Porous Carbon Nanotube Network Research Articles

Synergistic Electrocatalyst-Cathode Architecture for Stable Long-Term Cycling Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are a promising candidate for next-generation energy storage owing to the high theoretical capacity of sulfur (1,675 mAh g−1). However, the intrinsically low electrical conductivity of sulfur and complex multistep electrolyte-mediated redox reactions involving soluble lithium polysulfide intermediates engender critical challenges toward practical realization. Specifically, migration and diffusion of higher-order lithium polysulfides provokes continuous loss of active sulfur species, yielding premature capacity fade. Electrochemical kinetics also remain sluggish due to the insulating nature of sulfur cathodes, which require engineering designs to accelerate charge transfer.Rational morphological and compositional cathode tuning represents a compelling strategy for addressing fundamental Li-S limitations. Herein, we develop an extended cathode architecture composed of a porous carbon nanotube network decorated with homogenously dispersed nanocatalysts. Electron microscopy and spectroscopy analysis verify platinum group metals are well-incorporated both within internal channels and external surface sites of conductive carbon nanotubes. The composite framework affords multifaceted functionality arising from synergistic chemical and structural attributes of components. Nanocatalyst sites demonstrate a pronounced chemical affinity toward soluble polysulfide intermediates, effectively localizing them within cathode, minimizing diffusional losses toward the anode. This anchoring phenomenon is complemented by the inherent microporosity of the high-surface-area nanotube network, further obstructing polysulfide migration through a confinement effects. Concurrently, noble metal nanoparticles facilitate the redox conversion of trapped higher-order polysulfides into solid Li2S alleviating the precipitation of electrically insulating discharge products. The excellent electrical conductivity of CNTs ensures efficient charge transport to all incorporated sulfur active materials, further maximizing reversible utilization.As a result of complementary polysulfide confinement and electrocatalytic conversion functionalities, Li-S coin cells exhibit enhanced reversible capacities exceeding 900 mAh g−1 for over 500 cycles at 0.558 A g−1. Notably, over 500 cycles, minimal capacity decay of 0.018% per cycle and 92% retention of the initial capacity are obtained at moderate sulfur loadings highlighting the exceptional cycling stability enabled by engineered cathodes. Outstanding rate performance is also demonstrated with the delivery of 854 mAh g−1 capacity at a very high current density of 1.675 A g−1. Our rationally designed cathode architecture provides critical mechanistic insight toward addressing fundamental bottlenecks to progress Li-S technologies.

Nanomechanical characterization of carbon nanotube-based composite interfaces tailored by electrophoretic deposition

Carbon nanotube (CNT) addition to composite materials can offer both nanoscale reinforcement and a multifunctional element due to their extraordinary mechanical, thermal and electrical properties. Electrophoretic deposition (EPD) offers a scalable processing technique to incorporate CNTs into conventional fiber-reinforced polymer composites (FRPCs), facilitating the production of unique nanoscale structures in the critical interphase region. In this study, CNTs functionalized with polyethyleneimine (CNT-PEI) were deposited onto a planar substrate via EPD followed by the infusion of epoxy matrix in order to replicate the nanocomposite interphase region present in nanomodified FRPCs. The nanocomposite films have thicknesses ranging from several hundred nanometers to a few microns to represent different fiber-matrix interphase regions found in FRPCs. The morphology and mechanical performance of CNT-PEI/epoxy nanocomposites are examined using atomic force microscopy (AFM) in both tapping and nanoindentation modes. The EPD creates a homogeneously distributed porous CNT network bridged by PEI, forming the pathway of epoxy resin infusion through interconnected pores with diameters less than 100 nm. CNT-PEI/epoxy nanocomposites exhibited significant improvements in stiffness, hardness, and creep resistance compared to constituent porous CNT-PEI films and neat epoxy. The improvement was directly related to the ability of the load bearing CNTs chemically bonded with the epoxy matrix through the grafted PEI, providing an efficient load transfer mechanism. The chemical bond between the porous CNT-PEI and epoxy also produced far greater fracture surface in nanoscale scratch tests compared to unmodified epoxy, indicating the CNT-PEI/epoxy nanocomposite is capable of distributing load and absorbing more energy prior to fracture.

