Past and current research
Our established expertise in substituted perovskites such as LaxSr1-xMnO3 (LSMO) for their interesting magnetic properties gave us a head start in the careful characterization of those materials which happen to be of considerable interest in Solid-Oxide Fuel Cells (SOFC).
We initially examined the effect of interfacial stress on those materials and found that stress induced at the interface with other materials due to lattice (mis)matching can cause stoichiometric variations in the perovskite film. Indeed, we showed that changing the La to Sr ratio in LaxSr1-xMnO3 is one of nature’s ways of coping with a lattice mismatched interface because it changes the LSMO’s lattice constant. This, in turn, can have deleterious effects on the ionic and electronic conduction properties of LSMO, which are dependent on the La to Sr ratio. We conclude that induced strains on cathode materials should be considered carefully because they can generate significant chemical variations.
Our studies of the effect of lattice strain continue with other materials of interest in SOFC applications. The samples we use for these studies are pulsed laser deposited (PLD) by Shane Stadler of Southern Illinois University. By changing the thickness of a stress inducing lattice mismatched overlayer we can carefully tune the amount of stress and the resulting stoichiometric effects. We use X-ray Absorption Spectroscopy (XAS) for the chemical characterization and X-ray Resonant Scattering (XRS) to quantify the chemical migration of various atomic species near the interface. Some of our results will be published soon in the Proceedings of FUELCELL2006.
Material synthesis and cell characterization
Some of our more recent work is done in collaboration with Stephen Sofie of MSU’s engineering department. We are currently building a fuel cell testing apparatus that will allow us to characterize the performance of anode-electrolyte-cathode assemblies. The apparatus will give us the flexibility of changing fuel composition and feed rates, as well as the exterior load and operation temperature.
A major issue we are investigating is sulfur poisoning of SOFC anodes. One of SOFC’s advantages over other types of fuel cells is their fuel flexibility. However, alternative fuels to hydrogen, such as natural gas, may contain sulfur contaminants. In order to successfully use natural gas as a fuel without the added bulk and cost of a de-sulfurizer it is desirable to develop sulfur tolerant fuel cell materials. The first step in this process is understanding the poisoning mechanism, which we will accomplish by running fuel cells with hydrogen sulfide contaminated fuel, and subsequent careful characterization with powerful x-ray characterization techniques. Identification of the poisoning mechanism will direct future material synthesis and testing.
Our collaborative work with Dr. Sofie will expand our synthesis capabilities to industrially relevant tape casting techniques. In addition, we will continue to utilize MOCVD and PLD deposition to generate samples meant to investigate specific and fundamental material properties.