F/g at 0.5 A/g. MCS-850 shows long-term cycling stability with capacitive retention of more than 96% after 2000 cycles in 6 M KOH electrolyte. In addition, a fabricated two-electrode symmetric cell obtained 86% retention after 2000 cycles. The two-electrode symmetric device exhibited a specific capacitance of 63 F/g at 5 mV/s with an energy density of 7.1 Wh/kg.

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.

Nitrogen-doped porous carbon sphere supported Pt nanoparticles for methanol and ethanol electro-oxidation in alkaline media

A simple method for the preparation of porous nitrogen-doped carbon spheres (MNCS) with honeycomb-like structures through the self-assembly of colloidal silica by using polyaniline as the nitrogen source and a carbon precursor is reported. The BET surface area calculated from N₂ adsorption/desorption measurement of the MNCS is up to 882 m² g⁻¹. The synthesized MNCS were employed as a support for Pt nanoparticles for the oxidation of methanol and ethanol in alkaline media. Compared to Pt supported on commercial Vulcan XC-72R carbon (Pt/C), Pt/MNCS exhibit higher electro-catalytic performance and greater stability, indicating that MNCS have potential application prospects as electro-catalyst supports for alcohol oxidation in alkaline media. This enhancement in performance is due to the honeycomb-like porous structure of the MNCS and the doping with nitrogen.

We synthesized honeycomb-like porous nitrogen-doped carbon spheres, which can be used as support of Pt for alcohol oxidation.

Dopamine Assisted One-Step Pyrolysis of Glucose for the Preparation of Porous Carbon with A High Surface Area

Herein, a facile dopamine assisted one-pot synthesis approach is proposed for the preparation of porous carbon with a specific surface area (SSA) up to 2593 m²/g through the direct pyrolysis of a mixture of glucose, NH₄Cl, and dopamine hydrochloride (DAH). The glucose is adopted as the carbon source and foaming agent, NH₄Cl is used as the blowing agent, and DAH is served as collaborative carbon precursor as well as the nitrogen source for the first time. The effect of dopamine on the component, structure, and SSA of the as-prepared porous carbon materials are systematically studied. The moderate addition of dopamine, which influences the condensation and polymerization of glucose, matches better with ammonium salt decomposition. The SSA of porous carbon increases first and then decreases with the increasing amount of dopamine. In our case, the porous carbon produced with 5 wt% dopamine (PC-5) achieves the maximum SSA of up to 2593 m²/g. Accordingly, it also shows the greatest electrochemical performance. The PC-5 shows a capacitance of 96.7 F/g calculated from the discharge curve at 1 A/g. It also has a good capacitive rate capacity, the specific capacitance can still maintain 80%, even at a high current density of 10 A/g. Moreover, PC-5 exhibits a good cycling stability of 98.1% capacitive retention after 1000 cycles. The proposed method may show promising prospects for preparing porous carbon materials as advanced energy storage materials, storage, and catalyst supports.

Millerite Core-Nitrogen-Doped Carbon Hollow Shell Structure for Electrochemical Energy Storage

Nickel sulfides have drawn much attention with the benefits of a high redox activity, high electrical conductivity, low cost, and fabrication ease; however, these metal sulfides are susceptible to mechanical degradation regarding their cycling performance. Conversely, hollow carbon shells exhibit a substantial electrochemical steadiness in energy storage applications. Here, the design and development of a novel millerite core-nitrogen-doped carbon hollow shell (NiS-NC HS) structure for electrochemical energy storage is presented. The nitrogen-doped carbon hollow shell (NC HS) protects against the degradation and the millerite-core aggregation, giving rise to an excellent rate capability and stability during the electrochemical charging-discharging processes, in addition to improving the NiS-NC HS conductivity. The NiS-NC HS/18h supercapacitor electrode displays an outstanding specific capacitance of 1170.72 F g^-1 (at 0.5 A g^-1 ) and maintains 90.71% (at 6 A g^-1 ) of its initial capacitance after 4000 charge-discharge cycles, owing to the unique core-shell structure. An asymmetric-supercapacitor device using NiS-NC HS and activated-carbon electrodes exhibits a high power and energy density with a remarkable cycling stability, maintaining 89.2% of its initial capacitance after 5000 cycles.

