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Flash-spun nonwoven (FS-NW) is gaining attention in the PPE field due to its excellent barrier and mechanical properties resulting from its non-uniform diameter distribution and unique filament morphology. The unique network structure of flash-spun filaments (FSF) comprising the FS-NW can be controlled by phase separation behavior in the supercritical fluid (SCF) process. This study proposes a simple method to control the microstructure of FSFs by controlling the pressure-induced phase separation (PIPS) process in polymer/SCF solution. This phase separation behavior of an HDPE/SCF solution was confirmed by using a high-pressure view cell. A multistage nozzle allowing for phase-separated pressure to form different phases was also designed. HDPE-FSFs were synthesized by flash-spinning, and their morphology, crystallinity, and mechanical properties were investigated. The results demonstrated that the filaments obtained by PSP control at 220 °C and with an HDPE concentration of 8 wt% showed a network structure composed of strands, wherein the diameters ranged from 1.39 to 40.9 μm. Optimal FSF was obtained at 76 bar, with a crystallinity of 64.0% and a tenacity of 2.88 g/d. The PIPS method can thus effectively control the microstructure more feasibly than temperature- or solvent-induced techniques and can allow the effective synthesis of various products. [ABSTRACT FROM AUTHOR]

A systematic study considering the microstructural effect of carbon materials on the electrochemical or electrocatalytic performance is essential for developing carbon electrode materials of electric vehicles and smart grids that require durable and robust energy supply. In this study, the edge sites within activated carbons (ACs) were physically modified via thermal treatment to clarify the relationship between the edge density and hydrogen evolution reaction (HER). Moreover, their dominant contribution to the electrochemical performance of lead-carbon batteries was demonstrated. The ACs exhibited decreased defect density and enhanced crystallinity due to the merger of micro-domains during a high-temperature thermal treatment (HTT). In contrast to the specific surface area, the edge area of the ACs, which was quantified via temperature programmed desorption up to 1800 °C, decreased significantly with increasing HTT temperature. We have confirmed a close relationship between the edge densities and HER parameters. The lead-carbon battery unit cell employing HTT1600 with the lowest edge ratio (0.81%) exhibited a higher charging efficiency, higher cycling stability, and lower water loss than the cell employing pristine AC with a high edge ratio (8.42%). The edge ratio of carbon materials can be considered an important parameter in designing electrode materials for electrochemical energy storage. [Display omitted] [ABSTRACT FROM AUTHOR]

Nitrogen (N)-doped nanostructured carbons have been actively examined as promising alternatives for precious-metal catalysts in various electrochemical energy generation systems. Herein, an effective approach for synthesizing N-doped single-walled carbon nanohorns (SWNHs) with highly electrocatalytic active sites via controlled oxidation followed by N2 plasma is presented. Nanosized holes were created on the conical tips and sidewalls of SWNHs under mild oxidation, and subsequently, the edges of the holes were easily decorated with N atoms. The N atoms were present preferentially in a pyridinic configuration along the edges of the nanosized holes without significant structural change of the SWNHs. The enriched edges decorated with the pyridinic-N atoms at the atomic scale increased the number of active sites for the oxygen reduction reaction, and the inherent spherical three-dimensional feature of the SWNHs provided good electrical conductivity and excellent mass transport. We demonstrated an effective method for promoting the electrocatalytic active sites within N-doped SWNHs by combining defect engineering with the preferential formation of N atoms having a specific configuration. [ABSTRACT FROM AUTHOR]

