Harnessing chloride to drive catalyst reconstruction for durable and efficient seawater electrolysis

Direct seawater electrolysis offers an attractive route for sustainable hydrogen production, yet its practical implementation remains constrained by the corrosive nature of chlorion (Cl^-). Here, we reveal that trace amounts of Cl^-, rather than being detrimental, can play a constructive role in directing the structural evolution of transition-metal catalysts. Guided by this insight, NiS₂ nanoparticles with controlled loading amounts on NiFe-MOF nanosheets (denoted as NiFe-MOF-S) are designed to enable fine regulation of Cl^- proximity to the active metal sites. This design promotes the in situ reconstruction of catalyst into a dense γ-NiFeOOH phase with short Ni-Fe bond lengths, which triggers a mechanistic shift from the lattice-oxygen-mediated pathway to oxide path mechanism. NiFe-MOF-S achieves high oxygen evolution performance in alkaline seawater (1 M KOH + seawater), requiring a much lower overpotential of 213 mV to reach 500 mA cm^-2 in alkaline seawater than that in alkaline water (1 M KOH) (268 mV). Furthermore, the electrocatalyst demonstrates high durability with a degradation rate of only 1.4 μV h^-1 for over 7000 hours at 1.0 A cm^-2 in alkaline seawater. A kilowatt-level alkaline seawater electrolyzer equipped with NiFe-MOF-S/NF operates reliably for over 1500 hours at industrially relevant conditions.