Graphite Substrate Research Articles

Effects of bath parameters on structure characteristic of Ni-W Electrodeposited alloy

This study describes the effects of the bath parameters (temperature, current density, additive concentrations and stirring) on tungsten content and microstructures of Ni-W deposits prepared from thiourea-containing bath, on graphite substrate to protect it from oxidation at high temperature. The morphology of the deposits was studied by optical microscope (TEM) and the approximate composition by energy dispersive spectroscopy (EDS).Increasing the concentration of thiourea refining the structure of the deposits, while the increasing in the current density and temperature led to increase the W content with and without stirring.

Binder-free TiN/graphite based thin film negative electrode for flexible energy storage devices

Transition metal nitrides are trustworthy electroactive materials due to their merits like good electrical conductivity, wettability, multi-oxidation state, and higher specific capacity than metal oxides and carbon materials. In the present work, titanium nitride is deposited over a highly flexible graphite substrate using physical vapour deposition process. The physiochemical studies confirmed the formation of TiN film over the graphite substrate and also exhibited flexible characteristics. The nitrogen content of the electrode provides considerable wettability to the electrode surface while having better conductivity. Noticeably, the as-fabricated negative electrode showed pseudocapacitive property with a good specific capacitance of 86 mF cm−2 at 1 mA cm−2 and stable cycling performance with 80% capacitance retention even after 3000 cycles at 3 mA cm−2 . The results of this study demonstrate that these metal nitrides can be considered as an alternative negative electrode for supercapacitor applications.

Evolution of Lewis acidity by mechanochemical and fluorination treatment of silicon carbide as novel catalyst for dehydrofluorination reactions

Transforming potent greenhouse gasses, hydrofluorocarbons (HFCs) to hydrofluoroolefins (HFOs) is an environmentally friendly and low energy input route compared with traditional incineration method. During the conversion process, Lewis acidity of the catalysts play a vital role in the activity. Here, inspired by the fluorinated metal oxide, a novel nonmetallic catalyst SiC was fabricated via sequentially mechanochemical treatment and fluorination. With series characterizations, it demonstrated that on the super surface of SiC, there are thin layers of graphite, COOH species, SiO2 and Si4C4-xO2 substrates. Through the mechanochemical treatment, the layers of graphite, COOH species and partial SiO2 could be grinded off. Hence, the exposed SiO2 residue could be removed via the fluorination by HFC-152a and HF forming volatile SiF4. At the same time, the transition layer, Si4C4-xO2 was fluorinated to Si4C4-xF2 accompanied with enhanced Lewis acidity. As a result, the activity of the treated SiC was significantly superior than the unmilled SiC. These findings provide a feasible way to develop the catalytic performances of nonmetallic catalysts for the dehydrofluorination.

Microstructural evolution and thermal-physical properties of YTaO4 coating after high-temperature exposure

YTaO4 is a promising candidate materials for next thermal barrier coatings (TBCs) due to low thermal conductivity, high thermal expansion coefficients, high melting point and low modulus. However, the current research on YTaO4 coating is relatively limited, there are obvious gaps of thermo-mechanical properties between bulks and coating. In this work, the YTaO4 coating was deposited on graphite substrate and TC4 substrate via atmospheric plasma spraying (APS). The phase transition temperature of M ↔ T phase is about 1426 ± 7 °C, which cause to the formation of ferroelastic domain structure. YTaO4 coating have an excellence anti-sintering performance due to a stable porosity during heat treatment, and the bonding strengths of YTaO4 coating on TC4 substrate has the maximum (35.12 ± 2.34 MPa) when the top coating thickness is ~250 μm. Compared with YTaO4 bulk, the thermal conductivity (0.53 W·m−1·K−1, 900 °C) of YTaO4 coating is reduced by 67–70 % in the entire temperature range. The low thermal conductivity for YTaO4 coating is the results of phonon scattering by porosity, domain boundaries and point defects. Moreover, the healing of intersplat pores with the increase of sintering temperature had significantly improved the hardness and elastic modulus of the coating.

