conditions. Assuming Pt reduces O2 to H2O through a net 4-electron process (as evidenced through the absence of ring-current and Koutecký-Levich analysis in Figure ), the limiting current density measured for p(NDI-T2 P75) suggests the electrode is highly selective for the 2electron product. High Faradaic efficiencies for H2O2 were additionally observed through collection on the ring electrode (Figures ), Koutecký-Levich analysis (Figures ), and constant current electrolysis performed in an H-cell (Figure ). The polymer exhibited stable performance at -2 mA cm -2 for two hours in the H-cell measurements (Figure ) with negligible changes in chemical structure observed through post-mortem 1 H NMR analysis (Figure ). We observe a decrease in limiting current densities with increasing pH. In accordance with observations by McCreery et al., the pH-dependent variation of limiting current density suggests the reaction proceeds through a single-electron transfer reduction of dioxygen to superoxide followed by disproportionation of superoxide into hydro(gen) peroxide and dioxygen. This is explained in detail in Section 7 of the Supplementary Information.