Surface Of Nitrogen-doped Carbon Nanotubes Research Articles

NiS2 nanoparticles anchored on Co-carbon nanotubes for supercapacitor and overall water splitting

Exploiting low-cost and efficient electrode materials with catalytic activity toward water splitting and supercapacitor has a crucial role with sustainable energy development. Herein, a composite structure is created in which nickel sulfide nanoparticles are loaded on the surface of nitrogen-doped carbon nanotubes (Co-CNTs) encapsulated with cobalt nanoparticles as multifunctional catalysts. The growth in situ of NiS2 nanoparticles results in the Co-CNTs@NiS2 composite with ideal interface effect which remarkable improves the performance in supercapacitor, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity. As a supercapacitor electrode, Co-CNTs@NiS2 activated carbon asymmetric supercapacitor performs a high specific capacitance of 370 F g−1 at 1 A g−1, revealing high retention of 68.8% after 3000 cycles. As an electrocatalyst, it is just needed to afford the overpotential of 235 and 309 mV in HER and OER to reach a current density of 10 mA cm−2 without iR correction. The Co-CNTs@NiS2 composite with optimized exposed surface just requires an overall cell voltage of 1.73 V to achieve 10 mA cm−2 in electrolyzer. The results supply great potential in the application of renewable energy.

Confining NiCo2O4 nanoparticles in nitrogen doped carbon nanotubes embedded in 3D porous graphene aerogels for superior lithium storage

The huge volume expansion and poor electrical conductivity have seriously hindered the further development of redox-based electrode materials such as NiCo2O4 (NCO). Herein, we designed a novel NiCo2O4@nitrogen-doped carbon nanotube@3D graphene (NCO@CT@3DG) aerogel through hydrothermal assembly and high-temperature carbonization. In this aerogel, graphene nanosheets constructed the framework of the aerogel and NCO nanoparticles were deposited on the surface of nitrogen-doped carbon nanotubes which served as active materials for Lithium-ion batteries. The NCO decorated carbon nanotubes connecting the graphene sheets served as the scaffold to support the 3D cross-linked graphene network. As anode material of lithium-ion batteries, the optimized NCO@CT@3DG exhibited excellent electrochemical properties with high capacity as well as superior cycle and rate performance, which could maintain the discharge specific capacity of 810.3 mAh/g at the current density of 1.0 A/g after 500 cycles. The excellent properties are ascribed to the synergistic effect of each individual component and the unique graphene aerogels hybrid structure. This study demonstrates the great application prospects of 3DG aerogel hybrid structure in improving electrochemical properties of active materials with high volume expansion and poor conductivity.

An electrochemical sensor based on synergistic enhancement effects between nitrogen-doped carbon nanotubes and copper ions for ultrasensitive determination of anti-diabetic metformin

Metformin (MET) is the primary medicine for type II diabetes, which produces carcinogenic byproducts during chlorine disinfection, so the detection of MET in aqueous environment is crucial. In this work, an electrochemical sensor based on nitrogen-doped carbon nanotubes (NCNT) has been constructed for ultrasensitive determination of MET in the presence of Cu(II) ions. The excellent conductivity and rich π-conjugated structure of NCNT facilitate the electron transfer rate of fabricated sensor and benefit the adsorption of cation ions. Cu(II) ions can chelate with MET to form MET-Cu(II) complex, which are easily accumulated on the surface of NCNT through cation-π interaction. Attributing to the synergistic enhancement effects of NCNT and Cu(II) ions, the fabricated sensor exhibits excellent analytical performances with a low detection limit of 9.6 nmol L−1, high sensitivity of 64.97 A mol−1 cm−2 and wide linear range of 0.3–10 μmol L−1. The sensing system has been successfully applied for rapid (20 s) and selective determination of MET in real water samples with satisfactory recoveries (90.2 %–108.8 %). This study provides a robust strategy for MET detection in aqueous environment and holds great promise for rapid risk assessment and early warning of MET.

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.

Co-Cr mixed spinel oxide nanodots anchored on nitrogen-doped carbon nanotubes as catalytic electrode for hydrogen peroxide sensing

Hydrogen peroxide (H2O2) is a significant biomarker in physiological processes. Abnormal levels of H2O2 are considered to be closely related to some acute diseases. Therefore, it is important to monitor the H2O2 levels in bio-samples. Herein, we present a novel non-enzymatic electrochemical H2O2 sensor based on the excellent electrocatalytic performance of a composite comprising Zn-Cr-Co ternary spinel metal oxide nanodots (ZnCrCoO4) anchored on the surface of nitrogen-doped carbon nanotubes (NCNTs), denoted as ZnCrCoO4/NCNTs, toward H2O2 reduction. ZnCrCoO4/NCNTs were synthesized using a facile one-pot hydrothermal strategy. The enhanced electrocatalytic performance of ZnCrCoO4 is resulted from the partial substitution of Co in spinel zinc cobaltate (ZnCo2O4) with Cr, which modifies the CoO electronic structure and enhances electroconductivity. The ZnCrCoO4/NCNTs-based H2O2 sensor exhibited a wide quantitative detection range from 1 to 7330 μM with a detection limit of 1 μM. The sensor showed excellent reproducibility and selectivity for H2O2 sensing. In addition, remarkable recoveries were obtained for H2O2-spiked fish serum samples. These results demonstrated that the as-developed sensor has a great potential in monitoring H2O2 levels in practical applications.

