Yttria-stabilized Zirconia Electrolyte Layer Research Articles

Enhanced performance of reversible solid oxide fuel cells by densification of Gd0.1Ce0.9O2−δ (GDC) barrier layer/La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428)-GDC oxygen-electrode interface

In reversible solid oxide cells (RSOCs) with yttria-stabilized zirconia (YSZ) electrolyte and LSCF6428-based oxygen electrode, a GDC barrier layer is used to prevent inter-diffusion of constituents. However, the performance of such RSOC is limited to the achievable density of GDC at prevailing temperatures of traditional fabrication methods. In this work, the GDC barrier layer was densified via infiltration with polyvinylpyrrolidone (PVP) chelated metal precursors sol and subsequent sintering at 1200 °C. The NiO-YSZ fuel electrode-supported RSOCs with YSZ electrolyte, porous or infiltrated GDC barrier layer and LSCF6428-GDC composite oxygen electrode were fabricated. The RSOCs were analyzed with respect to operating temperature (650–800 °C), water partial pressure at fuel electrode (pH2OFE=0.03–0.5 atm), oxygen partial pressure at oxygen electrode (pO2AE=0.02–0.21 atm) and current loading. The performance evaluation, using current-voltage curve and electrochemical impedance spectroscopy (EIS), showed that the RSOC with an infiltrated GDC barrier layer exhibited a 32–48% increase in performance in fuel cell (FC) mode in the 650–800 °C range, compared to that of the RSOC with a porous GDC layer. Similarly, in electrolysis cell (EC) mode, comparing current density at 1.3 V, chosen as the reference voltage for ease of comparison, based on a thermoneutral voltage of 1.285 V in electrolysis cell (EC) operation at 750 °C[1], the RSOC with an infiltrated GDC barrier layer exhibited values of over 1.2 A∙cm−2, in contrast to the RSOC with a porous GDC barrier layer, which showed 0.8 A∙cm−2. In the case of the RSOC with infiltrated GDC, a durability test was conducted at 750 °C under an EC current density of 1A∙cm−2for 100 h. Our experimental results demonstrate that the RSOC with an infiltrated GDC barrier layer not only exhibits enhanced performance but also maintains stability. Comparative analysis was conducted using Distribution of Relaxation Time (DRT) analysis of Electrochemical Impedance Spectroscopy (EIS) data, to further understand the differences between the cells.

Multistep magnetron sputtering process and in-situ heat treatment to manufacture thick, fully oxidized and well crystallized YSZ films

In this work, yttria stabilized zirconia electrolyte layers were deposited by reactive pulsed DC magnetron sputtering on various substrates (i.e. silicon wafer, glass plates, NiO/YSZ cermets). The sputtering process was studied by following the cathode voltage and gas pressure evolutions with the reactive flow rate. The substrate temperature was found to play a role on the transition between the elemental and reactive sputtering modes. The influence of the sputtering parameters and deposition conditions on the film properties was investigated. Thick (about 2 μm) and dense deposits were manufactured both in elemental and in reactive sputtering modes. Ex-situ and in-situ heat treatments were applied to promote crystallization and oxidization of the deposits. The oxygen content was evaluated by Rutherford backscattering spectroscopy before and after heat treatments which confirmed that fully oxidized material was obtained. Optical transmission measurements on deposits synthesized on glass slides were also performed for a cross check of the oxidation state. X-ray diffraction technique revealed that heating of the substrate is necessary to get a crystallized as-deposited film. However, further annealing is required to synthesize the desired YSZ cubic phase. It has been proved that with the proposed multistep process including in-situ short heating steps, thick YSZ films could be synthesized without any stress cracking as usually observed after complete oxidation. Those films have shown very low leakage rate (6.67 × 10−4 mbar·l·s−1) which is required for the application.

