Proton transfer dynamics control the mechanism of O2 reduction by a non-precious metal electrocatalyst

Abstract

© 2016 Macmillan Publishers Limited. All rights reserved. Many chemical and biological processes involve the transfer of both protons and electrons. The complex mechanistic details of these proton-coupled electron transfer (PCET) reactions require independent control of both electron and proton transfer. In this report, we make use of lipid-modified electrodes to modulate proton transport to a Cu-based catalyst that facilitates the O2reduction reaction (ORR), a PCET process important in fuel cells and O2reduction enzymes. By quantitatively controlling the kinetics of proton transport to the catalyst, we demonstrate that undesired side products such as H2O2and O2-arise from a mismatch between proton and electron transfer rates. Whereas fast proton kinetics induce H2O2formation and sluggish proton flux produces O2-, proton transfer rates commensurate with O-O bond breaking rates ensure that only the desired H2O product forms. This fundamental insight aids in the development of a comprehensive framework for understanding the ORR and PCET processes in general.