Electrolyte-supported SOFC Research Articles

Stabilisation of composite LSFCO–CGO based anodes for methane oxidation in solid oxide fuel cells

A La 0.6Sr 0.4Fe 0.8Co 0.2O 3–Ce 0.8Gd 0.2O 1.9 (LSFCO–CGO) composite anode material was investigated for the direct electrochemical oxidation of methane in intermediate temperature solid oxide fuel cells (IT-SOFCs). A maximum power density of 0.17 W cm −2 at 800 °C was obtained with a methane-fed ceria electrolyte-supported SOFC. A progressive increase of performance was recorded during 140 h operation with dry methane. The anode did not show any structure degradation after the electrochemical testing. Furthermore, no formation of carbon deposits was detected by electron microscopy and elemental analysis. Alternatively, this perovskite material showed significant chemical and structural modifications after high temperature treatment in a dry methane stream in a packed-bed reactor. It is derived that the continuous supply of mobile oxygen anions from the electrolyte to the LSFCO anode, promoted by the mixed conductivity of CGO electrolyte at 800 °C, stabilises the perovskite structure near the surface under SOFC operation and open circuit conditions.

Time Dependent Properties and Performance of a Tubular Solid Oxide Fuel Cell

Abstract Time dependent properties and performance of tubular solid oxide fuel cells were studied numerically and experimentally. The numerical model incorporated local characteristics such as porosity, tortuosity, grain size, and conductivity and was used to evaluate the specific and relative changes in performance caused by the effect of time-dependent material changes of those characteristics. A 500 hour experimental study was conducted at 800°C in 97%H2∕3%H2O on an extruded LSCo-La0.6Sr0.4CoO3∕LSGM∕Ni electrolyte-supported tubular SOFC made in our laboratory. Changes in current density with time (at constant voltage) formed a curve with initial convex (upward) curvature, becoming monotonic decreasing. The microstructure of the constituent layers was examined by scanning electron microscopy. Comparisons between model predictions and experimental observations were made. For the situation modeled and tested, the porosity and ionic conductivity were found to be most influential on performance. More importantly, the effect of porosity is a trade-off between the influence on gas transport and the mixed conductor influence on the electrochemical reactions at the electrode.

Development of interconnect materials for solid oxide fuel cells

The state of the art development of interconnect materials for solid oxide fuel cells (SOFCs) is reviewed. The specific interconnect requirements from a materials design point of view are described in detail. Doped-LaCrO 3 ceramics considered as interconnects for electrolyte-supported planar SOFC suffer from their extreme sensitivity to oxygen partial pressure and high manufacturing cost. Advent of anode-supported planar SOFC allows lower operating temperatures and great efforts have been directed towards the development of metallic interconnects. Chromia formed on the surface of chromium-based alloys are intrinsically too volatile to be viable as interconnects for SOFCs operating above 800 °C. Some intermediate phases occurring between iron-based interconnect and cathode significantly increase the contact resistance. Metallic materials that are capable of developing stable oxide scales with acceptable growth rate and reasonably high electrical conductivity over the expected SOFC lifetime need to be developed.

Planar SOFCs and Stacks Development at IPPE

Institute for Physics and Power Engineering (IPPE) has been developing planar SOFCs and power systems based on them since 1996. The R&D work includes SOFC materials investigations, single cell and stack design, manufacturing and testing, small-scale power plant design development, and creation of the base for power plant long-term tests. Currently our efforts are concentrated mainly on development and optimization of electrolyte-supported and anode-supported planar SOFC technologies. More than two hundred single SOFCs have been tested. Maximum power density of 700 mW/cm 2 at 950°C has been achieved. Recently several three- and five-cell planar SOFC stacks have been tested. The status of R&D work on planar SOFC at IPPE and some results are discussed in this paper.