Effects of Surface Modification on the Electrochemical Oxidation Reactivity of Activated Carbon in Direct Carbon Fuel Cells

A direct carbon fuel cell (DCFC) is the only fuel cell type that converts the chemical energy stored in solid carbon, which could be obtained from coal and biomass, into electricity directly via an electrochemical route with a higher energy efficiency and less pollution than conventional coal-fired power plants [1, 2]. In this work, the effect of the surface properties of carbon fuel on its electrochemical oxidation reactivity is investigated. Activated carbon (AC) is pre-treated with HNO3 and NaOH, respectively, both of which decrease the graphitization degree and increase the oxygen content of AC. The amount of hydroxyl groups on the surface of AC increases after the treatments with HNO3 and NaOH, and then decreases during the subsequent heating process in an inert atmosphere. On the contrary, the carbonyl groups on the surface of AC-HNO3 remain stable during the heating process. AC-HNO3 shows the highest reactivity towards oxidation and reverse Boudouard reactions due to its lowest graphitization degree and highest oxygen content. The performance of the cell supported by a 380-μm-thick yttria stabilized zirconia electrolyte layer with 60 mol% La0.6Sr0.4Co0.2Fe0.8O3-40 mol% Gd2O3 doped CeO2 as the electrodes is investigated with various fuels. The cell with AC-HNO3 as the fuel exhibits the highest maximum power density of 81 mW cm-2 at 800 oC. Fig. 1. I-V and I-P curves of single cells with various carbon fuels at 800 oC References [1] Jiang C, Ma J, Corre G, et al. Chemical Society Reviews, 2017, 46(10): 2889-2912 [2] Jang H, Park Y, Lee J. Chemical Engineering Journal, 2017, 308: 974–979. Figure 1

Tailoring the pore structure of cathode supports for improving the electrochemical performance of solid oxide fuel cells

Two types of lanthanum doped strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) composite cathodes were prepared, one with the finger-like straight open pores by the phase inversion tape casting, and the other with the randomly distributed tortuous pores by the conventional tape casting. A gas permeation flux of 42.5 × 105 Lm−2 h−1 was measured under a trans-membrane pressure of 0.6 bar for the former while only 10.6 × 105 Lm−2 h−1 for the latter. Fuel cells supported on the as-prepared LSM-YSZ composite cathodes were fabricated, comprising a 15 μm thick YSZ electrolyte layer and a 20 μm thick NiO-YSZ anode. The electrochemical performance of the fuel cells was measured using H2 as fuels and air as oxidants. The cell supported on the phase-inversion derived cathode showed a maximum power density of 362 mWcm−2 at 850 °C, while only 149 mWcm−2 for the cell supported on the cathode formed by the conventional method. The difference in the electrochemical performance between the two cells can be attributed to the pore structure of the cathode supports. It is concluded that the phase inversion tape casting provides a simple and effective approach for tailoring the pore structure of the cathode support and thus enhancing the electrochemical performance.

TEM and ETEM Study on SrZrO3 Formation at the LSCF/GDC/YSZ Interfaces

Transmission electron microscopic (TEM) studies have elucidated SrZrO3 formation and growth at La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)/ Ce0.9Gd0.1O2 (GDC) / yttria-stabilized zirconia (YSZ) interfaces in the solid oxide fuel cell (SOFC). SrZrO3 forms firstly at the GDC/YSZ interface: at the interface between GDC dense layer and YSZ, at grain boundaries in the GDC dense layer and on the surface of the GDC dense layer during sintering LSCF at 1100 oC. Then, SrZrO3 grows to the both sides of YSZ electrolyte and porous GDC layer. Electron energy loss spectroscopy revealed the inter-diffusion of La, Ce and Gd as well as Sr and Zr in the vicinity of the GDC/YSZ interface. La is solute in SrZrO3, and SrZrO3 shows tetragonal crystal structure, which has the double pseudocubic perovskite subcell. Nucleation and growth of SrZrO3 orthorhombic phase was observed at 800 oC under an O2 atmosphere in an environmental TEM.

