Strain Engineered Co³⁺ Sites Promoted Electro-Generation of Active CoO₂ Species for Efficient Iodide Oxidation...

Iodide oxidation reaction (IOR) is regarded as a feasible alternative to the sluggish oxygen evolution reaction (OER) due to its lower energy demand and valuable iodate production. In this regard, high-valent metal sites are essential to drive the reaction efficiently. Although Co-based Prussian blue analogues (Co-PBAs) can generate high valent metal sites under anodic potential, the implementation of Co-PBAs for IOR remains elusive. Moreover, the nature of the true active sites, as well as the effect of electronic features of the parent PBA, is still underexplored. Herein, we report strain-engineered Co³⁺ sites in Fe-Co(O)OH via electrochemical reconstruction of a nitroprusside-based Co-PBA precatalyst. Spectroscopy and microscopy manifested the compressive strain in Co³⁺ sites of active Fe-Co(O)OH catalyst. In situ Raman spectroscopy revealed the dynamic generation of Co⁴⁺ (CoO₂) species, which act as key active centers for both OER and IOR. Mechanistic investigations have demonstrated that IOR proceeds via a proton-coupled electron transfer (PCET) pathway, while the OER follows a lattice oxygen mechanism (LOM) through a proton-decoupled electron transfer (PDET) pathway. Notably, Fe-Co(O)OH delivered 100 mA cm^-2 current density at 1.35 V versus RHE potential for IOR. In situ electrochemical impedance spectroscopy (EIS) have further validated the accelerated reaction kinetics and enhanced charge transfer properties of Fe-Co(O)OH.