Unmasking active sites in linker coordinated nickel–cobalt hydroxide for the electrocatalytic iodide oxidation reaction

Abstract

Identification of the active sites responsible for both the oxygen evolution reaction (OER) and the iodide oxidation reaction (IOR) is critical for the rational design of high-performance catalysts. However, active sites for the IOR have not been previously explored to the best of our knowledge. Herein, we investigate the active sites of the OER and IOR on a benzoate-coordinated NiCo-hydroxide (BZ-NiCo-H) catalyst. Spectroscopic studies reveal that benzoate coordination modulates the electronic and coordination environment, facilitating the generation of high-valent metal species. BZ-NiCo-H exhibited excellent catalytic activity, delivering 100 mA cm⁻² at 1.42 V vs. RHE potential for the IOR and 1.63 V vs. RHE potential for the OER. In situ Raman spectroscopy coupled with electrochemical analyses identifies Ni⁴⁺ in γ-Ni(O)OH as the OER active site, whereas Ni³⁺ in β-Ni(O)OH functions as the active site for the IOR. Mechanistic investigations demonstrate that benzoate coordination activates lattice oxygen, enabling the OER to proceed via a lattice oxygen mechanism (LOM). Furthermore, in situ electrochemical impedance spectroscopy and kinetic studies show that benzoate coordination significantly enhances charge transfer and lowers kinetic barriers for both reactions. These findings elucidate the distinct active sites for the OER and IOR, highlighting the beneficial role of organic ligand coordination in tuning catalytic performance.