Carbon Nanotube Cathode Research Articles

A hollow tubular NiCo layacknered double hydroxide@Ag nanowire structure for high-power-density flexible aqueous Ni//Zn battery

Flexible aqueous Ni//Zn batteries have attracted much attention as promising candidates for energy storage in the field of flexible electronics. However, the Ni-based cathodes still face the challenges of poor conductivity, confined charge/mass transfer, and non-flexibility. In this work, we designed a hollow tubular structure consisting of a conductive silver nanowire (AgNW) wrapped by active NiCo layered double hydroxide (LDH), for enhancing the electrical conductivity, improving the charge/mass transfer kinetics, and facilitating the ion penetration. By optimizing the contents of Ni, Co and AgNW, the Ni4Co LDH@Ag1.5NW composite shows a maximum specific capacity of 115.83 mAh g−1 at 0.1 A g−1 measured in a two-electrode system. Highlightingly, the flexible aqueous Ni//Zn battery assembled by Ni4Co LDH@Ag1.5NW interwoven with multi-walled carbon nanotube cathode and Zn foil anode realizes a high power density of 160 μW cm−2 at the energy density of 23.14 μWh cm−2, which is superior compared with those of oxide/hydroxide based devices and even higher than those of many carbon-based supercapacitors, showing its promising potentials for flexible energy storage applications.

Highly-porous Super-Growth carbon nanotube sheet cathode develops high-power Lithium-Air Batteries

Lithium-Air Battery (LAB) is expected to develop ultra-high energy density batteries, but the low rate performance and poor cycle life of present LAB cells hinder practical development. Here we report that a highly porous carbon nanotube (CNT) cathode dramatically enhances the rate capability of LAB. Single-walled CNTs (SWCNTs) with wavy patterns prepared from the Super-Growth (SG) method successfully provided CNT sheets with high porosity of up to 94%. The pore structure was characterized by two distinct pores in size, namely, highly extended mesoscale (approximately 5–200 nm) pores formed inside CNT bundles that provide large surface area for oxygen reduction reaction (ORR) and inter-bundle gaps in a micrometer scale that works for oxygen diffusion path. This porous CNT sheet cathode significantly increased the discharge rate of LAB cells, specifically enabling a high discharge current density of 3.0 mA/cm2 securing practical cell capacity of 3.3 mAh/cm2, which is comparable to the current LiB technology that provides ∼3 mAh/cm2 cell capacity at ∼1C rate (∼3 mA/cm2) discharge. Furthermore, this highly porous cathode was also effective for extending the cycle life of LAB cells. Such bimodal pore architecture of the CNT sheet cathode paves the new strategy for developing high-power energy-dense LAB.

Suppressing Singlet Oxygen Formation during the Charge Process of Li-O2 Batteries with a Co3O4 Solid Catalyst Revealed by Operando Electron Paramagnetic Resonance.

Aprotic lithium-oxygen (Li-O2) batteries promise high energy, but the cycle life has been plagued by two major obstacles, the insulating products and highly reactive singlet oxygen (1O2), which cause higher overpotential and parasitic reactions, respectively. A solid-state catalyst is known to reduce overpotential; however, it is unclear whether it affects 1O2 generation. Herein, Co3O4 was employed as the representative catalyst in Li-O2 batteries, and 1O2 generation was investigated by ex-situ and operando electron paramagnetic resonance (EPR) spectroscopy. By comparing a carbon nanotube (CNT) cathode with a Co3O4/CNT cathode, we find that 1O2 generation in the charge process can be suppressed by the Co3O4 catalyst. After carefully studying the discharge products on the two electrodes and the corresponding decomposition processes, we conclude that a LiO2-like species is responsible for the 1O2 generation during the early charge stage. The Co3O4 catalyst reduces the amount of LiO2-like species in discharge products, and thus the 1O2 formation is suppressed.

Effective Ru/CNT Cathode for Rechargeable Solid-State Li-CO2 Batteries.