Core-Shell Nitrogen-Doped Carbon Hollow Spheres/Co3 O4 Nanosheets as Advanced Electrode for High-Performance Supercapacitor

Co₃ O₄ /nitrogen-doped carbon hollow spheres (Co₃ O₄ /NHCSs) with hierarchical structures are synthesized by virtue of a hydrothermal method and subsequent calcination treatment. NHCSs, as a hard template, can aid the generation of Co₃ O₄ nanosheets on its surface; while SiO₂ spheres, as a sacrificed-template, can be dissolved in the process. The prepared Co₃ O₄ /NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co₃ O₄ itself. A higher specific capacitance of 581 F g^-1 at 1 A g^-1 and a higher rate performance of 91.6% retention at 20 A g^-1 are achieved, better than Co₃ O₄ nanorods (318 F g^-1 at 1 A g^-1 and 67.1% retention at 20 A g^-1 ). In addition, the composite is employed as a positive electrode to fabricate an asymmetric supercapacitor. The device can deliver a high energy density of 34.5 Wh kg^-1 at the power density of 753 W kg^-1 and display a desirable cycling stability. All of these attractive results make the unique hierarchical Co₃ O₄ /NHCS core-shell structure a promising electrode material for high-performance supercapacitors.

Synthesis of Core-Shell Structured Porous Nitrogen-Doped Carbon@Silica Material via a Sol-Gel Method

Core-shell structured nitrogen-doped porous carbon@silica material with uniform structure and morphology was synthesized via a sol-gel method. During this process, a commercial triblock copolymer and the in situ formed pyrrole-formaldehyde polymer acted as cotemplates, while tetraethyl orthosilicate acted as silica precursor. The synergetic effect of the triblock copolymer and the pyrrole-formaldehyde polymer enables the formation of the core-shell structure. Herein, the pyrrole-formaldehyde polymer acted as not only the template, but also the nitrogen-doped carbon precursor of the core. The obtained core-shell structured porous material possesses moderate Brunauer-Emmett-Teller specific surface area (410 m² g^-1) and pore volume (0.53 cm³ g^-1). Moreover, corresponding hollow silica spheres or nitrogen-doped porous carbon spheres can be synthesized by calcining the core-shell structured material in air or etching it with HF. The X-ray photoelectron spectroscopy results reveal that the nitrogen states of the obtained material are mainly pyridinic-N and pyridonic-N/pyrrolic-N, which are beneficial for carbon dioxide adsorption. The carbon dioxide uptake capacity of the nitrogen-doped carbon spheres can reach 12.3 wt % at 273 K and 1.0 bar, meanwhile, the material shows good gas adsorption selectivities for CO₂/CH₄ and CO₂/N₂.

Synthesis of Olive-Like Nitrogen-Doped Carbon with Embedded Ge Nanoparticles for Ultrahigh Stable Lithium Battery Anodes

The development of environment-friendly and high-performance carbon materials for energy applications has remained a great challenge. Here, a novel and facile method for synthesis of olive-like nitrogen-doped carbon embedded with germanium (Ge) nanoparticles using widespread and nontoxic dopamine as carbon and nitrogen precursors is demonstrated, especially by understanding the tendency of pure GeO₂ nanoparticles forming ellipsoidal aggregation, and the chelating reaction of the catechol structure in dopamine with metal ions. The as-synthesized Ge/N-C composites show an olive-like porous carbon structure with a loading weight of as high as 68.5% Ge nanoparticles. A lithium ion battery using Ge/N-C as the anode shows 1042 mAh g^-1 charge capacity after 2000 cycles (125 d) charge/discharge at C/2 (1C = 1600 mA g^-1 ) with a capacity maintaining efficiency of 99.6%, significantly exceeding those of the previously reported Ge/C-based anode materials. This prominent cyclic charge/discharge performance of the Ge/N-C anode is attributed to the well-dispersed Ge nanoparticles in graphitic N-doped carbon matrix, which facilitates high rates (0.5-15 C) of charge/discharge and increases the anode structure integrity. The synthesis strategy presented here may be a very promising approach to prepare a series of active nanoparticle-carbon hybrid materials with nitrogen doping for more and important applications.

Metal-polydopamine frameworks and their transformation to hollow metal/N-doped carbon particles

We present a new strategy for in situ transformation of metal-organic framework (MOF) crystals to hollow metal-organic structures through polycondensation of dopamine. The hollow metal-polydopamine (PDA) particles are formed by a coordination assembly of metal ions (Co and Zn) and PDA, inheriting the morphology of MOF (ZIF-67 and ZIF-8) crystals. The hollow porous metal/N-carbon particles morphosynthetically transformed from hollow metal-PDA particles exhibit excellent oxygen reduction electrocatalytic activity. The strategy presented here is promising for synthesizing hollow metal-organic polymer (metal-carbon) particles with diverse morphologies for energy and environmental applications.