Redefining ·CO₃^– Formation Chemistry: Zundel-like Switches Drive Carbonate-·OH Interfacial Reactivity

The formation of carbonate radicals (·CO₃^–) via carbonate-hydroxyl radicals (·OH) reaction is the cornerstone of environmental oxidative cycles, yet its molecular mechanism has long been limited to homogeneous bulk-phase paradigms, a view that conflicts with enhanced reactivity in interfacial-rich systems. Characterizing these processes is hindered by the transience of ·OH, system heterogeneity, and the inability to resolve in situ pathways. Herein, we combine ab initio molecular dynamics and machine learning molecular dynamics to redefine ·CO₃^– formation chemistry. We reveal that the gas–liquid interfacial reaction dominates ·CO₃^– generation, mediated by two proton-coupled electron transfer pathways (concerted proton–electron transfer and stepwise proton-transfer followed by electron-transfer). Critical to this reactivity are Zundel/Zundel-like hydrogen-bonded configurations, which act as “molecular switches” to trigger rapid reactions, enabled by the intrinsic interfacial enrichment of ·OH (85.2%) and HCO₃^– (92.2%). The interfacial pathway outperforms bulk reactions in ·CO₃^– formation, with (90 ± 6.13)% yield [vs (80 ± 8.94)% in bulk] and approximately 100-fold faster rate [(1.15 ± 0.01) × 10¹¹ M^–1 s^–1 vs (9.63 ± 0.03) × 10⁸ M^–1 s^–1], attributed to the partial solvation of ·OH at the interface. Additionally, ·OH reacts with bulk-phase CO₃^2– via heterogeneous electron transfer (bulk → interface), yielding a rate approximately 10-fold faster ·CO₃^– formation than homogeneous bulk reactions. These findings challenge bulk-centric paradigms, establish the interface as the dominant ·CO₃^– source, and provide actionable insights for optimizing advanced oxidation processes, water remediation, and catalyst design by leveraging interfacial microenvironments.