Promotional effect of Ni–Co/ordered mesoporous carbon as non-noble hybrid electrocatalyst for methanol electro-oxidation

Journal of Applied Electrochemistry - The development of a ternary hybrid catalytic system, inclusive of Ni species/Co species/ordered mesoporous carbon (catalyst/co-catalyst/support) and its...     

Optimized structure and electrochemical properties of sulfonated carbon nanotubes/Co–Ni bimetallic layered hydroxide composites for high-performance supercapacitors

Technical development in electronic devices is frequently stifled by their insufficient capacity and cyclic stability of energy-storage devices. The nano-structured materials have sensational importance for providing novel and optimized combination to overcome exiting boundaries and provide efficient energy storage systems. Metal hydroxide materials with high capacity for pseudo-capacitance properties have grabbed special attention. Lately, the blend of nickel and cobalt hydroxides has been considered as a favorable class of metallic hydroxide materials owing to their comparatively high capacitance and exceptional redox reversibility. The sulfonated carbon nanotube fluid (SCNTF) was prepared by the ion exchange method to be utilized as the exceptional templates due to astonishing specific surface area, ensuring the maximum utilization of the active material. The CoNi-layered double hydroxides (LDHs)/SCNTF core-shell nanocomposite was prepared by the simple solvothermal method. Structural analysis showed that the composite material had the high conductance of carbon materials, the pseudo-capacitance characteristics of metal hydroxides, and porous structure, which facilitates the ion shuttle when the electrolyte reacts with the active material. Electrochemical analysis results showed that CoNi-LDHs/SCNTF had excellent rate performance, reversible charge-discharge properties and cycle stability. It exhibited an extreme specific capacity of 1190.5 F g^?1 at a current density of 1 A g^?1; whereas specific capacity remained 953.7 F g^?1 at the current density was 10 A g^?1. In addition, the capacity retention rate after 5000 charge-discharge cycles at a current density of 20 A g^?1 was 81.0%. The results indicated that the CoNi-LDHs/SCNTF core-shell nanocomposite material is cost efficient and an effective substitute in energy storage applications.     

One-step hydrothermal synthesis of hybrid core-shell Co3O4@SnO2–SnO for supercapacitor electrodes

We successfully synthesized a novel core-shell hybrid metal oxide via a simple one-step hydrothermal method without annealing. This composite of Co₃O₄ particles covered with SnO₂–SnO (Co₃O₄@SnO₂–SnO) predicted better performance compared to pure Co₃O₄, which strongly depends on the synthetic temperature. The Co₃O₄@SnO₂–SnO prepared at a temperature of 250 °C (labeled Co₃O₄@SnO₂–SnO-250) exhibited an outstanding specific capacitance of 325 F g⁻¹ under the current density of 1 A g⁻¹, which was much higher than those of Co₃O₄ (12.6 F g⁻¹) and other composites. Additionally, the sample also exhibited good cycle stability performance with a retention rate of 100% after 5000 cycles at a current density of 5 A g⁻¹. Through X-ray photoelectron spectroscopy analysis, the presumed mechanism was that Sn-O_x decreases the surface electron densities of Co₃O₄, which is beneficial to OH⁻ adsorption and specific capacitance improvement, and the synthetic temperature had a strong impact on the microstructure and thus on the surface electron densities. The most.obvious finding to emerge from this study is that the specific capacitance can be improved through adjusting the surface electron densities of transition metal oxides.     

Electrophoretic co-deposition of Bi2O3–multiwalled carbon nanotubes coating as supercapacitor electrode

