Geometric synergy of Steam/Carbon dioxide Co-electrolysis and methanation in a tubular solid oxide Electrolysis cell for direct Power-to-Methane

Abstract

Power-to-methane (PtM) is a strategy for seasonal energy storage to enable wider energy share through the existing natural gas networks H2O/CO2 co-electrolysis and methanation reaction can synchronously occur in a single tubular solid oxide electrolysis cell (SOEC) reactor to facilitate direct PtM. In this study, we aim to intensify the synergy between geometrical structure and complex physical–chemical processes in a tubular SOEC reactor for higher Electricity-to-CH4 efficiency. First, we divided the reactor into two parts: Electrolysis region and Methanation reaction (MR) region, and investigated their respective contribution and interaction. According to a self-developed multi-physics tubular SOEC model, we optimized the geometry of the reactor to synergistically regulate the field temperature of the Electrolysis and MR region. The results indicate that CH4 production ratio and Electricity-to-CH4 efficiency can be enhanced through the lengthening of either the Electrolysis region or the MR region. When fed with a cathode gas of 75%H2O + 20%CO2 + 5%H2 (20 mL min−1), an tubular SOEC reactor optimized with an Electrolysis region of 0.10 m and a MR region of 0.045 m can convert 91% of CO2 to CH4 at 1.5 V with an Electricity-to-CH4 efficiency of 49%. An improved synergy between pressure, operating voltage and gas flow can significantly improve CH4 production with less electricity. A tubular SOEC reactor with the optimized geometry can convert 95% of CO2 to CH4 at 1.2 V and 16 bar with an Electricity-to-CH4 efficiency of 81%, producing 52 vol% of dry CH4 at the cathode outlet. After optimization, tubular SOEC reactor can realize a more efficient PtM, thus, promote the combination of renewable power and natural gas networks.