Sonochemical Deposition of Palladium Nanoparticles Onto the Surface of N-Doped Carbon Nanotubes: A Simplified One-Step Catalyst Production Method

This work presents an easy, one-step procedure for catalyst preparation. A small fraction of palladium ions was reduced to Pd nanoparticles and deposited onto the surface of nitrogen-doped carbon nanotubes (N-BCNT) by acoustic cavitation using high-intensity ultrasound in aqueous phase, where N-BCNT served as a reducing agent. The formation of elemental palladium and palladium oxides were confirmed and the particle size is < 5 nm. The catalytic activity of the synthesized Pd/N-BCNT catalyst was tested in nitrobenzene hydrogenation at four different temperature (273–323 K) and 20 bar pressure. The catalyst showed high activity despite the presence of palladium oxide forms, the conversion of nitrobenzene to aniline was 98% at 323 K temperature after 40 min. The activation energy was 35.81 kJ/mol. At 303 K and 323 K temperature, N-methylaniline was formed as by-product in a small quantity (8 mmol/dm3). By decreasing the reaction temperature (at 273 K and 283 K), the reaction rate was also lower, but it was favourable for aniline selectivity, and not formed n-methylaniline. All in all, Pd/N-BCNT catalyst was successfully produced by using a one-step sonochemical method, where further activation was not necessary as the catalytic system was applicable in nitrobenzene hydrogenation.Graphic

Hydrogenation of nitrobenzene over a composite catalyst based on zeolite supported N-doped carbon nanotubes decorated with palladium

A catalyst nanocomposite was synthesized based on zeolite supported nitrogen-doped carbon nanotubes (N-CNT) decorated with palladium nanoparticles. Zeolite beads impregnated with nickel nitrate solution were used as CCVD catalyst support during the synthesis of N-CNT. Then the zeolite supported N-CNT was decorated with palladium nanoparticles and the final nanocomposite was tested in nitrobenzene hydrogenation. The structure of the nanocomposite was characterized by SEM. The surface of the zeolite beads is extensively covered by N-CNT. The particle size distribution of the palladium nanoparticles on the surface of N-CNT is relatively homogenous (< 7 nm). The catalytic activity of the nanocomposite was the highest at 10 bar and 323 K while the achieved nitrobenzene/aniline conversion was 99.9% after 4 h of hydrogenation.

Binder-free supercapacitive of ultrathin Co(OH)2 nanosheets-decorated nitrogen-doped carbon nanotubes core-shell nanostructures

Three-dimensional (3D) nitrogen-doped carbon nanotubes (N-CNTs)/Co(OH)2 core-shell nanostructures as binder-free supercapacitor electrode have been synthesized via electrodeposition and chemical vapour deposition. The ultrathin Co(OH)2 nanosheets are uniformly coated on the surface of N-CNTs. Such unique well-designed binder-free electrode exhibits a high areal capacitance (0.46 F cm−2 at a current density of 1 mA cm−2) and good cycling stability (81.2% capacitance retention after 2000 cycles). In the electrode, the cable-like N-CNTs around Ni foam with close contact act as current collector, facilitating the electrical transport, while two-dimensional Co(OH)2 nanosheets grown on external surface increase the surface area and provide good contact with ions at electrode/electrolyte interface, exhibiting low charge transfer resistance (Rct) and better charge storage performance. As a result, such combined synthetic strategy may provide design guidelines for constructing advanced binder-free supercapacitors electrode.

Comprehensive Study of an Earth-Abundant Bifunctional 3D Electrode for Efficient Water Electrolysis in Alkaline Medium.

We report efficient electrolysis of both water-splitting half reactions in the same medium by a bifunctional 3D electrode comprising Co3O4 nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) that in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm(2) in 0.1 M KOH solution at overpotentials of only 0.47 and 0.38 V for OER and HER, respectively. Additionally, the experimental observations are understood and supported by analyzing the Co3O4:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER.

Nitrogen doped carbon nanotubes with encapsulated ferric carbide as excellent electrocatalyst for oxygen reduction reaction in acid and alkaline media

Nitrogen doped carbon nanotubes (NCNTs) with encapsulated Fe3C nanoparticles (Fe3C@NCNTs) are synthesized by a simple direct pyrolysis of melamine and ferric chloride. The characterization results reveal that Fe3C is mainly encapsulated in the interior of NCNTs and N species is mainly distributed on the outside surface of NCNTs. Iron and iron carbide catalyze the growth of NCNTs and are wrapped by carbon to form Fe3C@NCNTs. The as-prepared Fe3C@NCNTs catalyst exhibits superior oxygen reduction reaction (ORR) activity, excellent methanol tolerance and long-term stability in both acid and alkaline media. It is proven that the doped N is the main active site for ORR and the inner Fe3C with outside carbon form the synergetic active site to enhance ORR activity. The ORR mechanism of direct four electron transfer pathway is proved in acid and alkaline media.