Nafion is suggested as an efficient assistant in preparing supercapacitor by employing nanoparticles. In this work, using a bi-additive of 0.10-mM NaOH + 0.10 g L⁻¹ Nafion, Nafion-assisted electrophoretic co-deposition of Bi₂O₃–multiwalled carbon nanotubes (MWCNTs) coating is successfully realized in ethanol solvent. The capacitance performances of the electrophoretic coatings in 6.0-M KOH electrolyte are investigated by cyclic voltammetry and galvanostatic charge–discharge techniques. Comparing with Bi₂O₃ coating prepared with electrophoretic deposition (EPD) by employing other additive (such as polyethyleneimine), the Bi₂O₃ coating prepared by Nafion-assisted EPD shows a better capacitance performance. Benefiting from the improvement in coating conductivity caused by MWCNTs, with a small additional amount of 4.0 wt.%, the Bi₂O₃–MWCNTs coating exhibits an amazing 164% increase of mass-specific capacitance (473 F g⁻¹ at the current density of 1.0 A g⁻¹) in comparison with pure Bi₂O₃ coating (179 F g⁻¹ at the current density of 1.0 A g⁻¹). The cyclic stability test exhibits excellent capacitance retention of 88.7% over 3000 cycles at a constant current density of 10.0 A g⁻¹. This work combines the advantages of MWCNTs, Nafion, and EPD to provide a facile route for preparing Bi₂O₃-based coating as a high-performance supercapacitor electrode.     

Construction of Zn–Co–Ni–Se nanosheet arrays on nickel foam for hybrid supercapacitors

The polymetallic selenides exhibit rich redox reactions and high conductivity, making them promising electroactive materials for hybrid supercapacitors (HSCs). Herein, a two-step hydrothermal strategy was developed to grow ternary metal selenides (Zn–Co–Ni–Se) nanosheet arrays on Ni foam (NF) for HSCs. The Zn–Co–Ni–Se nanosheets uniformly covered on NF are favorable to boosting the energy storage activity because they can afford abundant pores, which is beneficial to increase the contact areas and promote ion transport. The binder-free feature can further improve the rate and cyclic performance. As an innovative binder-free electrode, the Zn–Co–Ni–Se NA@NF can deliver 2.5 C cm^–2 at 3.1 mA cm^–2. Strikingly, the Zn–Co–Ni–Se NA@NF//AC HSC can afford 0.13 mWh cm^–2 at 1.27 mW cm^–2. The capacity retention of Zn–Co–Ni–Se NA@NF//AC HSC is 92.9% after 5000 cycles at 6.4 mA cm^–2. A Zn–Co–Ni–Se NA@NF//AC HSC device could successfully drive a small fan for about 150 s, displaying the bright application prospect of Zn–Co–Ni–Se@NF. Therefore, the present work demonstrates that Zn–Co–Ni–Se NA@NF is an excellent electroactive material for HSCs.     

Selective growth of single-walled carbon nanotubes over Co–MgO catalyst by chemical vapor deposition of methane

The selective synthesis of SWCNTs with narrow chirality and diameter distribution by methane decomposition over a Co–MgO catalyst is reported. Raman spectroscopy, temperature programmed oxidation (TPO), UV–Vis–NIR absorption spectroscopy, and nitrogen physisorption were used to probe SWCNTs morphology, reaction selectivity, SWCNTs chirality and diameter distribution, and carbon yield. The catalyst was examined by nitrogen physisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), and UV–Vis-diffuse reflectance spectroscopy to elucidate the structure and chemical state of the species responsible for SWCNT growth. The results established a clear link between the degree of dispersion of Co species inside the MgO lattice and the catalyst activity and selectivity for SWCNT growth. High dispersion and stabilization of Co species influenced catalytic activity for methane decomposition and the high SWCNT selectivity. The yield of carbon and SWCNT selectivity increased with an increase in temperature, however, SWCNTs diameter distribution shifts to larger diameter tubes as synthesis temperature was increased.     

