Abstract
Out of practicality, ambient air rather than oxygen is preferred as a fuel in electrochemical systems, but CO(2) and H(2)O present in air cause severe irreversible reactions, such as the formation of carbonates and hydroxides, which typically degrades performance. Herein, we report on a Na-air battery enabled by a reversible carbonate reaction (Na(2)CO(3)·xH(2)O, x = 0 or 1) in Nasicon solid electrolyte (Na(3)Zr(2)Si(2)PO(12)) that delivers a much higher discharge potential of 3.4 V than other metal-air batteries resulting in high energy density and achieves > 86 % energy efficiency at 0.1 mA cm(-2) over 100 cycles. This cell design takes advantage of moisture in ambient air to form an in-situ catholyte via the deliquescent property of NaOH. As a result, not only reversible electrochemical reaction of Na(2)CO(3)·xH(2)O is activated but also its kinetics is facilitated. Our results demonstrate the reversible use of free ambient air as a fuel, enabled by the reversible electrochemical reaction of carbonates with a solid electrolyte.