Doped Carbon Nanotubes Research Articles

Efficient and stable nanoporous functional composited electrocatalyst derived from Zn/Co-bimetallic zeolitic imidazolate frameworks for oxygen reduction reaction in alkaline media

A facile synthesis approach for metal-organic frameworks (MOFs) materials was studied for developing electrocatalysts with high electrochemical catalytic activity and stability. The prepared composite material contains two essential components: a predesigned bimetallic hybrid Zn/Co zeolitic imidazole frameworks (BMZIFs) and N-doped graphitic carbon (NGC) with various contents of carbon nanotubes (CNTs). Among which, NGC@CNTs-40 (100 mg NGC with 40 mg CNTs) exhibits the best oxygen reduction reaction (ORR) performance in alkaline media. In addition, NGC@CNTs-40 shows high surface area of 353.9 m2 g−1, coexisting micro/mesoporous N-doped carbon, low ID/IG ratio and abundant N atomic species. Remarkably, NGC@CNTs-40 exhibited a limiting current density of 5.66 mA cm−2 and a half-wave potential of 0.81 V, which is comparable with commercial Pt/C (5.22 mA cm−2 and 0.81 V) and most reported non-precious metal catalysts. Moreover, NGC@CNTs-40 exhibits better stability than Pt/C. The transferred electron number of NGC@CNTs-40 is 3.92, close to the ideal value of 4.0. The doping of CNTs into MOFs and the synergetic effect of Zn/Co-BMZIFs can enhance the conductivity of conventional MOFs and the blocked transfer of active substances in MOFs crystals, shedding new light on future applications.

Efficient oxygen reduction reaction catalyst derived from ZnO@ zeolite imidazolate framework nanowire composite

The oxygen reduction reaction (ORR) is one of the core reactions that occur in fuel cells and metal air batteries. Metal-free catalysts such as porous carbons are promising candidates for ORR and the performance of porous carbons strongly depends on their nanostructure. Herein, we reported the synthesis of high surface area N doped carbon nanotube (CNT-900) by using ZnO@zeolite imidazolate framework (ZnO@ZIF-8) nanowire as a precursor. When used for an ORR catalyst, the CNT-900 show obvious superior performance compared with the carbon derived from ZIF-8. In addition, it exhibits comparable activity with 20 wt% Pt/C and superior stability. Combined with green and facile synthesis strategy, the method in this work can be easily extended to synthesis other nanomaterials for energy storage and conversion application.

Poly(ferrocenedimethano)cyclotriphosphazene to Homogenously Fe, N, P, O Doped Carbon Nanotubes: An Efficient and Tremendous Electrocatalyst for Oxygen Reduction Reaction

Development of heteroatoms doped one-dimensional carbon nanotubes (1D CNTs) have grabbed great attentions for energy applications. A precise approach for the synthesis of homogenous-doped atoms 1D CNTs remains a big challenge, particularly due to foreign doping of the metal atoms. Herein, we reported homogeneous doing of metal (Fe) and non-metal (N, P, O) atoms into carbon lattice via synthesis of novel iron-containing Poly(ferrocenedimethano)cyclotriphosphazene (PFC) 1D NTs followed by their pyrolysis at various temperatures (600, 800, 1000°C). These electrocatalysts were represented as PFC-600, PFC-800 and PFC-1000, respectively and they exhibited a homogeneous distribution of Fe, N, P, O into carbon lattice. Cyclic voltammetry measurements depicted a notable cathodic peak at 0.86 V vs RHE and maximal current density 2.43 mA cm2 for PFC-800 infers its substantial enhanced ORR performance compared with its counterpart electrocatalysts (PFC-600, PFC-1000) and Pt/C. The PFC-800 also showed superior stability and higher methanol tolerance compared commercial Pt/C. The higher performance was attributed to 1) a precise and homogeneous distribution of Fe atoms resulting in promotion of initial O2 adsorption and generate more active sites; 2) highest surface area and hierarchical porous structure contribute for enhanced-flux mass transport. This design will provide a facile pathway for homogeneous doping of other metals and non-metals atoms into carbon lattice to construct a highly efficient and cost-effective ORR catalyst.

A tool box to ascertain the nature of doping and photoresponse in single-walled carbon nanotubes.

