Carbon Nanotube Cathode Research Articles

Three-dimensional spongy framework as superlyophilic, strongly absorbing, and electrocatalytic polysulfide reservoir layer for high-rate and long-cycling lithium-sulfur batteries

In the development of lithium-sulfur (Li-S) batteries, various approaches have been adopted to enhance the electronic conductivity of the sulfur cathode and alleviate the shuttle effect of polysulfides; however, the strategies providing efficient solutions are still limited. To further improve the electrochemical performance of Li-S batteries, in this work we propose a new strategy involving the incorporation of a three-dimensional functional spongy framework as polysulfide reservoir layer, with strong absorbability and electrocatalytic activity towards sulfur species. The spongy framework has a hierarchical architecture composed of highly conductive Ni foam/graphene/carbon nanotubes/MnO2 nanoflakes (NGCM). The strongly interconnected Ni foam, graphene, and carbon nanotubes of the NGCM sponge facilitate electron transfer during discharge/charge processes; moreover, the superlyophilic properties of the NGCM sponge ensure good wettability and interface contact with the Li-S electrolyte, and the porous MnO2 nanoflakes provide strong chemisorptive and electrocatalytic effects on polysulfides (as confirmed theoretically and experimentally). The NGCM sponge, serving as a polysulfide reservoir layer attached on a conventional sulfur-mixed carbon nanotubes (S/CNTs) cathode, can provide improved reversible capacity, rate capability (593 mAh·g–1 at 3.0 C), and cycling stability. In addition, the self-discharge rate is greatly reduced, owing to the efficient conservation of polysulfides in the NGCM spongy framework.

Formation of Nanosized Defective Lithium Peroxides through Si-Coated Carbon Nanotube Cathodes for High Energy Efficiency Li-O2 Batteries.

The formation and decomposition of lithium peroxides (Li2O2) during cycling is the key process for the reversible operation of lithium-oxygen batteries. The manipulation of such products from the large toroidal particles about hundreds of nanometers to the ones in the scale of tens of nanometers can improve the energy efficiency and the cycle life of the batteries. In this work, we carry out an in situ morphology tuning of Li2O2 by virtue of the surface properties of the n-type Si-modified aligned carbon nanotube (CNT) cathodes. With the introduction of an n-type Si coating layer on the CNT surface, the morphology of Li2O2 formed by discharge changes from large toroidal particles (∼300 nm) deposited on the pristine CNT cathodes to nanoparticles (10-20 nm) with poor crystallinity and plenty of lithium vacancies. Beneficial from such changes, the charge overpotential dramatically decreases to 0.55 V, with the charge plateau lying at 3.5 V even in the case of a high discharge capacity (3450 mA h g-1) being delivered, resulting in the high electrical energy efficiency approaching 80%. Such an improvement is attributed to the fact that the introduction of the n-type Si coating layer changes the surface properties of CNTs and guides the formation of nanosized amorphous-like lithium peroxides with plenty of defects. These results demonstrate that the cathode surface properties play an important role in the formation of products formed during the cycle, providing inspiration to design superior cathodes for the Li-O2 cells.

Degradation of aniline by electrochemical activation of peroxydisulfate at MWCNT cathode: The proofed concept of nonradical oxidation process

Enhanced elimination of aniline in aqueous solution was achieved by coupling electrosorption of aniline and electrochemical activation of peroxydisulfate (PDS) at multi-walled carbon nanotube (MWCNT) cathode, in which a synergistic effect occurred. It was found that PDS could be effectively activated under a small voltage at MWCNT cathode owing to the specific pore structures of MWCNTs. A nonradical oxidation pathway instead of radical-based oxidation was proposed from the cathodic activation of PDS, wherein PDS molecules with a modified electronic structure was suggested to be the principal reactive species. Meanwhile, the influences of various operation parameters such as electrode potential, PDS concentration, presence of chloride ions on the elimination efficiency, and the stability of MWCNT electrode were also attempted. Therefore, the electrochemical activation of PDS by MWCNT cathode is a promising energy-saving method for the treatment of organic pollutants in wastewater.

