Carbon Nanotube Cathode Research Articles

ZCNC Beaded Heterostructure toward High-Performance Aluminum Batteries.

We designed and prepared the ZnSe/CoSe2@NC/CNTs (ZCNC) cathode material for aluminum batteries (ABs). The ZCN (ZnSe/CoSe2@NC) is connected by the interwoven carbon nanotube (CNT) conductive network to form a beaded structure. CNTs and the carbon formed by carbonization of organic ligands is beneficial to improving the electrical conductivity of the material and reducing structural damage during cycling. The internal electric field generated at the interface of heterostructures can promote the transfer of electrons/ions. This special structure promotes ZCNC excellent electrochemical properties. At 100 mA/g, the specific capacity of the first discharge reaches 338 mAh/g, while the specific capacity after 500 cycles still reaches 217 mAh/g. Compared with ZCN and CN(CoSe2@NC), it demonstrates a great advantage.

Ag/CNT Catalyst Synthesized by Plasma-Enhanced Atomic Layer Deposition for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) have recently gained attention as a viable alternative to proton exchange membrane fuel cells (PEMFC), offering the potential for high output without relying on expensive platinum (Pt) catalysts. PEMFCs operate in an acidic environment characterized by a high concentration of H+, necessitating the use of platinum-based catalysts to ensure both performance and stability in such conditions. In contrast, AEMFCs operate in an alkaline environment (OH-), affording the use of high-performance catalysts like silver (Ag), which is sensitive to acidity. Moreover, the cost of Ag is approximately 1/50 of Pt, offering significant cost advantages for fuel cell commercialization. Atomic layer deposition (ALD) has garnered substantial attention as a valuable technique for crafting high-performance nano-catalysts. ALD's self-limiting nature, based on the sequential exposure of vaporized precursors and reactants, enables precise control over catalyst size and composition. In this study, we employed plasma-enhanced ALD (PEALD) to fabricate cutting-edge AEMFC cathodes comprised of carbon nanotubes (CNTs) adorned with Ag. This approach yielded impressive results, achieving an AEMFC output exceeding 300 mW cm-2 or more than 2 W mgAg -1 at 65 °C with a CNT cathode featuring an exceedingly low Ag loading of less than 0.15 mg cm-2. Notably, this represents the world's highest reported Ag-AEMFC performance to date. The Ag-decorated cathode created through ALD played a pivotal role in significantly reducing resistance in the polarization region, a major contributor to overall energy losses in AEMFCs. Additionally, when evaluating the durability of the Ag-decorated CNT anode in an alkaline environment, we observed excellent long-term stability. In this presentation, we will discuss a more detailed exploration of the relationship between AEMFC performance, featuring ALD-fabricated Ag-CNT catalysts, and the intricate catalyst structure.

Bright spatially coherent beam from carbon-nanotube fiber field-emission cathode

Bright spatially coherent beam from carbon-nanotube fiber field-emission cathode

Development of Flexible High‐Efficient Aluminum ion Supercapacitors With 2D Niobium MXene Electrode

ABSTRACTA high‐performance aluminum‐ion supercapacitor is fabricated using 2D few‐layered Nb2CTx MXene, as an active electrode material and Al2(SO4)3 electrolyte for efficient energy storage. Nb2CTx MXene has been synthesized from Nb2AlC MAX phase using HF. Nb2CTx MXene coated on carbon cloth (Nb@CC) displays a capacitance of 307 F g−1 with 90% coulombic efficiency. The specific capacitance of Nb@CC in Al2(SO4)3 electrolyte is exceptionally high compared to those (≤32.2 F g−1) in H2SO4, Na2SO4, and MgSO4 electrolytes. Both symmetric and asymmetric aluminum ion supercapacitors are fabricated with Nb@CC electrode. The Nb@CC//Nb@CC symmetric device exhibits a capacitance of 122 F g−1 with a high energy density (Ed) of 33.2 Wh kg−1 at 1.41 kW kg−1 power density (Pd). An asymmetric supercapacitor device (ASC), Nb@CC//CNT@CC, with carbon nanotube (CNT@CC) cathode delivers a maximum Ed of 24.7 Wh kg−1 at 3.41 kW kg−1 Pd and excellent stability with 90% capacitance retention after 4000 cycles. A remarkably high Pd of 34 kW kg−1 is maintained with 13.2 Wh kg−1 Ed, and the rate capability is 53% for a 10‐fold increase in current density. These results offer the feasibility of efficient aqueous supercapacitors with Al‐ion as guest species, presenting new possibilities for supercapacitors.

