High efficiency electrical energy storage using a methane–oxygen solid oxide cell

Reversible solid oxide cells (SOCs) are potentially useful for electrical energy storage due to their good storage scalability, but have not been seriously considered due to concerns over round-trip efficiency. Here we propose an SOC storage chemistry where the fuel cycles between H2O–CO2-rich and CH4–H2-rich gases. The unique feature is the formation of CH4 during electrolysis, a less endothermic process than the usual H2- or CO-forming reactions, enabling improved efficiency. Thermodynamic calculations and preliminary experiments show that the CH4-rich storage chemistry is produced during SOC operation at reduced temperature (∼600 °C) and/or increased pressure (∼10 atm). Balance of plant storage system requirements are discussed briefly.