Electrochemical detection of catechol at integrated carbon nanotubes electrodes

The mechanical stability of the electrode plays a very important role in the long-term stability of electrochemical behavior. In this paper, multi-wall carbon nanotubes (MWCNTs) electrodes were prepared in the holes of glass directly by microwave plasma chemical vapor deposition and the electrochemical behavior of catechol at the integrated MWCNT electrodes was investigated. The oxygen plasma treated CNTs had excellent electrochemical behavior for the analysis of catechol. The catechol was detected in the linear concentration range of 1.0 × 10^− 6 mol L^− 1–1.0 × 10^− 3 mol L^− 1. And because CNTs were integrated directly on the substrate, the stable response to catechol solution showed that the carbon nanotubes electrodes had long-term stability.     

Effective synthesis of well graphitized high yield bamboo-like multi-walled carbon nanotubes on copper loaded α-alumina nanoparticles

A high-yield bamboo like multiwalled carbon nanotubes (CNTs) were successfully synthesized on copper substituted alumina nanoparticles by thermal chemical vapor deposition (CVD) technique under atmospheric pressure. The obtained products were characterized by various techniques like FESEM with EDX, HRTEM and Raman spectroscopy, which reveals the formation of CNTs and are of bamboo shaped (stacking arrangement) multiwalled type with graphene layers having a diameter between 4 and 9 nm. The appearance of two peaks at 1597 cm^− 1 and 1302 cm^− 1 in Raman spectra are noticed as G-band and D-band for graphitic nature and defects due to bending & curvature of bamboo like carbon nanotubes (b-CNTs), respectively. The influence of reaction parameters such as time, temperature and flow rate was also studied to increase the carbon yield.     

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.     

Preparation-microstructure-property relationships in double-walled carbon nanotubes/alumina composites

Double-walled carbon nanotube/alumina composite powders with low carbon contents (2–3 wt.%) are prepared using three different methods and densified by spark plasma sintering. The mechanical properties and electrical conductivity are investigated and correlated with the microstructure of the dense materials. Samples prepared by in situ synthesis of carbon nanotubes (CNTs) in impregnated submicronic alumina are highly homogeneous and present the higher electrical conductivity (2.2–3.5 S cm⁻¹) but carbon films at grain boundaries induce a poor cohesion of the materials. Composites prepared by mixing using moderate sonication of as-prepared double-walled CNTs and lyophilisation, with little damage to the CNTs, have a fracture strength higher (+30%) and a fracture toughness similar (5.6 vs 5.4   MPa m^1/2) to alumina with a similar submicronic grain size. This is correlated with crack-bridging by CNTs on a large scale, despite a lack of homogeneity of the CNT distribution.     

Improved thermal interface property of carbon nanotube–Cu composite based on supercritical fluid deposition

In this paper, we present a new synthesis method of carbon nanotubes (CNTs)-copper (Cu) composite on a silicon substrate using combination of supercritical fluid deposition (SCFD) and electrochemical plating (ECP) process. Deposition of a Cu layer onto CNTs is carried out under supercritical condition, and the CNTs–Cu composite with high-density Cu is synthesized by additional ECP process. The Cu layer deposited by SCFD functions as a seed layer for ECP, and spaces between neighboring CNTs are filled by Cu. The measured density of the CNTs–Cu composite is 8.2 ± 0.3 g/cm³, and the volume percentage of voids is 3–6%. The evaluated thermal resistance including the thermal interface resistance and bulk resistance of the composite is as low as 28.4 mm² K W⁻¹ at a contact pressure of 0.2 MPa. A CNT brush formed on the composite surface can reduce the thermal resistance to be 68.4 mm² K W⁻¹ at a contact pressure of 0.25 MPa. The CNTs–Cu composite shows the ability applicable to many microelectronics applications as a thermal interface material.     

Low temperature growth of carbon nanotubes on Si substrates in high vacuum

Carbon nanotube (CNT) growth was carried out on SiO₂/Si substrates using an alcohol gas source in a high vacuum without any carbon decomposition processes. In the Raman spectra of the grown CNTs, both the G/Si peak intensity ratio and G/D peak intensity ratio indicated that the optimum growth temperature became lower as the pressure decreased. By reducing the pressure to 1 × 10^− 4 Pa, CNTs could be grown at 400 °C, and the G/D ratio was about 16, indicating that the quality of the grown CNTs was good, taking into account the low growth pressure. In addition, the Raman spectra in the radial breathing mode (RBM) region showed that the diameter distribution of the grown CNTs was dependent on both the growth pressure and temperature, and the relative intensity of the RBM peaks from small-diameter CNTs increased as the growth pressure and/or temperature was reduced.     

