Sodium-air fuel cell for high energy density and low-cost electric power

Abstract

Alkali metal-air batteries have exceptional theoretical energy densities but suffer from poor rechargeability and low power largely due to the formation of solid discharge products. An alternative concept demonstrated here is a liquid sodium metal-air fuel cell incorporating a solid electrolyte membrane, wherein controlled humidification of the air stream continuously removes sodium hydroxide discharge product as a deliquesced liquid. This fuel cell reaches stack-level energy densities of 1,200 Wh/kg (1,295 Wh/L) at 80 mA/cm² and 1,540 Wh/kg (1,760 Wh/L) at 40 mA/cm² current density, while consuming up to 2.3-cm thickness of sodium metal (2,500 mAh/cm² areal capacity) in continuous operation. The sodium hydroxide discharge product also readily captures ambient CO₂. Combined with the high planetary abundance and low cost of sodium, the sodium-air fuel cell may be a more sustainable power source for hard-to-decarbonize transportation and stationary electrical power applications.