An effective Ru/CNT electrocatalyst plays a crucial role in solid-state lithium-carbon dioxide batteries. In the present article, ruthenium metal decorated on a multi-walled carbon nanotubes (CNTs) is introduced as a cathode for the lithium-carbon dioxide batteries with Li1.5Al0.5Ge1.5(PO4)3 solid-state electrolyte. The Ru/CNT cathode exhibits a large surface area, maximum discharge capacity, excellent reversibility, and long cycle life with low overpotential. The electrocatalyst achieves improved electrocatalytic performance for the carbon dioxide reduction reaction and carbon dioxide evolution reaction, which are related to the available active sites. Using the Ru/CNT cathode, the solid-state lithium-carbon dioxide battery exhibits a maximum discharge capacity of 4541 mA h g-1 and 45 cycles of battery life with a small voltage gap of 1.24 V compared to the CNT cathode (maximum discharge capacity of 1828 mA h g-1, 25 cycles, and 1.64 V as voltage gap) at a current supply of 100 mA g-1 with a cutoff capacity of 500 mA h g-1. Solid-state lithium-carbon dioxide batteries have shown promising potential applications for future energy storage.

Artificial Solid‐Electrolyte Interphase and Bamboo‐like N‐doped Carbon Nanotube Enabled Highly Rechargeable K‐CO2 Batteries

AbstractMetal‐CO2 (Metal = Li, Na, K) batteries demonstrate an attractive strategy for utilizing the excessively released CO2 emissions into electrochemical energy storage devices. Among them, K‐CO2 batteries represent a promising energy storage system owing to high potential (2.48 V), high energy density, and earth‐abundant K resources. The cycle stability and electrochemical mechanism are still far beyond satisfactory because of the active potassium metal, although the first rechargeable K‐CO2 battery has been reported very recently. Herein, a high‐performance K‐CO2 battery is fabricated using passivated K anodes with artificial surface film and N‐doped carbon nanotubes cathodes. The battery shows high specific full discharge capacity (9436 mAh g−1), good rate capability with small overpotential gap (0.81 V at 50 mA g−1), and long cycle life (450 cycles or 3100 h with a curtailing capacity of 500 mAh g−1). The reaction of 3CO2 + 4K ⇋ 2K2CO3 + C reversibly occurs in the charge/discharge processes. Moreover, the assembled fiber‐shaped battery demonstrates a long operation time of 57 h and stable output under different bending conditions. This work provides an option for the possible recycling utilization of the CO2 in future space exploration.

Asymmetric Fiber Supercapacitors Based on a FeC2O4/FeOOH-CNT Hybrid Material

The development of new flexible and lightweight electronics has increased the demand for compatible energy storage devices to power them. Carbon nanotube (CNT) fibers have long been known for their ability to be assembled into yarns, offering their integration into electronic devices. They are hindered, however, by their low intrinsic energy storage properties. Herein, we report a novel composite yarn, synthesized through solvothermal processes, that attained energy densities in the range between 0.17 µWh/cm2 and 3.06 µWh/cm2, and power densities between 0.26 mW/cm2 and 0.97 mW/cm2, when assembled in a supercapacitor with a PVDF-EMIMBF4 electrolyte. The created unique composition of iron oxalate + iron hydroxide + CNT as an anode worked well in synergy with the much-studied PANI + CNT cathode, resulting in a highly stable yarn energy storage device that maintained 96.76% of its energy density after 4000 cycles. This device showed no observable change in performance under stress/bend tests which makes it a viable candidate for powering wearable electronics.

Investigation of the Effect of Structural Properties of a Vertically Standing CNT Cold Cathode on Electron Beam Brightness and Resolution of Secondary Electron Images.

