Electrochemical Vapor Deposition Research Articles

In situ electrolyte replenishment with atmospheric pressure-chemical/electrochemical vapour deposition for molten carbonate fuel cells

Molten carbonate fuel cells (MCFCs) offer several advantages in energy applications, but their lifetime is limited especially by electrolyte depletion. In this study, a novel in situ method for replenishing the electrolyte in MCFCs by injecting gaseous electrolyte precursors (EP) that form liquid electrolyte through reactions with CO2/O2 gases or CO32- ions is introduced. The selection of EP species (LiI, NaI, and KOH) are guided by thermodynamic considerations including high vapour pressures and conversion rates to Li/K or Li/Na carbonates. The proposed approach addresses two electrolytic depletion stages: consumption of the electrolyte in the electrode (Stage 1) and in the matrix pores (Stage 2). Atmospheric-pressure electrochemical vapour deposition (AP-EVD) and atmospheric-pressure chemical vapour deposition (AP-CVD) are demonstrated to replenish electrolyte in the electrode and matrix pores, respectively. The applied techniques sustained a cell with a low (Li/Na)2CO3 electrolyte level for long-term operation (>1,000 h) while maintaining stable performance (>0.8 V at 150 mA cm−2). The method also returned an inactive cell to its normal operating conditions (OCV: 1.054 V, RΩ: 0.61 Ω cm2, (Li/K)2CO3 electrolyte). These results promise enhanced durability of MCFCs and render them much more viable for use in energy applications.

Electrochemical vapor deposition of semiconductors from gas phase with a solid membrane cell.

We demonstrate the feasibility of semiconductor deposition via the electrochemical reduction of gaseous precursors by the use of an anhydrous proton-conducting membrane, the solid acid CsHSO4, at 165 °C. This membrane electrode assembly was operated within the oxidation of hydrogen on a porous Pt anode and the deposition of Si or Ge under bias at the cathode from chloride-based gaseous precursors; SiCl4 and GeCl4 in an Ar flow with a reduction potential over -1.0 V (vs RHE).

Analyses of reinforcing effects of in situ grown CNTs on carbon fibre fabric/epoxy composites at micro- and macroscale

Carbon nanotubes (CNTs) have been in situ grown on the surface of carbon fibre fabric (CFF) by electrochemical oxidation, urea hydrolysis and chemical vapour deposition process. The reinforcing efficiency of the in situ grown CNTs (I-CNTs) was analysed at micro- and macroscale by atomic force microscopy (AFM), single fibre pull out tests and mechanical properties of I-CNTs reinforced CFF/epoxy composites. AFM analyses indicated that the bonding strength between a single piece of I-CNTs and carbon fibre (CF) was ∼50–700 nN, which was much higher than that between CF and CNTs on the surface of CF adsorbed in CNTs suspension. Further investigation of single fibre pull out tests showed that the interfacial bonding strength between CF with I-CNTs and epoxy resin was 39% higher than that between pristine CF and epoxy resin. Correspondingly, the bending strength and interlaminar shear strength of I-CNTs/CFF/epoxy were 26 and 52% higher than those without reinforcement of I-CNTs. The significant improvement could be ascribed to the high strength of uniformly dispersed I-CNTs themselves, high bonding force between I-CNTs and CF, and improved interfacial bonding strength between the reinforcers and matrix.

Template Synthesis and Growth Mechanism of Metal Nanowire/Carbon Nanotube Heterojunctions

Copper (Cu) and Cobalt (Co) with remarkable difference in the catalytic activity for the growth of carbon nanotubes (CNTs) have been used to prepare metal-nanowire/CNT heterojunctions. The ordered arrays of Cu nanowire/CNT (CuNW/CNT) and Co nanowire/CNT (CoNW/CNT) heterojunctions were prepared by combining electrochemical deposition and chemical vapor deposition. The interfaces between CNTs and Cu or Co nanowires have been examined and compared. At the interface of CuNW/CNT heterojunction, the tip of CuNW is encapsulated by carbon material (named "cap") and connected the CNT consisting of amorphous carbon (a-C). Two-segment CuNW/amorphous CNT (CuNW/a-CNT) hybrid nanostructure was obtained for the CuNW/CNT heterojunctions due to low catalytic activity of Cu. It is also interesting that a hollow gap was observed between the "cap" and the CuNW. By contrast with the case of Cu, multi-walled CNT (MWCNT) was achieved and no hollow gap was observed at the interface of CoNW/CNT heterojunctions. Three-segment CoNW/MWCNT/a-CNT hybrid nanostructure was observed for the CoNW/CNT heterojunctions because of high catalytic activity of Co. Because no stable copper carbides are observed, we infer that the growth mechanism of CuNW/CNT heterojunctions is different from that of CoNW/CNT. Possible growth models of CuNW/CNT and CoNW/CNT heterojunctions are proposed based on experimental results, respectively.

