Cermet Substrates Research Articles

Anode Supported Protonic Solid Oxide Fuel Cells Fabricated Using Electrophoretic Deposition

AbstractIntermediate temperature solid oxide fuel cells (IT‐SOFCs) were fabricated depositing proton conducting BaCe0.9Y0.1O3–x (BCY10) thick films on cermet substrates made of nickel oxide–yttrium doped barium cerate (NiO–BCY10) using electrophoretic deposition (EPD) technique. The influence of the EPD parameters on the microstructure and electrical properties of BCY10 thick films was investigated. Deposited BCY10 thick films together with green anode substrates were co‐sintered in a single heating treatment at 1,550 °C for 2 h to obtain dense electrolyte and suitably porous anodes. The half‐cells were characterised by field emission scanning electron microscopy (FE‐SEM) and by X‐ray diffraction (XRD) analysis. A composite cathode specifically developed for BCY electrolytes, made of La0.8Sr0.2Co0.8Fe0.2O3(LSCF, mixed oxygen‐ion/electronic conductor) and BaCe0.9Yb0.1O3–δ (10YbBC, mixed protonic/electronic conductor), was used. Fuel cells were prepared by slurry coating the composite cathode on the co‐sintered half‐cells. Fuel cell tests and electrochemical impedance spectroscopy (EIS) were performed in the 550–700 °C temperature range. A maximum power density of 296 mW cm–2 was achieved at 700 °C for electrolyte deposited at 60 V for 1 min.

Laser chemical vapor deposition of TiN film on Ti(C,N)-based cermet substrate using Ti(OiPr)2(dpm)2-NH3 system

TiN films were prepared on Ti(C,N)-based cermet substrate by laser chemical vapor deposition using titanium isopropoxide dipivaloylmethane [Ti(OiPr)2(dpm)2] and ammonia (NH3) as precursors. The effects of deposition temperature (Tdep) and laser power (PL) on the crystal phase, microstructure and adhesion were investigated. TiN film was prepared at Tdep > 903 K (PL > 100 W). The microstructure of TiN film changed from rose-like grains to pyramid-like grains to aggregate grains with increasing PL and Tdep. Highly adhesive film was obtained at moderate Tdep = 1047 K (PL = 120 W).

Deposition of .ALPHA.-Al2O3 films on Ti(C, N)-based cermet substrate by laser chemical vapor deposition using a diode laser

α-Al2O3 film was first deposited on Ti(C, N)-based cermet substrate by laser chemical vapor deposition (LCVD) in a CO2–H2 atmosphere. The effects of atmosphere, laser power (PL), total pressure (Ptot) and deposition temperature (Tdep) on the crystal phase and microstructure were investigated. α- and γ-phase mixture film was prepared at Tdep = 833 K. Single phase α-Al2O3 film was obtained at Tdep = 903 K. The surface morphology of α-Al2O3 film changed from a cauliflower-like to a granular-like structure with increasing Tdep and decreasing Ptot. α-Al2O3 film with a well-developed facet structure was obtained at Ptot = 0.6 kPa and Tdep = 933 K.

Low‐temperature operation of thin film solid oxide fuel cells prepared by RF magnetron sputtering

AbstractThin film solid oxygen fuel cells (SOFC) with yttria‐stabilized zirconia (YSZ) electrolyte films 3 to 12 μm thick, grown by RF magnetron sputtering on porous Ni‐YSZ cermet substrates for use as fuel electrodes, were studied to determine their power generation properties at lower operating temperatures in the vicinity of 700 °C. Single SOFCs with a YSZ electrolyte film thickness of 3 μm could be effectively operated at 800 °C and had a V–I performance measure of 700 mV–300 mA/cm2. The open circuit voltage (OCV) of the cells was nearly the same as the theoretical value. However, the OCV drop became larger as the thickness of the YSZ film was decreased, because grain boundaries and pores occurred in the film due to the surface roughness of the substrate. The voltage drop of the cells was due mainly to resistance loss in the YSZ film, and the dominance of this factor increased as the operating temperature decreased. The film conductivity at an operating temperature of 800 °C was two orders of magnitude smaller than the theoretical conductivity of the bulk electrolyte. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 50–57, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10047

La9.33Si6O26 electrolyte thin films for IT-SOFC application deposited by a HIPIMS/DC hybrid magnetron sputtering process

Apatite-type La9.33Si6O26 thin films were elaborated by co-sputtering of two metallic La and Si targets powered, respectively, by high power impulse magnetron sputtering and direct current sources, in pure Ar atmosphere, followed by a subsequent high temperature oxidation treatment in air. The structural and chemical features of these films have been assessed by X-ray diffraction and scanning electron microscopy (SEM). The film with near lanthanum silicate La/Si atomic ratio deposited on a porous Ni-YSZ cermet substrates was initially amorphous. After thermal oxidation at 1,173 K in air, the coating crystallised under the expected apatite structure. SEM observation revealed that both film compactness and thickness increased after thermal oxidation. The conductivity evolution with temperature of the pure apatite-like lanthanum silicate coatings, as measured by complex impedance spectroscopy, showed that the activation energy of is quite low compared to the literature data.