Carbon nanotube (CNT)-based cold cathodes are promising sources of field emission electrons for advanced electron devices, particularly for ultra-high-resolution imaging systems, due to their high brightness and low energy spread. While the electron field emission properties of single-tip CNT cathodes have been intensively studied in the last few decades, a systematic study of the influencing factors on the electron beam properties of CNT cold cathodes and the resolution of the secondary electron images has been overlooked in this field. Here, we have systematically investigated the effect of the structural properties of a CNT cold cathode on the electron beam properties and resolution of secondary electron microscope (SEM) images. The aspect ratio (geometric factor) and the diameter of the tip of a vertically standing CNT cold cathode significantly affect the electron beam properties, including the beam size and brightness, and consequently determine the resolution of the secondary electron images obtained by SEM systems equipped with a CNT cold cathode module. Theoretical simulation elucidated the dependence of the structural features of CNT cold cathodes and electron beam properties on the contribution of edge-emitted electrons to the total field emission current. Investigating the correlations between the structural properties of CNT cold cathodes, the properties of the emitted electron beams, and the resolution of the secondary electron images captured by SEM equipped with CNT cold cathode modules is highly important and informative as a basic model.

Tunable carbon nanotube diode with varying asymmetric geometry

We propose and demonstrate a carbon nanotube (CNT)-based field emission nanoscale diode to realize a fully integrated nanoscale system, namely, a true nanosystem. To the best of our knowledge, this is the first time a nanodiode simultaneously achieves ease of fabrication and individual tunability of multiple CNT diodes on the nanoscale on the same substrate in a one-time process. A nanodiode comprises a single-wall CNT cathode placed on a substrate, layered insulator, and metal anode. The proposed nanodiode allows us to adjust the turn-on voltage from 1 to 2.4 V by varying the surface area of the anode. Furthermore, as an example of a basic nano-electronic system, nanodiode-based fundamental logic gates (OR and NAND) are demonstrated on a CNT. We propose a theoretical model that derives the theoretical I–V characteristics based on the image-charge method to design the nanodiode quickly. The results in this study contribute to the development of carbon-based nanoelectronic systems.

Study on the mechanism of tetracycline removal in electrocoagulation coupled with electro-fenton reaction system with Fe anode and carbon nanotube cathode

In this work, an efficient electrochemical system (Fe-CNT system) for the treatment of tetracycline (TC) was constructed using Fe plate anode and carbon nanotube (CNT) roller cathode. Compared with the traditional Fe-Fe electrocoagulation (EC) system, this Fe-CNT system exhibited higher TC removal rate and shorter reaction time. The best removal rate of 97.21% was achieved at pH of 7, the conductivity of 500 μS cm−1, initial TC concentration of 50 mg L-1, the voltage of 5 V, and reaction time of 25 min. The results demonstrated that the removal rate of total organic carbon was 52.79% at 25 min and 82.84% at 60 min, respectively. The excellent performance of the Fe-CNT system was mainly due to the use of CNT cathode slowed down the floatation in the system, which was conducive to the aggregation and growth of flocs. As a result, the flocs with larger size and more loose structure showed stronger adsorption and aggregation to organic molecules. At the same time, the concentration of hydrogen peroxide in-situ produced was in the range of 7.76 mg L-1 and 30.17 mg L-1. Furthermore, hydroxyl radical as the primary active specie was also produced on the cathode surface by electro-Fenton reaction, which could degrade TC rapidly. In addition, the intermediates involved in the degradation process of TC were identified, and the possible degradation paths were proposed. This work provides insights for improving the cathode utilization rate and removal ability of organic matter and adds a feasible option for the practical application of EC technology.

A Cylindrical Triode Ultrahigh Vacuum Ionization Gauge with a Carbon Nanotube Cathode.

In this study, a cylindrical triode ultrahigh vacuum ionization gauge with a screen-printed carbon nanotube (CNT) electron source was developed, and its metrological performance in different gases was systematically investigated using an ultrahigh vacuum system. The resulting ionization gauge with a CNT cathode responded linearly to nitrogen, argon, and air pressures in the range from ~4.0 ± 1.0 × 10−7 to 6 × 10−4 Pa, which is the first reported CNT emitter-based ionization gauge whose lower limit of pressure measurement is lower than its hot cathode counterpart. In addition, the sensitivities of this novel gauge were ~0.05 Pa−1 for nitrogen, ~0.06 Pa−1 for argon, and ~0.04 Pa−1 for air, respectively. The trend of sensitivity with anode voltage, obtained by the experimental method, was roughly consistent with that gained through theoretical simulation. The advantages of the present sensor (including low power consumption for electron emissions, invisible to infrared light radiation and thermal radiation, high stability, etc.) mean that it has potential applications in space exploration.

