Unveiling the coupling effect of sp² domain size and local active sites in switching the selectivity of nanocarbon catalysts toward the oxygen electro-reduction.

Abstract

Carbon-mediated active site engineering has demonstrated remarkable electrocatalytic activities for oxygen reduction reactions (ORR), yet the relationship between carbonaceous structure and ORR selectivity remains unclear. Herein, we show that local active sites and sp² domain size jointly regulate ORR selectivity. Specifically, we demonstrate that while local active sites determine the rate-limiting intermediate type (from O₂^-* to OOH*), increasing sp² domain size can either promote OOH* formation and subsequent O-O bond dissociation or facilitate OOH* consumption to enhance the reaction rate, all of which enable the ORR pathway to switch from 2e^- to 4e^-. This coupling is also validated using nitrogen-doped carbon soot to induce a profound change in ORR selectivity, where the synergistic interplay between small carbon domain sizes and nitrogen dopants boosts the 2e^- selectivity from ~50% to over 90%. Ultimately, p-band theory integrates these coupling mechanisms, offering a fundamental principle for designing highly selective nanocarbon electrocatalysts.