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"... Instead of a battery, the new concept is a kind of fuel cell — which is similar to a battery but can be quickly refueled rather than recharged. In this case, the fuel is liquid sodium metal, an inexpensive and widely available commodity. The other side of the cell is just ordinary air, which serves as a source of oxygen atoms. In between, a layer of solid ceramic material serves as the electrolyte, allowing sodium ions to pass freely through, and a porous air-facing electrode helps the sodium to chemically react with oxygen and produce electricity.
In a series of experiments with a prototype device, the researchers demonstrated that this cell could carry more than three times as much energy per unit of weight as the lithium-ion batteries used in virtually all electric vehicles today. ..."
From the highlights and abstract:
"Highlights
• A liquid sodium-humidified air fuel cell using a solid electrolyte is demonstrated
• Stack-level energy density reaches 1,200 Wh/kg (1,295 Wh/L) at 80 mA/cm2
• Continuous operation consumes up to 2.3-cm-thick Na metal (2,500 mAh/cm2)
• The sodium hydroxide discharge product spontaneously captures atmospheric CO2
Summary
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."
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