Field emission characterization of field-aligned carbon nanotubes synthesized in an environmental transmission electron microscope

Optimizing the synthesis of carbon nanotubes (CNTs) for applications like field emission (FE) sources requires a fundamental understanding of the growth kinetics of individual CNTs. In this article, we explore how applying electric fields during CNT synthesis influences the as-grown nanotubes and their FE performance. We observe growth and undertake FE measurements in real time using an environmental transmission electron microscope. This is achieved through a polarizable capacitor gap within a microchip sample heater specifically designed for this purpose. Individual nanotubes are easily resolved and are predominantly single-wall CNTs. At low-applied fields, the growing nanotubes can span the gap and link with the opposite electrode, albeit with some loss due to mechanical failure. With a high-applied field and positive bias for FE, we continue to observe the oriented growth of nanotubes. However, this growth is constrained within the gap due to the possibility of FE occurring during the growth process, which can result in either saturation or damage. At any given time, we have the flexibility to halt the growth process and conduct in situ FE experiments. This approach enables us to comprehensively track the complete development of the CNTs and gain insights into the various mechanisms responsible for limiting the performance of CNT cathodes. Interestingly, we report an original self-oscillation induced destruction mechanism that has not been reported before.

Imprinted CNTs field emission cathode for electron brushing

Microchannel plates (MCPs) are the key components for low-level light night vision systems. Electron brushing is a crucial processing for MCPs manufacturing. In this paper, an imprinted carbon nanotubes (CNTs) field emission cathode is fabricated and tested. And the electron brushing experiment based on this cathode is carried out. The result shows that the imprinted CNTs cathode has some advantages and can be used in electron brushing. This research lays the foundation for massive, low cost and highly efficient electron brushing applications in the future.

Boosting the electron beam transmittance of field emission cathode using a self-charging gate

The gate-type carbon nanotubes cathodes exhibit advantages in long-term stable emission owing to the uniformity of electrical field on the carbon nanotubes, but the gate inevitably reduces the transmittance of electron beam, posing challenges for system stabilities. In this work, we introduce electron beam focusing technique using the self-charging SiNx/Au/Si gate. The potential of SiNx is measured to be approximately −60 V quickly after the cathode turning on, the negative potential can be maintained as the emission goes on. The charged surface generates rebounding electrostatic forces on the following electrons, significantly focusing the electron beam on the center of gate hole and allowing them to pass through gate with minimal interceptions. An average transmittance of 96.17% is observed during 550 hours prototype test, the transmittance above 95% is recorded for the cathode current from 2.14 μA to 3.25 mA with the current density up to 17.54 mA cm−2.

Boosting field electron emission of carbon nanotubes through small-hole-patterning design of the substrate

High field emission of carbon nanotube (CNT) cold cathodes is realized by printing modified CNT paste on small-hole-patterned substrates. The field emission characteristics and stability of samples under DC continuous and pulse driving modes have been investigated. The results show that the maximum emission current of CNT emitters can be up to 45 mA at an electric field of 2100 V (7.0 V μm−1), corresponding to a high current density of 643 mA cm−2 under continuous mode. The cathodes also demonstrate stable electron emission without obvious attenuation. In pulse (10 μs and 200 Hz) mode, the peak current can reach 250 mA and the corresponding current density is 3.57 A cm−2 under an electric field of 14.0 V μm−1. The hole-patterned CNT cathode presents unique advantages in field emission current, stability and especially endurance of high electric field. This work makes it possible to fabricate highly efficient emission CNT cold electron sources, which have broad application prospects in vacuum electronic devices requiring both large current and high current density.