The effect of doping on the electronic properties in bulk single-walled carbon nanotube (SWCNT) samples is studied for the first time using a new in situ Raman spectroelectrochemical method, and further verified by DFT calculations and photoresponse. We use p-/n-doped SWCNTs prepared by diazonium reactions as a versatile chemical strategy to control the SWCNT behavior. The measured and calculated data testify an acceptor effect of 4-aminobenzenesulfonic acid (p-doping), and a donor effect (n-doping) in the case of benzyl alcohol. In addition, pristine and covalently functionalized SWCNTs were used for the preparation of photoactive film electrodes. The photocathodic current in the photoelectrochemical cell is consistently modulated by the doping group. These results validate the in situ Raman spectroelectrochemistry as a unique tool box for predicting the electronic properties of functionalized SWCNTs in the form of thin films and their operational functionality in thin film devices for future optoelectronic applications.

Catalytic trends of nitrogen doped carbon nanotubes for oxygen reduction reaction.

Replacing the state-of-the-art fuel cell catalyst platinum for a cheaper and abundant alternative would make the hydrogen economy viable. Both nitrogen-doped graphene and nitrogen-doped carbon nanotubes (N-CNT) have been shown to be capable of acting as a metal-free catalyst for the oxygen reduction reaction (ORR). Until now, most of the research has been focused on the nitrogen doping and less on the structure of the nanotubes. Here, density functional theory calculations are used to calculate trends in ORR catalytic activity of graphitic-N-doped CNTs of different sizes and chirality of selected tubes between (4,0) and (20,10). This includes 13 armchair tubes, 17 zig-zag tubes and 42 chiral tubes, or 72 N-CNTs in total. 22 tubes are predicted to have a lower overpotential than the platinum catalyst and 46 tubes have lower overpotential than nitrogen doped graphene. The most active tubes are (14,7), (12,6), and (8,8), and display an overpotential of around 0.35 V, or 0.1 V lower overpotential than predicted on Pt(111) with the same level of theory.

Inter-Particle Electronic and Ionic Modifications of the Ternary Ni-Co-Mn Oxide for Efficient and Stable Lithium Storage

A combined electronic and ionic interparticular modification strategy is designed for the improvement of lithium storage in the layer structured ternary Ni-Co-Mn oxide (LiNi0.6Co0.2Mn0.2O2) in the form of spherical particles. In this design, a thin layer of the ion conducting polypropylene carbonate is applied to wrap the individual oxide particles for three purposes: (1) prevention of direct stacking and packing between oxide particles that will otherwise impede or block ions from accessing all the surface of the oxide particles, (2) provision of additional ionic pathways between the oxide particles, and (3) stabilization of the oxide particles during lithium storage and release. The design includes also the use of nitrogen doped carbon nanotubes for electronic connection between the polymer coated individual spheres of the layered nickel-rich LiNi0.6Co0.2Mn0.2O2. According to the physicochemical and electrochemical characterizations, and laboratory battery tests, it can be concluded that the LiNi0.6Co0.2Mn0.2O2 composite has a unique porous structure that is assembled by the polymer coated ternary oxide microspheres and the nitrogen-doped carbon nanotube networks. Significant improvements are achieved in both the ionic and electronic conductivities (double or more increase), and in discharge specific capacity (201.3 mAh·g−1 at 0.1 C, improved by 13.28% compared to the non-modified LiNi0.6Co0.2Mn0.2O2), rate performance and cycling stability (94.40% in capacity retention after 300 cycles at 1.0 C).

Catalyst free N-doped carbon nanotube arrays based on a ZnO nanorod template with high performance field emission

Nitrogen doped carbon nanotube arrays (NCNTA) were synthesized by a catalyst-free chemical vapor deposition (CVD) method using ZnO nanorod arrays as a template.

Electronic properties of Aluminum Doped Carbon Nanotubes with Stone Wales Defects: Density Functional Theory -=SUP=-*-=/SUP=-

AbstractAl-doped single wall carbon nanotube with Stone Wales defect was theoretically analyzed, two different orientations of chiral (8, 4) carbon nanotubes was doped among the joints of defective carbon rings. Density functional theory was implemented to study structural and electronic properties of Al-doped chiral carbon nanotubes. Doping bond lengths as well as their geometrical structure were determined at the different orientations. The electronic properties were also illustrated by evaluation band of the gap energies at each possible doping site. Our results indicated that not only Al-doping tune the band structure, but also dopant site played a crucial rule on manipulating physical properties of chiral carbon nanotubes.