Quasi-Solid-State Rechargeable Li–O2 Batteries with High Safety and Long Cycle Life at Room Temperature

As interest in electric vehicles and mass energy storage systems continues to grow, Li-O2 batteries are attracting much attention as a candidate for next-generation energy storage systems owing to their high energy density. However, safety problems related to the use of lithium metal anodes have hampered the commercialization of Li-O2 batteries. Herein, we introduced a quasi-solid polymer electrolyte with excellent electrochemical, chemical, and thermal stabilities into Li-O2 batteries. The ion-conducting QSPE was prepared by gelling a polymer network matrix consisting of poly(ethylene glycol) methyl ether methacrylate, methacrylated tannic acid, lithium trifluoromethanesulfonate, and nanofumed silica with a small amount of liquid electrolyte. The quasi-solid-state Li-O2 cell consisted of a lithium powder anode, a quasi-solid polymer electrolyte, and a Pd3Co/multiwalled carbon nanotube cathode, which enhanced the electrochemical performance of the cell. This cell, which exhibited improved safety owing to the suppression of lithium dendrite growth, achieved a lifetime of 125 cycles at room temperature. These results show that the introduction of a quasi-solid electrolyte is a potentially new alternative for the commercialization of solid-state Li-O2 batteries.

A tripolar-electrode ionization gas sensor using a carbon nanotube cathode for NO detection

Nitric oxide accounts for more than 95% of the total NOX emission from power plants, which is a major air pollutant. Therefore, it is imperative to accurately detect NO for environmental protection. A tripolar-electrode ionization sensor with a carbon nanotube (CNT) cathode is proposed for NO detection. The non-self-sustaining discharge state and the tripolar-electrode configuration ensures a long nanotube life, which ensures a good stability and fast response of the sensor. Experimental results demonstrate that the tripolar-electrode ionization sensor with 120 µm separations has an intrinsic monotonously decreasing response to NO and exhibits a fast response time of 7 s and recovery time of 8 s. More consumption of the two metastable states N2(A3 ∑ u+) and N2(aʹ1 ∑ u+) of N2 with the increasing of NO concentration is responsible for this. The tripolar-electrode ionization sensor also shows excellent long-term stability of at least one month due to the long CNT life. In addition, the weak effect of SO2 introduction on NO response indicates a good selectivity of the sensor to NO.

Electronic Pulses from Pulsed Field Emission of CNT Cathodes

We presented a demonstration of infrared laser irradiated field emission electronic pulse based on carbon nanotube (CNT) cathodes. Electronic pulses greatly depended on pulsed infrared laser and were almost synchronous with laser pulses. We have designed a pulsed field emission cathode based on CNTs and investigated correlation between electronic pulse and laser pulse, acquiring the shortest width of electronic pulses about 50 ms and turn-on field less than 0.14 V/μm. Besides, we have studied the thermal effect on the pulsed field emission of CNT cathodes caused by laser heating. Interestingly, the thermal effect has caused an enhancement of emission current but resulted in a waveform distortion on short electronic pulses. The application of laser pulses on CNT cathodes would extend conventional electron sources to a pulsed electron source and offered a possibility of pulsed field emission. These results were encouraging us to prepare further studies of ultrafast electronic pulses for high-frequency electron sources.