2-(Trimethylsilyloxy)ethyl methacrylate (SMA)-derived mesoporous carbon nanofiber composite containing MnO 2 (Si-Mn-CNF) is fabricated by electrospinning method and found to be a very promising candidate for supercapacitor electrodes. Si-Mn-CNF possesses a large surface area of 707 m 2 g − 1 , high pore volume of 2.35 cm 3 g − 1 , and high mesopore fraction of 65%. Herein, SMA is used as an activating agent to develop the mesoporous structure by the thermal decomposition of SMA without activation process. As a result, Si-Mn-CNF exhibits a high specific capacitance of 200 Fg − 1 at a discharge current density of 1 mAcm − 2 and energy density of 23.72 Whkg − 1 at a power density of 400 Wkg − 1 in 6 M KOH aqueous electrolyte, due to the pseudocapacitive character associated with the surface redox-type reactions of the MnO 2 nanoparticles (NPs). Furthermore, the Si-Mn-CNF electrode retains a specific capacitance of over 85% of the initial value at a discharge current density of 20 mAcm − 2 compared with only 40% for Mn-CNF without using SMA, due to the rapid diffusion of electrolyte ions and the decrease of resistive characteristics through the developed mesoporous structures. Therefore, Si-Mn-CNF with high mesoporosity induced by SMA exhibits excellent electrochemical performance in terms of high specific capacitance and energy density, and excellent capacitance retention. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile (PAN) fibers are typically used as precursor fibers for carbon fiber production, produced through wet-spinning processes. The drawing process of the spun fiber can be classified into dry and wet drawing processes. It is known that the drawing stability and stretching ratio differ depending on the drawing process; however, the elementary characteristics are approximately similar. In this study, the mechanical properties of PAN fibers have been examined based on these two drawing processes with the differences analyzed through the analysis of microstructures. Further, to examine the composition of the fiber, element analysis has been conducted, and thereafter, the microstructure of the fiber is examined through X-ray diffraction analysis. Finally, the characteristics of PAN fibers and its mechanical properties has been examined according to each drawing condition. There are differences in moisture content and microstructure according to the drawing process, and it affects the tensile behavior. The results obtained could have potential implications if the processes are combined, as it could result in a design for a stable and highly efficient drawing process. [ABSTRACT FROM AUTHOR]

To store more energy in limited spaces, the volumetric performance of energy storage devices used in electric vehicles and portable electronics has attracted more research attention than their gravimetric performance. Herein, we describe the preparation of N/O co-doped single-walled carbon nanohorns (SWCNH) using chemical vapor deposition with pyridine followed by acid treatment to obtain a supercapacitor electrode material with high specific volumetric capacitance. The synthesized N/O co-doped SWCNH (N and O contents of 6.1 and 9.1 at%, respectively) electrode had a higher bulk density (1.05 g cm−3) than that of the pristine SWCNH electrode (0.86 g cm−3). Moreover, the N/O co-doped SWCNH supercapacitor electrode exhibited drastically increased specific volumetric, gravimetric, and areal capacitances (123 F cm−3, 117 F g−1, and 91.4 μF cm−2, respectively) in 1 M H 2 SO 4 electrolyte, compared with those of a pristine SWCNH electrode (36 F cm−3, 42 F g−1, and 11.4 μF cm−2, respectively). The superior electrochemical performances are associated with enhanced pseudocapacitive contribution and high bulk density of electrode upon N/O co-doping. The simple method described herein for producing SWCNH electrodes with high bulk density and high specific volumetric capacitance should contribute to the development of supercapacitors with high volumetric performance. Image 1 • N/O co-doped SWCNHs are prepared using a straightforward method. • N/O co-doped SWCNHs can be used as active materials in supercapacitor electrodes. • Electrochemical performance of SWCNHs is enhanced by N/O co-doping. • N/O co-doping increases pseudocapacitive contribution and electrode bulk density. [ABSTRACT FROM AUTHOR]

• NaOH-modified activated carbon fiber removes to heavy metals, cost-effectively. • The NaOH modification induced abundant oxygen functional groups in micropore. • Heavy metals adsorbed by a polar oxygen functional groups and pore filling mechanism. This manuscript describes an efficient and cost-effective method to remove heavy metals of Hg and Cd in aqueous solutions via adsorption on activated carbon fibers after modification with NaOH solution (NaACF). The Hg and Cd metals in the aqueous solution exist as Hg(OH) 2 and Cd2+ in the experimental condition of pH 6–8. Surface characterization of the NaACF reveals uniform and narrower micropores with an increase in oxygen functional groups of phenol and lactone compared with the original ACF (pACF). The NaACF demonstrates a superior adsorption rate to both aqueous samples of heavy metal compounds. The granular activated carbon (GAC) with diverse pore structures consisting of micropores, mesopores, and macropores adsorbed the heavy metals at a relatively slow rate. The adsorption mechanisms of the heavy metals into NaACF pores are proposed as pore-filling with non-ionic Hg(OH) 2 and electron sharing of oxygens in phenolic, lactone, and carboxylic acid groups with ionic Cd2+. The results from continuous feeding are also reported for the sample blend of 10 wt% NaACF and 90 wt% GAC in increasing the cost performance ratio. [ABSTRACT FROM AUTHOR]

