Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes

The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g^?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g^?1 for the CNOs/Ppy bilayer (electrochemical deposition).     

Facile Synthesis of A 3D Flower‐Like Mesoporous Ni@C Composite Material for High‐Energy Aqueous Asymmetric Supercapacitors

A 3D flower‐like mesoporous Ni@C composite material has been synthesized by using a facile and economical one‐pot hydrothermal method. This unique 3D flower‐like Ni@C composite, which exhibited a high surface area (522.4 m² g^?1), consisted of highly dispersed Ni nanoparticles on mesoporous carbon flakes. The effect of calcination temperature on the electrochemical performance of the Ni@C composite was systematically investigated. The optimized material (Ni@C 700) displayed high specific capacity (1306 F g^?1 at 2 A g^?1) and excellent cycling performance (96.7 % retention after 5000 cycles). Furthermore, an asymmetric supercapacitor (ASC) that contained Ni@C 700 as cathode and mesoporous carbon (MC) as anode demonstrated high energy density (60.4 W h kg^?1 at a power density of 750 W kg^?1).     

Hierarchical Activated Mesoporous Phenolic‐Resin‐Based Carbons for Supercapacitors

A series of hierarchical activated mesoporous carbons (AMCs) were prepared by the activation of highly ordered, body‐centered cubic mesoporous phenolic‐resin‐based carbon with KOH. The effect of the KOH/carbon‐weight ratio on the textural properties and capacitive performance of the AMCs was investigated in detail. An AMC prepared with a KOH/carbon‐weight ratio of 6:1 possessed the largest specific surface area (1118 m² g^?1), with retention of the ordered mesoporous structure, and exhibited the highest specific capacitance of 260 F g^?1 at a current density of 0.1 A g^?1 in 1 M H₂SO₄ aqueous electrolyte. This material also showed excellent rate capability (163 F g^?1 retained at 20 A g^?1) and good long‐term electrochemical stability. This superior capacitive performance could be attributed to a large specific surface area and an optimized micro‐mesopore structure, which not only increased the effective specific surface area for charge storage but also provided a favorable pathway for efficient ion transport.     

LiNi0.8Co0.2O2/CNTs Composite used as the Materials for Supercapacitor Electrodes

Stupercapacitors or electrochemical capacitors(ECs) have attracted considerable attentionas an intermediate power source between conventional capacitors and batteries since they possesshigh power density and energy density, exhibit excellent reversibility, and have long cycle life1.Conductive polymers2, electrically conductive metal oxide3,4, activated carbon5 and carbonnanotubes(CNTs) 6-9 have been used as supercapacitor electrode materials. LiNi0.sCo0.2O2 is apromising lithium battery material because it has some advantages of both LiNiO2 and LiCoO2besides its low cost and high power10.In this paper, the electrochemical properties of supercapacitors based on LiNi0.8Co0.2O2/carbonnanotubes composite and LiNi0.8Co0.2O2/acetylene black composite and CNTs in 1 mol/LLiClO4/EC+DEC [V(EC):V(DEC)=1:1] electrolyte have been investigated by means of constantcharge/discharge current tests. The experiment results show that the LiNi0.8Co0.2O2/carbon nanotubescomposite has better properties than others, and the maximun specific capacitance of thesupercapacitor can reach 284.88F/g, while the energy density is up to 158.27Wh/Kg.That discharge capacities, coulombic efficiencies and energy densities at the first cycle and themaximum value and capacity retention at the 100th cycle for supercapacitors using differentelectrode materials (A) LiNi0.8Co0.2O2/acetylene black, (B) LiNi0. 8Co0.2O2/CNTs, (C) CNTs is listedin table 1*Capacity retention rate obtained by dividing the discharge capacity at the 100th cycle by themaximum valueFrom above, the LiNi0. 8Co0.2O2/carbon nanotubes composite should be a good candidatesupercapacitor electrode material.     

Hierarchically Designed Three‐Dimensional Macro/Mesoporous Carbon Frameworks for Advanced Electrochemical Capacitance Storage

Mesoporous carbon (m‐C) has potential applications as porous electrodes for electrochemical energy storage, but its applications have been severely limited by the inherent fragility and low electrical conductivity. A rational strategy is presented to construct m‐C into hierarchical porous structures with high flexibility by using a carbon nanotube (CNT) sponge as a three‐dimensional template, and grafting Pt nanoparticles at the m‐C surface. This method involves several controllable steps including solution deposition of a mesoporous silica (m‐SiO₂) layer onto CNTs, chemical vapor deposition of acetylene, and etching of m‐SiO₂, resulting in a CNT@m‐C core–shell or a CNT@m‐C@Pt core–shell hybrid structure after Pt adsorption. The underlying CNT network provides a robust yet flexible support and a high electrical conductivity, whereas the m‐C provides large surface area, and the Pt nanoparticles improves interfacial electron and ion diffusion. Consequently, specific capacitances of 203 and 311 F g^?1 have been achieved in these CNT@m‐C and CNT@m‐C@Pt sponges as supercapacitor electrodes, respectively, which can retain 96 % of original capacitance under large degree compression.     

