Rational design of nitrate-intercalated NiFe LDH with dual chloride-blocking mechanisms for stable alkaline seawater oxidation

Abstract

The development of chloride-resistant electrocatalysts for alkaline seawater oxidation (ASO) is crucial for sustainable hydrogen production, yet remains fundamentally challenged by competitive chloride oxidation and structural degradation. In this work, we report a molten salt-derived nitrate-intercalated NiFe layered double hydroxide that achieves an ultralow overpotential of 360 mV while demonstrating exceptional stability over 1100 h at 1000 mA cm-2 for ASO. Through comprehensive characterization, we reveal that nitrate intercalation induces in situ surface reconstruction into an amorphous-crystalline Ni/FeOOH heterostructure to enhance ASO activity. More importantly, we identify a dual chloride-blocking mechanisms against chloride corrosion: surface-chemisorbed NO3- species create an electrostatic shielding effect through negative charge accumulation at the Helmholtz plane, and nitrate-induced interfacial water restructuring increases the network water content by 14.3% via hydrogen-bond anchoring, forming a dense hydration layer that physically blocks Cl- penetration. This synergistic combination of electrostatic repulsion and physical blocking effects enables unprecedented chloride resistance. Furthermore, the reconstructed interfacial water network facilitates efficient hydroxide ion transport through the Grotthuss mechanism, further boosting ASO kinetics. When implemented in a prototype electrolyzer, the catalyst demonstrates practical viability with a low cell voltage of 2.16 V (at 1000 mA cm-2) and negligible degradation over 100 h of continuous operation.