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Given environmental friendliness, high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) can be the alternative power source for clean power generation. However, neither developments nor strategies of diffusion media are actively conducted yet to achieve high‐performance HT‐PEMFCs. Herein, a nanoporous carbon nanotube (CNT) sheet, a new anode diffusion layer between the gas diffusion layer|bipolar plate interface that improves fuel cell performance and durability by CNT purification for facilitating fuel accessibility with uniform interfacial contact for reducing acid loss, is reported. Configuration of the optimal CNT‐inserted fuel cell is examined and proposed under the operating temperature of 140–200 °C. The underlying mechanism of this new diffusion layer with multiphysics simulation elucidates that the nanoporous nature induces gas‐wall collision, enabling uniform dispersion within adjacent diffusion media. These fuel cells outperform performance over two times higher and have a voltage decay rate nearly two times lower than conventional HT‐PEMFC. [ABSTRACT FROM AUTHOR]

In proton exchange membrane fuel cells (PEMFCs), securing sufficient hydration in perfluorosulfonic acid (PFSA) membrane is considered an indicator of performance and durability. Here, we present a straightforward yet effective strategy that sandwiches the nanoporous carbon nanotube (CNT) sheet between the cathodic gas diffusion backing layer (GDBL) and bipolar plate (BP) of a conventional membrane electrode assembly (MEA). CNT sheets are synthesized through the cost-effective direct spinning method. The carbon source, winding rates, and the number of layers are varied to tailor the thickness and nanoporous morphology of the CNT sheets (5, 15, and 30 μm). CNT interlayer MEAs are evaluated for their performance in various temperature and relative humidity (RH), ranges of 80–120 °C and 25–100% RH. With these nanoporous CNT sheets, reactants disperse homogeneously, enhancing membrane hydration and interfacial contact, thereby fulfilling superior performance compared to conventional under entire conditions. Among CNT interlayers, the 30 μm records a 115.4% enhanced peak power density (0.28 W cm−2) and 89.2% extended durability (∼187 h) than conventional under 120 °C and 25% RH. Our strategy delivers a broader perspective of PEMFCs and other fuel cell types based on their ease of production and reproducibility. [Display omitted] • Nanoporous CNT functional interlayers were prepared by direct spinning. • CNT interlayer notably boosts the performance of PEFMCs under all test conditions. • CNT interlayer also achieves 89.2% extended durability of PEMFCs. • These promising boosting mechanisms were demonstrated and optimized. [ABSTRACT FROM AUTHOR]

Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst's exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (–OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate ( SO 4 2 − ) than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal–sulfur bonds (such as S2− and S n 2 − ). The hydroxyl group (–OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors. [ABSTRACT FROM AUTHOR]

In this study, high-purity single-walled carbon nanotubes (SWCNTs) are synthesized with additional carrier gas through floating catalyst chemical vapor deposition. The presence of Ar during the SWCNT aerogel formation affects to the precursor decomposition and to the formation of different reactive hydrocarbons. Furthermore, the concentration of produced various carbon species is sensitive to the carrier gas compositions. The in-situ sampling methods prove the thermodynamic pathway for the hydrocarbon cracking during carbon nanotube (CNT) aerogel formation process. The addition of Ar promoted the formation of reactive hydrocarbon species, such as CH3, CH4, and C2H4/CO, to improve CNT morphology and graphitization. Ar has improved purity of CNTs compared to when only H2 is used. The synthesized CNTs were narrow in size, and the diameter decreased from 1.8 to 1.2 nm with the carrier gas composition (Rx) according to Ar addition. The IG/ID ratio of the CNTs changed from 78 to 3 at R0.1 and R0.57, respectively. Furthermore, the purity also increased to approximately 10% from 78% to 91% depending on Rx.

