Origins of hydrogen peroxide selectivity during oxygen reduction on organic mixed ionic-electronic conducting polymers

Electrochemical reduction of atmospheric oxygen provides carbon emission-free pathways for the generation of electricity from chemical fuels and for the distributed production of green chemical oxidants like hydrogen peroxide. Recently, organic mixed ionic-electronic conducting polymers (OMIECs) have been reported as active electrode materials for the oxygen reduction reaction. This work sets out to identify the operative oxygen reduction mechanism of OMIECs through a multi-faceted experimental and theoretical approach. Using a combination of pH-dependent electrochemical characterization, operando UV-Vis and Raman spectroscopy, ab initio calculations, and steady-state microkinetic simulations, we find that the n-type OMIEC, p(NDI-T2 P75), reduces oxygen selectively to hydrogen peroxide through a non-catalytic, outer-sphere pathway. This pathway serves as a general guide to understand the reactivity of an expanded set of n- and p-type OMIECs investigated in this work and provides a framework to rationalize when (or if) organic compounds function as heterogeneous catalysts for oxygen reduction.