Catalyst-induced enhancement of direct methane synthesis in solid oxide electrolyser

Abstract

CO2 valorisation to fuels and chemicals in solid oxide electrolytic cells (SOECs) has been a topic of great interest for the past few years. Methane is one such highly valuable fuel, but its in-situ generation in SOECs is an emerging technology. For the first time, we explain how the introduction of a methanation catalyst metal into the cathode affects the electrokinetics of in-situ methane generation in an electrolyte-supported symmetric tube cell while electrolysing a mixture of H2/CO2 . Fe–Ag and Fe–GDC–Ag electrodes were studied in the applied voltage range of 1.3–1.8 V and temperature range of 500–700°C. While Fe guaranteed good catalytic activity towards methanation reactions, Ag ensured good electrical conductivity of the electrode. Addition of GDC to the cathode remarkably improved CO2 electrolysis and modified Fe work function under loaded conditions, thus increasing methane generation to a maximum of 2.5% at 600°C and 1.6 V. For the Fe–Ag electrode, gaseous mass transport at the cathode was the rate-limiting step up to ~1.4 V, whereas at higher potentials, CO2 electrolysis at the triple-phase boundary became the rate-determining step. Short-term cell testing at 1.7 V and 500°C revealed the presence of a Fe3C phase on the cathode, which affected the electrochemical performance of the cell.