Zero-Strain Na3 V2 (PO4 )2 F3 @Rgo/CNT Composite as a Wide-Temperature-Tolerance Cathode for Na-Ion Batteries with Ultrahigh-Rate Performance.

Sodium-ion batteries (SIBs) are widely considered a hopeful alternative to lithium-ion battery technology. However, they still face challenges, such as low rate capability, unsatisfactory cycling stability, and inferior variable-temperature performance. In this study, a hierarchical Na3 V2 (PO4 )2 F3 (NVPF) @reduced graphene oxide (rGO)/carbon nanotube(CNT) composite (NVPF@rGO/CNT) is successfully constructed. This composite features 0D Na3 V2 (PO4 )2 F3 nanoparticles are coated by a cross-linked 3D conductive network composed of 2D rGO and 1D CNT. Furthermore, the intrinsic Na+ storage mechanism of NVPF@rGO/CNT through comprehensive characterizations is unveiled. The synthesized NVPF@rGO/CNT exhibits fast ionic/electronic transport and excellent structural stability within wide working temperatures (-40-50 °C), owing to the zero-strain NVPF and the coated rGO/CNT conductive network that reduces diffusion distance for ions and electrons. Moreover, the stable integration between NVPF and rGO/CNT enables outstanding structural stability to alleviate strain and stress induced during the cycle. Additionally, a practice full cell is assembled employing a hard carbon anode paired with an NVPF@rGO/CNT cathode, which provides a decent capacity of 105.2 mAh g-1 at 0.2 C, thereby attaining an ideal energy density of 242.7Wh kg-1 . This work provides valuable insights into developing high-energy and power-density cathode materials for SIBs.

Synergistic advancements in sewage-driven microbial fuel cells: novel carbon nanotube cathodes and biomass-derived anodes for efficient renewable energy generation and wastewater treatment

Microbial fuel cells (MFCs) offer a dual solution of generating electrical energy from organic pollutants-laden wastewater while treating it. This study focuses on enhancing MFC performance through innovative electrode design. Three-dimensional (3D) anodes, created from corncobs and mango seeds via controlled graphitization, achieved remarkable power densities. The newly developed electrode configurations were evaluated within sewage wastewater-driven MFCs without the introduction of external microorganisms or prior treatment of the wastewater. At 1,000°C and 1,100°C graphitization temperatures, corncob and mango seed anodes produced 1,963 and 2,171 mW/m2, respectively, nearly 20 times higher than conventional carbon cloth and paper anodes. An advanced cathode composed of an activated carbon-carbon nanotube composite was introduced, rivaling expensive platinum-based cathodes. By optimizing the thermal treatment temperature and carbon nanotube content of the proposed cathode, comparable or superior performance to standard Pt/C commercial cathodes was achieved. Specifically, MFCs assembled with corncob anode with the proposed and standard Pt/C cathodes reached power densities of 1,963.1 and 2,178.6 mW/m2, respectively. Similarly, when utilizing graphitized mango seeds at 1,100°C, power densities of 2,171 and 2,151 mW/m2 were achieved for the new and standard cathodes, respectively. Furthermore, in continuous operation with a flow rate of 2 L/h, impressive chemical oxygen demand (COD) removal rates of 77% and 85% were achieved with corncob and mango seed anodes, respectively. This work highlights the significance of electrode design for enhancing MFC efficiency in electricity generation and wastewater treatment.