Versatile hybrid polyethyleneimine–mesoporous carbon nanoparticles for targeted delivery

To meet the needs of targeted drug delivery and medical imaging, uniform mesoporous carbon spheres (UMCS) were functionalized using hyperbranched polyethyleneimine (PEI) covalently linked with fluorescein isothiocyanate (FITC) and folic acid (FA). Folate-receptor-positive KB cancer cells internalized five times more nanoparticles than A549 cells deficient in folate receptors in vitro using flow cytometry and confocal microscopy. The in vivo distribution results also confirmed that the FA–PEI–FITC–UMCS nanoparticles could target the FA-positive tumors. In addition, the specifically targeted hybrid carbon nanoparticles exhibited non-cytotoxic and controlled intracellular release (pH dependent) of the loaded agents. The in vivo antitumor effect of the paclitaxel (PTX)-loaded nanoparticles was investigated in Kunming mice harboring a hepatic H22 tumor. PTX-loaded FA–PEI–UMCS nanoparticles displayed superior antitumor effects compared to other PTX formulations, and the tumor growth inhibition rate was 86.53% compared with the control group (saline) for the enhanced targeted accumulation of NPs in tumor cells.     

Corrosion resistance of Pb–Sn composite coatings reinforced by carbon nanotubes

Carbon nanotubes/Pb–Sn composite coatings were prepared by electrodeposition technology. The polarization curves and electrochemical impedance of the Pb–Sn coatings and carbon nanotube/Pb–Sn composite coatings were studied in 3.0 wt% HCl, 10 wt% NaOH, and 3.5 wt% NaCl electrolyte solutions, respectively. The results show that the corrosion potential of carbon nanotubes/Pb–Sn composite coatings were improved in the three kinds of corrosive medium, especially in 3.5 wt% NaCl electrolyte solution, where it increased significantly from −0.592 V (vs SCE) to −0.535 V (vs SCE). In addition, composite coatings have higher electrochemical impedance. Carbon nanotubes can improve the corrosion resistance of lead–tin electroplated coatings.     

Cathode materials based on carbon nanotubes for high-energy-density lithium–sulfur batteries

The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77 mg cm⁻² were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32 mg cm⁻², a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288 mAh g_S⁻¹, while the specific capacity based on the whole electrode was quite low as 84 mAh g_{C/S+binder+Al}⁻¹ at 0.2 C. Moderate increase in the areal sulfur loading to 2.02 mg cm⁻² greatly improved the initial discharge capacity based on the whole electrode (280 mAh g_{C/S+binder+Al}⁻¹) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77 mg cm⁻², a high initial areal discharge capacity of 3.21 mAh cm⁻² (864 mAh g_S⁻¹) was achieved on the composite cathode.     

Graphene–terpyridine complex hybrid porous material for carbon dioxide adsorption

A graphene-based porous material for carbon dioxide sorption was designed and fabricated through an azide–alkyne click reaction between alkynyl group modified graphene oxide (alkynyl-GO) and azido-terpyridine complex. In the preparation of graphene terpyridine complex hybrid porous materials (GTCF), alkynyl-GO sheets were synthesized and used as the building blocks, which were then cross-linked with azido-terpyridine complexes through a copper (I) ion-catalyzed click reaction (Huisgen cycloaddition reaction). The incorporation of the non-planar terpyridine complexes between graphene sheets increases the porosity in the GTCF materials. Meanwhile, three kinds of nitrogen-containing groups (amine, triazole, and terpyridine groups) were introduced or formed during the modification and cross-linking, which offer more basic sites for the acidic gas sorption. Gas sorption analysis shows that the GTCF hybrid porous materials possess high specific surface area and their carbon dioxide capacity could reach up to 11.7 wt.% at 273 K.     

Controllable melting and flow of β-Sn in flexible amorphous carbon nanotubes

A high-yield of carbon nanotubes filled with β-Sn nanowires has been produced by the thermal pyrolysis of acetylene over SnO₂ catalysts. Electron beam irradiation (EBI) induced melting and flow of Sn in the nanotubes and this could be controlled by changing the electron beam current density. The mass flow rate of the Sn ranged from 0.9 to 8.2 fg/s. The melting of the nanowires is a result of the temperature rise caused by the EBI. Many factors, including temperature variation, charging, and EBI induced deformation of the carbon shells, contribute to the flow of Sn.     