Killing Two Birds with One Stone: A Highly Active Tubular Carbon Catalyst with Effective N Doping for Oxygen Reduction and Hydrogen Evolution Reactions

The oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are two of the core reactions that occur in fuel cells and water electrolysis devices. Heteroatom-doped carbon materials are promising metal-free electrocatalysts to improve the conversion efficiency of these devices. To optimize the nanostructures of such carbon-based catalysts, herein, we reported an effective template method to synthesize N doped carbon nanotubes by using polydopamine as a precursor. The use of the ZnO nanowire not only serves as a self-sacrificial template to direct the formation of the nanotube, but also greatly extends the porosity of the carbon nanotube. Moreover, the polydopamine precursor also leads to effective N doping. An optimized sample, NCNT-900, shows high ORR performance comparable with that of Pt/C as well as good HER performance in both alkaline and acid media, making it one of the most effective carbon-based HER catalysts. This strategy offers an opportunity to synthesize catalysts with higher activity by rational design of a carbon precursor with higher N content or multi-heteroatom co-doping.

Highly efficient and acid-corrosion resistant nitrogen doped magnetic carbon nanotubes for the hexavalent chromium removal with subsequent reutilization

Highly efficient and acid-corrosion resistant for carbon adsorbent in hexavalent chromium removal is a significant property in the practical application. In this study, nitrogen doped carbon nanotubes with encapsulated Fe and Fe3C were synthesized through a facile pyrolysis procedure using melamine and ferric chloride as precursors, displaying an excellent efficiency and stability for hexavalent chromium removal. High maximum removal capacities with 35.26 and 970.87 mg g−1 were obtained in neutral and acid solutions, respectively, due to the adsorption process, reduction reaction between Fe0 or Fe2+ nanoparticles and Cr(VI) ions. The unexpected high stability in acid solution (pH at 1) after five recycles was observed for the first time, ascribed to N doping and the tubular structure with encapsulated ferric carbide, which could be resistant to the acid corrosion. After a simple treatment, the used adsorbent could be re-utilized as catalysts for the electrochemical reduction of CO2 with high faradic efficiency (over 90% total efficiency and about 50% for CO production at −0.6 V), demonstrating a promising potential for reutilizing the used carbon adsorbents.

Polyoxometalate‐Derived Hexagonal Molybdenum Nitrides (MXenes) Supported by Boron, Nitrogen Codoped Carbon Nanotubes for Efficient Electrochemical Hydrogen Evolution from Seawater

AbstractMXenes and doped carbon nanotubes (CNTs) have entered into research arenas for high‐rate energy storage and conversion. Herein, a method of postsynthesis of MXenes in boron, nitrogen codoped CNTs (BNCNTs) is reported with their electrocatalytical hydrogen evolution performance. The encapsulation of hexagonal molybdenum nitrate nanoparticles (h‐MoN NPs) into BNCNTs protects h‐MoN NPs from agglomeration and poisoning in the complex environment. In principle, the synergism of B and N dopants on the doped CNTs and confined h‐MoN NPs produces extremely active sites for electrochemical hydrogen evolution. Density functional theory calculations reveal that the active sites for hydrogen evolution originate from the synergistic effect of h‐MoN(001)/CN (graphitic N doping) and h‐MoN(001)/BNC. The h‐MoN@BNCNT electrocatalyst exhibits a small overpotential of 78 mV at 10 mA cm−2 and Tafel slope of 46 mV per decade, which are dramatically improved over all reported MoN‐based materials and doped CNTs. Additionally, it also exhibits outstanding electrochemical stability in environments with various pH values and seawater media from South China Sea.

Co Nanoparticles Decorated with Nitrogen Doped Carbon Nanotubes for Boosting Photocatalytic Water Splitting

Photocatalytic water splitting reaction has been deemed as a promising and sustainable method for solar-to-chemical energy conversion. Therefore, the development of cost-effective and visible-light-driven water splitting photocatalysts is highly desirable. Herein, the Co nanoparticles decorated with nitrogen doped carbon nanotubes (Co-NCNT-T, T = pyrolysis temperature) were rationally designed by a simple pyrolysis process at different temperature using for boosting photocatalytic oxygen evolution and hydrogen evolution. The results show that as-obtained Co-NCNT-800 exhibits a considerable hydrogen evolution rate of 14.7 mmol h–1 g–1 and oxygen yield of 51%. In addition, a turnover number (TON) of 25.8 and turnover frequency (TOF) of 0.86 s–1 for water oxidation are attained under optimized conditions. The excellent activity is mainly ascribed to the effective electron transfer between the catalyst and photosensitizer, which is verified by photoluminescence (PL) spectra and transient photocurrent response...

