High Temperature X‑ray Absorption Spectroscopy of the Local Electronic Structure and Oxide Vacancy Formation in the Sr₂Fe_1.5Mo_0.5O_6−δ Solid Oxide Fuel Cell Anode Catalyst

Perovskite based catalysts have recently been investigated as replacements for traditional solid oxide fuel cell (SOFC) anode materials to tolerate carbon containing fuels in these devices and resist graphite formations that can lead to device failure. The use of X-ray absorption spectroscopy with a custom built reactor assembly will allow for the noninvasive exploration of the redox chemistry of the perovskite anode catalyst Sr₂Fe_1.5Mo_0.5O_6−δ (SFMO) when exposed to SOFC device operational conditions at a temperature of 800 °C. Specifically, XANES and EXAFS studies of the Fe and Mo K-edges were used to understand the local electronic structure and oxygen vacancy formation of these metals in SFMO under reducing and oxidizing atmospheres. While there was minimal change in the oxidation state of the Fe atom in SFMO, as observed with XANES, there were significant oxygen vacancies formed around this metal as seen with EXAFS modeling. Interestingly, the opposite was true for Mo where there was a significant change in the oxidation state of the Mo atom with marginal changes to the oxygen environment surrounding this metal. The findings from these experiments will provide an understanding of the roles that the Fe and Mo atoms play in the ionic and electronic conducting properties of this material under standard SOFC operating device conditions. More importantly, this work will provide a unique perspective into SFMO’s ability to act as an effective anode catalyst in SOFCs.