Surface borate layer dramatically enhances the stability of NiFe-layered double hydroxide for alkaline seawater oxidation

Abstract

Seawater electrolysis presents a sustainable approach for producing green hydrogen using renewable energy sources. However, chloride ions (Cl⁻) and their derivatives significantly reduce the durability of anode catalysts, severely hindering their practical application. In this work, we developed a borate (B_i) modified NiFe layered double hydroxide on nickel foam (NiFe LDH@NiFe-B_i/NF) to blocks Cl⁻ and mitigates chlorine reactions during alkaline seawater oxidation (ASO). In situ electrochemical spectroscopic studies show that the B_i layer effectively promotes NiOOH formation, thereby enhancing oxygen evolution reaction (OER) activity. Specifically, the B₄O₇²⁻-rich anionic overlayer effectively prevents Cl⁻ adsorption and thus protect the active site during ASO. As a result, NiFe LDH@NiFe-B_i/NF requires a lower overpotential (ƞ) of 354 mV to achieve an industrial current density (j) of 1000 mA cm⁻² compared to NiFe LDH/NF, which requires 407 mV, in a 1 M KOH + seawater. Notably, NiFe LDH@NiFe-B_i/NF exhibits exceptional long-term electrochemical durability, maintaining stable operation for 600 h at a j of 1000 mA cm⁻² in alkaline seawater. Additionally, membrane electrode assembly fabricated with NiFe LDH@NiFe-B_i/NF requires lower ƞ to reach the same voltages than Pt/C/NF||RuO₂/NF. Furthermore, Pt/C/NF||NiFe LDH@NiFe-B_i/NF operates at 300 mA cm⁻² for 150 h without significant activity degradation.