This work studies synthesis of carbon nanotube (CNT) sheet using the high temperature (1400 °C) floating catalyst chemical vapor deposition (FC-CVD) method. Three metallocenes—ferrocene, nickelocene, cobaltocene—and their combinations are used as precursors for metal catalysts in the synthesis process. For the carbon source, an alcohol fuel, a combination of methanol and n-hexane (9:1), is used. First, the metallocenes were dissolved in the alcohol fuel. Then, the fuel mixture was injected into a tube furnace using an ultrasonic atomizer with Ar/H2 carrier gas in a ratio of about 12/1. The synthesis of CNTs from a combination of two or three metallocenes reduces the percentage of metal catalyst impurity in the CNT sheet. However, there is an increase in structural defects in the CNTs when using mixtures of two or three metallocenes as catalysts. Furthermore, the specific electrical conductivity of the CNT sheet was highest when using a mixture of ferrocene and cobaltocene as the catalyst. Overall, the multi-catalyst method described enables tailoring certain properties of the CNT sheet. However, the standard ferrocene catalyst seems most appropriate for large-scale manufacturing at the lowest cost. [ABSTRACT FROM AUTHOR]

We present a post-treatment method for directly-spun ultra-thick carbon nanotube fibers (CNTFs) with a high linear density of ∼ 6 tex (g km−1), which can possibly meet industrial-scale productivity. The treatment consists of consecutive steps of swelling of CNTFs in chlorosulfonic acid, stretching, and coagulation. The swelling of CNTFs makes even distribution of the CNT bundles, which are the subunits of CNTFs, and thereby promotes the removal of the interstitial voids and macroscopic pores during subsequent coagulation. The stretching straightens tortuous CNT bundles, and thereby facilitates dense packing of aligned bundles along the fiber axis that are evenly distributed by swelling. However, highly-tortuous CNT bundles in the high linear-density CNTF leads to incremental improvement of structure and properties. The stretching is only effective at stretching ratio (R S) > 20%, and both tensile strength and electrical conductivity gradually increase as R S increases, to 27- and 8.7-times at the maximum R S = 100%. We believe that our study on the influence of R S on the structure and properties of high linear-density CNTFs provide a new opportunity for designing the industrial process of the post-treatment to commercialize CNTFs. Image 1 [ABSTRACT FROM AUTHOR]

The commercial conducting materials (Cu, Ag, Al etc.) have achieved their saturation due to their high density and Joule's heating effect in terms of efficiency. In this outlook, carbon nanotubes (CNTs) are the most versatile, light weight and high electrically conducting material for advance generation. But it is difficult to weave them for commercialization. For the growth of 3-D CNT assemblies such as CNT fiber, CNT sheet, CNT rope and CNT ribbon, direct spinning is the most suitable technique because of its simplicity for continuous growth of CNT fiber. In the present work, different growth parameters were analysed for the growth of CNT fibers. The growth of CNT fibres has been carried out through direct spinning of as-synthesised CNT aerogel. CNT fibers were grown successfully via optimizing different processing parameters like temperature, pressure and argon to hydrogen ratio. The morphology of as-spun fibers was investigated via microscopic techniques such as optical microscopy, SEM and TEM. Moreover, the defects and metallicity of as-spun fibers have been analysed using Raman spectroscopy. The change in resistance with change in temperature was also measured for quality of as-made CNT fiber which shows metallic behavior as CNT fiber has positive temperature coefficient. Above 151K, conducting CNTs are dominating and below this temperature, semiconducting CNTs are showing their nature in R v/s T curve. Furthermore, the measured electrical conductivity of as-made fiber is 3.9x10³ S/m. These as-spun metallic fibers can outperform the currently used Cu wire. Hence, as-synthesized conductive CNT fibers have great potential as conducting wires. [ABSTRACT FROM AUTHOR]

