Multi-walled Carbon Nanotube Cathodes Research Articles

A 3.5 V-class organic sodium-ion battery using a croconate cathode

Sodium-ion batteries (SIBs) based on organic cathode materials have received considerable attention owing to high theoretical capacities, cost-effectiveness, and raw material abundance. However, high-voltage organic cathodes have been rarely investigated for SIBs mainly due to their electrical insulation and dissolution in electrolytes. In this study, sodium croconate (C5O5Na2) is utilized as a high-voltage cathode material for SIBs, designing an interface using a functionalized multi-walled carbon nanotube (MWCNT). The composite C5O5Na2 cathode with carboxylic-acid-functionalized-(COOH–) MWCNT exhibits a 3.5 V-class high-voltage redox activity with a cycle performance higher than that of non-functionalized MWCNT/C5O5Na2 composite cathodes; the capacity retention ratio is improved from 0 % to 34 % after 30 cycles at 0.1C. Raman, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance reveal the formation of hydrogen bonding between COOH groups on MWCNT and carbonyl groups in C5O5Na2 molecules; leading to suppression of organic molecules and improvement on the cycle performance. A full cell assembled with the C5O5Na2/COOH–MWCNT cathode and a hard carbon anode also shows a high-voltage redox plateau at around 3.5 V and a 1st discharge capacity of 123 mAh g−1 at 1C. These results suggest the feasibility of developing a high-energy-density storage system using completely common-metal components.

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.

Iron and Nickel Phthalocyanine‐Modified Nanocarbon Materials as Cathode Catalysts for Anion‐Exchange Membrane Fuel Cells and Zinc‐Air Batteries**

AbstractIron and nickel phthalocyanines along with different carbon supports, i. e., multi‐walled carbon nanotubes (MWCNT), graphene, carbide‐derived carbon, Vulcan carbon, and mesoporous carbon (MC, from Pajarito Powder, LLC), are used to prepare six bimetallic (Fe, Ni) N‐doped carbon‐based catalysts. The aim of this work is to investigate the electrocatalytic activity of bimetal phthalocyanine‐modified nanocarbon catalysts, e. g., the effect of carbon supports on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), including the anion‐exchange membrane fuel cell (AEMFC) and rechargeable zinc‐air battery (RZAB) configuration. The catalysts exhibit excellent electrocatalytic activity as exemplified by their half‐wave potential (E1/2) for ORR and the potential at which the OER current density reaches 10 mA cm−2 (Ej=10), but the best performing catalysts are FeNiN−MC (E1/2=0.88 V, Ej=10=1.58 V) and FeNiN−MWCNT (E1/2=0.87 V, Ej=10=1.59 V). In AEMFC analyses, FeNiN−MWCNT cathode provides peak power density (Pmax) of 406 mW cm−2, slightly higher than that of FeNiN−MC (Pmax=386 mW cm−2). Both catalysts exhibit a good RZAB performance (Pmax of 85 mW cm−2 for FeNiN−MWCNT). The assembled RZABs run stably for 48 h without any significant loss of performance.

Nanostructured Poly(hydroquinonyl-benzoquinonyl sulfide)/Multiwalled Carbon Nanotube Composite Cathodes: Improved Synthesis and Performance for Rechargeable Li and Mg Organic Batteries

Cost-effective, simple, and easily reproducible synthesis methods of polymers are of profound significance when it comes to extracting high battery performance metrics from polymeric redox-active materials. This work reports a procedure for the solvothermal synthesis of a poly(hydroquinonyl-benzoquinonyl sulfide) (PHBQS) polymer and the development of its nanostructured composites with multiwalled carbon nanotubes (MWCNTs). Polymers are tested as high-performance cathode materials for Li+ and Mg2+ batteries. In configurations, compared to neat PHBQS, the PHBQS@5%MWCNT cathode exhibits superior electrochemical performance with high active material utilization owing to improved ion/electron transport pathways. Galvanostatic characterization of the PHBQS@5%MWCNT cathode in lithium batteries exhibited peak capacity up to 358 mAh g–1 at a current density of 50 mA g–1 (C/8) and excellent rate performance with a discharge capacity of 236 mAh g–1 maintained even at high current density of 10C. The galvanostatic characterization in Mg batteries reveals more sluggish kinetics with a stable capacity of 200 mAh g–1 at 50 mA g–1.