Computer simulation of obtaining thin films of silicon carbide.

Silicon carbide films are potential candidates for the development of microsystems with harsh environmental conditions. In this work, the production of high-purity silicon carbide films by the electrolytic method is reproduced in a computer model. Single-layer SiC films were deposited on nickel, copper, and graphite substrates. The kinetic and structural characteristics related to the Si and C atoms in this compound are presented. The coefficient of self-diffusion of C atoms on all substrates is higher than that of Si atoms. In addition, the diffusion of atoms on a graphite substrate occurs much more intensively than on metallic (Ni and Cu) substrates. The first maximum of the radial distribution function g(r)SiC is at a shorter distance when the film is deposited on the graphite substrate. A detailed analysis of the structure, based on the construction of Voronoi polyhedra, indicates that the degree of crystallinity of the film increases when changing the substrate in the order from nickel to graphite. The resulting SiC films are subject to local stresses, the strongest of which appear on the copper substrate, however the average stresses in the film do not appear to be high.

Production of tib2 coatings on graphite substrates by electrophoretic deposition in NaF-AlF3 melt

In this paper a novel method for fabrication of TiB2 coatings on graphite substrates by electrophoretic deposition of TiB2 nanoparticles in NaF-AlF3 melt at 980?C has been explored. With an applied cell voltage of 1.2 V (i.e. electric field 0.6 V/cm), a flat and dense TiB2 coating with a thickness of around 50 ?m has been prepared. It was found that the surface consisted of TiB2 flakes with a nanoscale size. In addition, the average value of hardness of the TiB2 coating was determined as 3585 ? 139 HV0.1 (36.6 ? 1.4GPa) measured by a Vickers micro-hardness tester.

Atomic layer deposition of CoF2, NiF2 and HoF3 thin films.

The present study describes atomic layer deposition (ALD) processes and characterization of CoF2, NiF2, and HoF3 thin films. For CoF2 deposition CoCl2(TMEDA) (TMEDA = N,N,N',N'-tetramethylethylenediamine) and NH4F were used as precursors. CoF2 deposition was studied at 180-275 °C, resulting in a growth per cycle (GPC) of 0.7 to 1.2 Å. All the films consist of tetragonal CoF2 according to XRD. The impurity contents were measured with ToF-ERDA and less than 1 at% of N and Cl were detected in the films, indicating effective reactions. In addition, the F/Co ratio is close to 2 as measured by the same method. The saturation of the GPC with respect to precursor pulses and purges was verified at 250 °C. The common feature of ALD metal fluoride films - remarkable roughness - is encountered also in this process. However, the films became smoother as the deposition temperature was increased. CoF2 deposition was also demonstrated on graphite substrates. NiF2 deposition was studied at 210-250 °C by using Ni(thd)2 and TaF5 or a new fluoride source NbF5 as the precursors. Tetragonal NiF2 was obtained, but the oxygen and hydrogen contents in the films were remarkable, up to ∼11 at%, as measured by ToF-ERDA. This was observed also when the films were in situ capped with YF3. NbF5 was shown to be a potential fluoride precursor by combining it with Ho(thd)3 to deposit HoF3 films. Orthorhombic HoF3 was obtained at deposition temperatures of 200-275 °C. The films deposited at 235-275 °C are pure, and the Nb contents in films deposited at 250 and 275 °C are only 0.21 and 0.15 at%. The main impurity in both films is oxygen, but the contents are only 1.5 and 1.6 at%. The saturation of the GPC with respect to precursor pulses was verified at 250 °C. The GPC is ∼1 Å.