ChemInform Abstract: Electrochemical Vapor Deposition of Stabilized Zirconia and Interconnection Materials for Solid Oxide Fuel Cells

Abstract Due to the high operating temperatures (900–1000°C) the material demands upon Solid Oxide Fuel Cell (SOFC) components are quite stringent. Preferably lower operating temperatures (700–800°C) are desired so that gas feed lines, heat exchanges, and structure components can be fabricated from relatively cheap stainless steel components. Typically, the materials used in a SOFC are yttria-stabilized zirconia (YSZ) as the solid electrolyte, nickel-zirconia cermet as the anode, strontium-doped lanthanum manganite as the cathode, and magnesium-doped lanthanum chromite as the interconnection material. The electrolyte and interconnect are difficult to fabricate,, because they need to be gas tight, yet thin (30–50 microns) and mechanically stable. Due to the high volatility of CrO 3 the densfication of LaCrO 3 into thin layers is a more demanding challenge than the fabrication of the electrolyte. Electrochemical Vapor Deposition is the key technology for making thin layers of the solid electrolyte as well as the interconnection material LaCrO 3 . In the simplest case the oxide growth can be modeled with the Wagner oxidation theory for metals. In this paper theory and experiment of the growth of ionically conducting YSZ and electronically conducting LaCrO 3 will be discussed.

N-SiCN/P-Silicon Heterojunction With Porous Silicon Buffer Layer for Low-Cost and High-Temperature Ultraviolet (UV) Detecting Applications

In this paper, we study of n-SiCN/p-PS/p-silicon heterojunction with porous silicon (PS) buffer layer for low-cost and high-temperature ultraviolet (UV) detecting applications in details. The electrochemical anodization and rapid thermal chemical vapor deposition were applied sequentially to form the PS layer and the cubic crystalline n-SiCN film on the top of p-(100) silicon substrate. The PS layer has a high resistivity to suppress the dark current, and provides sponge-like structure to limit strain and cracks development after the post growth cooling. Thus, favors nucleation to result in a better single-crystal SiCN film. Consequently, the developed optical sensing device has a high photo/dark current ratio of 85.4 under room temperature (25degC), with and without irradiation of and 254 nm UV light with 0.5 mW/cm2 optical power. At 200degC the ratio is still equal to 7.42, which are better than the reported ZnO on GaAs substrate or beta-SiC on Si substrate UV detectors without porous treatment.

Growth mechanism of thin films of yttria-stabilized zirconia by chemical vapor infiltration using NiO–ceria substrate as oxygen source

The deposition of yttria-stabilized zirconia films on a NiO–ceria substrate by chemical vapor infiltration (CVI) using ZrCl 4 and YCl 3 as metal sources and NiO–ceria as oxygen source was studied. The resultant films were cubic YSZ with a Y 2O 3 content of 3.7–4.2 mol%, and were transparent and strong. A NiO content of NiO–ceria above 60 mol% increases the growth rate of the YSZ film from about 5 to 25 μm over 2 h, indicating that chemical vapor deposition (CVD) occurred in addition to electrochemical vapor deposition (EVD), whereas NiO contents below 60 mol% does not affect the growth rate, indicating that only electrochemical vapor deposition occurred. The growth mechanism of the YSZ film is determined and a YSZ thin film is successfully fabricated on NiO–ceria to improve mechanical strength.

Fabrication of hollow thin films of yttria-stabilized zirconia by chemical vapor infiltration using NiO as oxygen source

Deposition of yttria-stabilized zirconia films on surface oxidized Ni wire substrate by chemical vapor infiltration (CVI) using ZrCl 4 and YCl 3 as metal sources and NiO as oxygen source were studied. The resultant films were cubic crystals of YSZ with a Y 2O 3 content of 1.0–3.7 mol%. The growth rate is larger than that obtained by conventional method of chemical vapor deposition (CVD), increased with the flow rate and decreased with diameter of NiO fiber. The growth rate above its thickness of 4 μm decreased with an increase in the oxidation temperature since the porosity of NiO wire might decrease with an increase in the oxidation temperature. Growth of YSZ films with the CVI method simultaneously involved CVD and electrochemical vapor deposition (EVD).

Yttria-stabilized zirconia thin films deposited on NiO–(Sm 2O 3) 0.1(CeO 2) 0.8 substrates by chemical vapor infiltration

Fabrication of YSZ films deposited on NiO–samaria-doped ceria (SDC) substrate was studied by the chemical vapor infiltration method (CVI). A NiO–SDC substrate was used as oxygen source. The main mechanism of YSZ growth was electrochemical vapor deposition (EVD), while the contribution of oxygen in the carrier gas increased with increasing NiO content of the substrate above 60.6 mol%. The YSZ film on SDC used as the anode proved effective in obtaining high cell performance. In particular, a YSZ film thickness of 1 μm yielded the highest cell performance in the temperature range from 973 to 1073 K. The CVI method was useful for preparing a dense and strong YSZ film on the complex-shaped NiO–SDC substrate.