Cathode materials in microbial electrosynthesis systems for carbon dioxide reduction: recent progress and perspectives

Microbial electrosynthesis (MES) is an emerging technology that enables the synthesis of value-added chemicals from carbon dioxide (CO2) or inorganic carbon compounds by coupling renewable electricity to microbial metabolism. However, MES still faces challenges in achieving high production of value-added chemicals due to the limited extracellular electron transfer efficiency at the biotic-abiotic interfaces. To overcome this bottleneck, it is crucial to develop novel cathodes and modified materials. This review systematically summarizes recent advancements in cathode materials in the field of electrocatalyst-assisted and photocatalyst-assisted MES. The effects of various material types are further investigated by comparing metal-free and metal materials and photocatalyst materials of different semiconductor types. Additionally, the review introduces the maximum production rate of value-added chemicals and conversion efficiency achieved by these cathode materials while highlighting the advantages and disadvantages of different material types. To the best of our knowledge, in electrocatalyst-assisted systems, the maximum CH4 yield on graphene aerogel/polypyrrole cathode achieved 1,672 mmol m-2 d-1, and the maximum Faraday efficiency (FE) of CH4 reached up to 97.5% on graphite plate. Meanwhile, the maximum acetate yield achieved 1,330 g m-2 d-1 with CO2 conversion efficiency into acetate close to 100% on carbon nanotube cathodes. In photocatalyst-assisted systems, the maximum acetate yield could reach 0.51 g L-1 d-1 with the coulombic efficiency of 96% on the MnFe2O4/g-C3N4 photocathode. Finally, prospects for future development and practical applications of MES are discussed, offering theoretical guidance for the fabrication of cathode materials that can improve production efficiency and reduce energy input.

High-Performance Hydroxide Exchange Membrane Fuel Cell Comprising an Atomic Layer-Deposited Silver Cathode.

Atomic layer deposition (ALD) is emerging as an efficient tool for the precise manufacture of catalysts, owing to its sophisticated surface tailoring capabilities. To overcome the techno-economic limitations of fuel cell electric vehicles (FCEVs), which are considered suitable alternatives to battery electric vehicles (BEVs), the development of cost-efficient high-performance catalysts is essential. In this study, we successfully fabricated a Pt-free cathode for a hydroxide exchange membrane fuel cell (HEMFC) with excellent oxygen reduction activity under extremely low loading of Ag electrocatalysts using ALD. Microstructural analysis confirmed that the surface modification by ALD-Ag nanoparticles exhibited excellent step coverage characteristics on porous carbon nanotubes (CNTs). An HEMFC comprising a CNT cathode surface-decorated with ALD-Ag nanoparticles delivered a high peak power density of 2154 mW mgAg-1 in an alkaline environment at 65 °C. This study demonstrates the applicability of ALD for the manufacture of highly active low-cost electrocatalysts for high-performance HEMFCs.

“Double-high” field electron emission of screen-printed carbon nanotube cathodes

High performance cold cathodes based on carbon nanotubes (CNTs) are fabricated by using a screen-printing method. The CNT cathode shows stable electron emission with no significant deterioration and the temperature-dependent emission has been also investigated. The results demonstrate that the maximum emission current of CNT emitters can be reached to 16.9 mA at electric field of 7.6 V μm−1, corresponding to super-high current density of 562 mA cm−2 under continuous driving mode. Under pulse driving mode, the peak current of 70 mA with a high current density of 2333 mA cm−2 is further obtained at electric field of 11.5 V μm−1. The presented CNT emitters display high electron emission both in total current and current density under continuous and pulse driving modes. This work will open a new avenue towards designing “double-high” CNT cold electron sources for broad application prospects in vacuum electronic devices requiring high current and density simultaneously.

All-Round Enhancement in Zn-Ion Storage Enabled by Solvent-Guided Lewis Acid-Base Self-Assembly of Heterodiatomic Carbon Nanotubes.

Designing zincophilic and stable carbon nanostructures is critical for Zn-ion storage with superior capacitive activity and durability. Here, we report solvent-guided Lewis acid-base self-assembly to customize heterodiatomic carbon nanotubes, triggered by the reaction between iron chloride and α,α'-dichloro-p-xylene. In this strategy, modulating the solvent-precursor interaction through the optimization of solvent formula stimulates differential thermodynamic solubilization, growth kinetics, and self-assembly behaviors of Lewis polymeric chains, thereby accurately tailoring carbon nanoarchitectures to evoke superior Zn-ion storage. Featured with open hollow interiors and porous tubular topologies, the solvent-optimized carbon nanotubes allow low ion-migration barriers to deeply access the built-in zincophilic sites by high-kinetics physical Zn2+/CF3SO3- adsorption and robust chemical Zn2+ redox with pyridine/carbonyl motifs, which maximizes the spatial capacitive charge storage density. Thus, as-designed heterodiatomic carbon nanotube cathodes provide all-round improvement in Zn-ion storage, including a high energy density (140 W h kg-1), a large current activity (100 A g-1), and an exceptional long-term cyclability (100,000 cycles at 50 A g-1). This study provides appealing insights into the solvent-mediated Lewis pair self-assembly design of nanostructured carbons toward advanced Zn-ion energy storage.