(Sensor Division Outstanding Achievement Award) Mixed Potential Sensors for Hydrogen Safety and Automotive Applications

Mixed potential sensors are a class of non-equilibrium electrochemical sensors capable of detecting the presence of reducing or oxidizing gases. These devices usually consist of two electrodes supported on an electrolyte, and exposed to a sensing gas without the need for a separate reference electrode. The potential at each of the electrode/electrolyte interfaces is determined by the rates of electrochemical oxidation and reduction reactions. Since electrode composition, morphology and sample temperature control the rates of these reactions, it is theoretically possible to select a combination of electrodes and an operating temperature to provide sensitivity and selectivity to a desired gas species. Over the past 15 years Los Alamos National Laboratory (LANL) has developed yttria stabilized zirconia (YSZ) electrolyte based mixed potential sensors for various applications. Novel 4-electrode experiments were used to unravel the working principle of these sensors and it was determined that the sensor sensitivity was primarily controlled by the rate of oxygen reduction reaction (ORR) and amount of heterogeneous catalysis of the reducing/oxidizing gas. Electrodes with poor ORR kinetics and low heterogeneous catalysis rates yielded the highest mixed potentials. This observation led to the development of dense electrode and porous electrolyte morphologies for optimal sensitivity. Furthermore, the use of dense electrodes also improved the morphological stability of these devices leading to exceptional long-term durability. The LANL sensor design is unique and does not use the dense electrolyte and porous electrodes configuration that most sensors use. In this talk the development of new techniques including thin film deposition, tape casting and high temperature ceramic co-fired (HTCC) processes for the manufacturing of these novel sensors will be discussed. While tape casting and thin film deposition yield sensors with high sensitivity and long-term durability, they are not easily scalable for low cost manufacturing. LANL, in collaboration with ESL ElectroScience, has developed a HTCC process to manufacture low cost sensors that retain the unique advantages of the LANL design. This talk will focus on the development of nitrogen oxide (NOx), ammonia (NH3) and hydrogen sensors. The sensing electrodes for the nitrogen oxide, ammonia and hydrogen sensors are La1-xSrxCrO3- d, Au and Sn1-xInxO2- d respectively. All sensors use a Pt counter electrode and the LANL patented design, where dense electrodes are partially covered with a thin YSZ electrolyte layer. While the hydrogen and ammonia sensors are operated in the open circuit mode, the nitrogen oxide sensor is operated under a current bias to minimize selectivity to hydrocarbons and improve selectivity to both NO and NO2. This talk will also discuss the evaluation of these sensors in end-user applications. Data from dynamometer testing of NOx and NH3 sensors at Oak Ridge National Laboratory’s National Transportation Resource Center will be presented. Hydrogen safety sensor data from field trials at a hydrogen fueling station in California will also be presented. Finally the barriers and hurdles for the successful commercialization of these sensors will be discussed.

