In Situ Identification of Zinc Sites as Potential-Dependent Selectivity Switch over Dual-Atom Catalysts for H2O2 Electrosynthesis

Controllably breaking the activity–selectivity trade-offs in the electrocatalytic oxygen reduction reaction to produce H₂O₂ has long been a challenge in renewable energy technologies. Herein, by assigning the activity and selectivity requirements to two independent single-atom sites, we deliberately engineered a Co–Zn DAC for promising H₂O₂ electrosynthesis, from which the Co sites provided the activity response for oxygen reduction, and the Zn sites regulated the reaction selectivity toward the 2e^– pathway. Through multidimensional in situ characterizations, a potential-dependent switching function of the Zn sites was revealed, which made the increase in H₂O₂ production at various reaction stages controllable. As a result, efficient H₂O₂ selectivity switching from 11.1% in the single Co atom catalyst to 94.8% in the Co–Zn DAC was realized, with a prominent turnover frequency of 2.7 s^–1 among the reported H₂O₂-producing catalysts. Notably, a similar effect was also observed in M–Zn DACs (M = Pt, Ru, or Ni), which demonstrated the universal switcher role of the Zn sites. The real-time catalytic site behavior insights gained through this integrated experimental and theoretical study are envisioned to be valuable not only for the ORR but also for other energy catalysis reactions involving activity–selectivity trade-off issues.