Laser drilling of Ni–YSZ cermets

Pulsed Nd:YAG laser was used for efficient drilling of cylindrical hole patterns in porous Ni–YSZ cermet plates. Green NiO–YSZ oxide ceramic substrates obtained via tape casting technique were machined using 8–80 ns pulses at the fixed wavelength of 1064 nm. The etched volume, drill diameter, shape and depth were evaluated as a function of the processing parameters such as pulse irradiance and pulse number. The laser machining mechanism was discussed by means of laser–material interaction parameters such as beam absorptivity and plasma formation and the impact to the overall process discussed. Holes with uniform diameter from 30 to 110 μm and up to 1 mm depth were drilled with a high efficiency of up to 0.1 mm 3 per pulse. Green state machining showed significant efficiency whereas the properties of the cermet substrate were kept unchanged.

SOFC Based on Proton Conductors

We have fabricated a solid oxide fuel cell (SOFC) using BaCe0.8Y0.2Ox (BCY20) proton conductor as the electrolyte. An ≈10-μm-thick dense BCY film was prepared on a porous Ni/BCY cermet (i.e., ceramic/metal composite) substrate by a dip coating process. The gas-permeable Ni/BCY cermet substrate backed with nickel mesh was used as the anode, and a platinum paste backed with platinum mesh served as the cathode. The current-voltage characteristics of the BCY-based SOFC were measured in the temperature range 450-800{degree sign}C using wet air on the cathode side and hydrogen on the anode side. The power density of the fuel cell was ≈90 and ≈1500 mW/cm2 at 450 and 800{degree sign}C, respectively.

Fabrication and Characterization of Cermet Supported Cell with SDC Electrolyte

Cermet supported cells with Sm0.2Ce0.8O1.9 (SDC) electrolyte have been developed and scaled up to 55mm x 55mm at NRC-IFCI. A solid oxide fuel cell with SDC electrolyte of 10µm in thickness and Ni-SDC anode of 15µm in thickness on a 0.8mm thick Ni-YSZ cermet substrate was fabricated by tape casting, screen printing, and co-firing. A composite cathode, 75 wt% Sm0.5Sr0.5CoO3 (SSCo) + 25 wt% SDC, approximately 50µm in thickness, was printed on the co-fired half-cell, and sintered at 1000{degree sign}C. The cell with effective cathode area of 16 cm2 showed a high electrochemical performance at 600{degree sign}C, and peak power density of 0.9W cm-2 was obtained with hydrogen fuel.

Growth rate, microstructure and conformality as a function of vapor exposure for zirconia thin films by pulsed-pressure MOCVD

Thin solid films of zirconia were deposited on solid and porous substrates over a range of deposition conditions by the pulsed-pressure metalorganic chemical vapor deposition (PP-MOCVD) process. The PP-MOCVD process uses timed injections of a liquid precursor solution through an ultrasonic atomizer into a continuously evacuated reactor. Process variables include solution injection volume, reactor volume, base pressure, peak pressure, and precursor concentration. Solid nickel, co-sintered nickel cermet and [100] P-type silicon were investigated as substrates for a range of deposition conditions. The exposure of the substrate to the precursor vapor was defined using a non-dimensional parameter combining the process parameters other than temperature. Deposits were examined by SEM and XRD. Results showed that PP-MOCVD produces a smooth, thin film that follows substrate contours. High exposure rate results in a higher growth rate, and a thicker film with columnar microstructure that bridges most pores in the porous nickel cermet substrates. The nickel cermet samples were prepared as electrode materials for solid oxide fuel cells (SOFC's). For the first time we demonstrate that arrival rate has a minimal effect on morphology and texture compared to deposition temperature.

Ceramic Technologies for Anode-Supported Solid Oxide Fuel Cells

One of the most promising technologies for future applications of solide oxide fuel cells (SOFC)is the so-called “anode-supported” configuration: a dense yttria-stabilised zirconia (YSZ) ceramic electrolyte is deposited as a thin film over a porous Ni / YSZ cermet substrate anode, followed by a porous ceramic cathode such as La1-xSrxMnO3 (LSM). In this paper, a short review is made of the current technologies available to achieve this particular architecture, and to optimise the service behaviour. Then, alternative materials and fabrication technologies, as well as their possible impact on performance, are proposed and investigated.