3D Printing of Functional Layers for Solid Oxide Fuel Cells and Electrolysers

Energy conversion efficiencies of solid oxide fuel cells (SOFCs) and electrolysers (SOEs) can be increased, principally by increasing the density of triple phase boundaries (electrode | electrolyte | reactant gas in pores) where reactions occur. SOFCs and SOEs with infiltrated-scaffold composite electrode structures have been shown to have greater densities of triple phase boundaries (TPBs), and enhanced control of particle size and porosity compared with structures derived from powder mixing [ 1 ]. However, methods that fabricate reproducible and explicitly tailored scaffolds with micrometre length scales have yet to be reported. Hence, we are developing 3D inkjet printing, using a Ceradrop X-Series inkjet printer with three multi-nozzle print heads, to fabricate reproducible, structured ceramic frameworks with ca. 5 µm resolution, prior to sintering. Ultimately, this should enable fabrication of percolated (porous) cathode | (non-porous) electrolyte | (porous) anode structures much more reproducibly and with greater definition than hitherto, to achieve increased energy conversion performances. The reproducible geometries will also enable more facile comparison of experimental performance and model predictions [2]. One prerequisite is the development of stable dispersions (‘inks’) of sub-micrometre sized metal oxide particles (i.e. (ZrO2)0.92(Y2O3)0.08, NiO, La1-xSrxMnO3-δ) in liquid phases with suitable solids fractions and physical properties, for which results will be presented (Fig.1a). These inks have been used to print the functional layers of SOFCs/SOEs (Fig.1b). However, geometries of electrode | electrolyte structures are subject to limitations imposed by the requirement to minimise the spatial distributions of potential and current densities. Hence, results will also be presented for predictions (Fig.2) of those parameters, modelled using finite element software, and preliminary current density-potential difference data for a printed SOE. Firstly, yttria-stabilized zirconia (YSZ) particles were deposited onto a planar YSZ | NiO substrate, as pre-cursors to a thin (ca. 10 µm), gas-tight electrolyte, formed by heating the green structure to ca. 500°C to burn out organics used to stabilise ink particles against aggregation, followed by sintering YSZ at ca. 1400°C. Subsequently, YSZ and NiO nanoparticles were co-printed with an organic polymer to fabricate porous electrode structures on non-porous YSZ electrolyte layers. Reference M. Kishimoto, M. Lomberg, E. Ruiz-Trejo, N.P. Brandon, Enhanced triple-phase boundary density in infiltrated electrodes for solid oxide fuel cells demonstrated by high-resolution tomography, J. Power Sources, 266 (2014) 291-5.U. Doraswami, P. Shearing, N. Droushiotis, K. Li, N.P. Brandon and G.H. Kelsall, Modelling the Effects of Measured Anode Triple-Phase Boundary Densities on the Performance of Hollow Fiber SOFCs, Solid State Ionics, 192 (2011) 494–500. Figure 1

Fabrication of (Sm, Ce)O2−δ interlayer for yttria-stabilized zirconia-based intermediate temperature solid oxide fuel cells

Application of Sm0.5Sr0.5CoO3−δ (SSC) cathode in solid oxide fuel cells (SOFCs) has its advantage of reducing polarization loss at intermediate operating temperatures (600–800°C). However, the SSC cathode cannot be applied directly on yttria stabilized zirconia (YSZ) electrolyte due to the thermal mismatch and chemical reaction. In this work, Ce0.8Sm0.2O2−δ (SDC) thin interlayers are fabricated between YSZ electrolyte layers and Sm0.5Sr0.5CoO3−δ-SDC (SSC–SDC) cathode layers with dip-coating and pulsed laser deposition (PLD) methods. The 1400°C-sintered SDC interlayer deposited by dip-coating method exhibits a porous microstructure. PLD technique yields a thin and dense SDC layer at a low substrate temperature of 600°C and no additional peaks of (Zr, Ce)O2-based solid-solution are present. Besides, the electrochemical performance of the YSZ/SDC (electrolyte/interlayer) fuel cell has a great improvement at intermediate operating temperature.

Atomic layer deposition of ultrathin blocking layer for low-temperature solid oxide fuel cell on nanoporous substrate

An ultrathin yttria-stabilized zirconia (YSZ) blocking layer deposited by atomic layer deposition (ALD) was utilized for improving the performance and reliability of low-temperature solid oxide fuel cells (SOFCs) supported by an anodic aluminum oxide substrate. Physical vapor-deposited YSZ and gadolinia-doped ceria (GDC) electrolyte layers were deposited by a sputtering method. The ultrathin ALD YSZ blocking layer was inserted between the YSZ and GDC sputtered layers. To investigate the effects of an inserted ultrathin ALD blocking layer, SOFCs with and without an ultrathin ALD blocking layer were electrochemically characterized. The open circuit voltage (1.14 V) of the ALD blocking-layered SOFC was visibly higher than that (1.05 V) of the other cell. Furthermore, the ALD blocking layer augmented the power density and improved the reproducibility.

