Experimental and Theoretical Insights into the Borohydride-Based Reduction-Induced Metal Interdiffusion in Fe-Oxide@NiCoO for Enhanced Oxygen Evolution.

The oxygen evolution reaction (OER) plays a key role in determining the performance of overall water splitting, while a core technological consideration is the development of cost-effective, efficient, and durable catalysts. Here, we demonstrate a robust reduced Fe-oxide@NiCoO bilayered non-precious-metal oxide composite as a highly efficient OER catalyst in an alkaline medium. A bilayered oxide composite film with an interconnected nanoflake morphology (FeO@NiCoO) is reduced in an aqueous NaBH solution, which results in a mosslike FeO@NiCoO (reduced Fe-oxide@NiCoO; rFNCO) nanostructured film with an enhanced electrochemical surface area. The rFNCO film demonstrates an outstanding OER activity with an extraordinary low overpotential of 189 mV at 10 mA cm (246 mV at 100 mA cm) and a remarkably small Tafel slope of 32 mV dec. The film also shows excellent durability for more than 50 h of continuous operation, even at 100 mA cm. Furthermore, density functional theory calculations suggest that the unintentionally in situ doped Ni during the reduction reaction possibly improves the OER performance of the rFNCO catalyst shifting -band centers of both Fe and Ni active sites.