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

Abstract

Nickel-iron layered double hydroxides (Ni-Fe LDHs) consist of stacked Fe3+-doped positively charged Ni-hydroxide layers containing charge-balancing anions and water molecules between the layers. Although Ni-Fe LDHs are highly active in the oxygen evolution reaction (OER) under alkaline conditions, their poor operational stability remains an issue. Herein, based on density functional theory calculations, it is proposed that the inclusion of a higher Fe content (>40%) than the theoretical Fe3+ limit (≈25%) permitted by Ni-Fe LDHs can lead to improved structural stability. An Fe-rich Ni-Fe LDH electrode is therefore prepared via a growth strategy based on the controlled oxygen corrosion of an Fe substrate, by enabling the incorporation of additional Fe2+ into the Ni2+-Fe3+ LDH structure. Indeed, microstructural and elemental analysis confirm the presence of additional Fe2+. 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 stability under dynamic operating environments without any significant performance degradation or metal ion dissolution. Finally, the practical feasibility of the Fe-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 reliable OER electrodes for use in commercial water electrolyzers.