Approaching theoretical performances of electrocatalytic hydrogen peroxide generation by cobalt‐nitrogen moieties

Electrocatalytic oxygen reduction reaction (ORR) has been intensively studied for efficient and environmentally benign energy conversion processes. However, insufficient understanding of ORR 2e--pathway mechanism at the atomic level inhibits rational design of electrocatalysts with both high activity and selectivity, causing concerns including catalyst degradation due to Fenton reaction or poor efficiency of H2O2 electrosynthesis. Herein we show that the generally accepted ORR electrocatalyst design based on a Sabatier volcano plot argument optimises activity but is unable to account for the 2e--pathway selectivity; an extended “dynamic active site saturation” model that examines in addition the hydrogenation kinetics linked to the OOH* adsorption energy enables us to resolve the activity-selectivity compromise. Through electrochemical and operando spectroscopic studies on the ORR process governed by a series of Co-N x /carbon nanotube hybrids, a construction-driven approach that aims to create the maximum number of 2e- ORR sites by directing the secondary ORR electron transfer step towards the 2e- intermediate is proven to be attainable by manipulating O2 hydrogenation kinetics. Control experiments reveal the O2 hydrogenation chemistry is related to a catalyst reconstruction with lower symmetry around the Co active centre induced by the application of a cathodic potential. The optimised catalyst exhibits a ~100% H2O2 selectivity and an outstanding activity with an ORR potential of 0.82 V versus the reversible hydrogen electrode to reach the ring current density of 1 mA cm-2 by using rotating ring-disk electrode measurement, which is the best-performing 2e- ORR electrocatalyst reported to date, and approaches the thermodynamic limit.