Andrew M. Kiss

In-situ observation of nickel oxidation using synchrotron based full-field transmission X-ray microscopy

An in situ imaging-based approach is reported to study chemical reactions using full-field transmission x-ray microscopy (TXM). Ni particles were oxidized at temperatures between 400 and 850 °C in the TXM to directly observe their morphology change while the chemical composition is monitored by x-ray absorption near edge spectroscopy. Reaction rates and activation energies are calculated from the image data. The goal of this effort is to better understand Ni oxidation in electrode materials. The approach developed will be an effective technique for directly studying chemical reactions of particles and their behavior at the nano-scale.

In situ heater design for nanoscale synchrotron-based full-field transmission X-ray microscopy.

The oxidation of nickel powder under a controlled gas and temperature environment was studied using synchrotron-based full-field transmission X-ray microscopy. The use of this technique allowed for the reaction to be imaged in situ at 55 nm resolution. The setup was designed to fit in the limited working distance of the microscope and to provide the gas and temperature environments analogous to solid oxide fuel cell operating conditions. Chemical conversion from nickel to nickel oxide was confirmed using X-ray absorption near-edge structure. Using an unreacted core model, the reaction rate as a function of temperature and activation energy were calculated. This method can be applied to study many other chemical reactions requiring similar environmental conditions.

Backing Out Diffusion Coefficients in Alkaline Anion Exchange Membranes

Water diffusion coefficients for electrolyte membranes are a subject of interest due to the relationship between water content and ionic conductivity. These diffusion coefficients are functionally dependent on water content. Many existing techniques for measuring the diffusion coefficient suffer from experimental complexity or a lack the diffusion coefficients detailed behavior. This paper uses a simple technique for determining the water diffusion coefficient involving the use of experimental data coupled with a numeric model. This back out algorithm was validated through the use of Nafion®, a proton exchange membrane, with the results comparing well with NMR data from the literature. The process has also been applied to SnowPure ExcellionTM, an alkaline exchange membrane, to obtain the diffusion coefficient as a function of water content. It was found that these membranes are much less permeable to water with the diffusion coefficient being almost an order of magnitude less than that of Nafion®.