The discharge of the cell as shown in Figure indicates a significant amount of overpotential in the system. Impedance spectroscopy, shown in Figure , in the charged state indicates that there is a significant amount of ohmic resistance in the cell, which likely can be attributed to oxygen conduction through the YSZ tube, and lithium transport through the LLZO tube and molten salt. The low frequency feature is likely from the oxygen reduction reaction on the platinum electrode. Indeed, the cell overpotential during discharge corresponds to a resistance of approximately 65 Ohms, significantly lower than the DC resistance implied from the EIS data at open circuit (Re(Z) as frequency approaches zero), implying a non-linear current-overpotential relationship. In an optimized cell, the platinum electrode will need to be replaced with another oxygen reduction electrode which is more suitable for lower temperature operation. 0.5 cm 0.5 cm