Mechanistic insight into catalytic conversion of methane on a Sr2Fe1.5Mo0.5O6−δ perovskite anode: a combined EIS-DRT, DFT and TPSR investigation†

Abstract

The Sr₂Fe_1.5Mo_0.5O_6−δ (SFMO) perovskite has been considered as a promising candidate for the solid oxide fuel cell (SOFC) anode in hydrogen fuel, but exhibits poor performance when exposed to hydrocarbon fuels. In this study, the catalytic conversion of methane on a SFMO perovskite anode has been systematically investigated based on the distribution of relaxation times (DRT) method, density functional theory (DFT) calculations and temperature-programmed surface reaction (TPSR) measurement. A LSGM electrolyte-supported cell with the SFMO anode demonstrates a maximum power density of 0.63 W cm⁻² in wet hydrogen fuel at 800 °C, but it plummets to only 0.01 W cm⁻² when switched to wet methane fuel. DRT interpretation indicates that the cell performance in methane fuel is dominantly limited by these electrochemical processes within the intermediate frequency range of 1–30 Hz, which are mainly concerned with the methane catalytic conversion process in the SFMO anode. DFT analyses further reveal that methane cracking should be the key rate-limiting step for methane conversion on the SFMO perovskite anode. TPSR investigation suggests that the methane adsorption is also an ignorable rate-limiting step that affects the cell performance. These findings in the current study are expected to provide a fundamental basis for designing efficient perovskite-based SOFC anodes toward methane fuel.