Furthermore, (CN)2 gas is observed at ~>3.6 V peaking at the cut-off voltage. It is worth noting that the amount of (CN)2 compared to the other gasses is significantly smaller, evolving ~0.35 nmol (3 orders of magnitude less than the 2.5 V H2 peak) in each cycle, which equates to ~0.0018% of the PW lost to (CN)2. At first thought one might assume the peaks in CO2 and H2 are the start of direct electrochemical oxidation of the electrolyte. However, as we have shown in a previous study, EC only oxidises > 4.6 V vs Li + /Li (4.27 V vs Na + /Na) while this cell only goes up to 4.0 V vs Na + /Na 49 . Furthermore, no evidence of POF3 evolution is observed, which usually indicates that direct electrolyte oxidation does not occur. The heightened evolution in CO2/H2/C2H4 and the presence of CO at high cell voltages rather indicates Na-plating in the system (this particular cell had an N/P ratio <1) . The increased gassing (when HC is likely ≤0 V vs. Na + /Na) are likely a result of EC ring-opening and reduction on Na metal . et al. have shown through optical microscopy that carbonate electrolytes begin to bubble significantly when exposed to Na metal, additionally reporting that Na + based electrolyte suffer from reduction additionally forming CO . These results highlight the utility of gas analysis to study the onset of Na metal plating. There was little to no effect on the electrochemistry of the plating-induced cell, possibly because of the high electrolyte loading and solubility of the products. These effects would be exaggerated and much more evident in a commercial system where there is much less electrolyte to electrode surface area . Furthermore, since there is Nametal on the negative electrode at the time (CN)2 is observed, we can conclude that its onset potential is in fact 3.6 V vs Na + /Na. Therefore, the (CN)2 release starts immediately after PW has been completely desodiated and the standard cycling window (to 3.7 V vs Na + /Na) is on the cusp of (CN)2 release. There is more H2 evolution upon discharge at 2.5 V than in the normal cell, which is expected as the cell is pushed down to 0.0 V (as opposed to 1.30 V).