Unveiling the Abnormal Oxidizability of Ferricyanide in Alkaline Solution
Xue Long, Wendong Yang, Hua Jiang, Linfeng Wang, Yilin Zeng, Pei Liu, Xuan Cai, Yifan Zhang, Zuoxuan Gan, Huaiyu Ke, Jiabao Sun, Jiangjiang DuanABSTRACT
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.