Chloride regulation of Fe sites enabling durable NiFe oxide anodes for oxygen evolution in seawater

Clarification of Fe behavior during seawater OER: Demonstrating that Fe in NiFe oxides undergoes continuous dissolution under seawater OER conditions, but can be dynamically stabilized through chloride-regulated speciation rather than being irreversibly lost. • Identification of a chloride-regulated Fe stabilization mechanism: Reveling that dissolved Fe 3+ forms FeCl 4 - species in the electrolyte and dynamically redeposits onto the anode surface, enabling continuous regeneration of surface Fe motifs while suppressing chloride-induced corrosion. • Mechanistic link between Fe regulation and durable OER performance: Chloride-regulated Fe redistribution stabilizes high-valence Ni active sites, suppresses lattice oxygen participation, and accelerates OER kinetics, resulting in low overpotential and operating continuously in real seawater for 4,000 hours with an extremely low degradation rate of 3.49 µV h⁻¹. In seawater electrolysis, chloride corrosion and Fe leaching-related deactivation remain the main factors limiting the operational stability of NiFe-based anodes. Here, NiFe 2 O 4 is employed as a model catalyst to elucidate the dissolution-complexation-redeposition behavior of Fe species and their cooperative interactions with Cl − during the oxygen evolution reaction (OER). We reveal that although Fe dissolution is unavoidable, OER, a portion of the leached Fe 3+ does not remain in the bulk electrolyte but rapidly coordinates with Cl − to form soluble [FeCl 4 ] − complexes. These [FeCl 4 ] − species are subsequently driven back to the anode surface under anodic potentials, giving rise to a dynamic dissolution-redeposition equilibrium. The redeposited Fe, stabilized through Fe-Cl interactions, generates surface-bound chloride species that repel free Cl − from the electrolyte, simultaneously suppressing chloride corrosion and enhancing catalytic activity. Benefiting from this metal-halide synergistic stabilization, NiFe 2 O 4 exhibits outstanding OER performance, achieving 100 mA cm −2 at a low overpotential of 248 mV and exhibiting remarkable stability, operating continuously in chloride-containing electrolyte for over 4000 h with an extremely low degradation rate of 3.84 µV h −1 . Download: Download high-res image (403KB) Download: Download full-size image