To analyze this possibility, CORR was repeated on a Pt working electrode as the benchmark (Figure ). Pt was chosen because it is known to produce H2 with nearly 100% selectivity accompanied by a small amount of CH4, while does not produce C2H4, CH3CHO, or C2H5OH under the given reaction conditions . By comparing the m/z intensity change on Pt with that on Cu, it is easy to confirm if an increased m/z is somehow related to H2 formation. IM2 increased more on Pt than on Cu (Figure ) as expected due to the greater activity to H2 formation of Pt compared to Cu. Interestingly, IM31 increased even more compared to Cu. This suggests that the increase of IM31 is related to H2 formation, and thus the IM31 increase on Cu is likely not to be due to ethanol. This leads to the question of why increased H2 formation leads to an increased IM31 signal. If H2-induced pressure increase was the reason, all tracked m/z are expected to increase, but this is not seen in Figure 1. It must be due to a different phenomenon.