Aerosol-assisted Chemical Vapor Deposition Process Research Articles

Aerosol-assisted chemical vapour deposited vanadium oxide thin films on nickel foam with auspicious electrochemical water oxidation properties

Sustainable green hydrogen production via electrocatalytic water splitting could become viable if the oxygen evolution reaction (OER) is accomplished at extremely high rates on robust surfaces of low-cost transition metal catalysts. Herein, nanoscale vanadium oxide (VOx) thin films were deposited on porous nickel foam (NiF) by an aerosol-assisted chemical vapor deposition process with different deposition times and were further used as electrocatalysts for OER. The sample with 30 min of deposition time showed an enhanced OER response with a high current density of 1000 mAcm−2 at 1.7 V (η = 470 mV) vs. RHE. This sample demonstrated a small Tafel slope of 68 mV/dec, and high conductivity. Notably, VOx-30 (specified for samples deposited for 30 min) exhibited long-term durability by maintaining its initial current density even after 48 h of continuous exposure, thus outperforming several conventional OER catalysts under similar conditions. This distinct behaviour from other catalysts may be attributed to the nanoscale morphologies and the synergistic effect of vanadium-based catalysts with the underlying conductive nickel support.

Rapid synthesis of nickel–iron-oxide (NiFeOx) solid-solution nano-rods thin films on nickel foam as advanced electrocatalyst for sustained water oxidation

The development of earth-rich, noble-metal-free, and highly electroactive catalysts to accelerate the oxygen evolution reaction (OER) is a formidable challenge for the establishment of water-splitting technologies. Here, a solid-solution nickel-iron oxide (NiFeOx) electrocatalyst is readily grown on a Ni-foam (NF) substrate by a rapid and economical aerosol-assisted chemical vapor deposition process. In particular, the NiFeOx thin film fabricated in 40 min acquires a distinctive nanorod structure and proves to be stable and efficient for OER in alkaline solutions. It is shown that the catalyst needs a low over-potential of 226 mV to reach the typical current density of 10 mA/cm2, and it can approach a remarkable current density level of 1000 mA/cm2 by taking a slightly higher over-potential of 139 mV. The small Tafel slope of 64 mv.dec−1 and splendid electrochemical stability of 40 h at high current densities outperform many known FeNi-based anodes as well as commercial IrO2 and RuO2. The unique structure of the thin film offers many electroactive sites and a high surface area in combination with an improved electrical conductivity of NF, which is believed to play an imperative role in the excellent activity of the catalyst. The cost-effective and simple strategy to fabricate NiFeOx nano-fibrous is very attractive for the development of electrocatalysts for water splitting.

Performance Enhancement of Polymer Electrolyte Membrane Fuel Cells with Cerium Oxide Interlayers Prepared by Aerosol-Assisted Chemical Vapor Deposition

In this study, the performance and durability of a Pt/CeOx catalyst membrane electrode assembly (MEA) fabricated by chemical vapor deposition and sputtering using aerosols were investigated for use in a polymer electrolyte membrane fuel cell (PEMFC). The cost burden of Pt-based catalysts and the degradation of performance and durability owing to corrosion of the carbon support under certain conditions limit the commercialization of PEMFCs. To solve these problems, the development of Pt alloy catalysts (Pt–Co, Pt–Ni, and Pt–Fe), Pt-based core–shell catalysts (Pt–TiO2 and Pt–CeO2), Pt bimetallic catalysts (Pt–Pd, Pt–Ru, and Pt–Sn), and Pt-based nanocomposites (Pt/graphene and Pt/carbon nanotubes) is being actively researched. Inserting a CeOx interlayer between Pt and carbon has three advantages: (i) oxygen supply to Pt due to CeOx interlayer’s ability to store oxygen improves catalyst utilization, (ii) improves the dispersibility of Pt, and (iii) solves the problem of performance and durability degradation by preventing the formation of reactive intermediates. For the deposition of ceria, the aerosol-assisted chemical vapor deposition process, which is performed at atmospheric pressure and can be uniformly deposited over a wide area with spray-based precursor delivery characteristics, was applied. The performance and electrochemical surface area of the Pt/CeOx MEA were determined using I–V measurements and cyclic voltammetry, and the durability of the Pt/CeOx MEA was analyzed using electrochemical impedance spectroscopy and an accelerated degradation test. As a result, when the Pt/CeOx on the gas diffusion layer (GDL) MEA was used, the performance improved by 46% compared to that of Pt on the GDL.