Исследование структуры градиентного аморфного углерода, полученного закалкой жидкого углерода

A new method for obtaining graded amorphous carbon using quenching of a graphite melt on a diamond substrate is proposed. Using molecular dynamics modeling of liquid carbon quenching on a cold diamond substrate, it is shown that the amorphous carbon obtained in the experiment is a material with a strongly gradient structure and properties along the depth of the sample. This is due to the quenching rate decrease with the distance from the substrate in the range of 10^14-10^12 K/s. In this case, the density of amorphous carbon varies from 1.50 g/cm^3 to 1.93 g/cm^3. The spatial change in the structural characteristics of the obtained amorphous carbon was studied: the distribution of carbon atoms according to the degree of chemical bond hybridization (sp^1, sp^2, sp^3), the radial distribution function, the angular distribution function, and a statistical analysis of carbon rings were carried out. It is shown that at a pressure in liquid of 1 GPa, the carbon structure within the quenched zone changes from a highly porous structure with a large number of sp^1 chains of carbon atoms near the substrate to an amorphous graphene structure at the periphery.

Molecular dynamics simulation of the amorphous graphite-like membrane deposited on ideal graphite substrate.

To understand the growth mechanism of pyrolytic graphite on ideal graphite substrate by chemical vapor deposition (CVD), the process simulated by molecular dynamics is performed. The simulation revealed that only an amorphous graphite-like membrane (a-GLM) can be obtained using the Tersoff potential function. It is revealed that the formation process for the first layer of the a-GLM initiates from the firstly deposited carbon monomers, dimers, and trimers as growth points, on which Y-shaped long chain is formed, and then the network with pores are developed, and finally the graphene-like layer with six-membered dominated rings appears after repair treatment. The following deposition simulation for more deposited carbon atoms indicates that a second layer like-graphene is more prone to superpose onto the microdomains of the first layer like-graphene until the formation of the island-like bumps, and the concave zone around the bumps will be filled by deposited atoms and modified by defect repair. The growth mechanism for pyrolytic graphite prepared by CVD can be deduced by the simulation inspiration. The optimal deposition temperature of 2400 K is acquired by evaluating the integrity of the first deposited graphene film by statistics of five-to-seven-membered carbon ring number. This study can provide theoretical references for the design of the pyrolytic graphite production process.

On the role of functional groups in the formation of diazonium based covalent attachments: dendritic vs. layer-by-layer growth.

Multilayered growth is often observed upon electrografting aryl diazonium derivatives on graphitic substrates due to the reactive nature of aryl radicals. The mechanism of the multilayer formation has been investigated either by measuring the thickness of the grafted layer, the charge transfer, or via simulations. Spectroscopy and in particular microscopy approaches are underrepresented. Herein, we demonstrate a comparative characterization of the multilayer growth of two diazonium derivatives on highly oriented pyrolytic graphite using a combination of cyclic voltammetry, atomic force microscopy, and scanning tunneling microscopy. While dendritic growth is observed for 4-nitro phenyl diazonium (4-NBD), 4-carboxy phenyl diazonium (4-CBD) shows layer-by-layer growth upon increasing the molecular concentration, revealing the impact of the functional groups on the growth mechanism.

Performance study of palladium modified platinum anode in direct ethanol fuel cells: A green power source

The direct ethanol fuel cell is a green and renewable power source alternative to fossil fuels and produces less emissions compared to a combustion engine. Ethanol can be generated in great quantity from renewable resources like biomass through a fermentation process. Bio-generated ethanol is thus attractive fuel since growing crops for biofuels absorbs much of the carbon dioxide emitted into the atmosphere from the oxidation of ethanol. The platinum and palladium were co-deposited on graphite substrate by the galvanostatic technique and employed as anode catalyst for ethanol electrooxidation. The information on surface morphology, structural characteristics and bulk composition of the catalyst was obtained using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. The cyclic voltammetry (CV) were used for the estimation of the electrochemically active surface area (ECSA) of the synthesized catalysts in alkaline medium. The CVs for ethanol oxidation revealed superior catalytic activity of Pt–Pd/C compared to Pd/C and Pt/C. The effect of OH− on ethanol oxidation at Pt–Pd/C catalyst was studied using cyclic voltammetry, quasisteady-state polarization, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The Pt–Pd/C catalyst shows good stability and enhanced electrocatalytic activity is ascribed to the synergistic effect of higher electrochemical surface area, preferred OH− adsorption on the surface and palladium ad-atom contribution on the alloyed surface.

