Elucidating Electrocatalytic Oxygen Reduction Kinetics via Intermediates by Time-Resolved Electrochemiluminescence

Facile evaluation of oxygen reduction reaction (ORR) kinetics for massive electrocatalysts is critical for sustainable fuel cells development and industrial H2O2 production. Despite great success in ORR studies by mainstream strategies, such as membrane electrode assembly, rotation electrode technique and advanced surface-sensitive spectroscopy, the time/spatial distribution of reactive oxygen species (ROS) intermediates in the diffusion layer is still unknown. By time-resolved electrochemiluminescence (Tr-ECL), here we report an intermediate-oriented methodology for ORR kinetics analysis. Thanks to multiple ultra-sensitive stoichiometric reactions between ROS and the ECL emitter, except for electron transfer numbers and rate constants, the potential-dependent time/spatial distribution of ROS was successfully obtained for the first time. Such uncovered exclusive information would guide fuel cells and H2O2 production with maximized activity and durability, for instance, a larger overpotential would be beneficial to electrocatalysts of 2e reduction for H2O2 production, because of the high yield of H2O2 and low concentration of attackable O2•. This work would pave the exploration of not only the fundamentals of unambiguous ORR mechanism but also the durability of electrocatalysts for practical applications.