Aqueous MnV2 O6 -Zn Battery with High Operating Voltage and Energy Density.

Aqueous Zn ion batteries (AZIBs), featuring low cost, long-term cycling stability, and superior safety are promising for applications in advanced energy storage devices. However, they still suffer from unsatisfactory energy density and operating voltage, which are closely related to cathode materials used. Herein, the use of monoclinic MnV2 O6 (MVO) is reported, which can be activated for high-capacity Zn ions storage by electrochemically oxidizing part of the Mn2+ to Mn3+ or Mn4+ while the remaining Mn2+ ions act as binders/pillars to hold the layer structure of MVO and maintain its integrity during charging/discharging process. Moreover, after introducing carbon nanotubes (CNT), the MVO:CNT composite not only provides robust 3D Zn-ion diffusion channels but also shows enhanced structural integrity. As a result, a MVO:CNT cathode delivers a high midpoint voltage (1.38V after 3000 cycles at 2 A g-1 ) and a high energy density of 597.9 W h kg-1 . Moreover, DFT analyses clearly illustrate stepwise Zn ion insertion into the MnV2 O6 lattice, and ex-situ analyses results further verify the highly structural reversibility of the MnV2 O6 cathode upon extended cycling, demonstrating the good potential of MnV2 O6 for the establishment of viable aqueous Zn ion battery systems.

A Safe and Sustainable Lithium-Ion-Oxygen Battery based on a Low-Cost Dual-Carbon Electrodes Architecture.

People anticipate high-energy-density battery technology with better security, stability, and sustainability. By tuning the advantage of specific capacity, the lithium-metal anode is replaced with a graphite intercalation compound and a conceptual prototype lithium-ion-oxygen battery based on a low-cost dual-carbon electrodes architecture is proposed. The lithium-ion involves a (de)intercalation process into the graphite anode and an O2 /Li2 O2 redox conversion on the carbon-nanotube cathode. After a thorough examination as to the electrode compatibility with current electrolytes, a nonflammable fluorinated ether electrolyte is proposed to render a highly coordinated solvation sheath and low lithium salt concentration (1mol). Herein, the compatibility with graphite anode is investigated, which maintains high capacity retention (88.1%) after long-term lifespan (over 1 year). In view of the ultrahigh reversibility (average Coulombic efficiency over 99.93%) of the graphite anode, a lithium-ion-oxygen coin cell with high depth-of-discharge of 80% and 60% deliver a satisfactory life over 150 and 300 cycles, respectively. Moreover, systematic spectroscopy characterizations demonstrate a reversible and efficient 2e- O2 /Li2 O2 redox reaction without relying on noble-metal catalysts. Lastly, in the engineering aspect, a high-energy-density pouch cell (302.52 W h kg-1 based on the weight of the entire pouch) with cost-effective and environmentally friendly carbon-composed cell components is successfully fabricated.

Highly enhanced field emission properties of a carbon nanotube cathode on a titanium alloy substrate modified by alkali

Field emission electron sources with low turn-on electric fields, high emission current density, and good stability are of paramount importance in widespread applications, and in particular vacuum nanoelectronic equipment. Herein, an alkali modification approach was rationally designed to tailor the morphology of the commonly used compact and planar titanium alloy substrate. As expected, the modified substrate exhibited an interconnected porous network morphology, which offers remarkably strengthened adhesion with the screen-printed carbon nanotube cathode atop. As a result, the devices delivered comprehensively improved performance. Specifically, in the continuous driving mode, the turn-on electric field was as low as 0.79 V/μm, while the emission current of 85.13 mA/cm2 was relatively high. In parallel, in the pulse driving mode, the emission current density reached 1.266 A/cm2 under an electric field of 6.1 V/μm. Encouragingly, the cathode exhibited rather decent emission stability even under continuous operation for hours. This work provides a practical strategy for further enhancement of the field emission performance of carbon nanotube cathodes and highlights the significance of engineering titanium alloy substrates in future development.

