Unveiling the Abnormal Oxidizability of Ferricyanide in Alkaline Solution

ABSTRACT The ferricyanide/ferrocyanide ([Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− ) redox couple is widely used in energy storage and catalysis because of its rapid electron‐transfer kinetics and excellent reversibility. Yet its chemistry in highly alkaline media (pH ≥ 14) remains incompletely understood. In particular, [Fe(CN) 6 ] 3− displays unexpectedly strong oxidizing activity under alkaline conditions despite its moderate redox potential (∼0.45 V vs. SHE). Here, we show that this apparent contradiction arises from the redox‐mediated generation of hydroxyl radicals (•OH). Spectroscopic analyses, ab initio molecular dynamics (AIMD) simulations, and density functional theory (DFT) reveal that OH − penetrates and reorganizes the primary solvation shell of [Fe(CN) 6 ] 3− through hydrogen bonding (HB), enabling interfacial electron transfer from hydrogen‐bonded water‐hydroxide clusters (H 2 O···OH − ) to [Fe(CN) 6 ] 3− . Guided by this mechanism, we develop a [Fe(CN) 6 ] 3− ‐mediated Fenton‐like anodic reaction (FerroOR) as a low‐energy alternative to the oxygen evolution reaction (OER). When coupled with the hydrogen evolution reaction (HER), a catalyst‐free carbon felt (CF) anode delivers 100 mA cm −2 at 1.45 V. These findings resolve a long‐standing mechanistic puzzle and establish alkaline [Fe(CN) 6 ] 3− as a low‐cost redox mediator for energy‐efficient electrochemical oxidation.