Rational Design of a Stable Fe-rich Ni-Fe Layered Double Hydroxide for the Industrially Relevant Dynamic Operation of Alkaline Water Electrolyers

Abstract

Nickel-iron layered double hydroxides (Ni-Fe LDHs) consist of stackedFe3+-doped positively charged Ni-hydroxide layers containingcharge-balancing anions and water molecules between the layers. AlthoughNi-Fe LDHs are highly active in the oxygen evolution reaction (OER) underalkaline conditions, their poor operational stability remains an issue. Herein,based on density functional theory calculations, it is proposed that theinclusion of a higher Fe content (>40%) than the theoretical Fe3+limit(≈25%) permitted by Ni-Fe LDHs can lead to improved structural stability. AnFe-rich Ni-Fe LDH electrode is therefore prepared via a growth strategy basedon the controlled oxygen corrosion of an Fe substrate, by enabling theincorporation of additional Fe2+into the Ni2+-Fe3+LDH structure. Indeed,microstructural and elemental analysis confirm the presence of additionalFe2+. This Fe-rich Ni-Fe LDH electrode not only offers a low OER overpotential(≈270 mV at 200 mA cm−2) but also exhibits an excellent operational stabilityunder dynamic operating environments without any significant performancedegradation or metal ion dissolution. Finally, the practical feasibility of theFe-rich Ni-Fe LDH electrode is demonstrated in a single-cell (34.56 cm2)operation. These findings are expected to aid in the development of reliableOER electrodes for use in commercial water electrolyzers.