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.

Graphitic multi-walled carbon nanotube cathodes for rechargeable Al-ion batteries with well-defined discharge plateaus

One-dimensional multi-walled carbon nanotubes (MWCNTs) are promising electrode materials for rechargeable batteries. This paper reports that graphitic MWCNT (G-MWCNT) can serve as a cathode material for a rechargeable Al-ion battery and exhibits well-defined discharging plateaus at around 2 V. AlCl4−intercalates and de-intercalates into/from the graphitic MWCNT rather than simply adsorbing on the surfaces. Hence, the Al||G-MWCNT cell exhibits good electrochemical performance with a specific capacity of 64 mA h g−1 at a current density of 200 mA g−1. The discharge capacity is almost unattenuated and maintained at about 58 mA h g−1 (Coulombic efficiency: 99.5%) after 1000 charge/discharge cycles, which indicates that the Al||G-MWCNT cell has excellent cycling stability. In addition, the low self-discharging rate (~0.4% over 72 h of rest) suggests that the intercalated AlCl4− is stable in the spaces between the graphene layers of G-MWCNT. This work reveals that Al||G-MWCNT cells exhibit diffusion-controlled faradaic process rather than capacitor behavior, which may boost the development of aluminum batteries.

Peroxydisulfate activation by positively polarized carbocatalyst for enhanced removal of aqueous organic pollutants

Multi-walled carbon nanotubes (MWCNTs)/peroxydisulfate (PDS) is a green oxidative system for abatement of aqueous organic pollutants, while the powder form and poor cycling performance of the catalyst limit its practical application. To solve these problems, fabricating a MWCNT cathode (negative polarization) to coupling carbocatalysis-driven PDS activation with electrosorption of organic pollutant was previously demonstrated to be a possible solution to these problems. To further improve the activation efficiency of PDS, positive polarization of MWCNT electrode (anode) was adapted to activate PDS for removing acyclovir and phenol in this work. Under a working voltage of 1.2 V, the MWCNT anode was more efficient than the MWCNT cathode and the non-polarized MWCNT electrode for PDS activation and removal of organic pollutants, owing to the enhanced attraction between S2O82− anions and anode. Although the positive/negative polarization of MWCNT electrode doesn't alter the nonradical mechanism involved in MWCNTs/PDS system, theoretical calculations suggest that different polarization affect the electron configuration and oxidative capacity of activated S2O82− bounded to MWCNTs differently, and that the adsorbed S2O82− with stretched S–O bond and much higher oxidative capacity than that in the case of non-polarized MWCNT electrode is responsible for the MWCNTs anode, while adsorbed S2O82− with stretched O–O bond and slightly higher oxidative capacity is responsible for the MWCNTs cathode. Finally, implications of operation parameters including electrode potential, energy cost, pH, etc. on the elimination efficiency by MWCNT anode/PDS system were investigated and the results suggest that the MWCNT anode/PDS is an efficient and economical metal-free electrochemical oxidative system for organic contaminants remediation.

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.

Co(0.85)Se/Multi-Walled Carbon Nanotube Composite as Alternative Cathode Catalyst for Microbial Fuel Cells.

The development of low-cost and high-performance cathode catalyst remains a great challenge for constructing large-scale microbial fuel cells (MFCs). Here, the multi-walled carbon nanotube (MWCNT) supported cobalt selenide (Co0.85Se) composite was synthesized by a simple and effective hydrothermal process for the first time. Compared with uncomposited electrodes such as MWCNTs and Co0.85Se, the as-prepared Co0.85Se/MWCNT composite electrode exhibited significantly improved electrochemical performance and durability. The maximum power density of Co0.85Se/MWCNT composite electrode is 243.6 mW m–2, which is 12.2 fold higher than that of unmodified electrode and more than twice as much as those observed for MWCNTs cathode (114.1 mW m–2) and Co0.85Se cathode (119.8 mW m–2). This work may provide not only the fundamental studies on carbon supported transition-metal selenide but also a new kind of promising alternative electrode in the technology of power generation from MFCs.

