F.P.F. van Berkel

Intermediate temperature SOFC – a promise for the 21st century

World-wide a number of activities are concerned with the optimisation and development of cell materials and microstructures with the aim of reducing the solid oxide fuel cell (SOFC) operating temperature. Advantages for reduced operating temperatures are considered to be longer life time and reduced costs of the total system. Conventional zirconia based electrolyte cells with highly optimised electrodes have produced 500 mA/cm2 at 700 mV and 800°C. At a similar temperature and cell potential, small scale, co-fired, electrode supported thin-electrolyte cells have produced 700 mA/cm2. For SOFC operation at temperatures below 750°C the conventional 8 mol% Y2O3–ZrO2 electrolyte is replaced with either Ce0.9Gd0.1O1.95 (10GCO) or La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolytes. Up-scaled 10×10 cm2 or 12 cm circular 10GCO and LSGM cells have been manufactured and the initial results of cell tests are very promising.

Microstructure — ionic conductivity relationships in ceria-gadolinia electrolytes

Abstract Impedance spectroscopy has been used to separate grain interior and grain boundary conductivities in a series of measurements on thin Ce 0.8 Gd 0.2 O 2 − δ ceramic electrolytes with a range of different grain size distributions. The “brick layer” microstructural model has been used to provide an estimate of a true grain boundary conductivity and to relate the electrical properties of the ceramic to microstructural parameters. High resolution electron microscopy images show that insulating intergranular phases do not necessarily have to be present in order to cause a large grain boundary resistance. A clear relationship between grain boundary resistance and the number of grain boundaries was observed for samples of mean grain size of 3 μm or larger. For samples of sub-micron average grain sizes, measured grain boundary conductivities were inconsistent with model predictions, being significantly higher than predicted.

Characterization of solid oxide fuel cell electrodes by impedance spectroscopy and I–V characteristics

Abstract Impedance spectroscopy has been used to optimize the three-phase boundaries of porous electrodes in solid oxide fuel cells. The three-phase boundaries (TPBs) are the sites where the electrode reaction occurs and their nature is determined by the microstructure of the electrode. The three-phase boundary length (TPBL) of the cathode can be optimized by using small powder particles and a high loading of the particles on the electrolyte surface. The TPBL of the Ni/8YSZ anode can be optimized by using small Ni particles and a high 8YSZ/Ni-particle size ratio.

Silica poisoning of oxygen membranes

Perovskite oxide membranes (La0.6Sr0.4Co0.2Fe0.8O3) are used for the separation of oxygen from air. In oxygen permeation experiments these membranes showed a peculiar behavior. Besides poor performance, a characteristic coloring also appeared on the surface of the membranes. In order to understand what was happening to the surface of the membranes, they were analysed with Low-Energy Ion Spectroscopy (LEIS) and X-ray Photoelectron Spectroscopy (XPS). The analyses showed that the surface of the LSCF membrane was covered with a SiO2 layer, which obviously reduced the performance and caused the coloring. It was established that the source of the silicon was siloxane containing grease that was used in the manual valves of the setup. In a new improved permeation setup, where grease-free valves were used, the LSCF membranes showed remarkably better performance. The LEIS measurements showed also that the permeation experiment of 300 h did not affect the surface composition of the membranes. The contamination-free LSCF membranes only showed the presence of La, Sr and O in the outermost atomic layer. The observed absence of Co and Fe suggests that further improvement of the membrane performance is possible.

La ( Ni , Fe ) O3 Stability in the Presence of Chromia—A Solid-State Reactivity Study

The perovskite

Surface composition of ceramic CeGd-oxide

La(Ni_{0.6}Fe_{0.4})O_3

Cr-poisoning of a LaNi0.6Fe0.4O3 cathode under current load

(LNF) is a candidate material for the electrochemically active cathode layer, the cathode current collecting layer, and/or the interconnect protective coating in intermediate temperature solid oxide fuel cells (IT-SOFCs) operated at . Since these operating temperatures enable the use of relatively cheap interconnect materials such as chromia-forming ferritic stainless steel, investigation of the chemical stability of LNF in the presence of chromium species is of importance. This study demonstrates that LNF is chemically unstable at when it is in direct contact with

Impact of Cr-poisoning on the conductivity of LaNi0.6Fe0.4O3

Cr_2O_3

Impact of Cr-poisoning on the conductivity of different LaNi0.6Fe0.4O3 cathode microstructures

. It has been observed that Cr enters the perovskite phase, replacing first Ni and then Fe, already after 200h. At 600°C, however, only minor reaction products were detected after 1000h exposure to

Interplay between propylene and H2S co-adsorption on the H2 flux characteristics of Pd-alloy membranes employed in propane dehydrogenation (PDH) processes

Cr_2O_3