Analyzing the Oxygen Reduction Reaction at Solid-Gas Interfaces by Optical Impedance Spectroscopy

We report a new in situ measurement method to determine the kinetics of the oxygen reduction reaction (ORR) and oxygen incorporation into fluorite and perovskite type mixed conductors, PCO (PrxCe1-xO2-d) and STF... [ view full abstract ]

We report a new in situ measurement method to determine the kinetics of the oxygen reduction reaction (ORR) and oxygen incorporation into fluorite and perovskite type mixed conductors, PCO (Pr_xCe_1-xO_2-d) and STF (Sr(Ti_1-xFe_x)O_3-d). These materials are promising candidates for use as electrodes in SOFC, gas sensors, and oxygen storage materials involving an oxygen exchange reaction. However, the individual rate limiting reaction steps are not fully identified. Optically probing the oxidation state by absorption measurements is feasible for PCO and STF and can help to discern between surface and bulk rate limiting processes.

Optical relaxation measurements have been used in the past for this purpose. For our optical impedance spectroscopy (OIS) only a small signal voltage perturbation is applied to pump oxygen in and out of the film electrochemically, thereby changing its absorption. This generalized electrochemical impedance spectroscopy (GEIS) technique comes with the benefits of superior signal to noise ratio, and the toolbox of analysis techniques available for impedance data can be readily applied to the acquired measurement data.

We will present OIS measurements on model thin films, demonstrate the basic modeling approach and discuss the obtained results. The investigation also includes the electrochemical impedance of the thin films that is measured in parallel. We believe that this is a very promising new approach to provide answers for some of the most challenging questions in solid state ionics. 

This work was supported by JSPS Core-to-Core Program, A. Advanced Research Networks.