In the fabrication of safe, but powerful lithium ion batteries (LIBs), graphene-related materials are being actively examined in order to meet the demand for applications such as electric vehicles and smart grids. However, most of this work has focused on liquid-phase exfoliated graphene and reduced graphene oxide. Herein, we demonstrate a simple, but effective route for significantly improving the electrochemical performance of currently available LIBs by coupling current collector with catalytically grown large-area graphene. When coating current collectors with large-area three-layered graphene, a reduction in the internal resistance (or effective electron transfer) between the current collector and active materials was observed. The graphene also protected the underlying collector from corrosion, greatly improving the power capability and cyclability of LIBs. The three-layered graphene provided the best electrochemical performance and corrosion resistance because of its high electrical conductivity and mechanical stability during the transfer process. We believe that our approach using interfacial graphene coating can be used with all kinds of electrochemical energy-storage systems, in which high corrosion resistance, electrical conductivity, and flexibility are critical. Image 1 [ABSTRACT FROM AUTHOR]

The low density of porous carbon nanomaterials for supercapacitor electrodes has limited their widespread application, despite their ultra-high gravimetric capacitance. In this work, we successfully prepared highly densified composite electrodes of graphene and single-walled carbon nanohorns (SWCNHs) using a simple spray-drying method that is suitable for mass production. To prepare the high-density composite electrodes, water-based mixtures of oxidized SWCNHs (NHOs) and graphene oxides (GOs) were spray-dried in heated air; after spray-drying, GOs dispersed in water were agglomerated in spherical clusters containing NHO nanoparticles. The reduced spray-dried GO/NHO (rS-GO/NHO) composite electrodes exhibited an extremely high bulk density of 1.23 g·cm−3, which is almost double that of commercial activated carbon (AC) and reduced NHO (r-NHO) electrodes, and three times higher than that of rS-GO electrodes. Of the materials tested, the rS-GO/NHO composite electrode had the highest volumetric capacitance (80 F·cm−3 at 1 mA·cm−2) and a low sheet resistance (0.005 Ω· sq.−1), which are far superior to those of commercial AC (57 F·cm−3 at 1 mA·cm−2 and 0.293 Ω·sq.−1, respectively), without the need for a conductive material, such as carbon black. We expect that these high-density graphene/SWCNH composite electrodes with high volumetric capacitances can be substituted for commercial AC materials in energy storage devices, such as supercapacitors. Unlabelled Image • High-density graphene/single-walled carbon nanohorn composite was produced by facile spray-drying method. • The proposed method is suitable for mass production of this composite material. • The best composite electrode had a bulk density double that of commercial activated carbon electrodes. • The composite supercapacitor electrode exhibited high volumetric capacitance. [ABSTRACT FROM AUTHOR]

In this study, we investigated the possibilities and combination of cost-effective materials of carbon (C) and lead (Pb) with polypropylene (PP) polymer as a new kind of bipolar plate for unitized regenerative fuel cell and polymer electrolyte membrane fuel cell systems. The homogeneous composite structure of C:Pb developed through facile mechanical milling process, and optimized. The new bipolar plate was fabricated with PP using compression molding process with hot pressing techniques. A dense and smooth surface morphology of C:Pb bipolar plate was acquired with the uniform thickness of 1.33 (±0.17) mm. Compared to C, an improved electrical properties (~20%) obtained to the powdered C:Pb composite materials because of homogeneous composition of Pb metal particles with large surface area of C. The C:Pb bipolar plate revealed an efficient water contact angle behavior than the C bipolar plate, where the water contact angle for C and C:Pb bipolar plates are 82.4° and 93.1°, respectively. A sophisticated electrochemical stability performance has obtained to the C:Pb bipolar plate in acidic condition. According to Tafel plots analysis, higher corrosion resistance has observed to the C:Pb bipolar plate than the C bipolar plate. The fabricated new kind of C:Pb bipolar plate provides the many advantageous, thus it proves the insights for further developments and applicability in the practical application. In the perspective view, the performances of C:Pb bipolar plate can be further altered through modification of different carbon structures together with impregnation of Pb nanostructured materials into the pores and/or embedded throughout the surface, and efficient conductive polymers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous S-doped graphene was prepared by the chemical vapor deposition of thiophene. • Effects of S-doping on supercapacitor electrode performance were investigated. • Electrochemical performance of porous S-doped graphene was enhanced by S-doping. • S-doping increased the electrical conductivity, wettability, and pseudocapacitance. In this study, we successfully synthesized porous S-doped graphene spheres (SGSs) with an S content of 1.1 at% by chemical vapor deposition on a spherical layered double hydroxide (LDH) template using thiophene (C 4 H 4 S) as the S-containing carbon source. The doped S atoms were removed from the SGSs by heat treatment under a H 2 atmosphere to give desulfurized graphene spheres (De-SGSs) that retained the original pore structure. The effects of the S-doping on the electrochemical behavior of the SGS supercapacitor electrode were investigated by comparing these behaviors with those of the De-SGS electrode. The results revealed that the SGS electrode exhibited electrical conductivity and surface wettability with the electrolyte that were superior to those of the De-SGS electrode. Furthermore, the SGS electrode showed an extremely high capacitance retention of approximately 100% at a current density of 20 mA cm−2 in an electrolyte of 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (TEABF 4 /PC), while that of the De-SGS electrode under same conditions was approximately 40%. Thus, due to its excellent electrical conductivity, wettability, and the pseudocapacitive contribution of its S-dopants, the SGS electrode demonstrates an electrochemical performance that is superior to that of the De-SGS electrode. [ABSTRACT FROM AUTHOR]

