Selenate oxyanion-intercalated NiFeOOH for stable water oxidation via lattice oxygen oxidation mechanism

Transition metal-based compounds can serve as pre-catalysts to obtain genuine oxygen evolution reaction (OER) electrocatalysts in the form of oxyhydroxides through electrochemical activation. However, the role and existence form of leached oxygen anions are still controversial. Herein, we selected iron selenite-wrapped hydrated nickel molybdate (denoted as NiMoO/FeSeO) as a pre-catalyst to study the oxyanion effect. It is surprising to find that SeO₄²⁻ exists in the catalyst in the form of intercalation, which is different from previous studies that suggest that anions are doped with residual elements after electrochemical activation, or adsorbed on the catalyst surface. The experiment and theoretical calculations show that the existence of SeO₄²⁻ intercalation effectively adjusts the electronic structure of NiFeOOH, promotes intramolecular electron transfer and O–O release, and thus lowers the reaction energy barrier. As expected, the synthesized NiFeOOH-SeO only needs 202 and 285 mV to attain 100 and 1000 mA cm⁻² in 1 M KOH. Further, the anion exchange membrane water electrolyzer (AEMWE) consisting of NiFeOOH-SeO anode and Pt/C cathode can reach 1 A cm⁻² at 1.70 V and no significant attenuation within 300 h. Our findings provide insights into the mechanism, by which the intercalated oxyanions enhance the OER performance of NiFeOOH, thereby facilitating large-scale hydrogen production through AEMWE.