Tailoring the electronic structure of an exfoliated layered double hydroxide using a lanthanide for chloride-ion blocking in seawater splitting†

Abstract

Seawater is one of the most abundant sources of hydrogen in our environment, and it has great potential for the production of hydrogen via water electrolysis. However, seawater electrolysis is challenging as chloride ions could obstruct catalytic active sites, reducing *OH adsorption. Therefore, it is crucial to prevent chloride ions from accessing the active sites. Herein, we modulated the Lewis acidity of electrocatalysts to solve this problem. In particular, the Lewis acidity of Ni²⁺ and Fe³⁺ ions in a layered double hydroxide (LDH) was enhanced by incorporating the lanthanide dopant Ce, thereby tuning the surface electronic configurations to prefer OH* adsorption over Cl* adsorption. Further, the Ce-doped Ni–Fe LDH (CNF-LDH) was exfoliated via the O₂ plasma process to improve the accessibility of active sites for intermediates. The resultant CNF-LDH-E exhibited an overpotential of 230 and 169 mV at 100 mA cm⁻² for OER and HER, respectively, in alkaline freshwater (1 M KOH) and 290 and 285 mV, respectively, in simulated seawater (1 M KOH + 0.1 M NaCl) electrolytes. The impact of Lewis acidity on blocking the chloride ions was further investigated using density functional theory (DFT) calculations.