Performance of spray deposited Gd-doped barium cerate thin films for proton conducting SOFCs

Doped barium cerate is a promising solid electrolyte for intermediate temperature fuel cells as a protonic conductor. In the present paper, the nanocrystalline Gd-doped barium cerate (BaCe_0.7Gd_0.1Y_0.2O_2.9) thin films have been successfully deposited on alumina substrate by spray pyrolysis technique. The films deposited from 0.1 M concentration and annealed at five different temperatures were characterized with different physio-chemical techniques. The BCGY is crystallized in orthorhombic perovskite structure with slight shift to the lower 2θ value compared with barium cerate (BC) and yttrium doped barium cerate (BCY). The grain growth and hence densification is also investigated by using SEM and AFM. The grain growth is almost complete at 1000 °C and the surface of the film appears to be smooth with typical roughness of 152 nm. Raman spectrum of BCGY film shows intense band at 463.8 cm⁻¹ compared to pure BC and BCY indicating the presence of more oxygen vacancies due to Gd doping. The proton conductivity of BCGY thin film in moist atmosphere is 1×10⁻³ Scm⁻¹.     

Effect of substrate heating and microwave attenuation on the catalyst free growth and field emission of carbon nanotubes

Carbon nanotubes (CNTs) have been directly grown on Inconel 600 substrates by microwave plasma enhanced chemical vapor deposition without using any external catalyst. Grown CNTs were characterized by field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy and field emission measurements. Characterization results show that field emission current density increases from 200 μA/cm² at ∼5.5 V/μm to 14.5 mA/cm² at ∼1.6 V/μA when substrate is heat-treated and incident microwave is attenuated before reaching it. Detailed characterization reveals that heat-treatment results in migration of Cr and Fe oxides towards the top surface which completely changes substrate morphology also. Microwave attenuation reduces reflection of microwaves from the substrate and increases residence time of the precursor over the substrate promoting high density growth of CNTs. The combination of these two process parameters resulted in growth of long, dense CNTs with bamboo-like defects that contributes to enhanced current density at lower applied field.     

Electrical contacts to nitrogen incorporated nanocrystalline diamond films

The effect of surface plasma treatment on the nature of the electrical contact to the nitrogen incorporated nanocrystalline diamond (n-NCD) films is reported. Nitrogen incorporated NCD films were grown in a microwave plasma enhanced chemical vapor deposition (MPECVD) reactor using CH₄ (1%)/N₂ (20%)/Ar (79%) gas chemistry. Raman spectra of the films showed features at ∼ 1140 cm^− 1, 1350 cm^− 1(D-band) and 1560 cm^− 1(G-band) respectively with changes in the bonding configuration of G-band after the plasma treatment. Electrical contacts to both untreated and surface plasma treated films are formed by sputtering and patterning Ti/Au metal electrodes. Ohmic nature of these contacts on the untreated films has changed to non-ohmic type after the hydrogen plasma treatment. The linear current–voltage characteristics could not be obtained even after annealing the contacts. The nature of the electrical contacts to these films depends on the surface conditions and the presence of defects and sp² carbon.     

Enhanced rate capability of nanostructured three-dimensional graphene/Ni3S2 composite for supercapacitor electrode

Three-dimensional graphene/Ni₃S₂ (3DG/Ni₃S₂) composite electrodes were produced by a facile two-step synthesis route involving chemical vapor deposition (CVD) growth of graphene foam and in situ hydrothermal synthesis of Ni₃S₂. The porous structure of the prepared 3DG is ideal for use as a scaffold for fabricating monolithic composite electrodes. The relative content of Ni₃S₂ initially increased and then decreased with increasing hydrothermal reaction time. The basal surface of the electrode was completely covered after 6 h of hydrothermal reaction. The size of the Ni₃S₂ microspheres also increased with increasing hydrothermal reaction time. The composite electrodes exhibited good specific capacitance (11.529 F cm⁻² at 2 mA cm⁻², i.e., 2611.9 F g⁻¹ at 5 mV s⁻¹) and cyclability (retention of 88.97% capacitance after 1000 charge/discharge cycles at 20 mA cm⁻²). These results are attributed to the fact that the uniform distribution of the Ni₃S₂ microspheres increased the specific surface area of the electrode and facilitated electron transfer and ion diffusion. The 3D multiplexed and highly conductive pathways provided by the defect-free graphene foam also ensured rapid charge transfer and conduction to improve the rate capability of the supercapacitors.     

