Self-Adjusting Activity Induced by Intrinsic Reaction Intermediate in Fe-N-C Single-Atom Catalysts.

Fe-N-C single-atom catalysts (SACs) exhibit high activity for oxygen reduction reaction (ORR). However, it remains controversial how the active center mediates catalysis, and the predicted potential deviates from experimental results, hindering development of ideal SACs. Here, using first-principles calculations, we present a microkinetic model for ORR on Fe-N-C SACs, disclosing a self-adjusting mechanism induced by its intrinsic intermediate. The modeling results show that the single-atom Fe site of the FeN4 center of Fe-N-C is covered with an intermediate OH* from 0.28 to 1.00 V. Remarkably, such OH* becomes part of the active moiety, Fe(OH)N4, and can optimize intermediate bindings on the Fe site, exhibiting a theoretical half-wave potential of ∼0.88 V. Partial current density analysis reveals the dominating associative path over the dissociative ones. In addition, ORR on Mn-N-C and Co-N-C SACs is unveiled. This work demonstrates the necessity of assessing the effect of intrinsic intermediates in single-atom catalysis and provides practical guidance for rational design of high-performance SACs.