Preparation of a Porous Cermet SOFC Anode Substrate by Gelcasting of NiO–YSZ Powders

A porous NiO–YSZ substrate for anode‐supported solid oxide fuel cells has been prepared by gelcasting of NiO–YSZ powders using urea–formaldehyde monomers, followed by humidity‐controlled drying, binder removal, and sintering of the gelled bodies. The gelled bodies had sufficient strength to remove even 2‐mm‐thick samples from the mold immediately after gelation. A gelcast NiO–YSZ sample sintered at 1450°C for 2 h showed an open porosity of ∼53 vol%, and the porosity increased to ∼58% upon reduction with hydrogen. Pore sizes measured on the scanning electron microscopy photomicrograph of NiO–YSZ and Ni–YSZ cermet substrates are in the range of 2–5 μm. Urea–formaldehyde polymer, present in a high amount (∼13 wt%) in the gelcast body, acts as a template for pores.

A Low Operating Temperature Property of Thin Film Solid Oxide Fuel Cell Prepared by RF Sputtering

Solid oxygen fuel cell (SOFC) having yttria-stabilized zirconia (YSZ) electrolyte film thickness of 12-3μm, which was grown on the Ni-YSZ cermet substrate using as the fuel electrode by RF magnetron sputtering, has been studied on the operating property until lower temperature of 700°C. A single SOFC having YSZ electrolyte film thickness of 3μm could be well operated at 800°C and that could performed the V-I property of 700mV-300mA/cm2 indicating the development index of the cell. The open circuit voltage (OCV) of the cell gave nearly the same value as the theoretical electromotive force. However, the OCV drop became larger as making thin YSZ film, because the grain boundary and pore were caused in the film in consequence of a surface roughness on the substrate. The voltage drop of the cell was mainly occupied by the resistance loss in YSZ film and its percentage increased as the operating temperature decreased. Moreover, the film conductivity at the operating temperature of 800°C became smaller by two figures than the theoretical conductivity of the bulk electrolyte.

高周波スパッタリング法を用いて作製した薄膜固体酸化物型燃料電池のスタック特性

Stack characteristic of solid oxide fuel cell (SOFC) having yttria-stabilized zirconia (YSZ) electrolyte film has been studied on the operating property until lower temperature of 770°C. The YSZ electrolyte film was grown on the Ni-YSZ cermet substrate using as fuel electrode by the RF magnetron sputtering, Terminal voltage of a single cell decreased as lowering the operating temperature. In two parallel cells, the cell resistance reduced to half value and the load current became larger, as compared with the property of a single cell. As a result, it was confirmed that the compact cell stack of thin SOFC improved well the power generation characteristic at middle operating temperature of 770°C.

Internal shorting and fuel loss of a low temperature solid oxide fuel cell with SDC electrolyte

Abstract A solid oxide fuel cell with Sm0.2Ce0.8O1.9 (SDC) electrolyte of 10 μm in thickness and Ni–SDC anode of 15 μm in thickness on a 0.8 mm thick Ni–YSZ cermet substrate was fabricated by tape casting, screen printing and co-firing. A composite cathode, 75 wt.% Sm0.5Sr0.5CoO3 (SSCo) + 25 wt.% SDC, approximately 50 μm in thickness, was printed on the co-fired half-cell, and sintered at 950 °C. The cell showed a high electrochemical performance at temperatures ranging from 500 to 650 °C. Peak power density of 545 mW cm−2 at 600 °C was obtained. However, the cell exhibited severe internal shorting due to the mixed conductivity of the SDC electrolyte. Both the amount of water collected from the anode outlet and the open circuit voltage (OCV) indicated that the internal shorting current could reach 0.85 A cm−2 or more at 600 °C. Zr content inclusions were found at the surface and in the cross-section of the SDC electrolyte, which could be one of the reasons for reduced OCV and oxygen ionic conductivity. Fuel loss due to internal shorting of the thin SDC electrolyte cell becomes a significant concern when it is used in applications requiring high fuel utilization and electrical efficiency.

Development of intermediate temperature SOFC using LaGaO3based oxide film

The effect of the NiO–Fe3O4 (NiFeO)/Ce0·8Sm0·2O2-δ (SDC) ratio on the microstructure and electrochemical activity of cermet substrates was systematically investigated. Dense NiFeO–SDC substrates, which are suitable for the deposition of thin oxide films for example, La0·9Sr0·1Ga0·8Mg0·2O3-δ (LSGM) tend to be porous and applicable as anodes in intermediate temperature solid oxide fuel cells (IT SOFC). The porosity and electrical conductivity of the reduced substrates were evaluated with increasing NiFeO ratios. The lowest anode overpotential was measured in a substrate with a NiFeO/SDC ratio of 6:4, especially at a high current density. In a reduced substrate with this composition, continuous frames of SDC and NiFe alloy can be formed simultaneously, thus leading a longer triple phase boundary.