High-performance supercapacitors based on defect-engineered carbon nanotubes

Defect-engineered carbon nanotubes (CNTs) were prepared by KOH activation and subsequent nitrogen doping. Controlled KOH activation of the CNTs enlarged the specific surface area to 988 m² g⁻¹, which is about 4.5 times greater than that of pristine CNTs. In addition, a hierarchical pore structure and a rough surface developed at high degrees of activation, which are advantageous features for fast ion diffusion. The subsequent nitrogen doping changed the band structure of the CNTs, resulting in improved electrical properties. Symmetric supercapacitors fabricated using these nitrogen-doped and activated CNTs (NA-CNTs) successfully worked across a wide potential range (0–3.5 V) and exhibited a high capacitance of 98 F g⁻¹ at a current density of 1 A g⁻¹. Furthermore, a low equivalent series resistance (2.2 Ω) was achieved owing to the tailored nanostructure and electrical properties of the electrode materials. Over the voltage range from 0 to 3.5 V, supercapacitors based on NA-CNTs exhibited a high specific energy of 59 Wh kg⁻¹ and a specific power of 1750 W kg⁻¹. In addition, a specific power of 52,500 W kg⁻¹ with a 3-s charge/discharge rate was achieved with a specific energy of 26 Wh kg⁻¹. Moreover, the supercapacitors showed stable performance over 10,000 charge/discharge cycles.     

Nitrogen-, phosphorous- and boron-doped carbon nanotubes as catalysts for the aerobic oxidation of cyclohexane

Nitrogen-, phosphorous- and boron-doped carbon nanotubes (N-CNTs, P-CNTs and B-CNTs) were prepared by a chemical vapor deposition method using xylene as carbon source and aniline-NH₃, triphenyl phosphine and triethyl borate as nitrogen, phosphorous and boron precursors, respectively. By tailoring the composition of reactants and reaction atmosphere, N-CNTs with nitrogen contents from 0% to 4.36% and P-CNTs with phosphorous contents from 0.55% to 5.14% were synthesized. N- and P-CNTs are active for the oxidation of cyclohexane in the liquid phase with molecular oxygen as oxidant. The highest mass-normalized activity, 761 mmol g⁻¹ h⁻¹, was achieved over N-CNTs synthesized from aniline in an NH₃ atmosphere, while the highest surface-area-normalized activity, 28 mmol m⁻² h⁻¹, was observed over P-CNTs. B-doping does not improve the activity of CNTs. The effect of the number of nitrogen functionalities and defects was investigated to reveal the structure–activity relationship of the doped CNTs. By using the work function as an indicator of the electron donation of carbon, an exponential dependence of specific activity on work function was discovered for N- and P-CNTs, suggesting that the electron transfer on the surfaces of CNTs plays a central role in the CNT-catalyzed oxidation of cyclohexane.     

Effect of anodic and cathodic treatments on the charge transfer of boron doped diamond electrodes

This paper is concerned with the study of the influence of electrochemical pre-treatments on the behavior of highly boron doped diamond electrodes. Anodic and cathodic preconditioning, performed during 10 s either with 10^− 4 A/cm^− 2 (10^− 3 C cm^− 2) or 10^− 1 A/cm^− 2 (1 C cm^− 2), has been studied. Cyclic voltammetry at as-deposited, anodically and cathodically treated electrodes, in presence of 2 redox couples serving as electrochemical probes is analyzed in the light of the surface characterization given by XPS chemical analysis. Ce^4+/3+ redox couple in 0.5 M H₂SO₄ medium and Fe(CN)₆^3−/4− redox couple in 0.1 M KOH medium, have been studied before and after the different treatments. The results of Mott–Schottky plots and current voltage curves are reported and show that the electrochemical response of BDD electrodes is very dependent on the current density involved in the electrochemical preconditioning. The modification of surface bond termination – either hydrogen or oxygen – studied by XPS analyses is also strongly dependent on electrochemical pre-treatment. In particular, it is evidenced that the most important conversion of surface functionalities from hydrogen to oxygen is obtained when the anodic treatment is performed with the smallest current density. Finally, a correlation between surface terminations and charge transfer is evidenced.     