Kinetically Controlled Assembly of Nitrogen‐Doped Invaginated Carbon Nanospheres with Tunable Mesopores

Mesoporous hollow carbon nanospheres (MHCS) have been extensively studied owning to their unique structural features and diverse potential applications. A surfactant‐free self‐assembly approach between resorcinol/formaldehyde and silicon alkoxide has emerged as an important strategy to prepare MHCS. Extending such a strategy to other substituted phenols to produce heterogeneous‐atom‐doped MHCS remains a challenge due to the very different polymerization kinetics of various resins. Herein, we report an ethylenediamine‐assisted strategy to control the cooperative self‐assembly between a 3‐aminophenol/formaldehyde resin and silica templates. Nitrogen‐doped mesoporous invaginated carbon nanospheres (N‐MICS) with an N content of 6.18 at %, high specific surface areas (up to 1118 m² g^?1), large pore volumes (2.47 cm³ g^?1), and tunable mesopores (3.7–11.1 nm) have been prepared. When used as electrical double‐layer supercapacitors, N‐MICS show a high capacitance of 261 F g^?1, an outstanding cycling stability (≈94 % capacitance retention after 10 000 cycles), and a good rate performance.     

DNA‐Templated Synthesis of Cationic Poly(3,4‐ethylenedioxythiophene) Derivative for Supercapacitor Electrodes

A new cationic poly(3,4‐ethylenedioxythiophene)–DNA composite (P(EDOT‐N)‐DNA) has been prepared by in situ chemical oxidative polymerization of EDOT‐N monomer in the presence of salmon DNA as template. Scanning electron microscopy shows that the P(EDOT‐N)–DNA composite forms a porous pattern with a high surface area that is favorable for ion diffusion throughout the materials, which leads to improved capacitive activity. The P(EDOT‐N)–DNA composite exhibits superior capacitance behavior as well as good charge–discharge reversibility. The P(EDOT‐N)–DNA composite shows low cytotoxicity to living cells even at a concentration of 300 mg · L⁻¹. The good biocompatibility of P(EDOT‐N)–DNA imparts good potential as an environmentally friendly electrode material for energy storage devices, even in a biological environment owing to the combination of DNA with conjugated polymers.

     

Ordered Mesoporous Carbon Paste Electrodes for Electrochemical Sensing and Biosensing

Surface renewable ordered mesoporous carbon paste electrodes (OMCPE) were prepared by mechanical mixing ordered mesoporous carbon (OMC) and mineral oil. Electrochemical behavior of the composite electrode was evaluated and compared with the conventional graphite paste (GPE) and carbon nanotubes paste (CNTPE) electrodes. The OMCPE provided improved electron transfer kinetics and catalytic capabilities in connection with oxidation and/or reduction of different redox systems, such as ferricyanide and some biological species, e. g. ascorbic acid (AA), uric acid (UA), β‐nicotinamide adenine dinucleotide (NADH), dopamine (DA), epinephrine (EP), acetaminophenol (AP) and hydrogen peroxide. The substantial decrease in the over voltage of the hydrogen peroxide oxidation along with the facile incorporation of glucose oxidase (GOD) into the composite matrix allowed us successfully to fabricate a sensitive and selective glucose biosensor. A linear response up to 15 mM glucose was obtained for the OMCPE modified with 10% GOD (w/w) with a detection limit of 0.072 mM. In addition, we also successfully applied the OMCPE to the anodic stripping voltammetric analysis of heavy metal ions with improved sensitivities in comparison with CNTPE and GPE. The excellent experimental results implicate that the new developed paste electrode holds great promise in the design of electrochemical devices, such as sensors and biosensors.     

碳纳米管用作超级电容器电极材料

碳纳米管由于具有化学稳定性好、比表面积大、导电性好和密度小等优点,是很有前景的超级电容器电极材料。本文介绍了碳纳米管用作超级电容器电极材料的研究现状,总结了单纯碳纳米管电极材料和碳纳米管复合物电极材料的特点与性能,并探讨了今后碳纳米管电极材料的发展方向。     

Synthesis of N‐Doped Mesoporous Carbon Nanorods through Nano‐Confined Reaction: High‐Performance Catalyst Support for Hydrogenation of Phenol Derivatives

Traditional hard‐template methods for the preparation of mesoporous carbon structures have been well developed, but there are difficulties associated with complete filling of the organic precursors in ordered mesochannels and exact replication of the templates. Herein, mesoporous carbon nanorods (meso‐CNRs) were synthesized through thermal condensation of furfuryl alcohol followed by the nano‐confined decomposition of polyfurfuryl alcohol in silica nanotubes (SiO₂ NTs) with porous shells. Limited and slow release of gaseous water through the porous shells and finite polyfurfuryl precursor inside silica nanotubes are responsible for the formation of the mesoporous structures. Nitrogen can be doped into the meso‐CNRs by adding guanidine hydrochloride to the precursors. The nitrogen dopant not only stabilizes the ultrasmall and active Pd nanocatalyst in the meso‐CNRs but also increases the electron density of Pd and accelerates the dissociation of H₂, both of which increase the catalytic activity of the Pd catalyst in hydrogenation reactions.     