Multistep Wavelength Switching of Near-Infrared Photoluminescence Driven by Chemical Reactions at Local Doped Sites of Single-Walled Carbon Nanotubes.

Local chemical functionalization is used for defect doping of single-walled carbon nanotubes (SWNTs), to develop near-infrared photoluminescence (NIR PL) properties. We report the multistep wavelength shifting of the NIR PL of SWNTs through chemical reactions at local doped sites tethered to an arylaldehyde group. The PL wavelength of the doped SWNTs is modulated based on imine chemistry. This involves the imine formation of aldehyde groups with added arylamines, imine dissociation reaction, exchange reaction of bound arylamines in the imine, and the Kabachnik-Fields reaction of imine groups using diisopropyl phosphite. Using doped sites as a localized chemical reaction platform can exploit the versatile molecularly driven functionality of carbon nanotubes and related nanomaterials.

Hydrogen sorption and desorption behaviors of Mg-Ni-Cu doped carbon nanotubes at high temperature

Hydrogen sorption and storage in a solid matrix can greatly improve its safety and efficiency when compared to the compressed gas or liquid hydrogen storage system, and kinetics mechanisms are of interest towards the development of such materials. In this study, the composites of Mg-Ni-Cu doped with singe-walled carbon nanotubes (Mg-Ni-Cu/CNTs) were synthetized. The activation performance, isothermal hydrogen sorption and desorption were systematically tested, and the experimental data were analyzed using the shrinking core model. The results show that three cycles of hydrogen sorption and desorption may be enough to fully activate Mg-Ni-Cu/CNTs and the stability can be kept for 150 cycles. A 10.1 wt% of Cu and 50.3 wt% of Ni in Mg-Ni-Cu/CNTs facilitates the hydrogen sorption and a reversible hydrogen capacity of ∼3.35 wt% can be achieved at 310 °C and 3.0 atm, and hydrogen capacity and kinetics shows significant decline during contact with 1.0 vol% CO impurity. Considering desorption at 600 °C, the kinetic profiles are about linear and desorption is completed within minutes. The gas-solid reaction processes for hydrogen sorption undergo three different rate-limiting stages, and hydrogen desorption can only be divided into two stages of surface chemical reaction and product layer diffusion.

Direct synthesis of parallel doped N-MoP/N-CNT as highly active hydrogen evolution reaction catalyst

Doped phosphide is promising in earth-abundant element based catalysts for hydrogen evolution reaction (HER). Here we employ ammonium hypophosphite (NH4H2PO2) to synthesize a novel parallel doped catalyst, nitrogen doped molybdenum phosphide nanoparticles (NPs) supported on nitrogen doped carbon nanotubes (N-MoP/ N-CNTs ). The NH4H2PO2 as a bifunctional agent severs as both phosphidation agent and nitrogen source, which makes the synthetic route simple and efficient. The as-obtained parallel doped N-MoP/N-CNTs show an overpotential of 103±5 mV at 10 mA cm−2, which is 140 mV lower than that of MoP NPs. The enhanced HER performance is attributed to the electronic effect by doped MoP and CNTs supports. This work provides a facile route to synthesize doped phosphides for the potential applications in hydrogen energy.

Chlorate Elimination by Catalytically Hydrogenation, Catalyst Development and Characterization

In the course of the experiments nanostructured catalysts have been developed for hydrogenation of ClO3− ions. Different nitrogen doped carbon nanotube (N-BCNT) coated catalyst pellets have been synthetized by the catalytic chemical vapour deposition (CCVD) method. These core–shell structured pellets were used as supports of palladium catalysts. The catalysts were examined by scanning electron microscopy (SEM), energy dispersed X-ray spectrometry (EDX) and X-ray diffractometry (XRD). The catalytic activity of these Pd/BCNT pellets were tested in hydrogenation of chlorate in a continuous flow system. The hydrogenation process was followed by using of a miniaturized spectrophotometric cell developed by us. The catalysts proved to be efficient, because of the higher chlorate hydrogenation 90.5% chlorate conversion could be reached.

