In Situ X-ray and Electrochemical Studies of Solid Oxide Fuel Cell / Electrolyzer Oxygen Electrodes

The governing reaction mechanisms, and the electrode material compositions and structures, that controls the efficiency of the solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC) need to be identified and well-understood for significant technological improvements. Our study on the oxygen electrodes focuses on specifically the effect of electrode crystal structure and morphology on its electrochemical performance, and the evolution of the electronic and structural properties of the electrodes while under electrochemical conditions and high temperature. We found through electrochemical impedance spectroscopy experiments that the different crystal orientations in a given oxygen electrode material, for example La0.8Sr0.2MnO3+d (LSM), can show different initial performance, dissimilar processes governing the oxygen reaction mechanism, and different electrochemical activation behavior under DC bias at a given temperature in air. Our in-situ x-ray and electrochemical measurements at the Advanced Photon Source have identified the chemical states of the main components of the doped lanthanum manganite electrodes. We found that the bias and time dependent changes in the concentration and in the electronic state of the La (the A-site element of the perovskite) occurring only at the top air-electrode film interface can be responsible from the electrochemical improvement of the electrode under DC current. Our observation related to the La chemical state change is unexpected and probably unique to the electrochemical current-conditioning of the oxygen electrodes.