Atomic layer deposition of amorphous iron phosphates on carbon nanotubes as cathode materials for lithium-ion batteries

A non-aqueous approach was developed to synthesize iron phosphate cathode materials by the atomic layer deposition (ALD) technique. Deposition of iron phosphate thin films was achieved on nitrogen-doped carbon nanotubes (NCNTs) by combining ALD subcycles of Fe2O3 (ferrocene-ozone) and POx (trimethyl phosphate-water) at 200 – 350°C. The thickness of iron phosphate thin films depends linearly on the ALD cycle, indicating their self-limiting growth behavior. The growth per cycle of iron phosphate thin films was determined to be ∼ 0.2, 0.4, 0.6, and 0.5Å, at 200, 250, 300, and 350°C, respectively. Characterization by SEM, TEM, and HRTEM techniques revealed uniform and conformal coating of amorphous iron phosphates on the surface of NCNTs. XANES analysis confirmed FeOP bonding in the iron phosphates prepared by ALD. Furthermore, electrochemical measurement verified the high electrochemical activity of the amorphous iron phosphate as a cathode material in lithium-ion batteries. It is expected that the amorphous iron phosphate prepared by this facile and cost-effective ALD approach will find applications in the next generation of lithium-ion batteries and thin film batteries as either cathode materials or surface coating materials.

Coating of α-MoO3 on nitrogen-doped carbon nanotubes by electrodeposition as a high-performance cathode material for lithium-ion batteries

In this work, α-MoO3 nanoparticles are grown on the surface of nitrogen doped carbon nanotubes (N-CNTs) via a facile electrodeposition method. The morphology of as-prepared nanocomposite shows that the interconnected α-MoO3 nanoparticles are homogeneously distributed on the surface of N-CNTs. When investigated as a cathode material for lithium ion batteries, the nanocomposite reveals a high reversible discharge capacity of 250 mA h g−1 at a current density of 30 mA g−1, simultaneously with good cycling performance and excellent rate capability compared with pristine MoO3 powder. Kinetics of this process is investigated by electrochemical impedance spectroscopy to understand the difference in electrochemical performance and the interface properties between the α-MoO3/N-CNTs nanocomposite and pristine MoO3 powder electrode. The correlation between the unique structural features of α-MoO3/N-CNTs nanocomposite and its excellent electrochemical performance is also discussed. The excellent performance makes the as-prepared α-MoO3/N-CNTs nanocomposite a promising cathode material for high-performance lithium ion batteries.

CO oxidation on metal-free nitrogen-doped carbon nanotubes and the related structure–reactivity relationships

The reduction or elimination of noble metal used in carbon monoxide (CO) oxidation remains a challenge. Based on systematic research with methods using density functional theory, metal-free nitrogen-doped carbon nanotubes (NCNTs) are found to be effective catalysts for CO oxidation. The reaction route involves the direct oxidization of CO to CO2 by O2 adsorbed on the surface of NCNTs, as in CO + O2 → CO2 + O. The remaining O atom can further oxidize CO to CO2. The barrier heights of the rate-determining step range from 0.477 to 0.619 eV for different catalysts investigated in the present study. These values are quite close to those processes using noble metal catalysts. The catalytic ability of NCNTs is influenced by the tube length, diameter and number of doped N atoms. The barrier height for the rate-determining step slightly oscillates with increased tube length, and progressively increases with expanded tube diameter. The structure–reactivity relationships of NCNTs in CO oxidation are revealed. A lower negative charge of the doped N atom corresponds to more reactive NCNTs. NCNT–O2 with large spin densities on the O atom also show more powerful reactivity for CO oxidation. The present paper provides a way for the development of metal-free catalysts for CO oxidation.

Direct immobilization of Pt–Ru alloy nanoparticles on nitrogen-doped carbon nanotubes with superior electrocatalytic performance

Taking the advantage of the inherent chemical activity arisen from the nitrogen incorporation for nitrogen-doped carbon nanotubes (NCNTs), we have developed a facile strategy for the construction of binary Pt–Ru/NCNT electrocatalysts. Alloyed Pt–Ru nanoparticles have been directly immobilized onto the outer surface of NCNTs without pre-modification due to the nitrogen participation. The Pt–Ru nanoparticles have a high dispersion, a narrow size distribution of 2.5–3.5 nm and tunable chemical composition. These catalysts have been evaluated for methanol oxidation and show good stability and better CO tolerance than the monometallic Pt/NCNT catalyst due to the bifunctional and electronic effects. The Pt 5Ru 5/NCNT catalyst shows superior electrocatalytic performance to the commercial Pt 5Ru 5/C catalyst. The easy fabrication and excellent performance of the NCNT-based Pt–Ru alloy catalysts indicate their potential application in direct methanol fuel cells.