Scott Perry, Professor
Materials Science

The function and performance of devices based on ion conducting oxides films rely critically upon the details of interfacial reactions. Reactants for such reactions consist of fuel molecules arriving from the gas phase and oxygen anions diffusing from within the bulk to the surface. A number of reactions are possible, however redox processes are central to many applications. In such processes, reaction of the fuel at the interface produces oxidized products and electrons (harvested in fuel cell applications). Due to the need for ion mobility, these reactions are often carried out at elevated temperatures. As apparent from this description (see figure), a number of individual rates will contribute to the overall measured rate of reaction. These include the rate of oxygen ion diffusion, the rate (flux) of reactants to the surface, and the rate of the surface redox reaction. Early investigations of ion conducting oxide materials have focused on the bulk transport properties, seeking to tailor higher bulk diffusivity through control of composition and structure. As device dimensions are reduced (i.e. film thickness) in order to combat costs and realize higher performances, the rates of surface reactions become equally important to bulk diffusion rates, and in cases will be the rate-limiting step. To date, few studies have explored the details of oxide surface reactivity. We are conducting time-of-flight mass spectroscopic (TOF-MS) techniques to measure fundamental properties such as surface reaction yields, independent reaction rates, and the temperature dependence of oxidation processes at ion conducting oxide surfaces.

Atomic force microscope image of 240 nm thick La2NiO4+x film on (100) LaA1O3 single crystal
made by pulsed laser deposition at 850 K

The La2NiO4 films are thermo-mechanically compatible with commonly used electrolytes in solid oxide
fuel cells and, at the same time, exhibit faster oxygen transport than other well-established 
perovskite cathode materials.