Tailoring Cu Nanoparticles Motif Into Atomic‐Level Sites for Efficient H ₂ O ₂ Electrosynthesis

ABSTRACT The engineering of active motifs via ensemble effects has emerged as a powerful strategy for modulating oxygen reduction reaction (ORR) selectivity. While Cu‐based materials have demonstrated promising potential as ORR electrocatalysts, the correlation between ensemble effects in Cu active motifs and the selectivity toward hydrogen peroxide (H 2 O 2 ) production via the 2e − ORR pathway remains insufficiently investigated. Herein, we systematically demonstrate that structural evolution of carbon‐supported Cu electrocatalysts from nanoparticles to atomic‐level single Cu─C 2 sites and nanoclusters (denoted as Cu SA ─Cu clu /C) effectively eliminates accessible ensemble sites characteristic of nanoparticles and induces preferential end‐on adsorption of O 2 on atomic‐level sites, thereby significantly enhancing both the selectivity and activity for H 2 O 2 generation. Comprehensive evaluations through rotating ring‐disk electrodes, H‐cell testing, and flow cell amplification consistently verify their superior performance. Integrating experiments and theoretical modeling, we confirm that the 2e − ORR selectivity and activity exhibit progressive enhancement as the active motif dimension decreases from nanoparticles (multi‐atom ensembles) to nanoclusters (sub‐nm aggregates) and ultimately to single‐atom sites. This study provides the first experimental confirmation of the size‐dependent activity/selectivity trends in H 2 O 2 generation over Cu‐based electrocatalysts, establishing a generalizable framework that could be extended to other transition metal systems for precise regulation of ORR activity and selectivity.