An ultrahigh power Li–O2 battery

The nonaqueous Li–O2 battery has the highest energy density among various systems so far, often reported as comparable to that of gasoline; this exceptional energy potentiality has elicited worldwide interest as a superior energy storage system. Major challenges have limited the performance of Li–O2 batteries regarding high charging overpotential, low rate capabilities, and cycle stabilities. Many approaches to reducing the charging overpotential and resulting enhanced cycling performance have been suggested, whereas only a few studies have focused on high-power performance. For successful electric propulsion applications, it is required that high-power technologies are developed for advanced Li–O2 batteries. We show the operating possibility of the nonaqueous primary Li–O2 cell at the A/g level and cycle stability of the nonaqueous rechargeable Li–O2 cell using the electrolyte bis(trifluoromethane)sulfonimide lithium salt melted in dimethylglycol and single-walled carbon nanotube cathodes.

Screen-printed Dual-Particle-Containing Multicomponent-Blending Carbon Nanotube Cathode: Enhancement of Electron Emission Characteristics, Current Emission Stability, and Uniformity

The electron emission characteristics, current emission stability, and uniformity of screen-printed carbon nanotube were enhanced by introducing a novel dual-particle-containing multicomponent-blending carbon nanotube cathode via the comprehensive combination of baking in the air and sintering in the inert gas atmosphere. The dual-particle-containing multicomponent-blending carbon nanotube cathode’s design and manufacturing improvements ensured its steeper emission curve variation amplitude, larger maximum emission current, better electron emission current of 806.7 μA was only 2.56 V/μm. When it was increased from 2.78 to 2.91 V/μm, the enhancing current emission amplitude of the proposed cathode was increased by 600.7 μA versus 324.1 μA of the conventional non-blending carbon nanotube cathode. The maximum emission current of the proposed cathode was 3762.5 μA. After the vacant static state of 72 h, the measured emission current had no obvious attenuation, and the fluctuation rate of emission current did not exceed 5%. The backlight unit with dual-particle-containing multicomponent-blending carbon nanotube cathode was sealed, and the obtained emission image had high luminescence brightness and uniformity.

Convergence Study on the use of Electrolyzed Water Device with CNT Cathode in Health Field

An electrolytic water sterilization device was developed that employs CNT (carbon nano tube) as a cathode. CNT plastic composite material is pulverized with a waterdispersible acrylic anionic resin added with castor oil and a dispersion, polypropylene resin mixed with CNT, and thermoplastic elastomer to make pellets. This CNT composite material is a metal-free electric conductor with excellent chemical resistance and surface electrical resistance of 1Ω/□ or less. When this electrolytic water sterilizer was used as cleaning water for dental treatment and sink cleaning water, it was eco-friendly and showed excellent removal rate. This device can effectively remove pesticides from fruits, etc. and remove bacteria by washing pork. In addition, the water in the swimming pool can be sterilized and purified without using chemicals. In this case, environmental conservation and economic costs can be reduced by not generating wastewater that causes environmental pollution

Rechargeable K‐CO2 Batteries with a KSn Anode and a Carboxyl‐Containing Carbon Nanotube Cathode Catalyst

AbstractMetal K‐CO2 batteries suffer from large polarization and safety hazards, which mainly result from the difficult decomposition of K2CO3 and dendrite growth. Moreover, the battery redox mechanism remains not fully understood. Here we report K‐CO2 batteries with KSn alloy as the anode and carboxyl‐containing multi‐walled carbon nanotubes (MWCNTs‐COOH) as the cathode catalyst, proving the redox mechanism to be 4 KSn + 3 CO2 ⇄ 2 K2CO3 + C + 4 Sn. Compared with K metal, the less active and dendrite‐free KSn anode effectively enhances the safety and stability of CO2 batteries. More importantly, the strong electrostatic interaction between MWCNTs‐COOH and K2CO3 weakens the C=O bond in K2CO3 and thus facilitates K2CO3 decomposition. As a result, the K‐CO2 batteries show excellent cycling stability (an overpotential increase of 0.89 V after 400 cycles) and good rate performance (up to 2000 mA g−1). This work paves a way to develop highly stable and safe CO2‐based batteries.

