Unveiling the Abnormal Oxidizability of Ferricyanide in Alkaline Solution

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 (H₂O···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.