CuAlO2 thermoelectric compacts by SPS and thermoelectric performance improvement by orientation control

We fabricated CuO/Al₂O₃ green compacts from plate-like Al₂O₃ and granular CuO powders by multi-press forming and investigated the alumina orientation using Lotgering's method. The results showed that Al₂O₃ particles preferentially aligned perpendicular to the pressure direction and the orientation degree increased as the forming pressure was increased. We proposed a model describing the movement of the alumina particles to explain the pressure effect on their orientation. The orientation calculation was in good agreement with those by Lotgering's method. Furthermore, we prepared the CuAlO₂ compacts by regular or spark plasma sintering (SPS). However, the compacts sintered by SPS exhibited higher orientation degree and density than those produced by regular sintering. The electrical conductivity values of the orientation-controlled compacts sintered by SPS reached 770 S m⁻¹ at 928 K, which was close to that of CuAlO₂ single crystal. The power factor of the CuAlO₂ compacts with highest orientation degree is as high as 5.95 × 10⁻⁵ W m⁻¹ K⁻¹ at 928 K. Therefore, we can conclude that orientation control is an effective method to enhance the thermoelectric performance of compact polycrystalline CuAlO₂ bulks.     

Fabrication and characterization of in-situ duplex plasma-treated nanocrystalline Ti/AlTiN coatings

Plasma nitriding and plasma-assisted PVD duplex treatment was adopted to improve the load-bearing capacity, fatigue resistance and adhesion of the AlTiN coating. Ion etch-cleaning was applied for better adhesion before plasma nitriding. After plasma nitriding Ti interlayer was in-situ deposited by high power impulse magnetron sputtering (HIPIMS), followed by the AlTiN coating through in-situ deposition by advanced plasma-assisted arc (APA-Arc). The microstructure and properties of the duplex-treated coating were carefully characterized and analyzed. The results show that the thicknesses of the nitriding zone, the γ′-Fe₄N compound layer, the Ti interlayer and the AlTiN top layer with nanocrystalline microstructures are about 60 μm, 2–3 μm, 100 nm and 6.1 μm, respectively. The nitriding rate is about 30 μm/h and the AlTiN coating deposition rate reaches 6.1 μm/h. The interfacial adhesion of the Ti/AlTiN coating is well enhanced by ion etch-cleaning and a Ti interlayer, and the load-bearing capacity is also improved by duplex treatment. In addition, the instinct hardness of the Ti/AlTiN coating reaches 3368HV_0.05 while the wear rate coefficient of 5.394×10⁻⁸ mm⁻³/Nm is sufficiently low. The Ti/AlTiN coating, which possesses a high corrosion potential (E_corr=−104.6 mV) and a low corrosion current density (i_corr=4.769 μA/cm²), shows highly protective efficiency to the substrate.     

Synthesis,crystal structure,and magnetic property of a stepped tetranuclear copper(II) complex of 3,5-diisopropylpyrazole-1-methoxide

Reaction of copper(II) chloride dihydrate in methanol with deprotonated 3,5-diisopropylpyrazole-1-methanol (dippmOH) led to the tetranuclear copper(II) complex [(dippmO)CuCl]₄ (1). The crystal structure of 1 indicates that two copper(II) ions connect via the oxygen atoms of dippmO⁻ ligands each other in which two dimeric units are formed. Furthermore, one of the coordinated oxygen atoms in a dimer is bonded to an adjacent copper(II) ion positioned other dimer, which gives rise to a stepped tetranuclear structure. 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J₁ = − 239 cm^− 1) and weak antiferromagnetic couplings between the dimers (J₂ = − 15 cm^− 1).     

