Ultrafast in situ-formed FeOOH ultrathin overlayers on NiFe-LDH surfaces enable highly durable alkaline seawater oxidation

Abstract

This work presents a simple one-step strategy for in situ engineering of NiFe-layered double hydroxide (NiFe-LDH) surfaces into an ultrathin FeOOH overlayer by N₂-plasma irradiation. The FeOOH phase promotes the formation and stability of NiOOH and inhibits Cl⁻ ions from entering the active phase. Theoretical calculations show that NiFe-LDH/FeOOH has a superior adsorption energy toward OH⁻ than toward Cl⁻, reducing the Cl⁻ level near the catalyst surface. NiFe-LDH/FeOOH exhibits better OER activity and selectivity than NiFe-LDH in alkaline seawater electrolytes, indicating the critical role of the FeOOH film. The NiFe-LDH/FeOOH electrode can operate stably for 195 hours at 250 mA cm⁻² in 1 M KOH + 2.5 M NaCl and for 200 hours even under industrial conditions (6 M KOH + seawater, 60 °C), demonstrating remarkable durability. In alkaline natural seawater, an anion exchange membrane electrode assembly electrolyzer using NiFe-LDH/FeOOH as the anode delivers a high current of 500 mA cm⁻² at 2.114 V and robust durability with stable operation for over 100 hours at 250 mA cm⁻². This study provides a feasible avenue to prepare high-performance OER catalysts for alkaline seawater electrolysis.