Among the key components of a battery electrode, current collectors hold significant importance for the energy density of lithium ion batteries (LIBs) as metal foils account for a significant proportion of the total mass. Carbon nanotube sheet (CNTS) has garnered considerable attention because of its fascinating material features such as high electrical conductivity, low density, and excellent flexibility. In this study, we demonstrate the utilization of a direct-spun CNTS as a current collector in order to enhance the electrochemical performance and replace the conventional current collector, that is, aluminum (Al) foil, in LIBs. When the CNTS coated with NCM811 (NCM811/CNTS) is evaluated in LIBs, it delivers superior rate capability and cycle stability compared with Al foil-based and buckypaper-based NCM811 electrodes. It is because the CNTS with a large surface area and high electrical conductivity establishes a number of electronic pathways to the cathode electrode. In addition, the porous structure of the CNTS efficiently enhances the adhesive properties of the electrodes. Due to the synergistic benefits of CNTS, cells with stacked NCM811/CNTS electrodes are successfully fabricated. Electrode stacking with multiple NCM811/CNTS electrodes exhibits improved areal capacity and stable cycle stability, suggesting a new strategy to replace the concept of conventional thick electrodes. Moreover, pouch cells with LTO/CNTS as an anode and NCM811/CNTS as a cathode display stable electrochemical performance even under mechanical deformation (e.g., folding/unfolding) [Display omitted] [ABSTRACT FROM AUTHOR]

Industrial-scale use of carbon nanotube (CNT) materials and prototype development is limited by the availability of economic, high-throughput production methods. Recent investigations have demonstrated the feasibility of producing direct-spun macroscopic CNT materials via floating catalyst chemical vapour deposition. However, few quantitative results have been reported regarding process yield and correlations with product quality. Validation of results is therefore challenging as identification of the key fundamental process parameters is hindered. This first meta-analysis quantifies atomic input rates and correlates them with product outputs to map the current parameter space of 55 successful conditions leading to spinnable aerogels. All mapped processes fall within a bulk residence time of 5–240 s, operating temperature of 1100–1500 °C and an atomic S:Fe of 0.1–10. Low (high) S/Fe ratios favour single (multi)-wall CNTs in the direct-spun product. A high atomic carbon dilution, with only 3% of the input atoms being C, is a common feature across many systems. Furthermore, we connect the findings to known catalyst and product growth behaviour, as well as the thermodynamics of intermediates, to create an emerging picture of direct-spun CNT product formation. Elucidation of the most important factors influencing material synthesis, and the relationships between them, provides opportunities for gains in industrial-scale synthesis. Image 1 [ABSTRACT FROM AUTHOR]

The emerging fiber-shaped supercapacitors have motivated tremendous research interest in energy storage devices. However, obtaining thin gel electrolyte interlayers with small thickness and large contact interface area of electrodes, which are crucial for the high-performance realization, still remains challenging. Here, we demonstrate the facile and direct spinning of three-ply core-sheath graphene fiber supercapacitors with thin and continuous wrinkling gel electrolyte interlayer by a wet spinning approach through coaxial three-channel spinneret. The architectural feature of gel electrolyte interlayer can remarkably increase electrode/electrolyte contact interface area and facilitate transport of charges and ions. The resulting flexible core-sheath graphene fiber supercapacitors exhibit a high specific capacitance of 249 mF cm −2 , perfect cycling stability (96% retentions after 10000 cycles), and almost unaltered capacitance performance during repeated bending to 180°. The maximum power and energy densities are estimated to be 4.81 mW cm −2 and 44 μWh cm −2 , respectively. The energy density was further improved to 59 μWh cm −2 , when polyaniline was used. [ABSTRACT FROM AUTHOR]

Lightweight high-performance macroscopic fibers and yarns of oriented carbon nanotubes (CNTs) with high tensile strength and stiffness and electrical conductivities are in high demand for a wide range of applications. Among various production methodologies, the direct continuous spinning of CNT fibers from a chemical vapor deposition reactor has attracted interest because of its scalability potential. However, the presence of non-CNT impurities limits achieving high fiber tensile and electrical performances reproducibly. Here, we present for the first time a one-step protocol to purify direct-spun CNT fibers by mild sonication in acetone. Sonication reduced the impurity content by ~ 42%, which led to enhanced CNT fiber performance. In comparison to untreated fibers, the purified fibers showed a 50% and 100% increase in specific strength and stiffness, respectively. The CNT fiber electrical conductivity increased by 3-fold after purification. This improvement in fiber performance was observed despite a reduction in the nanotube bundle orientation after sonication. The better performance of the purified fibers is attributed to improved CNT bundle packing and densification. Our process is simple, quick, effective, and uses readily available acetone and hence, shows promise as a post-production purification method to direct CNT fiber spinning. [ABSTRACT FROM AUTHOR]