Photocatalytic NOx Oxidation of BiOCl Nanostructure-Based Films Grown Using Aerosol-Assisted Chemical Vapor Deposition

Coating of photocatalytic nanomaterials on various surfaces enables interesting applications. This work demonstrates the ability of the aerosol-assisted chemical vapor deposition (AACVD) approach to prepare high-quality BiOCl nanostructure-based films and also to tune the nanostructure and photocatalytic properties of the films by varying the solvent and carrier gas. Solvents have a dramatic impact on the surface morphologies and crystallite size. X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXRD) analyses indicate that BiOCl crystals displayed preferential growth in the (101) plane in most samples, while both the (101) and (102) planes were favored in films deposited using ethyl acetate and methanol. Surface energy and adsorption energy calculation reveal that the preferred growth depends on the interaction between the Bi atom and solvent molecules. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) characterizations showed that all films did not contain any impurity elements but did contain some oxygen vacancies. The obtained nanostructured BiOCl films show good photocatalytic properties. The highest photocatalytic NOx removal efficiency is achieved in the film prepared using ethyl acetate and air, which we attribute to the large crystallite size and therefore high mobility of the carriers. Herein, we show that different crystal morphologies and sizes of BiOCl have strong impacts on the photocatalytic activity toward NO oxidation, and both factors can be effectively tuned in the AACVD process. Such knowledge may be useful for future research on coating materials for resolving environmental problems.

Production of an EP/PDMS/SA/AlZnO Coated Superhydrophobic Surface through an Aerosol-Assisted Chemical Vapor Deposition Process.

In this study, a superhydrophobic coating on glass has been prepared through a single-step aerosol-assisted chemical vapor deposition (AACVD) process. During the process, an aerosolized precursor containing polydimethylsiloxane, epoxy resin, and stearic acid functionalized Al-doped ZnO nanoparticles was deposited onto the glass at 350 °C. X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy showed that the precursor was successfully coated and formed a nano/microstructure (surface roughness: 378.0 ± 46.1 nm) on the glass surface. The coated surface had a water contact angle of 159.1 ± 1.2°, contact angle hysteresis of 2.2 ± 1.7°, and rolling off-angle of 1°, indicating that it was superhydrophobic. In the self-cleaning test of the coated surface at a tilted angle of 20°, it was shown that water droplets rolled and washed out dirt on the surface. The stability tests showed that the surface remained superhydrophobic after 120 h of exposure to ultraviolet (UV) irradiation and even after heat exposure at 350 °C. In addition, the surface was highly repellent to water solutions of pH 1–13. The results showed that the addition of the functionalized nanoparticles into the precursor allowed for the control of surface roughness and provided a simplified single-step fabrication process of the superhydrophobic surface. This provides valuable information for developing the manufacturing process for superhydrophobic surfaces.

Aerosol-Assisted Chemical Vapor Deposition Growth of NiMoO4 Nanoflowers on Nickel Foam as Effective Electrocatalysts toward Water Oxidation.

The fabrication of active and durable catalysts derived from transition metals is highly desired for the realization of efficient water oxidation reactions. This is particularly important to address the slow oxygen evolution reaction (OER) kinetics and hence can contribute to the conversion and storage of sustainable energy. In this study, the deposition of crystalline flowerlike 2D nanosheets of nickel molybdate (NiMoO4) directly on nickel foam (NF) through an aerosol-assisted chemical vapor deposition process is reported. The NiMoO4 nanosheets were developed on NF by altering the deposition time for 60 and 120 min at a fixed temperature of 480 °C. The structural determination by XRD and XPS analyses revealed a highly crystalline single phase NiMoO4. The micrographs of NiMoO4 show that the surface consisted of vertically aligned 2D nanosheets assembled into flowerlike structures. The nanosheets produced after 60 min deposition time on a network of NF is found to perform better for OER as compared to the one developed for 120 min. A reference current density of 10 mA cm–2 was achieved at an overpotential (η) of 320 mV, which was better as compared to that reported for the benchmark OER catalyst in 1.0 M KOH. Moreover, a small Tafel value (75 mV dec–1) and good OER stability for >15 h were also observed.

