Performance and stability of renewable fuel production via H2O electrolysis and H2O–CO2 co-electrolysis using proton-conducting solid oxide electrolysis cells

Electrochemical production of commodity chemicals via H₂O electrolysis or H₂O–CO₂ co-electrolysis using solid oxide electrolysis cells (SOECs) offers a way to utilize excess renewables to address hard-to-decarbonize industrial sectors. Recently, proton-conducting SOECs (PCECs) have emerged as a promising type of SOEC in such applications, due to their unique properties of lower operating temperatures and flexible coupling with other chemical processes. However, the Faradaic efficiency (FE), i.e., the ratio of the experimentally produced H₂ to that which could be theoretically generated, of PCECs is less than 100 % and their stability, particularly under co-electrolysis operation, has yet to be verified. In this work, a systematic investigation of the variation of FE under different operating conditions and the stability of PCECs in both H₂O electrolysis and H₂O–CO₂ co-electrolysis is conducted. It is shown that the operating parameters have a significant effect on the apparent FE. During short-term stability testing, H₂O–CO₂ co-electrolysis mode presents much less favorable operating characteristics than H₂O electrolysis or H₂–CO₂ thermochemical conversion, with both FE and the catalytic activity of the negatrode (Ni-based fuel electrode) degrading gradually. Opportunities are identified to optimize operating parameters to maximize effectiveness and minimize degradation.