Improvement of Lighting Uniformity and Phosphor Life in Field Emission Lamps Using Carbon Nanocoils

The lighting performances and phosphor degradation in field emission lamps (FELs) with two different kinds of cathode materials—multiwalled carbon nanotubes (MWCNTs) and carbon nanocoils (CNCs)—were compared. The MWCNTs and CNCs were selectively synthesized on 304 stainless steel wire substrates dip‐coated with nanosized Pd catalysts by controlling the growth temperature in thermal chemical vapor deposition, and the film uniformity can be optimized by adjusting the growth time. FELs were successfully fabricated by assembling these cathode filaments with a glass bulb‐type anode. The FEL with the CNC cathode showed much higher lighting uniformity and light‐spot density and a lower current at the same voltage than that with the MWCNT cathode filament, and its best luminous efficiency was as high as 75 lm/W at 8 kV. We also found that, for P22, the phosphor degradation can be effectively suppressed by replacing MWCNTs with CNCs in the cathode, due to the much larger total bright spot area and hence much lower current density loading on the anode.

Power generation using polyaniline/multi-walled carbon nanotubes as an alternative cathode catalyst in microbial fuel cells

SUMMARY Optimization of the cathode catalyst is critical to the study of microbial fuel cells (MFCs). By using the open circuit voltage and power density as evaluation standards, this study focused on the use of polyaniline (PANI)/multi-walled carbon nanotube (MWNT) composites as cathode catalysts for the replacement of platinum (Pt) in an air-cathode MFC, which was fed with synthetic wastewater. Scanning electron microscopy and linear scan voltammogram methods were used to evaluate the morphology and electrocatalytic activity of cathodes. A maximum power density of 476 mW/m2 was obtained with a 75% wt PANI/MWNT composite cathode, which was higher than the maximum power density of 367 mW/m2 obtained with a pure MWNT cathode but lower than the maximum power density of 541 mW/m2 obtained with a Pt/C cathode. Thus, the use of PANI/MWNT composites may be a suitable alternative to a Pt/C catalyst in MFCs. PANI/MWNT composites were initially used as cathodic catalysts to replace Pt/C catalysts, which enhanced the power generation of MFCs and substantially reduced their cost. Copyright © 2014 John Wiley & Sons, Ltd.

Development of high spatial resolution x-ray radiography system equipped with multiwalled carbon nanotube field emission cathode

An x-ray radiography system (XRS) equipped with a multiwalled carbon nanotube cathode was developed. This system has ordinary scanning electron microscopy (SEM) functions available for the precise adjustment of focusing conditions including astigmatism and alignment of an electron beam. The electron beam diameter on a target, which is one factor that limits spatial resolution of XRS, was estimated as 50nm from the resolution of SEM images obtained. X-ray images were taken as a demonstration of the XRS, and clear images with resolution higher than 700nm were successfully obtained.

Development of a High Resolution X-ray Microscope Equipped with a Carbon Nanotube Field Emission Cold Cathode

A high resolution X-ray microscope equipped with a multi-walled carbon nanotube cathode was developed. This system has ordinary scanning electron microscopy functions available for the precise adjustment of focusing conditions including astigmatism and an alignment of an electron beam. By the adoption of a transmission type, X-ray images with high magnification can be easily obtained. The diameter of an electron probe, which is one of the factors limiting a spatial resolution of X-ray microscopes, was estimated to be about 270 nm from a resolution of obtained SEM images. Clear X-ray images with the resolution higher than 400 nm were successfully obtained.