Meaningful improvements on structural-thermal-electronic properties of copper based on 3D nitrogen (N) doped-carbon nanotubes (CNTs) interface fabricated by nano-self-assembly-sintering-modification

The development of a material with high ampacity to allow current to flow through narrow channels is one of the most promising ways to address the progressive miniaturization and light weight of electronic devices. The efficient synergistic electron transmission by compounding 1D/2D carbon materials with a metal matrix via various methods in recent years has attracted great research interest due to their potential utilization in electronics. In this study, a copper (Cu) matrix with a 3D nitrogen (N) doped-multi-walled carbon nanotubes (MCNTs) interface with prominent physical features is reported and fabricated, involving the use of nano-self-assembly-heat-modification by adopting polyethyleneimine-nano-Cu and carboxyl MCNTs. Young's modulus was enhanced from 28.8 to 92.2 GPa due to a higher efficiency of stress transfer and interfacial adhesion, and the hardness fitted by Gauss distribution was increased by ∼69% (∼39.7 HRC). Toward the stability after a modification of vacuum reduction sintering, the initial oxidation temperature (Td) was increased largely from 232 °C to 286 °C, and thermal conductivity was enhanced eminently from 358 to 548 W/(m K) due to more efficient electron/phonon motion. Moreover, synergistic electron transmission endowed the final Cu-N-CNTs with a higher ampacity (7.23–16.98 × 104 A cm−2), which could be further observed by the time-evolution of electrical resistivity under a constant current density. The improved physical features state that the assembled 3D N-CNTs interface possesses prominent characteristics and potential for directing the deep applications of 1D or 2D carbon materials in electronic science.

Work function tuning of the individual polyaniline/carbon nanotube nanostructures

Electrostatic force microscopy was used to study the dependence of the electron work function of individual polyaniline/nitrogen doped carbon nanotube (PANI/N-CNT) nanostructures on the duration of synthesis. The work function of nanostructures increases monotonically with the synthesis time increasing. These changes are interpreted as a result of the growth of the polymer layer thickness on CNTs and an increase in the degree of protonation of PANI during the synthesis of PANI/N-CNTs composite.

Atomistic- to Circuit-Level Modeling of Doped SWCNT for On-Chip Interconnects

In this paper, we present a hierarchical model for doped single-walled carbon nanotube (SWCNT) for on-chip interconnect application. Our model aims to study CVD grown SWCNTs while considering defects and contacts to metal electrodes. Both defects and poor contacts can worsen CNT conductivities and ultimately deteriorate their interconnect performance. We investigate the fundamental physical mechanism of charge-based doping with the purpose of improving SWCNT electrical conductivity as well as a potential solution to alleviating the impact of defects and contact resistances. We present an atomistic model to study the number of conducting channels of doped SWCNT with different vacancy defect configurations. Circuit-level electrical modeling and simulations are performed on SWCNT interconnect while considering the impact of doping, defects, and contact resistance. Simulation results show up to 80% resistance reduction by doping, where 17% of delay increases due to defects. Additionally, we observe doping can mitigate the impact of defects by more than 12%, but there is almost no improvement in the contact resistance.

In-situ reduction synthesis of La2O3/NiM-NCNTs (M = Fe, Co) as efficient bifunctional electrocatalysts for oxygen reduction and evolution reactions

Highly active and stable bifunctional catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a vital role in rechargeable zinc-air batteries. In this work, La2O3 and alloy nanoparticles (NiFe and NiCo) decorated nitrogen doped carbon nanotubes hybrids (denoted as La2O3/NiFe-NCNTs and La2O3/NiCo-NCNTs) were successfully prepared by the in-situ reduction procedure. The crystalline structure and morphology of hybrids were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). La2O3/NiFe-NCNTs revealed desirable bifunctional catalytic activities towards both oxygen reduction reaction (5.1 mA cm−2 at 0.3 V vs. RHE) and oxygen evolution reaction (1.69 V vs. RHE at 10 mA cm−2) in alkaline media. Furthermore, rechargeable zinc-air batteries fabricated with La2O3/NiFe-NCNTs as the bifunctional catalyst demonstrated a small charge-discharge voltage gap (1.04 V) and long-term stability after charge-discharge cycling for 100 cycles.