Tailoring Cu Nanoparticles Motif Into Atomic-Level Sites for Efficient H₂O₂ Electrosynthesis

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 (H₂O₂) 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─C₂ 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 O₂ on atomic-level sites, thereby significantly enhancing both the selectivity and activity for H₂O₂ 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 H₂O₂ 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.