六角密排多迭层碳纳米管阴极的大电子发射电流和高电子发射稳定性

六角密排多迭层碳纳米管阴极的大电子发射电流和高电子发射稳定性

Efficient Capacitive Deionization Using Thin Film Sodium Manganese Oxide

More energy efficient desalination methods are needed to address global water scarcity. Capacitive deionization (CDI) is an emerging electrochemical desalination technology that could outperform other desalination technologies if new electrode materials were developed with high salt sorption capacity and efficiency. In this paper, we report on the desalination performance of thin-film sodium manganese oxide (NMO). We deposit thin-film MnO via atomic layer deposition (ALD), and electrochemically convert the MnO to NMO in NaCl(aq). Charge storage capacity is tuned with NMO thickness, and the relationship between charge storage capacity and reversible salt sorption is probed. NMO coated electrodes exhibit increases in charge storage capacity up to 170 times higher than uncoated electrodes. Electrochemical quartz crystal microbalance (EQCM) measurements reveal that thin-film NMO leads to the efficient electrochemical removal of Na+ ions. A hybrid CDI (HCDI) cell comprised of NMO-coated carbon nanotube (CNT) cathode and Ag nanoparticle-decorated CNT anode yields a ∼20-fold improvement in charge storage over bare CNT electrodes. The HCDI cell has an anomalously high reversible charging efficiency, which we study using ab initio modeling and EQCM. This is the first CDI report using thin film NMO, and the high desalination efficiency we identify promises to facilitate the development of HCDI devices with enhanced performance.

An ionization gauge for ultrahigh vacuum measurement based on a carbon nanotube cathode.

This work reports on the complete design and the properties of an ionization gauge based on a carbon nanotube cathode, which can measure ultrahigh vacuum without thermal effects. The gauge is composed of a pressure sensor and an electronic controller. This pressure sensor is constructed based on a hot-cathode ionization gauge, where the traditional hot filament is replaced by an electron source prepared with multi-wall nanotubes. Besides, an electronic controller was developed for bias voltage supply, low current detection, and pressure indication. The gauge was calibrated in the pressure range of 10-8 to 10-4 Pa in a XHV/UHV calibration apparatus. The gauge shows good linear characteristics in different gases. The calibrated sensitivity is 0.035 Pa-1 in N2, and the standard deviation of the sensitivity is about 1.1%. In addition, the stability of the sensitivity was learned in a long period. The standard deviation of the sensitivity factor "S" during one year is 2.0% for Ar and 1.6% for N2.

A Design of Solid-State Li-S Cell with Evaporated Lithium Anode To Eliminate Shuttle Effects.

Li-S batteries hold great potential for energy storage systems due to their high theoretical capacity and low cost. However, the shuttle of polysulfides in conventional Li-S batteries with organic electrolyte results in severe problems, such as low Coulombic efficiency and poor cycling stability. Here, we developed a solid-state Li-S battery using Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid ceramic electrolyte instead of liquid electrolyte. Lithium film was deposited on one side of LAGP by an evaporation method to improve the contact between anode and LAGP. Sulfur-coated carbon nanotubes cathode (S-MWCNT) composition was casted on the other side of LAGP as the cathode and a small amount of ionic liquid was dropped in order to improve the ionic conductivity. This battery exhibited a high capacity of 1510 mAh g-1 in the first cycle and retained 1400 mAh g-1 after 30 cycles. Meanwhile, the Coulombic efficiency of the battery was almost 100% for each cycle, which indicated the shuttle effect was circumvented completely.

Enhanced Cycle Stability of Rechargeable Li-O2 Batteries by the Synergy Effect of a LiF Protective Layer on the Li and DMTFA Additive.

Li metal is an ideal anode for rechargeable Li-O2 batteries because of its large theoretical capacity (3860 mAh g-1). However, problems with the growth of dendrites and reaction with electrolytes and moisture during cycling have prevented its practical application. Herein, we report that the use of a 2 wt % N,N-dimethyltrifluoroacetamide (DMTFA) additive in a dimethyl sulfoxide (DMSO) electrolyte with a LiF layer on the Li anode allows for good cycling performance in Li-O2 batteries. Indeed, a Li-O2 cell with a multiwalled carbon nanotube (MWCNT) cathode, 1.0 M LiNO3/DMTFA + DMSO (2:98 v/v) electrolyte, and a LiF layer on the Li anode could be cycled 92 times at a current density of 1000 mA g-1 with a 1000 mAh g-1.