Vapor-Phase Deposition for Dense CeO2 Film Growth on Porous Substrates

Pure and Sm-doped thin films were deposited on porous substrates by vapor-phase deposition, which is similar to the well-known electrochemical vapor deposition (EVD). By supplying metal chlorides (, ; Ce and Sm) vapor and oxygen to a disk-shaped porous substrate from opposite directions, a dense oxide film was grown on the chloride side of the substrate with high homogeneity. The films deposited are suitable for the electrolytes in the ceria-based intermediate temperature solid oxide fuel cells (SOFCs). The growth kinetics of these films was also discussed along with an observed growth rate and theoretical analysis based on oxygen flux and oxygen potential gradient over the film and the substrate. It was found that the film growth was governed by rates of each competitive process: diffusion of oxygen molecules through substrate pores, oxygen reduction at the film/substrate interface, and transport of electrochemical species ( and ) through the growing dense film.

Effect of Deposition Conditions on Pt‐YSZ Cermet Anodes Made by PEVD

AbstractYttria stabilized zirconia (YSZ) was deposited onto porous platinum networks by polarized electrochemical vapor deposition (PEVD) to make composite SOFC anodes. Although performance was poor, both before and after deposition, it was found to be better when high deposition temperatures were used, despite significant loss of electrode porosity during high temperature deposition. When the deposition temperature was lowered, from 1,050 °C to 900 °C, the level of porosity was maintained, but the power output was generally lower. Performance was partially recoverable by increasing the magnitude of the polarizing voltage during deposition. Typically, this led to an increase in deposition current, which in all cases exceeded the required amount for YSZ formation. By increasing the delivery rates of the source materials for yttria and zirconia, the amount of deposit formed could be increased, but excess oxygen at the anode prevented the formation of a continuous layer, in most cases.

Fabrication of composite SOFC anodes using polarized electrochemical vapor deposition

Polarized electrochemical vapor deposition (PEVD) was used to fabricate composite anodes for solid oxide fuel cells (SOFCs) containing nearly 100% metal by coating a porous metallic anode. Densification of the metallic electrode during deposition is a problem; however, densification can be slowed by lowering the deposition temperature. Once in place the film, which appears to be cubic YSZ, offers many potential advantages, including acting as a protective barrier, allowing operation of the cell at higher temperatures and on fuels with higher impurity contents.

Fabrication of composite SOFC anodes

Polarized electrochemical vapour deposition (PEVD) was used to fabricate composite anodes for solid oxide fuel cells (SOFCs) containing nearly 100% metal by coating a porous metallic anode. Densification of the metallic electrode during deposition is a problem; however, densification can be slowed by lowering the deposition temperature. Once in place the film, which appears to be cubic YSZ, offers many potential advantages including acting as a protective barrier allowing operation of the cell at higher temperatures and on fuels with higher impurity contents.

Preparation of dense electrolyte layer using dissociated oxygen electrochemical vapor deposition technique

A dense layer of yttria-stabilized zirconia (YSZ) was deposited on a porous substrate by a modified type of electrochemical vapor deposition (EVD) technique, making use of dissociated oxygen from nickel oxide in the porous substrate as an oxygen source for the reaction. As the oxygen-supplying substrates, NiO–ceria porous pellets containing some depressions on the deposited face were used to fabricate modified planar-type SOFC based on the rough anode of Ni–ceria. The dissociated oxygen electrochemical vapor deposition (DOEVD) technique was very suitable for fabrication of this type of cell.

Fabrication of Dense Zirconia Electrolyte Films for Tubular Solid Oxide Fuel Cells by Electrophoretic Deposition

Electrophoretic deposition (EPD) is used to produce zirconia electrolyte films for tubular solid oxide fuel cells. A simple suspension chemistry (8‐mol%‐yttria‐stabilized zirconia particles in acetic acid) yields films of similar quality to those from conventional approaches (such as electrochemical vapor deposition), but at potentially much less expense. A key factor in obtaining high‐density, adherent films via the EPD approach is the application of a thin fugitive phase (carbon in this study) on the porous, doped lanthanum manganite cathode tubes prior to zirconia deposition.