Despite significant improvements in the synthesis of nitrogen (N)-doped carbon nanotubes (CNTs) and their versatile applications, there has always been a large difficulty in controlling the bonding configuration of N atoms within CNTs. In the current work, we report an effective chemical strategy to synthesize single-walled carbon nanotubes (SWNTs) with 100% of quaternary N via a chlorosulfonic acid(CSA) treatment. In this process, the pyridinic and pyrrolic groups were selectively and completely removed while retaining the quaternary N atoms. The presence of 2.04 at. % of quaternary N atoms within SWNTs was directly identified from a single sharp peak in the N 1s spectra of XPS, and indirectly supported by the downshift of C 1s peak in XPS, the upshift of G'-band in Raman spectroscopy, and the decrease of the work function from 5.46 to 4.59 eV. The doping effect of the quaternary N atoms on the macroscopic properties of SWNT fibers was verified by a large increase in the electrical conductivity from 0.63 to 2.17 MS/m. In perspective, our chemical approach can now be applied to synthesize carbon materials with controlled N functionalities for different applications. Image 1 [ABSTRACT FROM AUTHOR]

A facile fabrication of a porous carbon cryogel from a blend (PAEO) of fluorinated poly(amic acid) and poly(ethylene oxide) (PEO) is demonstrated. The porous carbons are prepared by carbonizing the freeze-dried cyrogels of polymer blend with various contents. The original channel structures of the cryogels with PEO content below 5 wt% are perfectly maintained in the carbon cryogels. In particular, the carbon cyrogel derived from the blend (PEO content: 5 wt%) shows very high specific surface areas, 2646 m 2 /g. From investigation of the carbonization mechanism, it is found that the incorporation of PEO creates mesoporous structure without generating hydrophobic or ambiphilic components, while elimination of fluorine moiety affects the formation of microporous structure in resulting-carbon. In addition, the porous structure in carbon cryogels of high PEO loading is shrunk because PEO component reduces the rigidity of the structure. Lastly, the performance of the carbon cryogels as a capacitor is investigated. [ABSTRACT FROM AUTHOR]

• Boron-doped activated carbon fiber effectively sensed to NO 2 gas, repetitively. • Boron doping induced high selectivity toward NO 2 via the strong binding energy. • The shallow, narrow and uniform pores on the surface worked as trap sites for NO 2. In the current work, a high performance NO 2 gas sensors has been fabricated from activated carbon fibers containing enriched boron moieties. The porous carbon fibers decorated with boron moieties exhibited rapid, repetitive and selective NO 2 sensing performance at room temperature. The shallow, narrow and uniform micropores on the surface of the carbon fiber allowed target gases to be adsorbed and desorbed very easily whereas boron moieties induced high selectivity toward NO 2 over NH 3 via the strong binding energy. The excellent NO 2 gas sensing performance of boron doped porous carbon fibers is attributed to synergetic effect of intrinsic pore structure of the carbon fibers and the boron moieties decorated on their surface. [ABSTRACT FROM AUTHOR]