Application of PVD methods to solid oxide fuel cells

a b s t r a c t In this paper, attention is paid to the application of such a method of vacuum physical vapor deposition (PVD) as magnetron sputtering for fabrication of a solid oxide fuel cell (SOFC) materials and structures. It is shown that the YSZ (yttria-stabilized zirconia) electrolyte and Ni-YSZ anode layers with required thick- ness, structure and composition can be effectively formed by PVD methods. The influence of parameters of pulsed power magnetron discharge on the deposition rate and the microstructure of the obtained YSZ electrolyte films were investigated. It is shown that the deposition rate of the oxide layers by magnetron sputtering can be significantly increased by using asymmetric bipolar power magnetrons, which creates serious prerequisites for applying this method on the industrial scale. Porous Ni-YSZ anode films were obtained by reactive co-sputtering of Ni and Zr-Y targets and subsequent reduction in the H2 atmosphere at a temperature of 800 ◦C. The Ni-YSZ films comprised small grains and pores of tens of nanometers.

Design of industrially scalable microtubular solid oxide fuel cells based on an extruded support

The current work describes the adaptation of an existing lab-scale cell production method for an anode supported microtubular solid oxide fuel cell to an industrially ready and easily scalable method using extruded supports. For this purpose, Ni–YSZ (yttria stabilized zirconia) anode is firstly manufactured by Powder Extrusion Moulding (PEM). Feedstock composition, extruding parameters and binder removal procedure are adapted to obtain the tubular supports. The final conditions for this process were: feedstock solid load of 65 vol%; a combination of solvent debinding in heptane and thermal debinding at 600 °C. Subsequently, the YSZ electrolyte layer is deposited by dip coating and the sintering parameters are optimized to achieve a dense layer at 1500 °C during 2 h. For the cathode, an LSM (lanthanum strontium manganite)–YSZ layer with an active area of ∼1 cm2 is deposited by dip coating. Finally, the electrochemical performance of the cell is measured using pure humidified hydrogen as fuel. The measured power density of the cell at 0.5 V was 0.7 W cm−2 at 850 °C.

Phase Inversion and Electrophoretic Deposition Processes for Fabrication of Micro-Tubular Hollow Fiber SOFCs

A novel combination of a phase inversion process followed by electrophoretic deposition was used to fabricate anode supported micro-tubular hollow fiber solid oxide fuel cells (SOFCs). The phase inversion process was used to produce 240 μm thick 60 wt% NiO - 40 wt% yttria-stabilized zirconia (YSZ) hollow fiber anode precursors with asymmetric porosity. Subsequently, electrophoretic deposition (EPD) was used to apply 40 μm thick, particulate YSZ electrolyte layers onto the un-sintered NiO-YSZ hollow fibers from a YSZ dispersion in ethanol at an applied electric field of ca. 22 kV m−1. The YSZ-coated NiO-YSZ fibers were sintered in a hydrogen atmosphere at 1500°C to produce gastight electrolytes. Two dispersions of YSZ and lanthanum strontium manganite (LSM) particles were then painted consecutively on top of the electrolyte layers, as ‘graded’ LSM-YSZ | LSM cathode precursors that were sintered at 1200°C. When fed with H2 fuel and air, a single such SOFC delivered peak power densities of 0.20, 0.18 and 0.14 W cm−2 during operation at 800, 750 and 700°C, respectively. A lumped parameter model, incorporating calculations of the contact, ohmic, activation and concentration polarization losses, is presented and the means are proposed by which certain potential losses may be obviated.

An ultra-fast fabrication technique for anode support solid oxide fuel cells by microwave

An effective and facile technique has been developed for high temperature anode-electrolyte co-sintering of anode support solid oxide fuel cells by using microwave activated sparking plasma. A high sintering temperature of 1600 °C can be achieved in a few minutes time by discharging effect. Anode support substrate pellet is uniaxially pressed, and then dip-coated with a 10 μm yttria stabilized zirconia electrolyte layer. After the microwave co-sintering, La 0.8Sr 0.2MnO x cathode is screen-printed onto electrolyte and sintered by conventional thermal method. The cell has stably operated in 3% humidified hydrogen for more than 130 h.