Studying the field emission cathode–gate structure based on carbon nanotubes for electron-optical systems with a sheet beam

Results of studying the cathode–gate structure based on carbon nanotubes (CNTs) are presented. Experimental samples of a matrix field emission cathode–gate structure based on a vertical array of CNTs with a cell diameter of 1 μm and microstructure period of 5 μm have been manufactured. Based on experimental data, an electron-optical system with a ribbon-type field emission CNT based cathode with a linear convergence of 6.25 and beam-current density of 4.46 A/cm2 has been proposed. Results of modeling a sheet 0.16-mm-thick electron beam formed by an electron gun with a CNT cathode demonstrated the possibility to obtain a low-perveance flow with a small deformation in the 0.3 × 0.8-mm beam tunnel of a slow wave 25-mm-long structure.

Investigation of Electrochemical Performance of Li-O2 Batteries Using Catalyst Containing Carbon Nanotube Cathodes

Batteries with high specific energy densities have attracted a lot of attention due to their demand in electric vehicles (EVs). Due to the increase in demand for energy storage devices for applications such as load-levelling of electrical energy supply and demand propulsion for electric vehicles and microelectro-mechanical devices, the research for new classes of electrode materials that provide high energy, high power and cycle life longer than lithium-ion batteries is being motivated. Lithium air batteries have high specific energy density and they can achieve four times higher energy density than the current lithium ion batteries. The search for high energy density batteries has motivated the research in lithium-air batteries. Catalysts have been shown to improve both the battery capacity and the recyclability of these batteries when used in cathodes. Several catalysts have been discovered for lithium air batteries. Debart et al. used several catalysts for lithium oxygen batteries with non-aqueous electrolyte. The electro-catalysts used by them included Pt, La0.8Sr0.2MnO3, Fe2O3, NiO, CuO, CoFe2O4. Co3O4 exhibited highest discharge capacity and best cycling performance. Later Debart et al. examined manganese oxides as catalysts for lithium oxygen batteries. Mn3O4, bulk Mn2O3, bulk α, β, λ, γ-MnO2, α-MnO2 nanowires and β-MnO2 nanowires were used as catalysts. The air cathode with α-MnO2 as the catalyst showed the highest capacity of about 3000 mAh/g (carbon) Lu et al. reported ORR studies on polycrystalline metal catalysts of palladium, platinum, ruthenium, gold and glassy carbon surfaces in non-aqueous electrolyte. In our study, we investigate various modes of loading palladium-based catalysts and their effect on the capacity and round-trip efficiency of lithium-air batteries. Our aim is to increase the first discharge capacity, improve the recyclability, increase capacity retention and improve the recyclability of the battery. The loading and morphology the catalyst-CNT cathode is studied using transmission electron microscopy. Electrochemical testing using electrochemical impedance spectroscopy and charge-discharge cycling is also investigated. Voltammetry, Raman spectroscopy, FTIR, XRD, UV/Vis spectroscopy and visual inspection of the discharge products using scanning electron microscopy confirms the increased stability of the electrolyte due to this encapsulation and suggest that this approach could lead the increasing Li-O2 battery capacity and cyclability performance.

Flexible Li-CO2 Batteries with Liquid-Free Electrolyte.

Developing flexible Li-CO2 batteries is a promising approach to reuse CO2 and simultaneously supply energy to wearable electronics. However, all reported Li-CO2 batteries use liquid electrolyte and lack robust electrolyte/electrodes structure, not providing the safety and flexibility required. Herein we demonstrate flexible liquid-free Li-CO2 batteries based on poly(methacrylate)/poly(ethylene glycol)-LiClO4 -3 wt %SiO2 composite polymer electrolyte (CPE) and multiwall carbon nanotubes (CNTs) cathodes. The CPE (7.14×10-2 mS cm-1 ) incorporates with porous CNTs cathodes, displaying stable structure and small interface resistance. The batteries run for 100 cycles with controlled capacity of 1000 mAh g-1 . Moreover, pouch-type flexible batteries exhibit large reversible capacity of 993.3 mAh, high energy density of 521 Wh kg-1 , and long operation time of 220 h at different degrees of bending (0-360°) at 55 °C.