NiO–YSZ cermets supported low temperature solid oxide fuel cells

Solid oxide fuel cells with thin electrolyte of two types, Sm 0.2Ce 0.8O 1.9 (SDC) (15 μm) single-layer and 8 mol% Yttria stabilized zirconia (YSZ) (5 μm) + SDC (15 μm) bi-layer on NiO–YSZ cermet substrates were fabricated by screen printing and co-firing. A Sm 0.5Sr 0.5CoO 3 cathode was printed, and in situ sintered during a cell performance test. The SDC single-layer electrolyte cell showed high electrochemical performance at low temperature, with a 1180 mW cm −2 peak power density at 650 °C. The YSZ + SDC bi-layer electrolyte cell generated 340 mW cm −2 peak power density at 650 °C, and showed good performance at 700–800 °C, with an open circuit voltage close to theoretical value. Many high Zr-content micro-islands were found on the SDC electrolyte surface prior to the cathode preparation. The influence of co-firing temperature and thin film preparation methods on the Zr-islands’ appearance was investigated.

Electrical properties of undoped bulk ZnO substrates

Undoped bulk ZnO crystals obtained from Tokyo Denpa show either resistive behavior [(5×104)−(3×105) Ohm cm) or low n-type conductivity (n ⋍1014 cm−3) with mobilities in the latter case of 130–150 cm2/V sec. The variation in resistivity may be related to the thermal instability of Li that is present in the samples. The Fermi level is pinned by 90-meV shallow donors that are deeper than the 70 meV and hydrogen-related 35-meV shallow donors in Eagle Pitcher and Cermet substrates. In all three cases, 0.3-eV electron traps are very prominent, and in the Tokyo Denpa material they dominate the high-temperature capacitance-frequency characteristics. The concentration of these traps, on the order of 2×1015 cm−3, is about 20 times higher in the Tokyo Denpa ZnO compared to the two other materials. The other electron traps at Ec −0.2 eV commonly observed in undoped n-ZnO are not detected in conducting Tokyo Denpa ZnO samples, but they may be traps that pin the Fermi level in the more compensated high-resistivity samples.

Solid Oxide Fuel Cells based on Proton Conducting Electrolytes

AbstractWe have fabricated a solid oxide fuel cell (SOFC) using BaCe0.8Y0.2Ox (BCY) proton conductor as the electrolyte. An ≈ 15-μm-thick dense BCY film was prepared on a porous Ni/BCY cermet (i.e., ceramic/metal composite) substrate by a colloidal spray deposition technique. The gas permeable Ni/BCY cermet substrate backed with nickel mesh was used as the anode, and platinum paste backed with platinum mesh served as cathode. The current-voltage characteristics of the BCY-based SOFC were measured in the temperature range 600-800°C using wet air on the cathode side and wet hydrogen on the anode side. The open circuit voltage was close to the theoretical value at all operating temperatures. The power density of the fuel cell was ≈240 and ≈875 mW/cm2 at 600 and 800°C, respectively.

高周波イオンプレーティング法による薄膜固体酸化物燃料電池の作製と特性評価

Solid oxide fuel cell (SOFC) having a thin yttria-stabilized zirconia (YSZ) electrolyte was prepared on the anode electrode of a porous Ni-YSZ cermet substrate using the RF ion plating method. The constitutional YSZ electrolyte films were characterized based on dependence on the electron beam current and annealing treatment. A thin YSZ electrolyte film evaporated at higher electron emission current indicated a columnar structure with longitudinal pinholes in the film. By annealing temperature above 1300°C, YSZ film was improved as a denser film having a bulk electrolyte structure. Furthermore, the conductivity of thin YSZ film was increased with increasing the annealing temperature, although its conductivity became smaller by about three figures than the theoretical value of the bulk electrolyte.

Effect of characteristics of Y 2O 3/ZrO 2 powders on fabrication of anode-supported solid oxide fuel cells

A comparative study is carried out on the effect of nano-sized and micron-sized Y 2O 3/ZrO 2 (YSZ) powders on the fabrication and performance of anode-supported solid oxide fuel cells. It is found that pellets made of nano-sized YSZ powder can achieve a relative density of 96% at a sintering temperature of 1400 °C and 92% at sintering temperature as low as 1200 °C. For pellets made of micron-sized YSZ powder, densification only occurred at a sintering temperature of 1400 °C. On co-sintering the nano-sized YSZ electrolyte film with the anode support/substrate, the electrolyte is unable to sinter fully at 1400 °C, but forms a porous structure which leads to a reduced open-circuit potential and poor cell performance. This is most likely due to the nano-sized YSZ electrolyte thin film having a very low green density and there being a significant difference in the sintering behaviour of the YSZ thin layer and the Ni/YSZ cermet substrates. The sintering behaviour and the nature of YSZ powders exert a significant effect on the fabrication and performance of Ni/YSZ anode-supported thin YSZ electrolyte cells.