Fabrication and characterization of Sm0.2Ce0.8O2−δ–Sm0.5Sr0.5CoO3−δ composite cathode for anode supported solid oxide fuel cell

The Sm0.5Sr0.5CoO3−δ (SSC) with perovskite structure is synthesized by the glycine nitrate process (GNP). The phase evolution of SSC powder with different calcination temperatures is investigated by X-ray diffraction and thermogravimetric analyses. The XRD results show that the single perovskite phase of the SSC is completely formed above 1100°C. The anode-supported single cell is constructed with a porous Ni–yttria-stabilized zirconia (YSZ) anode substrate, an airtight YSZ electrolyte, a Sm0.2Ce0.8O2−δ (SDC) barrier layer, and a screen-printed SSC–SDC composite cathode. The SEM results show that the dense YSZ electrolyte layer exhibits the good interfacial contact with both the Ni–YSZ and the SDC barrier layer. The porous SSC–SDC cathode shows an excellent adhesion with the SDC barrier layer. For the performance test, the maximum power densities are 464, 351 and 243mWcm−2 at 800, 750 and 700°C, respectively. According to the results of the electrochemical impedance spectroscopy (EIS), the charge-transfer resistances of the electrodes are 0.49 and 1.24Ωcm2, and the non charge-transfer resistances are 0.48 and 0.51Ωcm2 at 800 and 700°C, respectively. The cathode material of SSC is compatible with the YSZ electrolyte via a delicate scheme employed in the fabrication process of unit cell.

Direct ceramic inkjet printing of yttria-stabilized zirconia electrolyte layers for anode-supported solid oxide fuel cells

Electromagnetic drop-on-demand direct ceramic inkjet printing (EM/DCIJP) was employed to fabricate dense yttria-stabilized zirconia (YSZ) electrolyte layers on a porous NiO–YSZ anode support from ceramic suspensions. Printing parameters including pressure, nozzle opening time and droplet overlapping were studied in order to optimize the surface quality of the YSZ coating. It was found that moderate overlapping and multiple coatings produce the desired membrane quality. A single fuel cell with a NiO–YSZ/YSZ (∼6 μm)/LSM + YSZ/LSM architecture was successfully prepared. The cell was tested using humidified hydrogen as the fuel and ambient air as the oxidant. The cell provided a power density of 170 mW cm −2 at 800 °C. Scanning electron microscopy (SEM) revealed a highly coherent dense YSZ electrolyte layer with no open porosity. These results suggest that the EM/DCIJP inkjet printing technique can be successfully implemented to fabricate electrolyte coatings for SOFC thinner than 10 μm and comparable in quality to those fabricated by more conventional ceramic processing methods.

Improvement of plasma-sprayed YSZ electrolytes for solid oxide fuel cells by alumina addition

Atmospheric plasma spray is a fast and economical process for deposition of yttria-stabilized zirconia (YSZ) electrolyte for solid oxide fuel cells. YSZ powders have been used to prepare plasma-sprayed thin ceramic films on the metallic substrate employing plasma spray technology at atmospheric pressure. Alumina doping was employed to improve the structural characteristics and electrical properties of YSZ. The effect of alumina addition from 1 to 5 wt.% on the properties of plasma-sprayed YSZ films was investigated. It was found that the gas permeability of the Al-doped YSZ electrolyte layer reached a level of 8.6 × 10−7 cm4 gf−1 s−1, which is a necessary value for the practical operation of solid oxide fuel cells. Alumina doping considerably increased the ionic conductivity of plasma-sprayed YSZ. The open circuit voltage of the alumina-doped YSZ coating was approximately equal to the theoretical value for dense YSZ material.

