Curvature-Engineered Steering of Oxygen Electroreduction Pathways on Single-Atom Catalysts

Single-atom catalysts (SACs) are a promising class of electrochemical oxygen reduction reaction (ORR) catalysts, enabling either a four-electron (4e^-) pathway for energy conversion or a two-electron (2e^-) pathway for H₂O₂ production. However, the precise control and optimization of the ORR pathway remain challenging due to the lack of strategies for fine-tuning the SACs coordination structures. Herein, we developed a curvature engineering strategy that enables, for the first time, continuous steering of the ORR pathway from 2e^- to 4e^- over Cu-based SACs. Through theoretical calculations and in-situ spectroscopy, we revealed the essential mechanism by which active-site tensile strain and interfacial water restructuring, induced by carbon nanotubes with varying curvature, jointly govern ORR activity and selectivity. The Cu single-atom sites on high-curvature CNTs exhibit 4e^- ORR performance comparable to that of Pt/C, while those on low-curvature CNTs achieve up to 99.5% 2e^- ORR selectivity. Proof-of-concept solid-electrolyte electrolyzer equipped with Cu SACs demonstrates exceptional performance for H₂O₂ electrosynthesis, achieving H₂O₂ Faradaic efficiencies of 96.4% and 92.5% at 200 and 300 mA cm^-2, respectively, and sustaining >90% efficiency for over 100 h at a total current of 3 A. This work establishes curvature engineering as an ORR descriptor for precisely regulating SACs and designing advanced electrocatalysts.