Effect of Mg/Mo Ratio in Stoichiometric Sr2MgMoO6-δ (SMM) Redox-Stable Anode

Abstract

The state-of-the-art Ni/YSZ anode experiences a linear expansion of up to 1% when oxidized causing an irreversible microstructural change. Hence there is a need to develop redox stable anode materials with multifunctional properties like internal reforming, low temperature operation, and poison resistance. In this work, SMM, an oxygen-deficient, mixed valent perovskite has been studied to exploit its potential as a viable anode material in the SOFC application. The mixed valance of Mo (6+ and 5+) supports the electronic conductivity while losing oxygen. It also provides platform for catalytic activity for the oxidation of hydrogen and other hydrocarbon. It has been found that SMM experiences a volumetric reduction of only 0.03% in reducing atmosphere at 800oC compared to GDC and Ni/YSZ which experiences a volumetric expansion of about 0.2 and 1% respectively. Stoichiometric SMM has a conductivity of 50 S/cm in the reducing atmosphere and with consecutive redox cycling, the conductivity decreases. Effort has been made to understand the reason for the drop in electrical conductivity with increasing redox cycling. It has been found that SMM loses Mo with time at 800oC, accounting for the drop in conductivity. To improve the electrical performance of SMM, Mg/Mo ratio in stoichiometric SMM has been varied to compensate for Mo loss and its effect on thermal stability and electrical conductivity will be discussed in this work. Above all, these compositions will be tested as an anode in an electrolyte supported SOFC and the performance data will be compared with Mo rich SMM compositions. The change in microstructure of the anode after many operating hours will be examined and discussed in this topic. Also EIS analysis of the tested cells will be discussed in this work.