Mechanistic study of the gas-phase chemistry during the spray deposition of Zn(O,S) films by mass spectrometry

The mass spectrometer, is a powerful tool to identify species and investigate reactions in the gas phase. In this work, the mechanism of aerosol assisted chemical vapor deposition (AACVD) of Zn(O,S) films prepared from H2S and zinc acetylacetonate (Zn(acac)2) precursor solutions is elucidated by mass spectrometry. The thermochemical behavior of Zn(acac)2 is investigated by characterizing the influence of the solvent (H2O or ethanol), the pH value of the precursor solution and the effect of the reactant H2S, and by tracking gaseous intermediate products using mass spectrometry. Based on these results, a proton-promoted thermolysis mechanism for the AACVD Zn(O,S) film formation is then proposed, which is initiated by the hydrolysis with H2O as the first stage, followed either by the rearrangement with an intramolecular proton or by the reaction with an extramolecular proton to produce ZnO or Zn(O,S). A real time mass tracking of the AACVD process reveals that only an adequate amount of H2S promotes the chemical gas-phase decomposition and sulfurization process, while an excess of H2S depletes the gaseous Zn(acac)2 concentration and consequently reduces the film growth rate. The knowledge of the thermal decomposition process helps to optimize synthesis conditions and to adjust film properties to meet the requirement of the application in chalcopyrite or kesterite thin film solar cells.

Mathematical Modeling for the Design and Scale-Up of a Large Industrial Aerosol-Assisted Chemical Vapor Deposition Process under Uncertainty.

Aerosol-assisted chemical vapor deposition (AACVD) can be used to produce coatings and thin films such as transparent conducting oxide (TCO) films, which are used in self-cleaning surfaces, solar cells, and other electronic and optoelectronic applications. A process based on AACVD consists of a number of steps: aerosol generation, aerosol transport, aerosol delivery, and chemical deposition. Predicting the behavior of such a process at an industrial scale is challenging due to a number of factors: the aerosol generation creates droplets of different sizes, losses are incurred in the transport, the delivery must evaporate the solvent to release the precursors, and the reactions on the surface of the deposition target may be complex. This paper describes a full process model, including the prediction of the size distribution of the generated aerosol, the number and size of droplets delivered, the carrier gas temperature profile at the reaction site, the solvent evaporation time, and the rate of film formation. The key modeling challenges addressed include incorporating the impact of uncertainties in parameters such as heat and mass transfer coefficients and reaction rate constants. Preliminary simulations demonstrate a proof of concept for the use of simulation for gaining insights into the feasibility of a process scale-up for an industrial-scale AACVD.

Optically tuned and large-grained bromine doped CH3NH3PbI3 perovskite thin films via aerosol-assisted chemical vapour deposition

Herein, doping of methylammonium lead iodide perovskite thin films with bromine ions is successfully performed for the first time using the aerosol-assisted chemical vapour deposition process. Depending on the doping levels, photoluminescence spectra are shifted relative to their bandgap values. Detailed analysis of scanning electron microscope images showed that increasing the bromine levels linearly increased the grain sizes. The unchanged amount of detected lead provided evidence for the controlled processing conditions. Both bulk and surface compositional techniques confirmed the deposition of marginally iodine rich perovskite thin films.

Aerosol-assisted chemical vapor deposition of V2O5 cathodes with high rate capabilities for magnesium-ion batteries

The growth of orthorhombic vanadium pentoxide nanostructures was accomplished using an aerosol-assisted chemical vapor deposition process. These materials showed excellent electrochemical performance for magnesium-ion storage in an aqueous electrolyte; showing specific discharge capacities of up to 427 mAh g−1 with a capacity retention of 82% after 2000 scans under a high specific current of 5.9 A g−1. The high rate capability suggested good structural stability and high reversibility. We believe the development of low-cost and large-area coating methods, such as the technique used herein, will be essential for the upscalable fabrication of next-generation rechargeable battery technologies.

High-frequency supercapacitors based on doped carbon nanostructures

Carbon nanostructures are promising materials for electrochemical energy storage but their frequency response is usually poor, limiting their utilization in high-frequency applications. Here we demonstrate the growth of carbon nanostructures with different dopants of N, B, P/N, B/N, and Si, based on a scalable aerosol-assisted chemical vapor deposition process. The doped carbon nanostructures were directly grown on the conductive Ni substrates and exhibit an open and porous structure which is beneficial for fast ion transport and ion kinetics. Coin cells made of the doped carbon nanostructures demonstrate a frequency response as fast as 13,200 Hz at a phase angle of −45° and the smallest relaxation time constant of ∼77 μs. Together with a low equivalent series resistance and a large areal capacitance, the high-frequency supercapacitors based on doped carbon nanostructures could be promising in replacing traditional aluminium electrolytic capacitors for many high-frequency electronic devices.

