While gold had been established as the better material for the two-step reduction of oxygen, it was necessary to confirm that detectable amounts of hydrogen peroxide were being produced. This was undertaken using a gold IDE where one comb underwent CV 1.2 V to -1 V (generator) while the other was biased at a constant potential at 0.6 V (collector), suitable for oxidising hydrogen peroxide. Scans were performed at 50 mV/s to ensure that the produced hydrogen peroxide could diffuse to the collector before being consumed at the generator. Figure shows the result of this test performed in oxygen saturated ADW. The generator electrode measured a current of 31.95 nA, while the collector measured a current of 11.82 nA. From this, a collection efficiency of 44% was established significantly higher than previous reports for IDEs and ring-disc systems. This collection efficiency seems low in comparison to ferrocene (~95%), however due to the complex reaction mechanism associated with oxygen reduction, this is a very high for hydrogen peroxide. Full conversion from oxygen to hydrogen peroxide may not occur, but it is also possible that the subsequent reaction consuming the hydrogen peroxide may result in lower amounts of the species reacting at the detector. This is also why the collector scan shows a peak rather than a steady-state response, as the concentration of hydrogen peroxide is subsequently decreasing. Similarly, the reactions of the two individual species must be considered. In this case, the oxygen is being chemically altered, therefore a simple calculation for collection efficiency does not apply. Interestingly, significant redox cycling was observed, as evident by the change in overall shape of the CV. The first step of the oxygen reduction reaction is amplified, due to the oxygen/hydrogen peroxide redox couple being cycled between the collector and the generator, which enhances the current for this reaction. The total current remains the same however, as the second step in the oxygen reduction reaction cannot be redox cycled. A comparison of single mode and GC mode for gold is shown in the supporting Information (SI Fig4). The same test was performed on a platinum IDE to further confirm that hydrogen peroxide is not produced in greater quantities. Figure shows that the collector response for platinum under the same conditions is extremely small. The reverse sweep of the generator electrode measured 29 nA, while the collector sweep measured approximately 1.2 nA. Again, the collector efficiency cannot give the complete picture but for platinum it is only ~4%, significantly less than the gold electrode. Interestingly, the small amount of hydrogen peroxide produced is only measured on the forward sweep. On gold hydrogen peroxide was produced on the reverse sweep, albeit lower than the forward sweep. Platinum, however, showed no hydrogen peroxide production at all on the reverse sweep. This indicates that the presence of a surface platinum oxide in some way facilitates the production of hydrogen peroxide,. The amount produced, however, was still too low for platinum to be considered as a generator material for the sensor. Furthermore, there is no change to the platinum generator signal when the collector is appropriately biased, as no redox cycling occurs, highlighted in the supporting information (SI .