The effect of SiC coatings microstructure on their infrared emissivity

ABSTRACT Infrared temperature measurement is widely used in the MOCVD process, and improving the surface infrared emissivity of the graphite base is beneficial to improve the temperature measurement accuracy. In this study, SiC coatings were prepared by CVD on graphite substrate using different process parameters including CVD temperature, total pressure, H2/MTS ratio. The infrared emissivity of SiC coatings with different microstructures was investigated. All SiC coatings obtained were β-SiC. The infrared emissivities of the three samples with different surface morphologies are 0.93, 0.95 and 0.97, respectively. As the surface roughness increases, the reflection and scattering of thermally radiated electromagnetic waves increases, resulting in higher infrared emissivity. The loose structure of the grain surface makes the surface electromagnetic wave and light wave resonant coupling, thus increasing the infrared emissivity.

Nitrogen Reduction Reaction Catalyzed by Diatomic Metals Supported by N-Doped Graphite

In this article, for the transition metal-nitrogen ligand Mn-M@N6-C (M = Ag, Bi, Cd, Co, Cr, Cu, Fe, Hf, Ir, Mo, Nb, Ni, Os, Pd, Pt, Re, Rh, Ru, Sc, Ta, Tc, V, Y, Zn, Zr, Ti, W), by comparing the amount of change in the length of the N-N triple-bond, and calculating the adsorption energy of N2 and the change of charge around N2, it is shown that the activation effect of Sc, Ti, Y, Nb-Mn@N6-C on the single-atomic layer of graphite substrate is relatively good. The calculation of structural stability shows that the Mn-M@N6-C (M = Sc, Ti, Y) load is relatively stable when it is on the single-atomic layer of the graphite substrate. Through calculations, a series of data such as the adsorption free energy and reaction path are obtained, and the final results show that the preferred reaction mechanism of NRR is the alternating path on Mn-Ti@N6-C, and the reaction limit potential is only 0.16 eV, Mn-Ti@N6-C and has good NRR activity. In addition, the vertical path on Mn-Y@N6-C has a reaction limit potential of 0.39 eV. Mn-Y@N6-C also has good NRR catalyzing activity.

Edge states of α-bismuthene nanostructures

We present a systematic investigation of the edge states (ESs) of two-dimensional α-bismuthene (α-Bi) structures self-assembled on highly oriented pyrolytic graphite substrates, using scanning tunnelling microscopy and scanning tunnelling spectroscopy. The measurements are carried out for 3ML, 5ML and 7ML thick Bi structures. Our spectroscopy studies reveal clear features at the edges of the 5ML and 7ML thick structures, and the positions of the ESs coincide with the topographical step edges. In contrast, in 3ML structures the ESs appear to be absent and instead new states are sometimes observed, far from the topographical edge. These states are associated with a moiré pattern and result from strain-induced modulation of the topology. Our observations demonstrate the impact on the ESs of coupling to adjacent structures.

Superfluid transition of the second layer of [formula omitted]He on graphite: Does substrate corrugation matter?

The second layer of 4He adsorbed on a graphite substrate is studied by Quantum Monte Carlo simulations. We make use of a microscopic model of the substrate fully accounting for its corrugation, and compare the results to those obtained with a smooth substrate. The only effect of corrugation is a ∼20% reduction of the value of the superfluid fraction of the top layer, in the limit of zero temperature. No evidence of any commensurate (7/12) crystalline and/or “supersolid” phase is found; the superfluid transition temperature is estimated to be ∼0.75 K. We discuss the implication of these findings on the interpretation of recent experiments.

