Phase Evolution and Electrochemical Properties of Nanometric Samarium Oxide for Stable Protonic Ceramic Fuel Cells

Electrochemical properties of metal oxide have a strong correlation with the crystalline structures. In this work, the effect of calcination temperature on the phase evolution and electrochemical properties of Sm2 O3 was systematically evaluated. The results demonstrate that the sample calcinated at 700 °C (SM-700) is composed of a pure cubic phase while it begins to convert into a monoclinic phase at a temperature above 800 °C and fully converts into a monoclinic phase at 1100 °C. Moreover, the evolution process causes atomic redistribution, and more oxygen vacancies are formed in cubic phase Sm2 O3 , contributing to the improved ionic conductivity. The ionic conductivity of 0.138 S cm-1 and maximum power density of 895 mW cm-2 at 520 °C are achieved using SM-700 as electrolyte for protonic ceramic fuel cell (PCFC). The cubic structure remains stable in the durability testing process and the SM-700 based fuel cell delivers enhanced stability of 140 mW cm-2 for 100 h. This research develops a calcination evolution process to improve the ionic conductivity and fuel cell performance of the Sm2 O3 electrolyte for stable PCFC.