Experimental Characterization and Theoretical Modeling of Methane Production by H2O/CO2 Co-Electrolysis in a Tubular Solid Oxide Electrolysis Cell

Abstract

Methane production by H2O/CO2 co-electrolysis in solid oxide electrolysis cells (SOECs) is a promising method to store unstable renewable power and to reduce CO2 emission. In this paper, the CH4 synthesis characteristics in tubular SOECs (TSOECs) is studied by experiments and numerical simulation in the temperature range of 550–650°C. The experimental results show that the addition of H2 into the cathode inlet gas flow and the increase of electrolysis current could significantly promote CH4 production rate. In the case of the experiments without H2, the CH4 production ratio increased by less than 0.04% when the operating voltage varied from OCV to 1.5 V. After feeding the H2 into the cathode atmosphere, the CH4 production ratio increases by 3–4%. A CH4 yield of 9.94% and a CH4 production ratio of 12.34% were achieved at 550°C with 20% H2 fed into cathode and an applied voltage of 1.5 V. Finally, a theoretical model is developed by considering the chemical/electrochemical reaction and transport processes, and the thermal distribution and optimal operating condition of the TSOEC are studied. An designed thermal distribution in counter-flow mode with lower inlet steam partial pressure could dramatically improve the CH4 production.