The present study aimed to enhance the electrical conductivity of carbon nanotube (CNT) fibers by introducing copper sulfide (CuS) into them. CuS forms a very stable compound with an electrical conductivity as high as 10 S/m, and it was introduced into CNT fibers by treating them with polyethyleneimine (PEI) to introduce amine groups on the CNTs. The CNT fibers were then treated with a solution of copper sulfate/sodium thiosulfate, which increased their electrical conductivity by ≥100 % (4×10 S/m) relative to that of untreated CNT fibers. This study also examined how the CuS plating changed the structure, morphology, and mechanical properties of CNT fibers. The results indicate that the modulus of elasticity of CuS-plated CNTs increased by 2.86 times (11.34 N/tex) and the elongation-at-break decreased by half. [ABSTRACT FROM AUTHOR]

Highlights: [•] CNT fibers could be selectively synthesized by the processing conditions. [•] Type and crystalline quality of CNTs were characterized by RBM and I G/I D ratio. [•] Crystalline quality of CNTs could be improved by the processing parameters. [Copyright &y& Elsevier]

Carbon nanotube (CNT) sheet was sandwiched between the cathodic GDBL and a bipolar plate of polymer electrolyte membrane fuel cells (PEMFCs). The CNT sheets were synthesized through the direct spinning method and investigated their morphological characteristics. The electrochemical performances of MEA with CNT interlayer were measured via polarizations, iR-free, and electrochemical impedance spectra (EIS) compared to the conventional MEA under elevating backpressure. The performance of the MEA with CNT interlayer at 1.0 bar g was enhanced by 91.8% (364 mW cm−2 at 0.7 V), which was higher than the peak power density improvement of 13.0% (850 mW cm−2 at 0.48 V). We also identified that corresponding ohmic and charge-transfer resistances were reduced. Especially, the ohmic resistance was decreased by up to 42.2% with increasing operating pressure compared to the conventional MEA due to better hydration and interfacial contact. Notwithstanding that the performance was ameliorated with increased pressure, we found that the mass transport loss tends to become more sensitive at the high current density region, and thus optimum operating conditions were proposed. We concluded that the CNT sheet as a functional interlayer would be advantageous in improving the performance of commercialized PEMFCs. [Display omitted] • CNT sheet was sandwiched between cathodic GDBL and bipolar plate in PEMFCs. • CNT sheets were synthesized through the direct spinning method. • Power density at typical operating voltage enhanced 91.8% (364 mW cm−2 at 0.7 V). • Ohmic resistance was reduced by up to 42.2% with increasing operating pressure. [ABSTRACT FROM AUTHOR]

This study discusses the evaluation of stretch-breaking force and its CV% in the tow-toyarn direct spinning with 12k oxidized filament tow. We aimed to describe a new method for determining suitable draft conditions in the direct spinning to obtain the best oxidized yarn quality. To correlate the stretch-breaking force and the yarn quality, oxidized direct spun yarns were spun on a modified laboratory spinning frame for onestep conversion of a tow-to-yarn system. Base on the correlation of stretch-breaking force CV and direct oxidized yarn quality, the drafting ratio and roller gauge corresponding to the lower unevenness (CV%) of the direct oxidized yarn could be chosen as the suitable draft condition in direct yarn spinning to obtain the best oxidized yarn quality. Obviously, the results revealed that the technique of stretch-breaking force could be applied on the optimum draft condition of tow-toyarn direct spinning. [ABSTRACT FROM AUTHOR]