Iron Carbide Nanoparticles Encapsulated in Mesoporous Fe‐N‐Doped Carbon Nanofibers for Efficient Electrocatalysis

Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these energy conversion and storage devices. Here we report a novel NPMC consisting of Fe₃C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl₃ as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of ?0.02 V and half‐wave potential of ?0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.     

介孔碳纳米纤维制备与超电容性能研究

采用低分子量酚醛树脂/F127混合物填充多孔氧化铝模板孔道,制备了大尺寸介孔孔道、核-壳结构的介孔碳纳米纤维.分别以SEM、TEM及N2等温吸附-脱附观察分析样品形貌和孔结构参数.循环伏安与恒流充放电测定该介孔纳米纤维电极(阳极)的超电容性能.结果表明:介孔碳纳米纤维比电容明显增大,且在高扫速、大电流下具有良好的超电容特性.     

Superior Supercapacitor Properties of Composite Powders with Amorphous NiO Nanoclusters Distributed Uniformly in an Amorphous Carbon Matrix

Amorphous nickel oxide–carbon composite powders have been prepared using a facile spray‐drying process. The nickel nitrate–citrate hydrate precursor powders were transformed into an amorphous NiO–carbon composite powder through a post‐treatment at 250 °C for 1 h. The excellent supercapacitor performance of the amorphous NiO–carbon composite powder can be ascribed to the unique electrochemical behavior of the ultrafine amorphous NiO nanoclusters.     

Bioanalytical Application of the Ordered Mesoporous Carbon Modified Electrodes

An ordered mesoporous carbon modified electrode (OMCE) was prepared by film forming method. The electrochemical behavior of the OMCE was evaluated in connection with the electrochemistry of some electroactive biospecies, such as ascorbic acid (AA), acetaminophenol (AP), cysteine (CySH), dopamine (DA), epinephrine (EP), uric acid (UA), β‐nicotinamide adenine dinucleotide (reduced disodium salt hydrate, NADH), and hydrogen peroxide (H₂O₂) with cyclic voltammetry. Compared with the conventional carbon nanotubes (CNT) and graphite powder (GP) modified electrodes, the OMCE provided the best electrochemical reactivities in all cases associated with decreased over potential, better‐defined peak shape, and higher sensitivity. In addition, the OMC, CNT, and GP modified electrodes were employed as sensitive sensors for H₂O₂ and NADH quantification and as stable platforms for the fabrication of glucose and ethanol biosensors on which the enzymes were immobilized.     

Three‐Dimensional Nitrogen‐Doped Hierarchical Porous Carbon as an Electrode for High‐Performance Supercapacitors

A facile and sustainable procedure for the synthesis of nitrogen‐doped hierarchical porous carbons with a three‐dimensional interconnected framework (NHPC‐3D) was developed. The strategy, based on a colloidal crystal‐templating method, utilizes nitrogenous dopamine as the precursor due to its unique properties, including self‐polymerization under mild alkaline conditions, coating onto various surfaces, a high carbonization yield, and well‐preserved nitrogen doping after heat treatment. The obtained NHPC‐3D possesses a high surface area of 1056 m² g^?1, a large pore volume of 2.56 cm³ g^?1, and a high nitrogen content of 8.2 wt %. The NHPC‐3D is implemented as the electrode material of a supercapacitor and exhibits a specific capacitance as high as 252 F g^?1 at a current density of 2 A g^?1. The device also shows a high capacitance retention of 75.7 % at a higher current density of 20 A g^?1 in aqueous electrolyte due to a sufficient surface area for charge accommodation, reversible pseudocapacitance, and minimized ion‐transport resistance, as a result of the advantageous interconnected hierarchical porous texture. These results showcase NHPC‐3D as a promising candidate for electrode materials in supercapacitors.     