Effect of carbon nanotubes additives on mechanical properties of WC–6Co cemented carbide

In order to increase the toughness of WC–6Co cemented carbide, different contents of carbon nanotubes (CNTs) were added to the WC–6Co alloy powder to prepare cemented carbide by low-pressure sintering. The results showed that some of the CNTs were embedded between the grains of WC–6Co cemented carbide, which would hinder the growth of WC grain boundary, thus leading to grain refinement. In addition, CNTs inhibited the formation of decarbonized phase and guided the deflection and bridge of crack to hinder the crack extension. With the increase of CNTs content, the density increased at first and then decreased, and the transverse fracture strength increased at first and then decreased. When the content was 0.2 wt.%, the alloy had the best performance. The density of the alloy was 99.67%; the transverse fracture strength was up to 2937.5 MPa, which is about 100% higher than that of cemented carbide without CNTs. The fracture toughness was 9.84 MPa m^1/2, and the hardness was 1924.8HV₃₀.     

Catalytic CVD-growth of array of multiwall carbon nanotubes on initially amorphous film Co–Zr–N–O

The possibility of formation of arrays of multiwall carbon nanotubes on catalyst-containing amorphous thin film Co–Zr–N–O with low content of Co (~ 15 at.%) by chemical vapor deposition has been demonstrated. On heating the amorphous alloy crystallizes, whereby the faceted crystal clusters of cobalt are formed on the surface. The rest of the film is cobalt depleted. The growth of CNT occurs on cobalt clusters. When using acetylene at the substrate temperature of 650 °C the array of 12 μm high CNT is formed after 2 min of growing. The diameter of CNT in the array varies in the range 3–11 nm. CNTs with the diameter of 5–8 nm prevail. CNT growth process on a thin film of Co–Zr–N–O is low sensitive to the thickness of the film, making it technically attractive.     

Application of as-synthesized Co–Al layered double hydroxides for the preparation of the electroactive composites containing N-doped carbon nanotubes

A set of electrically conductive, porous and electrocatalytically active composites was prepared by catalytic chemical vapor deposition using Co–Al layered double hydroxides and acetonitrile. The effect of synthesis temperature, i.e. 600, 700 and 800 °C on their composition, structure and morphology was examined by means of X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, nitrogen sorption and scanning electron microscopy. Electrochemical properties of the composites were evaluated by cyclic voltammetry (CV) in alkaline solution in the presence and absence of oxygen. The composites were composed of metallic cobalt, metal oxides and turbostratic/graphitic carbon. Graphite-like carbon was doped with nitrogen (according to XPS analysis N concentration is 2 at.%) and occurred as multi-walled carbon nanotubes with diameters ranging from 10 up to 55 nm. The composites were a mixture of compounds showing strongly temperature-dependent crystallinity therefore they showed various specific surface areas (125, 114 and 53 m² g^− 1) and different specific capacitances (9, 7 and 3 F g^− 1). The oxygen reduction peak in the CVs recorded in 0.1 M KOH was observed at − 0.26, − 0.28 and − 0.31 V versus Ag/AgCl/KCl_sat electrode for the samples prepared at 600, 700 and 800 °C, respectively.     

Growth of carbon nanotubes on the surface of carbon fiber using Fe–Ni bimetallic catalyst at low temperature

This article provides a method for growing carbon nanotubes(CNTs) on carbon fibers(CFs) using iron and nickel as catalysts at low temperatures. This series of experiments was conducted in a vacuum chemical vapor deposition(CVD)furnace. It is found that Fe–Ni catalysts, which have a certain thickness and can be better combined with resins when manufacturing composite materials, are more ideal for the growth of CNTs than single metal catalysts. At the same time, it is proved that the CVD process worked best at 450 °C. The mechanical property test proved the reinforcing effect of CNTs on carbon fiber, the single-filament tensile strength of CFs obtained by using Fe–Ni catalyst at 450 °C was 11% higher than that of Desized CFs. The bonding strength of carbon fiber and resin has also been significantly improved. When synthesized at low temperature, CNTs exhibited a hollow multi-wall structure.     