Porous carbon nanotube networks and pillared graphene materials exhibiting high SF6 adsorption uptake and separation selectivity of SF6/N2 fluid mixtures: A comparative molecular simulation study

Abstract SF6 and SF6–N2 gas mixtures are well known insulators used in industry applications, but SF6 has to be recovered due to its high global warming potential. In this study, the adsorption of the pure SF6 and N2 fluids and the separation of their mixture with SF6:N2 = 1:9 composition, using three-dimensional porous carbon nanotube networks and pillared graphene materials has been studied by employing Monte Carlo and Molecular Dynamics simulations at ambient temperature and pressure up to 20 bar. The results obtained reveal a significant SF6 uptake and high adsorption selectivity for SF6 over N2, compared to the best performing materials in the literature. The selectivity for SF6 decreases in the case of pillared graphene and strongly depends on the nanotube pillar and graphene layer distances. The saturation capacity of the investigated materials is also achieved at very different pressure ranges, as it has been reflected on the calculated adsorption isotherms. Due to this fact, the translational diffusion coefficients of the adsorbed SF6 and N2 molecules in each material are significantly different at ambient conditions. The results obtained might be used as a springboard towards the rational design of carbon-based materials for the capture of the very potent greenhouse gas SF6.

Scalable Synthesis of Fe/N-Doped Porous Carbon Nanotube Frameworks for Aqueous Zn-Air Batteries.

Aqueous Zn-air batteries are emerging to be ideal next-generation energy-storage devices with high safety and high energy/power densities. However, the rational design and fabrication of low-cost, highly efficient, and durable electrocatalysts on the cathode side remain highly desired. Herein, template-assisted, scalable Fe-implanted N-doped porous carbon nanotube networks (Fe-N-CNNs) have been synthesized based on an environmentally friendly template hydroxyapatite nanowires (HAP NWs). Thanks to the hierarchical meso/micropores, high specific surface area, and abundant active sites, the optimized Fe-N-CNNs exhibit excellent oxygen reduction activity. Furthermore, the Zn-air batteries based on the Fe-N-CNNs cathode deliver a high discharge voltage of 1.27 V at a current density of 20 mA cm-2 and a large peak power density of 202.2 mW cm-2 . More far-reaching, this HAP-based template strategy opens a new avenue toward the mass production of efficient, cost-effective electrocatalysts, and the Fe-N-CNNs with hollow interiors are expected to extend their other potential uses in energy storage, molecular sieves, adsorbents, and biomedical engineering.

Fabrication of Self-Entangled 3D Carbon Nanotube Networks from Metal–Organic Frameworks for Li-Ion Batteries

Three-dimensional (3D) carbon nanomaterial assemblies are of great interest in emerging applications including electronic devices and energy storage because of their extraordinary high electrical conductivity and mechanical and thermal properties. However, the existing synthetic procedures of these materials are quite complex and energy-intensive. Herein, a facile approach is developed for fabricating a self-entangled carbon nanotube (CNT) network under convenient conditions (400 °C for 1 h), breaking the critical limitations of the current available methods. The keys of forming such 3D CNT network are the fragmentation of the sacrificial MOFs into nanosized particles, the reduction of metal elements in MOFs to highly active nanocatalysts by introducing hydrogen, and the supplement of external carbon source by introducing ethyne. In addition, the highly conductive 3D porous CNT network facilitates electron transfer and provides an excellent platform for high-performance Li-ion batteries (LIB).

Highly selective separation and adsorption-induced phase transition of SF6-N2 fluid mixtures in three-dimensional carbon nanotube networks

The separation of an equimolar SF6-N2 fluid mixture in a three-dimension porous carbon nanotube network has been investigated by means of classical molecular dynamics simulations at ambient conditions. The calculations performed have shown that the SF6 molecules are preferentially adsorbed over the nitrogen ones, yielding a high selectivity for sulfur hexafluoride. The adsorbed mixture is much denser than the bulk supercritical fluid, exhibiting a liquid-like behavior, which is reflected on the static structural, transport and dynamic properties of the confined mixture.

Ternary Hybrid Material for High-Performance Lithium-Sulfur Battery.

The rechargeable lithium-sulfur battery is a promising option for energy storage applications because of its low cost and high energy density. The electrochemical performance of the sulfur cathode, however, is substantially compromised because of fast capacity decay caused by polysulfide dissolution/shuttling and low specific capacity caused by the poor electrical conductivities of the active materials. Herein we demonstrate a novel strategy to address these two problems by designing and synthesizing a carbon nanotube (CNT)/NiFe2O4-S ternary hybrid material structure. In this unique material architecture, each component synergistically serves a specific purpose: The porous CNT network provides fast electron conduction paths and structural stability. The NiFe2O4 nanosheets afford strong binding sites for trapping polysulfide intermediates. The fine S nanoparticles well-distributed on the CNT/NiFe2O4 scaffold facilitate fast Li(+) storage and release for energy delivery. The hybrid material exhibits balanced high performance with respect to specific capacity, rate capability, and cycling stability with outstandingly high Coulombic efficiency. Reversible specific capacities of 1350 and 900 mAh g(-1) are achieved at rates of 0.1 and 1 C respectively, together with an unprecedented cycling stability of ∼0.009% capacity decay per cycle over more than 500 cycles.