Electrodeposition of Ni - Fe on graphite rod as an efficient and binder-free electrocatalyst for oxygen and hydrogen evolution reactions

In this paper, nickel-iron (Ni-Fe) on a graphite substrate was electrodeposited as an effective electrocatalyst for hydrogen and oxygen evolution reactions using the cyclic voltammetry method for the first time. Some important factors such as the range of applied potential, scan rate, and the number of cycles were optimized. In addition, the used substrate is a graphite rod, which is cheap, stable, and has good electrical conductivity. The main results show that the improved Ni-Fe coating on graphite rod has promising hydrogen evolution reaction (HER) activity, which exhibits small over voltages of − 191.2, − 394.0, and − 687.3 mV at the current densities of − 10, − 100, and − 400 mA. cm−2, respectively. Furthermore, the synthesized Ni-Fe electrocatalyst only needs 284 mV overpotentials to operate at a current density of 10 mA. cm−2, indicating its great performance for the oxygen evolution reaction (OER). This paper offers a method for generating a bifunctional, binder-free, affordable, and fast water splitting electrocatalyst that has excellent performance.

Eco-friendly direct-current pulsed electropolymerization of polyaniline nanofibers on synthetic graphite substrate for counter electrode in dye-sensitized solar cells

ABSTRACT This paper reports the study of the effect of varying duty cycles on the synthesis of PANI by pulsed electropolymerization method to the performance of PANI as a counter electrode in DSSC. The deposited PANI is in emeraldine salt form, confirmed by FTIR-ATR and Raman spectroscopy. SEM analysis observed that all PANIs has nanofiber morphology. PANI with a 10% duty cycle provides the smallest average diameters and lowest film thickness (11.56 μm), lowest RCT (59.00 Ω), lowest RS (40.06 Ω), highest VOC (0.688 V), and highest JSC (9.066 mA cm−2) that lead to the highest performance (η = 2.402%).

Self‐Assembly and Oriented Growth of Conductive Ni‐CAT‐1 Metal‐Organic Framework at Solid–Liquid Interfaces

AbstractTwo‐dimensional (2D) conductive metal‐organic frameworks (MOF) represent a unique class of electrode materials with high capacity and power density. Understanding molecular mechanisms and pathways for heterogeneous nucleation of 2D π‐conjugated MOFs is highly desirable for controlling the structure and properties of conductive MOFs on solid substrates. Herein, a systematic study of nucleation and growth of 2D π‐conjugated Ni‐catecholate (Ni‐CAT‐1) MOFs on highly oriented pyrolytic graphite (HOPG) and copper substrates is reported. It is discovered that the nucleation density and growth kinetics of the MOF film can be controlled by varying substrate interactions with the organic linker. Specifically, π–π interactions between the linker and the HOPG dictate lower nucleation density, whereas π–metal interactions between the linker and the copper substrate dictate faster nucleation and higher nucleation densities. These studies reveal the key mechanism for Ni‐CAT‐1 nucleation on different surfaces and provide insights into interfacial control over the growth of other 2D π‐conjugated MOF films on solid substrates to inform synthesis of functional materials.

Pulse Electrodeposition of SnO2 Films on Graphite Substrates for Application in Lithium-Ion Batteries

Pulse Electrodeposition of SnO2 Films on Graphite Substrates for Application in Lithium-Ion Batteries

A comparison between growth of direct and pulse current electrodeposited crystalline SnO2 films; electrochemical properties for application in lithium-ion batteries

Tin oxide (SnO2) films were electrodeposited on graphite substrates using direct and pulse current electrodeposition techniques. The influence of applied current density on the morphological properties, crystal structure, and electrochemical behavior of the resulting films were studied by scanning electron microscope, X-ray diffraction spectroscopy, Mott–Schottky analysis, cyclic voltammetry, and electrochemical impedance spectroscopy techniques. The results showed that pulse electrodeposited films have porous flower-like morphology with smaller crystallite size and high donor density in comparison with direct current electrodeposited films that include equiaxed particles in their morphologies, such characteristics give them better electrochemical performance (higher degree of reversibility, higher specific capacitance, and faster lithium-ion diffusion) than those films that were synthesized by conventional direct current electrodeposition method. Furthermore, using higher applied current densities leads to the improvement of SnO2 films’ electrochemical performance due to the formation of the films with finer morphology that include more porosity and oxygen vacancies in their respective crystal structure.