Oxygen Reduction at LSM–YSZ Cathodes Deposited on Anode-Supported Microtubular Solid Oxide Fuel Cells

Three-electrode methods were employed to evaluate the electrochemical activity of the oxygen reduction reaction (ORR) at lanthanum strontium manganite (LSM)–yttria stabilized zirconia (YSZ) composite cathodes deposited on the outer surface of microtubular, anode-supported, solid oxide fuel cells . The performance of these cathodes, deposited on the highly curved, electrophoretically deposited, thin YSZ electrolyte layers in the microtubular configuration, was compared against LSM-YSZ cathodes, deposited similarly and having the same microstructure, on thick YSZ layers in standard SOFC planar cells. While the EIS response of the high and low frequency arcs for LSM-YSZ in the two-cell geometries differed somewhat, the total polarization resistance and the ORR activation energy were similar. It was also demonstrated that LSM-YSZ cathode performance in the system can be further enhanced when the cell is sintered at 1150 vs .

Aqueous electrophoretic deposition of YSZ electrolyte layers for solid oxide fuel cells

A 6-μm-thick, dense, and uniform yttria-stabilized zirconia (YSZ) thin-film electrolyte for solid oxide fuel cell was able to be formed, via aqueous electrophoretic deposition, onto a porous Ni-YSZ cermet anode, which was made via attrition mill, pressure casting, and pressureless sintering. Nonconductive yet suitably porous substrates could be used for electrophoretic deposition, with the help of an auxiliary electrode. Ni/YSZ cermet presintered at 1,200 °C and reduced at 700 °C, on the other hand, behaved like a metal electrode and required no more the use of such an auxiliary electrode. It was also found that the deposition rate increased with increasing current density and with decreasing NH4-polyacrylate concentration.

Electrochemical Performance of Anode Supported Single Cells of Solid Oxide Fuel Cell with Anode/Electrolyte and Cathode/Electrolyte Interlayers

Single cells of solid oxide fuel cell(SOFC) with thin film composite interlayers were fabricated in order to improve charge transfer reaction in the electrode/electrolyte interface. Yttria-stabilized zirconia(YSZ) slurry was prepared by mixing YSZ powder with typical organic dispersants, and the optimum YSZ slurry composition for the interlayer dip-coating was determined by employing backscattering flux measurements. By the insertion of interlayer, a denser YSZ electrolyte layer could be prepared and the electrochemical performance of SOFC could be enhanced significantly.

Fabrication and characterization of anode-supported electrolyte thin films for intermediate temperature solid oxide fuel cells

Anode-supported electrolyte thin films for improving the solid oxide fuel cell (SOFC) performance at intermediate temperature (IT) have been manufactured by a wet-chemical process, and their microstructures, gas permeabilities, and electrical performances have been investigated. NiO–YSZ anode supports of a flat tube type were prepared by the extrusion method, and their surfaces were modified via slurry coating of fine NiO–YSZ particles for controlling the surface roughness and the pore size. An anode-supported yttria-stabilized zirconia (YSZ) electrolyte was fabricated by dip-coating YSZ slurry (viscosity 4.5 cP, solid contents 2.7 vol.%) onto the modified anode support, then it was coated with YSZ sol (viscosity 2.5 cP), and sintered at 1400 °C. The cathode consisted of three consecutive layers of LSM–YSZ composite, strontium-doped lanthanum manganite (LSM), and La 0.6Sr 0.4Co 0.2Fe 0.8O 3−δ (LSCF). After each successive slurry layer was applied it was co-fired at 1200 °C. The thickness of YSZ electrolyte layers could be controlled below 15 μm, and the YSZ layers’ acceptability as an electrolyte film for an SOFC was estimated from the result of the gas impermeability ranging below 2 bar. The unit cells fabricated in this work showed a good electrical performance of 550 mW cm −2 at 850 °C. This is attributed to the reduced resistance through the thin YSZ electrolyte.