Nitrogen‐Doped Carbon Monolith for Alkaline Supercapacitors and Understanding Nitrogen‐Induced Redox Transitions

A nitrogen‐doped porous carbon monolith was synthesized as a pseudo‐capacitive electrode for use in alkaline supercapacitors. Ammonia‐assisted carbonization was used to dope the surface with nitrogen heteroatoms in a way that replaced carbon atoms but kept the oxygen content constant. Ammonia treatment expanded the micropore size‐distributions and increased the specific surface area from 383 m² g^?1 to 679 m² g^?1. The nitrogen‐containing porous carbon material showed a higher capacitance (246 F g^?1) in comparison with the nitrogen‐free one (186 F g^?1). Ex situ electrochemical spectroscopy was used to investigate the evolution of the nitrogen‐containing functional groups on the surface of the N‐doped carbon electrodes in a three‐electrode cell. In addition, first‐principles calculations were explored regarding the electronic structures of different nitrogen groups to determine their relative redox potentials. We proposed possible redox reaction pathways based on the calculated redox affinity of different groups and surface analysis, which involved the reversible attachment/detachment of hydroxy groups between pyridone and pyridine. The oxidation of nitrogen atoms in pyridine was also suggested as a possible reaction pathway.     

Nitrogen‐Doped Ordered Mesoporous Carbon Supported Bimetallic PtCo Nanoparticles for Upgrading of Biophenolics

Hydrodeoxygenation (HDO) is an attractive route for the upgrading of bio‐oils produced from lignocellulose. Current catalysts require harsh conditions to effect HDO, decreasing the process efficiency in terms of energy and carbon balance. Herein we report a novel and facile method for synthesizing bimetallic PtCo nanoparticle catalysts (ca. 1.5 nm) highly dispersed in the framework of nitrogen‐doped ordered mesoporous carbon (NOMC) for this reaction. We demonstrate that NOMC with either 2D hexagonal (p6m) or 3D cubic (Im m) structure can be easily synthesized by simply adjusting the polymerization temperature. We also demonstrate that PtCo/NOMC (metal loading: Pt 9.90 wt %; Co 3.31 wt %) is a highly effective catalyst for HDO of phenolic compounds and “real‐world” biomass‐derived phenolic streams. In the presence of PtCo/NOMC, full deoxygenation of phenolic compounds and a biomass‐derived phenolic stream is achieved under conditions of low severity.     

Nitrogen‐Doped Porous Graphitic Carbon as an Excellent Electrode Material for Advanced Supercapacitors

An advanced supercapacitor material based on nitrogen‐doped porous graphitic carbon (NPGC) with high a surface area was synthesized by means of a simple coordination–pyrolysis combination process, in which tetraethyl orthosilicate (TEOS), nickel nitrate, and glucose were adopted as porogent, graphitic catalyst precursor, and carbon source, respectively. In addition, melamine was selected as a nitrogen source owing to its nitrogen‐enriched structure and the strong interaction between the amine groups and the glucose unit. A low‐temperature treatment resulted in the formation of a NPGC precursor by combination of the catalytic precursor, hydrolyzed TEOS, and the melamine–glucose unit. Following pyrolysis and removal of the catalyst and porogent, the NPGC material showed excellent electrical conductivity owing to its high crystallinity, a large Brunauer–Emmett–Teller surface area (S_BET=1027 m² g^?1), and a high nitrogen level (7.72 wt %). The unusual microstructure of NPGC materials could provide electrochemical energy storage. The NPGC material, without the need for any conductive additives, showed excellent capacitive behavior (293 F g^?1 at 1 A g^?1), long‐term cycling stability, and high coulombic efficiency (>99.9 % over 5000 cycles) in KOH when used as an electrode. Notably, in a two‐electrode symmetric supercapacitor, NPGC energy densities as high as 8.1 and 47.5 Wh kg^?1, at a high power density (10.5 kW kg^?1), were achieved in 6 M KOH and 1 M Et₄NBF₄‐PC electrolytes, respectively. Thus, the synthesized NPGC material could be a highly promising electrode material for advanced supercapacitors and other conversion devices.     

Engineered Molecular Chain Ordering in Single‐Walled Carbon Nanotubes/Polyaniline Composite Films for High‐Performance Organic Thermoelectric Materials

Single‐walled carbon nanotubes (SWNTs)/polyaniline (PANI) composite films with enhanced thermoelectric properties were prepared by combining in situ polymerization and solution processing. Conductive atomic force microscopy and X‐ray diffraction measurements confirmed that solution processing and strong π–π interactions between the PANI and SWNTs induced the PANI molecules to form a highly ordered structure. The improved degree of order of the PANI molecular arrangement increased the carrier mobility and thereby enhanced the electrical transport properties of PANI. The maximum in‐plane electrical conductivity and power factor of the SWNTs/PANI composite films reached 1.44×10³ S cm^?1 and 217 μW m^?1 K^?2, respectively, at room temperature. Furthermore, a thermoelectric generator fabricated with the SWNTs/PANI composite films showed good electric generation ability and stability. A high power density of 10.4 μW cm^?2 K^?1 was obtained, which is superior to most reported results obtained in organic thermoelectric modules.