Effect of the AACVD based synthesis atmosphere on the structural properties of multi-walled carbon nanotubes

The synthesis of multi-walled carbon nanotubes (MWCNTS) has been the focus of considerable research effort for more than twenty-five years and it continues to receive increasing attention because of its importance to produce carbon nanotubes with suitable parameters for future applications. To the best of our knowledge this study presents for the first time the complex studies concerning the effect of aerosol-assisted chemical vapour deposition (AACVD) process conditions (including temperature (750–1200°C) and the composition of the carrier gas (N2, Ar, He, 5% H2-95% Ar, 3% H2O-97% Ar)) on the conversion of the carbon source and on the properties of the carbon nanotubes. In addition, it was also found that oxidative or reductive atmosphere applied during the AACVD process have a great impact on the quality and the degree of toluene conversion into the carbon solids obtained during the synthesis. X-ray Diffraction (XRD), Specific Surface Area and Porosity analysis (BET), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Transmission Electron Microscopy (TEM), Raman spectroscopy and Thermo-gravimetric Analysis (TG) were used to characterize the carbon nanotubes.

High Performance Anode-Supported Solid Oxide Fuel Cells with Thin Film Yttria-Stabilized Zirconia Membrane Prepared by Aerosol-Assisted Chemical Vapor Deposition

In this study, we have successfully fabricated yttria-stabilized zirconia (YSZ) electrolyte thin films by aerosol-assisted chemical vapor deposition (AACVD) for solid oxide fuel cells (SOFCs) working at an intermediate temperature range under 600°C. The mix ratio of precursor sources and the deposition temperature of the AACVD process are optimized to obtain target composition and crystal structure of the YSZ film. The optimized AACVD YSZ membrane is incorporated onto Ni-YSZ anodes supported without interlayers for evaluation of SOFC performance. Fully dense 1-μm-thick AACVD YSZ electrolyte successfully produces a stable open circuit voltage (OCV) greater than 1 V at all test temperatures in the range of 450–600°C. Power output of the test cell is measured as about 600 mW cm−2 at 600°C. Performance of our cell is compared to that of a reference cell with the same structure but with an 8-μm-thick membrane produced by screen-printing; our cell produces 1.4 to 4 times as much power as the reference cell at all test temperatures. Electrochemical impedance analysis has confirmed that the power enhancement with the thin AACVD YSZ membrane is due to effective reduction of both ohmic and polarization resistances.

Growth rate induced high efficient light trapping/photon conversion ZnO:Nd3+ nanodisk shaped thin films deposited by AACVD process

This research work is a detailed study of the effect of deposition conditions on the combined light trapping and photon conversion properties of Nd3+ ions doped ZnO nanodisk thin films. Hexagonal wurtzite phased ZnO:Nd films were deposited at the temperature range of [370–500 °C] by aerosol assisted chemical vapor deposition (AACVD) process at atmospheric pressure. Actually, annealing treatment at 1000 °C in air atmosphere led to the increase of crystallinity, decrease of the porosity of the films and enhancement of their optical properties. Moreover, this work has demonstrated that annealing strongly modifies the local structure and the crystal field of the Nd3+ ions embedded in ZnO, leading to a high efficiency of visible-to-infrared downconversion (DC) emissions. The optimized 2.805 at.% Nd embedded in ZnO shaped nanodisk thin film exhibits a strong and resolved 920 and 1060 nm DC emissions. In addition, this film presents a low reflectance percentage of 17.1% with average external quantum efficiency (EQE) of 51.0% in the [400–800 nm] range, leading to an improvement of quantum efficiency of 12.5%. These findings show that the combined photon conversion and light trapping properties in semiconducting ZnO:Nd nanodisk shaped thin film is a well known passive approach that can boost c-Si solar cells efficiency.

Antireflection and downconversion response of Nd3+ doped Y2O3/Si thin film deposited by AACVD process

Nd3+:Y2O3 nanograins-like structure films with various Nd concentrations, were deposited on Si (100) substrates by aerosol assisted chemical vapor deposition (AACVD) process. The intense 900nm emission of Nd3+ corresponding to the 4F3/2→4I9/2 transition was investigated as a function of the annealing temperature. The reflectance percentage of the optimized 5mol.% Nd:Y2O3 film was recorded at about 16% in 400–1000nm range. The refractive index (n=1.94) and the low porosity (P=2.74%) showed the high transparency of this film. The obtained results demonstrate that this film can enhance the Si solar cell efficiency by light trapping and spectrum shifting.