Flexible Li‐CO2 Batteries with Liquid‐Free Electrolyte

AbstractDeveloping flexible Li‐CO2 batteries is a promising approach to reuse CO2 and simultaneously supply energy to wearable electronics. However, all reported Li‐CO2 batteries use liquid electrolyte and lack robust electrolyte/electrodes structure, not providing the safety and flexibility required. Herein we demonstrate flexible liquid‐free Li‐CO2 batteries based on poly(methacrylate)/poly(ethylene glycol)‐LiClO4‐3 wt %SiO2 composite polymer electrolyte (CPE) and multiwall carbon nanotubes (CNTs) cathodes. The CPE (7.14×10−2 mS cm−1) incorporates with porous CNTs cathodes, displaying stable structure and small interface resistance. The batteries run for 100 cycles with controlled capacity of 1000 mAh g−1. Moreover, pouch‐type flexible batteries exhibit large reversible capacity of 993.3 mAh, high energy density of 521 Wh kg−1, and long operation time of 220 h at different degrees of bending (0–360°) at 55 °C.

An update on carbon nanotube-enabled X-ray sources for biomedical imaging.

A new imaging technology has emerged that uses carbon nanotubes (CNT) as the electron emitter (cathode) for the X-ray tube. Since the performance of the CNT cathode is controlled by simple voltage manipulation, CNT-enabled X-ray sources are ideal for the repetitive imaging steps needed to capture three-dimensional information. As such, they have allowed the development of a gated micro-computed tomography (CT) scanner for small animal research as well as stationary tomosynthesis, an experimental technology for large field-of-view human imaging. The small animal CT can acquire images at specific points in the respiratory and cardiac cycles. Longitudinal imaging therefore becomes possible and has been applied to many research questions, ranging from tumor response to the noninvasive assessment of cardiac output. Digital tomosynthesis (DT) is a low-dose and low-cost human imaging tool that captures some depth information. Known as three-dimensional mammography, DT is now used clinically for breast imaging. However, the resolution of currently-approved DT is limited by the need to swing the X-ray source through space to collect a series of projection views. An array of fixed and distributed CNT-enabled sources provides the solution and has been used to construct stationary DT devices for breast, lung, and dental imaging. To date, over 100 patients have been imaged on Institutional Review Board-approved study protocols. Early experience is promising, showing an excellent conspicuity of soft-tissue features, while also highlighting technical and post-acquisition processing limitations that are guiding continued research and development. Additionally, CNT-enabled sources are being tested in miniature X-ray tubes that are capable of generating adequate photon energies and tube currents for clinical imaging. Although there are many potential applications for these small field-of-view devices, initial experience has been with an X-ray source that can be inserted into the mouth for dental imaging. Conceived less than 20 years ago, CNT-enabled X-ray sources are now being manufactured on a commercial scale and are powering both research tools and experimental human imaging devices. WIREs Nanomed Nanobiotechnol 2018, 10:e1475. doi: 10.1002/wnan.1475 This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Revealing the reaction mechanisms of Li-O2 batteries using environmental transmission electron microscopy.