Copper tracks processing on alumina by laser cladding: Elaboration and characterization

A laser process allows achieving in air electrical tracks on alumina substrates with an electrical conductivity of 5.10⁶ S m^?1. Copper paste was first put on alumina substrates and it was heated following a narrow track (c.a. 400 μm wide). Copper melted and oxidized partially during treatment forming cuprite Cu₂O. A reaction occurs between Cu₂O and alumina substrates which provides, after cooling, a good bonding of the copper-based tracks onto the substrates. Conditions of laser exposure have to be sharply controlled: if insufficient, tracks do not adhere to the substrate, and if too long, alumina substrates are hollowed, cracked, with vaporizations of copper and ejections of alumina. However the feasibility of such a process is now established.     

3D NiCo2S4 nanorod arrays as electrode materials for electrochemical energy storage application

It is essential to develop new electrode materials for electrochemical energy storage to meet the increasing energy demands, reduce environmental pollution and develop low-carbon economy. In this work, binder-free NiCo₂S₄ nanorod arrays (NCS NRAs) on nickel foam electrodes are prepared by an easy and low energy-consuming route. The electrodes exhibit superior electrochemical properties both for alkaline and Li-ion batteries. In 3 M KOH electrolyte, the NCS NRAs achieve a specific capacity of 240.5 mA h g⁻¹ at a current density of 0.2 A g⁻¹, and 105.7 mA h g⁻¹ after 1500 cycles at the current density of 5 A g⁻¹ with capacity retention of 87.3%. As the anode for LIBs, it shows a high initial capacity of 1760.7 mA h g⁻¹ at the current density of 100 mA g⁻¹, corresponding coulombic efficiency of 87.6%, and a rate capacity of 945 mA h g⁻¹ when the current density is improved 10 times. Hence, the NiCo₂S₄ nanorod arrays are promised as electrode materials with competitive performance.     

Aqueous slurry of S-doped carbon nanotubes as conductive additive for lithium ion batteries

S-doped carbon nanotubes (SCNTs) obtained by a post treatment approach are used as conductive additive for LiFePO₄ (LFP) cathodes in Lithium ion batteries (LIBs). The SCNTs exhibit higher specific surface area, higher conductivity and better hydrophily as compared to the pristine CNTs because of S doping. Thus the SCNTs can be stably dispersed in water, forming an aqueous conductive slurry. The LFP cathode using the aqueous SCNTs slurry as conductive additive exhibits excellent electrochemical performances in terms of capacity (143 mA h g⁻¹ at 2 C), rate capability and cycling stability (99.6% of initial capacity after 200 cycles) due to the uniform dispersibility of SCNTs in the bulk of electrodes forming a continuous conductive network. The full cell configuration with graphite as anode, affords a high reversible capability (150 mA h g⁻¹ at 0.2 C), good cycling stability (capacity retention of 87.6% at 2 C), ultrahigh energy density of 163.7 W h kg⁻¹ and power density of 296.8 W kg⁻¹. Our results provide an easy approach to prepare high performance LIB cathodes using water as solvent, thus leading to lower cost and more secure for the electrode production.     

Integration of tailored reduced graphene oxide nanosheets and electrospun polyamide-66 nanofabrics for a flexible supercapacitor with high-volume- and high-area-specific capacitance

Nanofiber fabric is firstly introduced to replace common microfiber fabrics as the platform for flexible supercapacitors. Nanofiber and microfiber electrodes can be simply fabricated using a dipping process that impregnates reduced graphene oxide (RGO) nanosheets into electrospun polyamide-66 (PA66) nanofiber and microfiber fabrics. RGO nanosheets are tailored to various sizes and only RGO with a medium diameter of 250–450 nm (denoted as M-RGO) can effectively penetrate the pores of nanofiber fabrics for constructing smooth conductive paths within PA66 nanofiber fabrics. The synergistic effect between suitable sizes of RGO nanosheets and nanofiber fabrics with a high specific area provides a symmetric supercapacitor composed of M-RGO/PA66 nanofiber fabric electrodes with high-volume and high-area specific capacitance (C_S,V and C_S,A, equal to 38.79 F cm⁻³ and 0.931 F cm⁻² at 0.5 A g⁻¹, respectively), which are much larger than that of a symmetric supercapacitor composed of RGO/PA66 microfiber fabric electrodes (8.52 F cm⁻³ and 0.213 F cm⁻² at 0.5 A g⁻¹). The effect of impregnating nanofiber fabrics with suitably sized RGO to promote C_S,V and C_S,A of flexible supercapacitors has been demonstrated.