Hierarchical materials constructed by 1D hollow nickel–cobalt sulfide nanotubes supported on 2D ultrathin MXenes nanosheets for high-performance supercapacitor

To design and prepare novel composites with strong electrode structure and superior electrochemical performances via a facile and convenient synthesis method is a significant challenge to develop the high-performance materials for energy storage and conversion devices. Herein, we fabricated a novel hybridization of two dimensional (2D) Ti₃C₂-MXenes nanosheets and one dimensional (1D) nickel-cobalt sulfide (NiCo₂S₄) hollow nanotubes though the favorable electrostatic interaction between the negatively charged Ti₃C₂ and positively charged NiCo₂S₄ nanotubes. The electrode combined the good metallic conductivity of Ti₃C₂-MXenes and high pseudo-capacitance of NiCo₂S₄ demonstrated the outstanding electrochemical performance for supercapacitors. Herein, 2D Ti₃C₂-MXenes/1D NiCo₂S₄ hybrid electrode achieved an excellent specific capacitance of 1927 F g^-1 at 2 mV s^-1, long cycling stability for 4000 cycles and charming rate performances, which is mainly ascribed to the synergistic effect and interfacial interaction between two components. Particularly, the novel hybrid material with 1D and 2D hierarchical structures can provide additional electrochemical reaction sites, supply shorter paths for ions diffusion and electron transport, and effectively raise the charge transfer kinetics during the electrochemical process, which explores a new strategy aimed to develop 2D Ti₃C₂-MXenes energy storage devices with high electrochemical performance, and is possible potential for expansion into other application fields.     

Co–Ni Catalysts Derived from Hydrotalcite-Like Materials for Hydrogen Production by Ethanol Steam Reforming

A series of Co–Ni catalysts, prepared from hydrotalcite (HT)-like materials by co-precipitation, has been studied for the hydrogen production by ethanol steam reforming. The total metal loading was fixed at 40% and the Co–Ni composition was varied (40–0, 30–10, 20–20, 10–30 and 0–40). The catalysts were characterized using X-ray diffraction, N₂ physisorption, H₂ chemisorption, temperature-programmed reduction, scanning transmission electron microscope and energy dispersive spectroscopy. The results demonstrated that the particle size and reducibility of the Co–Ni catalysts are influenced by the degree of formation of a HT-like structure, increasing with Co content. All the catalysts were active and stable at 575 °C during the course of ethanol steam reforming with a molar ratio of H₂O:ethanol = 3:1. The activity decreased in the order 30Co–10Ni > 40Co ~ 20Ni–20Co ~ 10Co–30Ni > 40Ni. The 40Ni catalyst displayed the strongest resistance to deactivation, while all the Co-containing catalysts exhibited much higher activity than the 40Ni catalyst. The hydrogen selectivities were high and similar among the catalysts, the highest yield of hydrogen was found over the 30Co–10Ni catalyst. In general, the best catalytic performance is obtained with the 30Co–10Ni catalyst, in which Co and Ni are intimately mixed and dispersed in the HT-derived support, as indicated by the STEM micrograph and complementary mapping of Co, Ni, Al, Mg and O.     

Porous Co/Co–Ni–Pt nanostructures prepared by galvanic replacement towards methanol electro-oxidation

The nanostructured Co/Co–Ni–Pt catalyst were synthesized by electrodeposition process and galvanic replacement reaction. The alloy prepared on a copper electrode (Cu/Co/Co–Ni–Zn) was dipped in platinum containing alkaline solution to produce a porous Cu/Co/Co–Ni–Pt catalyst. The catalyst was characterized by energy dispersive X-ray and scanning electron microscopy techniques and its electrocatalytic properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry techniques. The results showed that the Co/Co–Ni–Pt coatings are porous, and composed of discrete Pt nanoparticles with the crystallite size of about 66 nm. It was shown from cyclic voltammograms in alkaline solutions that the oxidation current of methanol on the nanostructured Cu/Co/Co–Ni–Pt electrode was much higher than that on flat platinum. Electrochemical impedance spectra on the Co/Co–Ni–Pt electrode reveal that the charge transfer resistance decreases with the increase of anodic potentials. All results show that the Co/Co–Ni–Pt catalysts can be potential anode catalysts for the direct methanol fuel cell.