Nano- LiFePO4 ∕ MWCNT Cathode Materials Prepared by Room-Temperature Solid-State Reaction and Microwave Heating

The precursors of were prepared by room-temperature solid-state reaction using , , as raw materials. Citric acid was added to reduce the particle size of , and multiwalled carbon nanotubes (MWCNTs) were adopted to improve the electrical conductivity. The samples were synthesized for a few minutes by microwave heating. X-ray diffraction and transmission electron microscope were used to characterize their structures and morphologies. The results showed that all samples had the same olivine phase structure. When both citric acid and MWCNTs were added, nanoparticles of homogeneously coated on the MWCNTs. An electrochemical test showed that , with both citric acid and MWCNTs addition, demonstrated an excellent electrochemical capacity of at C/2 and stable cycle ability. Citric acid expansion reduced the particle size, thus reducing the length of diffusion or improving the reversibility of the lithium ion intercalation/deintercalation. MWCNTs functioned as a lead to connect the particles and enabled active materials to transport lithium ions and electrons at fast rates.

Formula omitted], He and Ar sorption on arc-produced cathode deposit consisting of multiwalled carbon nanotubes—graphitic and diamond-like carbon

H 2 , He and Ar sorption characteristics in a mixture of multiwalled carbon nanotubes (MWCNT), graphite and diamond-like carbon produced as a cathode deposit during the Kratscmer Hoffman arc process were investigated. A dynamic technique was used to determine the adsorption equilibrium parameters in a temperature range of 30–200 °C. Adsorption equilibrium constants were evaluated using the moment analysis of the chromatographic peaks. At 30 °C, the adsorption equilibrium constant of H 2 on the MWCNT cathode deposit was found to be 8.91 × 10 - 4 m 3 kg - 1 , whereas it has value of 5.65 × 10 - 4 at 200 °C. Heats of adsorption of H 2 , He and Ar on the MWCNT cathode deposit were determined as - 2.89 , - 2.94 and - 3.01 kJ mol - 1 , respectively. The values of heat of adsorption obtained indicated weaker interactions of gases, implying physical adsorption of H 2 , He and Ar on the MWCNT cathode deposit used.

Improved field-emission characteristics of a multiwalled carbon-nanotube cathode by argon plasma pretreatment and krypton-fluoride laser irradiation

An effect of argon (Ar) plasma pretreatment, followed by krypton-fluoride (KrF) laser irradiation, of multiwalled carbon-nanotube (MWCNT) cathodes on field-emission (FE) characteristics was investigated. With an Ar plasma pretreatment of 100W, the FE current density was increased to 32.6mA∕cm2 at an electric field of 4.92V∕μm after laser irradiation, the value of which was about 30 times higher than the current density without plasma pretreatment. The emission-site density (ESD) was also increased by 25 times by a plasma pretreatment of 100W. However, the further increase in plasma power at and above 150W deteriorated both FE characteristics and ESD, which was due to the decrease in the number of MWCNT emission sites.

Field emission properties of plasma treated multiwalled carbon nanotube cathode layers

Improved field emission stability and lifetime have been observed for multiwalled carbon nanotube (MWCNT)-paste cathode layers, after plasma conditioning. Initially, MWCNT paste was synthesized and screen printed on an indium tin oxide coated glass substrate to obtain the cathode layers. These cathode layers were exposed to the Xe∕Ne plasma for a period of ∼1 or ∼3min under different biasing conditions (∼250 and ∼300V). The scanning electron microscopy micrographs, recorded for the untreated (virgin) and plasma treated cathode layers, showed significant variations in their morphology. The field emission analysis showed that the onset macroscopic field was increased from its virgin value of ∼4.65to∼9.05±0.05V∕μm for the plasma treated samples, with a subsequent decrease in the mean field-enhancement factor γav from 1251±13 to 779±43, computed from the Fowler-Nordheim plot. The variations in the current density was measured as a function of time, under low (∼10−6Torr) as well as high (∼10−8Torr) vacuum conditions, and corresponding degradation rates were computed. The degradation rate was found to be reduced by a factor of ∼103 under high vacuum conditions. The lifetime study revealed that the half-lifetime of the plasma treated samples was increased from its virgin value of ∼15to∼400h, at ∼10−6Torr. In another study, the estimated half-lifetime of the plasma treated cathode layers was found to be more than ∼20000h under high vacuum conditions (∼10−8Torr). The details of the analysis are presented.