Applying polarized electrochemical vapor deposition (PEVD) to solid state ionic devices

A new vapor deposition process, polarized electrochemical vapor deposition (PEVD), has been developed recently. The significance of PEVD is that it applies solid state ionic techniques to modify the widely accepted CVD technique under well-controlled conditions in a solid electrochemical cell. This provides PEVD with easy process control and unique electrocrystallization behavior. Consequently, it holds promise for a wide range of potential applications for solid state ionic devices. Investigations show that PEVD is the most suitable technique to improve solid electrolyte/electrode contact and, subsequently, the performance of solid state ionic devices. In this paper, current applications of PEVD for potentiometric gaseous oxide sensors and solid oxide fuel cells is discussed.

Polarized electrochemical vapor deposition for cermet anodes in solid oxide fuel cells

A new process originally developed for sensors shows promise for coating porous nickel substrates with a layer of yttria stabilized zirconia (YSZ) for cermet anodes in solid oxide fuel cells (SOFCs). Traditionally, the cermets are deposited using randomly interspersed nickel and stabilized zirconia powders. However, the conducting nickel is a mostly discontinuous phase and thus the conductivity is impeded. With this new polarized electrochemical vapor deposition (PEVD) technique, the deposition of a uniform layer of YSZ was demonstrated using a platinum substrate, which had previously been sintered to a continuous layer over the fuel cell electrolyte. Films deposited over a 24 h period with a −0.300 V applied potential were on average 1–3 μm thick. After 5 days, the film becomes fully dense with few large blocked pores. Preliminary EDX testing indicates that the amount of deposition product decreases away from the substrate, indicating that deposition and film growth commence at the triple phase boundary.

Cyclic Voltammetric Study of a Polarized Electrochemical Vapor Deposition Process

The recently developed polarized electrochemical vapor deposition (PEVD) is a process which actively uses mass and charge transport within Wagner's electrochemical tarnishing theory for product formation. Since the migration of charged ionic and electronic carriers during PEVD is a kinetic process, it is imperative to solve the PEVD reaction rate‐limiting steps for samples undergoing both stage I and II growth. The PEVD process for auxiliary phase deposition at the working electrode of a potentiometric sensor was selected for the current solid electrolyte cyclic voltammetry studies. The results from this investigation not only confirm the previous steady‐state potentiostatic studies for samples undergoing stage II growth, but also reveal qualitatively the kinetics of the PEVD reaction and subsequent product formation in a PEVD system during stage I growth. At lower temperatures and working electrode overpotentials, the PEVD reaction rate‐limiting step is the charge transfer reaction. At higher temperatures and lower working electrode overpotentials, the rate‐limiting step is the diffusion of across the product. At higher working electrode overpotentials for all temperatures, the rate‐limiting step is the surface diffusion of neutral reactants. © 2000 The Electrochemical Society. All rights reserved.

Electrochemical Study of a Polarized Electrochemical Vapor Deposition Process

The interfacing of modern vapor deposition technology and solid‐state ionic technology has led to the recent development of polarized electrochemical vapor deposition (PEVD). Due to the unique electrocrystallization behavior of its products and easy process control through a solid electrochemical cell, PEVD holds promise for a wide range of potential applications. However, the migration of charged ionic and electronic carriers during PEVD is a kinetic process. The task related to studying PEVD working electrode kinetics in this investigation is to explain the sequence of partial reactions constituting the overall PEVD electrochemical reaction for product formation at the working electrode. The PEVD process for auxiliary phase deposition at the working electrode of a potentiometric sensor was selected for the current electrochemical studies. The dependence of current density, or of reaction rate, upon various working electrode overpotentials and temperatures (500–550°C) was studied by a steady‐state potentiostatic method. The PEVD reaction rate‐limiting steps are solved for samples undergoing second‐stage growth. The results from this investigation help in understanding the kinetics of the PEVD reaction and subsequent product formation in a PEVD system, improve knowledge of PEVD kinetics, and elucidate the possibility of further process control in PEVD. © 2000 The Electrochemical Society. All rights reserved.

A New Vapor Deposition Method to Form Composite Anodes for Solid Oxide Fuel Cells

A solid oxide fuel cell (SOFC) is a complete solid‐state energy conversion device with the potential advantages of high efficiency, silent operation, and low emissions. However, the current performance of SOFCs is still limited by a number of problems. Investigations in this field have indicated that it is imperative to fabricate efficient and compatible anodes for SOFCs to minimize polarization loss and to concurrently achieve long‐term stability. In this paper, a critical review of previous studies is given and several criteria for the theoretically ideal anode are summarized. Accordingly, a newly developed vapor deposition technique, polarized electrochemical vapor deposition (PEVD), is applied to fabricate composite anodes to meet these criteria. The initial experimental results in the present study show that PEVD is capable of depositing a thin layer of yttria‐stabilized zirconia on a porous metallic electrode to form a composite anode. This will not only provide continuous ionic and electronic conducting paths in the anode to reduce the overpotential loss and resistance, but also protect the metallic electrode from further sintering, vapor loss, and poisoning in the harsh SOFC operating conditions.