Prior to all electrochemical experiments, p(NDI-T2 P75) was purified to remove residual Pd contamination from polymer synthesis (Figure , Table ), resulting in low Pd concentrations of 2 -5 ppm. While it has been reported that a polymer much like p(NDI-T2 P75) primarily produces H2O upon reducing O2 in a 4-electron reaction, we demonstrate that the removal of residual Pd is crucial for evaluating intrinsic performance. We find residual Pd impurities result in a positive shift in the measured halfwave voltage, E1/2, for oxygen reduction and modifies the selectivity from H2O2 towards H2O as the majority product (Figure ). We use rotating ring-disk electrochemistry (RRDE) to investigate the behavior of p(NDI-T2 P75) in [K + ] = 1 M aqueous electrolytes with pH varied between 7.0 and 14.2. Characteristic voltammograms at a scan rate of 5 mV s -1 for p(NDI-T2 P75) in Ar-saturated electrolytes are shown in Figure . For all tested pH values, three reversible redox peaks are observed. The first two peaks, which appear at more positive voltages, correspond to electron polaron formation and the third peak corresponds to the formation of the electron bipolaron. We confirm the n-type nature of these electron polaron formation reactions through conductivity measurements using an interdigitated electrode array in an organic electrochemical transistor (OECT) architecture (Figure ). The formation of the electron polaronic state is associated with electron/cation doping of the polymer film resulting in an electronic conductivity enhancement by a factor of >10 . We hypothesize that the voltage offset for the first two electron polaron peaks arises from contributions of the mixed side chain composition and the influence of mesoscopic domains of ordered (crystalline) and disordered (amorphous) aggregates in the polymer film. It has been demonstrated that inter-chain electronic state hybridization can occur in ordered domains, which stabilizes the LUMO state (most positive reduction voltage) similar to the effect of charge-transfer hybridization, potentially resulting in a shift of the observed reduction voltage. Integration of the reduction current suggests ~50% of the film can be reduced to the bipolaronic state at 5 mV s -1 (corresponding to a charging time of 4 minutes), confirming fast charge transport through the bulk of the polymer electrode. Figure . a) Ar-saturated reduction/oxidation voltammograms at a scan rate of 5 mV s -1 . b) O2saturated RRDE measurement at 1600 r.p.m. with a scan rate of 0.5 mV s -1 , showing a high ring current (Ering = 1.20 V vs. RHE). c) Percent H2O2 produced calculated using the ring current from (b) and the electrode collection efficiency (N = 0.25). d) Number of electrons transferred during the ORR as calculated through Koutecký-Levich analysis. e) Quantification of Faradaic efficiency obtained from constant current electrolysis (-2 mA cm -2 ) in an H-cell performed on a carbon fiber paper supported p(NDI-T2 P75) film in 0.1 M KOH.