Rechargeable K-CO2 Batteries with a KSn Anode and a Carboxyl-Containing Carbon Nanotube Cathode Catalyst.

Metal K-CO2 batteries suffer from large polarization and safety hazards, which mainly result from the difficult decomposition of K2 CO3 and dendrite growth. Moreover, the battery redox mechanism remains not fully understood. Here we report K-CO2 batteries with KSn alloy as the anode and carboxyl-containing multi-walled carbon nanotubes (MWCNTs-COOH) as the cathode catalyst, proving the redox mechanism to be 4 KSn + 3 CO2 ⇄ 2 K2 CO3 + C + 4 Sn. Compared with K metal, the less active and dendrite-free KSn anode effectively enhances the safety and stability of CO2 batteries. More importantly, the strong electrostatic interaction between MWCNTs-COOH and K2 CO3 weakens the C=O bond in K2 CO3 and thus facilitates K2 CO3 decomposition. As a result, the K-CO2 batteries show excellent cycling stability (an overpotential increase of 0.89 V after 400 cycles) and good rate performance (up to 2000 mA g-1 ). This work paves a way to develop highly stable and safe CO2 -based batteries.

Highly-efficient degradation of organic pollutants and synchronous electricity generation in a photocatalytic fuel cell based on the catalytic reactions of hydroxyl and chlorine radicals

Organic compounds in wastewater are significant energy sources. Given this situation, a novel and high-performance photocatalytic fuel cell (PFC) integrated with NaOCl/Cu (II) was successfully constructed to effectively convert hazardous organics into clean energy. This designed system is comprised of nickel oxide (NiO)/TiO2 nanotubes (TNTs) photoanode and polyaniline (PANI)/multi-walled carbon nanotubes (MWCNTs) cathode. Compared to the single PFC, the combined system exhibited better performance. This coupled PFC/NaOCl/Cu (II) system enhanced the photocatalytic reaction and strengthened the reaction range of reactive species from the surface of electrodes to the whole liquid phase via generation of reactive chlorine radicals (Cl•, Cl2•–, ClO•) and reactive oxygen species (HO•, •O2–, HO2•). Hence, PFC/NaOCl/Cu (II) exhibited excellent cell efficiency, increasing the AB113 degradation by 48.1% and electrical power generation by 59.38% compared to the PFC system without adding NaOCl/Cu (II). The effects of the important operating parameters (initial pH, NaOCl/Cu (II), and concentration of substrate) on the PFC performance were investigated by response surface methodology (RSM). The results showed that the different model compounds could be used as fuel. The highest short circuit current density of 3.1 mA cm –2, and maximum power density of 1.12 mW cm–2 were obtained using citric acid as the substrate. This study provided an efficient approach to dispose of organic waste and to generate synchronous electrical power.

Performance evaluation of carbon/PrBaCo2O5+δ composite electrodes for Li–O2 batteries

Herein, a new type of perovskite oxide PrBaCo2O5+δ (PBCO) was synthesized and optimized by cooperating with carbon nanotubes (CNT) or carbon nanoparticles (BP2000), which was further applied into Li–O2 battery cathode as a bi-functional cathode catalyst, achieving a high discharge capacity of 15.1 mA h, the number of which is over four times than that of single PBCO or CNT cathode, and seven times than single BP2000 cathode. Furthermore, a significantly enhanced stability was achieved as sustained more than 290 cycles at a fixed capacity, the number of which exceeds most carbon-based and even other perovskite catalytic Li–O2 batteries. The charge transfer resistance (Rct) of PBCO was reduced 46.6% after cooperating with carbon materials, which is almost half of single PBCO. All these results demonstrated that the big defect of PBCO can be remedied through the surface decorating with electronic conductors, such as, carbon nano-materials, and thus resulting in a substantially enhanced cathodic performance.