The role of hydrogen in the aerosol-assisted chemical vapor deposition process in producing thin and densely packed vertically aligned carbon nanotubes

Aerosol-assisted catalytic chemical vapor deposition (CCVD) is an efficient single-step process to synthesize vertically aligned carbon nanotube (VACNT) arrays from ferrocene and toluene precursors. While no promoters are needed, adding hydrogen to the carrier gas assists the process. In order to understand the role of hydrogen, we performed syntheses at 850 and 800°C. The product distribution along the length of the reactor was analyzed by electron microscopy to follow the effect of the hydrogen, as well as the characteristics of the CNT and catalyst nanoparticles. Increasing the hydrogen content shifts the CNT growth towards the furnace entrance and strongly reduces the CNT diameters, while the CNT number density increases. Hydrogen demonstrably affects the gas phase phenomena by lowering the decomposition temperature of ferrocene and increasing the nucleation site density of the catalytic nanoparticles. The yield under hydrogen remains reasonable in the aerosol-assisted CCVD process, and is even improved at 800°C. Hydrogen content appears to be an interesting parameter to control the characteristics of vertically aligned CNT.

Aerosol-Assisted CVD of SnO<sub>2</sub> Thin Films for the Room-Temperature Detection of Hydrogen Sulfide

High-quality SnO2 thin-film materials capable of detecting H2S gas of low concentrations at room temperature was demonstrated in this paper. We employed aerosol-assisted chemical vapor deposition process for the deposition of SnO2 thin films on alumina substrates with pre-patterned electrodes. The gas-sensing performances of the films prepared under different deposition conditions were systematically compared and analyzed. When SnCl2·2H2O was used as the precursor, a response sensitivity of 98.4 toward 50 ppm of H2S at room temperature was achieved. At room temperatures, the resistance upon the H2S gas exposure could recover to 90% of the initial resistance of the sensor when the H2S gas flow was turned off.

Nanocomposite Coatings Codeposited with Nanoparticles Using Aerosol-Assisted Chemical Vapour Deposition

Incorporating nanoscale materials into suitable matrices is an effective route to produce nanocomposites with unique properties for practical applications. Due to the flexibility in precursor atomization and delivery, aerosol-assisted chemical vapour deposition (AACVD) process is a promising way to synthesize desired nanocomposite coatings incorporating with preformed nanoscale materials. The presence of nanoscale materials in AACVD process would significantly influence deposition mechanism and thus affect microstructure and properties of the nanocomposites. In the present work, inorganic fullerene-like tungsten disulfide (IF-WS2) has been codeposited with Cr2O3coatings using AACVD. In order to understand the codeposition process for the nanocomposite coatings, chemical reactions of the precursor and the deposition mechanism have been studied. The correlation between microstructure of the nanocomposite coatings and the codeposition mechanism in the AACVD process has been investigated. The heterogeneous reaction on the surface of IF-WS2nanoparticles, before reaching the substrate surface, is the key feature of the codeposition in the AACVD process. The agglomeration of nanoparticles in the nanocomposite coatings is also discussed.

The incorporation of preformed metal nanoparticles in zinc oxide thin films using aerosol assisted chemical vapour deposition

The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 °C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400–450 °C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented.

Processing and Characterization of Nanocomposite Coatings using Aerosol-assisted Chemical Vapor Deposition (AACVD) Method

This paper presents the use of a variant of the CVD process called aerosol-assisted chemical vapor deposition (AACVD) for the fabrication of nanocomposite coatings. AACVD involves the generation and delivery of aerosol precursors to the deposition region. The flexibility of atomizing precursor solution or suspension in the AACVD process makes it possible for the incorporation of pre-formed nanoparticles in the precursor solution and to co-deposit the particles and matrix concurrently on the substrate surface to form the desired nanocomposite coatings. Our recent results have demonstrated that AACVD is a promising method for the synthesis of nanocomposite coatings with the incorporation of nanoparticles into ceramic matrices. The synthesis of inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles, as well as the processing and deposition mechanism of IF-WS2/Cr2O3 will be presented. The microstructure and properties of IF-WS2 and IF-WS2/Cr2O3 will also be highlighted.