The performances of a Li-O2 battery depend on a complex interplay between the reaction mechanism at the cathode, the chemical structure and the morphology of the reaction products, and their spatial and temporal evolution; all parameters that, in turn, are dependent on the choice of the electrolyte. In an aprotic cell, for example, the discharge product, Li2O2, forms through a combination of solution and surface chemistries that results in the formation of a baffling toroidal morphology. In a solid electrolyte, neither the reaction mechanism at the cathode nor the nature of the reaction product is known. Here we report the full-cycle reaction pathway for Li-O2 batteries and show how this correlates with the morphology of the reaction products. Using aberration-corrected environmental transmission electron microscopy (TEM) under an oxygen environment, we image the product morphology evolution on a carbon nanotube (CNT) cathode of a working solid-state Li-O2 nanobattery and correlate these features with the electrochemical reaction at the electrode. We find that the oxygen-reduction reaction (ORR) on CNTs initially produces LiO2, which subsequently disproportionates into Li2O2 and O2. The release of O2 creates a hollow nanostructure with Li2O outer-shell and Li2O2 inner-shell surfaces. Our findings show that, in general, the way the released O2 is accommodated is linked to lithium-ion diffusion and electron-transport paths across both spatial and temporal scales; in turn, this interplay governs the morphology of the discharging/charging products in Li-O2 cells.

Large field emission current and density from robust carbon nanotube cathodes for continuous and pulsed electron sources

Highly adhesive cold cathodes with high field emission performance are fabricated by using a screen-printingmethod. The emission density of carbon nanotube (CNT) cold cathode reaches 207.0 mA cm−2 at an electric field of 4.5 V μm−1 under continuous driving mode, and high peak current emission of 315.8 mA corresponding to 4.5 A cm−2 at the electric field of 10.3 V μm−1 under pulsed driving mode. The emission patterns of the cold cathodes are of excellent uniformity that was revealed by vivid luminescent patterns of phosphor coated transparent indium tin oxide (ITO) anode. The cold cathodes also exhibit highly stable emission under continuous and pulsed driving modes. The high adhesion of CNTs tomolybdenum substrates results in robust cold cathodes and is responsible for the high field emission performance. This robust CNT emitter could meet the operating requirements of continuous and pulsed electron sources, and it provides promising applications in various vacuummicro/nanoelectronic devices.

Flexible free-standing air electrode with bimodal pore architecture for long-cycling Li-O2 batteries

Li-O2 batteries have been proposed as next-generation energy-storage devices, but this technology is hindered by serious problems including parasitic reactions, degradation, and leakage of the electrolyte. Li-O2 batteries are also currently designed to have a rigid bulky structure, which cannot satisfy the flexibility demands of modern electronics. Herein, we report the significant enhancement of the electrochemical performance and flexibility of a Li-O2 battery by introducing a free-standing, binder-free carbon nanotube cathode with a bimodal pore architecture. This electrode structure imparted stability to active sites during the recovery of discharge products to the initial state, providing long-term cyclability of more than 100 cycles in a tetraethylene glycol dimethyl ether electrolyte system. The O2 transportation and conductivity were also improved, yielding an increased discharge capacity of 5500 mAh g−1 (nearly twice that of a non-porous cathode) and minimizing parasitic reactions. This novel bimodal-pore cathode exhibited an increased tri-phase boundary for the Li-O2 reactive zone in the interconnected CNT network. The small pore structures (∼50 nm) accommodated Li2O2, and the large pore structures (∼385 nm) enabled effective oxygen diffusion without clogging the pores. Moreover, Li+ and oxygen diffusion were facilitated by the two independent channels provided by the pore structures.

Miniature X-Ray Sources

This paper presents an overview of the design and technology of miniature X-ray sources of various types, which can be useful in the portable instruments for diagnosis and precision medical therapy, as well as in industrial applications. Several examples of X-ray sources using the pyroelectric and piezoelectric effects and tubes with thermal and field-emission electron sources have been described. A concept of an X-ray source integrated on one chip, made by the use of microengineering techniques, concludes this paper. In this micro-electro-mechanical system-type construction, a miniature field-emission electron source with carbon nanotube cathode and a recently developed high-vacuum micropump are applied. [2016-0214]