In order to determine the potential dependence of such on over-oxidation process of PW while at the same time decoupling it from the HC, symmetric PW|NP40|PW cells were additionally cycled potentiodynamically both to the equivalent of 4.1 V (Fig. ) and 4.9 V vs Na + /Na. Figure shows the current along with the three observed gases, CO2, (CN)2 and POF3 as PW is pushed to 4.9 V vs. Na + /Na. The counter PW electrode is over-sized and predesodiated to 60 mAh/g, the end of the HS-FeN plateau at 3.1 V vs. Na + /Na. Since CO2 is observed, we can conclude that not all the CO2 seen in the Na-plating cell was due to the reaction between the electrolyte and Na-metal, but rather a secondary process related to the PW. (CN)2 gas (instead of O2). However, the amount of (CN)2 appears to be correlated to electrode potential since there is a dramatic increase in evolution amount between Fig. (a) and Figure .