Highly monodispersed Li2SO4 crystals towards Li2S-based lithium-sulfur battery cathodes

Li2S as a cathode of lithium sulfur batteries (LSB) and a precursor of advanced solid electrolytes have been widely investigated. However, suffered from the high cost and the low ionic/electronic conductivity, the controllable fabrication of Li2S crystals from the carbothermal conversion of Li2SO4 need to be improved urgently. Herein, polyacrylic acid (PAA) as a blocking agent is introduced to fabricate the monodispersed Li2SO4 (m-Li2SO4) crystals and the m-Li2S/carbon nanotube (CNT) cathode via subsequent carbothermal reaction. Our constructed Li2S/CNT||Li cells deliver a high initial discharge capacity of ∼900 mAh/g and a reversible specific capacity of 500 mAh/g at 2C. These results suggest the importance of regulating size and morphology of Li2SO4 crystals towards high-performance Li2S crystals.

A High-Performance Li-O2/Air Battery System with Dual Redox Mediators in the Hydrophobic Ionic Liquid-Based Gel Polymer Electrolyte

Lithium–oxygen (Li-O2) batteries have captured worldwide attention owing to their highest theoretical specific energy density. However, this promising system still suffers from huge discharge/charge overpotentials and poor cycling stability, which are related to the leakage/volatilization of organic liquid electrolytes and the inefficiency of solid catalysts. A mixing ionic liquid-based gel polymer electrolyte (IL-GPE)-based Li-O2 battery, consisting of a 20 mM 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) 40 mM N-methylphenothiazine (MPT)-containing IL-GPE and a single-walled carbon nanotube cathode, is designed for the first time here. This unique dual redox mediators-based GPE, which contains a polymer matrix immersed with mixed ionic liquid electrolyte, provides a proper ionic conductivity (0.48 mS cm−1) and effective protection for lithium anode. In addition, DBBQ, as the catalyst for an oxygen reduction reaction, can support the growth of discharge products through the solution–phase pathway. Simultaneously, MPT, as the catalyst for an oxygen evolution reaction, can decompose Li2O2 at low charge overpotentials. Hence, the DBBQ-MPT-IL-GPE-based Li-O2 battery can operate for 100 cycles with lower charge/discharge overpotentials. This investigation may offer a promising method to realize high-efficiency Li-O2/air batteries.

Durable Lithium–Sulfur Batteries Based on a Composite Carbon Nanotube Cathode

Durable Lithium–Sulfur Batteries Based on a Composite Carbon Nanotube Cathode

Microwave-regulated Bi nanoparticles on carbon nanotube networks as a freestanding electrode for flexible sodium-ion capacitors

High capacity, long cycle life, and fast kinetics are highly desired for alloying anodes in sodium ion capacitors (SICs). However, the huge repeatedly volume changes during the alloying/dealloying process cause electrode pulverization, seriously degrading the capacity and cycling stability. To address this issue, we developed a microwave irradiation technology for the in-situ growth of nano-sized Bi uniformly anchored on the surface of carbon nanotubes (CNTs). The as-synthesized freestanding electrode film effectively retards the pulverization of Bi nanoparticles, enabling fast sodium storage kinetics for high-power performance (278.1 mAh g−1 @ 30 A g−1), as well as high-capacity retention of 94% for over 3,500 cycles. The coin-cell type SICs of a Bi/CNTs anode paired with an activated carbon (AC)/CNTs cathode can deliver a maximum energy density of 128.5 Wh kg−1 and a high power density of 12.3 kW kg−1 with a remaining energy density of 85 Wh kg−1. Additionally, the flexible quasi-solid SICs using a gel electrolyte demonstrated a high volumetric energy density of 21 mWh cm−3 with good cycling stability (90%) for over 1500 cycles. These results show great promise for our developed SICs as the next-generation energy storage to bridge the performance gap between batteries and supercapacitors, as well as for flexible energy storage applications.

