Anode-supported Electrolyte Research Articles

Single-Chamber SOFCs with a Ce[sub 0.9]Gd[sub 0.1]O[sub 1.95] Electrolyte Film for Low-Temperature Operation

Single-chamber solid oxide fuel cells (SOFCs) with an anode-supported electrolyte were operated in a mixture of butane and air at furnace temperatures of 200-300°C. The electromotive force (emf) of the cell and the voltage drop were strongly influenced by the catalytic activity of the anode for the partial oxidation of butane. The promotion of hydrogen formation by the addition of Ru to the anode caused an increase in the emf and a reduction in the voltage drop. As a result, stable power densities of 44 and 176 mW cm−2 were obtained at 200 and 300°C, respectively. © 2004 The Electrochemical Society. All rights reserved.

Manufacturability of Very Thin Electrolyte Tapes for SOFCs in an ISO 9001 Environment

Commercial possibilities of solid oxide fuel cells improve with technological progress. However, success of this technology depends on bringing economic advantage to market and profit to materials, cells and systems manufacturers. Tape casting, a well-established technique, currently provides materials for several fuel cell programs. Anode tapes for anode-supported cells and electrolyte tapes for anode- and electrolyte-supported cells are manufactured in laboratory and large prototype volumes. Dense, crack-free, electrolyte tapes provide the high ionic conductance required for cells to function. Efficiency and area specific resistance are related to electrolyte ionic resistivity. Thin electrolyte tape, capable of meeting overall system requirements is therefore desirable. The technological advantage, however, presents a manufacturing challenge. This paper discusses the ability to cast YSZ tapes that fire to full density in thicknesses <12.5 μm and equipment and procedures required to make these measurements in prototype and manufacturing environments. Manufacturing under ISO 9001 conditions ensures reproducibility in the laboratory and eases scale-up to manufacturing. Incoming materials inspection ensures consistent powder properties such as particle morphology and surface area. Slurry viscosity and casting parameter limits control green tape properties. Green and fired thickness, and fired density measurements confirm quality. SPC charts of this data will be presented.

Characterization of YSZ–YST composites for SOFC anodes

Porous composites of Sr 0.88Y 0.08TiO 3− δ (YST) and yttria-stabilized zirconia (YSZ) were formed by tape-casting methods and examined as potential anodes for Solid Oxide Fuel Cells (SOFC). Even after calcination to 1773 K, the YSZ and YST crystallites remain as separate phases, as demonstrated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with EDX analysis. Furthermore, it was possible to fabricate anode-supported electrolytes by calcination of a bilayer tape formed by casting a thin YSZ tape over the green, YSZ–YST tape. Cells with anodes having 50-wt.% YST and 80-wt.% YST were tested and shown to yield good open-circuit voltages (OCV), although the power densities in H 2 and CH 4 between 973 and 1173 K were modest. Impedance spectra of the cells suggest that the conductivity of the YST–YSZ composites is insufficient for high performance.

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.

Impedance Spectroscopy for the Characterization of Cu-Ceria-YSZ Anodes for SOFCs

The performance of electrodes in direct-utilization, solid oxide fuel cells (SOFCs) has been studied on anode-supported and electrolyte-supported cells using impedance spectroscopy, coupled with calculations of the potential distribution in the electrolyte. The cells in these studies were composed of a Cu-ceria-yttria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, and a Sr-doped (LSM)-YSZ cathode and were operated at 983 K using both and n-butane as fuel. Both calculations and experiments show that three-electrode measurements on anode-supported electrolytes, with the reference electrode opposite the anode, provide no additional information over two-electrode measurements and cannot be used to estimate the performance of individual electrodes. Three-electrode measurements were able to estimate anode and cathode performance on thick, electrolyte-supported cells, with symmetric placement of the working electrodes. However, both experiments and calculations demonstrate that differences in the kinetics of the two electrodes make perfect separation of anode and cathode processes difficult. The cathode performance of LSM-YSZ in these experiments was described by a single arc in the Cole-Cole plot, with a frequency of 2 kHz and a resistance of The performance of the anode in was also characterized by a single arc, with a frequency of 4 Hz and a resistance of While anode performance in is only weakly dependent on current density, nonlinear processes are observed with n-butane, so that the area-specific resistances depend strongly on the current density. © 2003 The Electrochemical Society. All rights reserved.

Current Collection and Stacking of Anode-Supported Cells with Metal Interconnects to Compact Repeating Units

Repeat element and short stack development is presented using ASE (anode supported electrolyte) cells for 0.5 kW/L.

Breakdown of Losses in Thin Electrolyte SOFCs

Two anode-supported thin electrolyte cells were characterized by impedance analysis and under DC load at a range of temperatures in various H 2 /H 2 O-gas-mixtures. Effects of diluting the fuel with N 2 or He were also investigated. The losses ascribable to finite diffusion rate in the anode support are deduced from the experiments, allowing the cell resistance to be split into ohmic losses, anode diffusion losses, and reaction losses.

Fabrication of Anode Supported Electrolyte with CeScSZ Electrolyte and NiO- CeScSZ Anode by EPD Technique

We investigated fabrication of anode-supported electrolyte by EPD technique and subsequent co-firing process. Ceria-doped scandia-stabilized zirconia (CeScSZ) thin electrolyte films, around 10 μm thick, were successfully fabricated on the NiO-CeScSZ anode substrates. Results of SEM observation and OCV measurements indicated that all anode supported CeScSZ films co-fired at various temperatures from 1473 K to 1548 K were fully dense and showed good chemical stability under a large oxygen potential gradient typical of SOFCs. The power generation test with platinum cathode indicated a poor performance due to the low activity of platinum electrode for the cathode reaction. On the other hand, with a lanthanum strontium manganite (LSM) cathode, the cell performance improved and the power density reached 480 mWcm -2 at a current density of 0.8 Acm -2 at 1073 K.