Surface enhanced Raman spectroscopy on silver-nanoparticle-coated carbon-nanotube networks fabricated by electrophoretic deposition

In this study, the efficiency of silver nanoparticle (AgNP) decorated carbon nanotube (CNT) based porous substrates has been investigated for surface-enhanced Raman spectroscopy (SERS) applications. The fabrication of uniform thin coatings of carbon nanotubes is accomplished by Electrophoretic Deposition (EPD) on organosilane functionalized silicon substrates. The deposition process exemplifies a fast, reproducible and single-step room temperature coating strategy to fabricate horizontally aligned porous CNT network. Surfactant stabilized AgNPs were deposited on the CNT networks by immersion coating. The acquired Raman spectra of Rhodamine6G (R6G) analyte examined on the fabricated Ag-CNT-Si substrates exhibited enhanced signal intensity values when compared to SERS-active planar AgNP-Si substrates. An overall enhancement factor of ∼109 was achieved for the tested analyte which enables pushing the limit of detection to 1 × 10−12 M (1 pM). The enhancement can be attributed to the large surface area offered by the AgNP-CNT porous network, which is expected to increase the number of effective “hot spots” for the SERS effect.

Separation of CO2–N2mixtures in 3D carbon-based porous nanotube networks: a molecular dynamics investigation

The separation of an equimolar CO2-N2 mixture in a 3D porous carbon nanotube network has been investigated. An enhanced CO2 adsorption selectivity has been observed. The diffusion coefficients of the adsorbed molecules have been related to their residence dynamics in the vicinity of the carbon atoms of the nanopore.

Preparation of continuous carbon nanotube networks in carbon fiber/epoxy composite

In order to optimize carbon nanotube (CNT) dispersion state in fiber/epoxy composite, a novel kind of CNT organization form of continuous networks was designed. The present work mainly discussed the feasibility of preparing continuous CNT networks in composite: Fiber fabric was immersed into CNT aqueous solution (containing dispersant) followed by freeze drying and pyrolysis process, prior to epoxy infusion. The morphologies of fabric with CNTs were observed by Scanning Electron Microscope. The relationship between CNT networks and flowing epoxy resin was studied. Properties of composite, including out-of-plane electrical conductivity and interlaminar shear strength (ILSS), were measured. The results demonstrated that continuous and porous CNT networks formed by entangled CNTs could be assembled in fiber fabric. Most part of them were preserved in composite due to the robustness of network structures. The preserved CNT networks significantly improved out-of-plane electrical conductivity, and also have an effect on ILSS value.

A pressurized filtration technique for fabricating carbon nanotube buckypaper: Structure, mechanical and conductive properties

Self-supporting carbon nanotube (CNT) buckypaper has unique structural and conductive properties which can be utilized in various applications. A pressurized filtration technique was developed to fabricate the buckypaper, and tailor its porous structures and properties. Compared with the conventional vacuum filtration technique, the pressure applied in the pressurized filtration process increased from 1atm to as high as 12atm. Filtration behaviors of the CNT solutions during the vacuum and pressurized filtration processes were studied. The results indicated that the filtration behaviors were largely dependent of the applied pressure. Micro-morphologies of the buckypaper were also characterized and appeared to be corresponding to the filtration behaviors well. Upon applying high pressure during the filtration, porosity of the buckypaper was reduced slightly by ∼1.9% due to the flexibility of the porous CNT network structure. Dimensions of the gaps within the interior of highly intermingled CNT bundles or junctions also decreased, resulting in higher intertube interactions. The higher intertube interactions improved the overall mechanical properties, as well as electrical and thermal conductivities of the buckypaper significantly.

Soft, Highly Conductive Nanotube Sponges and Composites with Controlled Compressibility

Porous carbon nanotube networks represent a type of material that can achieve both structural robustness and high flexibility. We demonstrate here controlled synthesis of soft to hard sponges with densities ranging from 5 to 25 mg/cm(3), while retaining a porosity of >99%. The stable sponge-like structure allows excellent compressibility tunable up to 90% volume shrinkage, and the ability to recover most of volume by free expansion. Electrical resistivity of the sponges changes linearly and reversibly after 300 cycles of large-strain compression. Nanotubes forming the three-dimensional scaffold maintain good contact and percolation during large-strain deformation, polymer infiltration, and cross-linking process, suggesting potential applications as strain sensors and conductive nanocomposites.

Carbon nanotube network modified carbon fibre paper for Li-ion batteries

Here we report on the direct deposition of large quantities of highly porous carbon nanotube networks onto a carbon fibre paper support; subsequently utilised as the anode in a Li-ion battery application showing improved long-term performance and chemical stability with a significant fully reversible capacity of 546 mAh g−1.

Fabrication of porous carbon nanotube network

We used the spin-coating method combined with ultrasonic atomization as a continuous, one-step process to generate a two-dimensional honeycomb network that was constructed from pure multi-walled carbon nanotubes.