Influence of Capping Agents on the Synthesis of Mn3O4 Nanostructures for Supercapacitors

Nanotechnology offers powerful strategies for the synthesis of advanced materials for supercapacitors. It is hypothesized that the size reduction of Mn3O4 nanoparticles can eliminate time-consuming electrochemical activation and increase the electrochemical pseudocapacitance of this material. Moreover, due to the redox properties and specific features of its chemical synthesis procedure, Mn3O4 can potentially outperform other promising cathode materials for energy storage in supercapacitors. A facile room temperature method to fabricate Mn3O4 nanoparticles is described, which is based on the application of advanced capping agents (CAs) for nanofabrication. Building on the strong adsorption power of the catechol ligand, we utilize tetrahydroxy-1,4-quinone, catechin, and gallocyanine as CAs for the preparation of Mn3O4. The use of the catecholate molecules as CAs for chemical precipitation facilitates the preparation of Mn3O4 platelet nanoparticles with a typical size of 5 nm. The reduction of the particle size allows the fabrication of advanced Mn3O4 multiwalled carbon nanotube cathodes with 40 mg cm–2 active mass (AM), which show a significant increase in capacitance in a 0.5 M Na2SO4 electrolyte. The highest capacitances of 7.03 F cm–2 (175.8 F g–1) at a potentiodynamic sweep rate of 2 mV s–1 and 9.13 F cm–2 (228.3 F g–1) at a constant current density of 3 mA cm–2 are obtained at a low impedance using gallocyanine as a CA. Obtained electrodes outperform MnO2-based cathodes of similar mass. Another important finding is the possibility to avoid the time-consuming activation process for Mn3O4-based electrodes. Analysis of the testing results provides evidence of the influence of the CA structure on the electrode performance. The results of this investigation pave the way for the application of Mn3O4 in advanced high-AM supercapacitor cathodes.

An atomic/molecular-level strategy for the design of a preferred nitrogen-doped carbon nanotube cathode for Li-O2 batteries

The formation and growth of Li2O2, the primary discharge product with extremely low conductivity, will cause the passivation of the cathode and the failure or even death of Li-O2 batteries. In this paper, by means of molecular dynamics and density functional theory, we systematically investigated the morphology evolution and electron transport pathway of (Li2O2)n on the surface of nitrogen-doped carbon nanotubes (NCNTs) and the effects of the possible N configuration on the growth stability of (Li2O2)n. Our results demonstrated that the morphology of (Li2O2)n on the surface of NCNTs undergos a process from scattered small-sized clusters to film-like (axial) and toroidal (circumferential) large clusters, and finally completely surrounded the NCNTs. Compared with graphitic N1 and graphitic N2, Li2O2 tends to aggregate stably on the surface of pyridinic N3 and pyridinic N4, which can effectively reduce the capacity loss caused by Li2O2 branches and free state Li2O2. In addition, a stable gap exists between Li2O2 and NCNTs, which is attributed to the Coulomb force and van der Waals interaction. Importantly, (Li2O2)n with p-type semiconductor characteristics acts as a bridge between NCNTs, and electrons are mainly transferred along the surface of (Li2O2)n clusters. Moreover, increasing the wall number of NCNTs and using NCNT bundles were found to be beneficial to improving the deposition stability of (Li2O2)n. Notably, pyrrolic N3 with unstable structure is not recommended for practical application. These results offer general guidelines for designing highly active catalysts for Li-O2 batteries in terms of the optimization of the NCNT-based cathode, and the unique research methods also shed more light on the analysis of the discharge product behavior of other potential metal-air batteries.