Dual‐ion engineering of Fe‐doped Ni ₃ ( <scp>OH</scp> ) ₄ ( <scp> NO ₃ </scp> ) ₂ for Cl ⁻ ‐resistant oxygen evolution reaction in alkaline medium

Abstract Seawater electrolysis offers a sustainable pathway for green hydrogen production, yet the development of oxygen evolution reaction (OER) catalysts with robust Cl¯ resistance remains a critical challenge. Here, we propose a dual‐ion modification strategy, incorporating NO 3 ¯ and Fe 3+ cations into Ni(OH) 2 (denoted as Fe‐NiNH/NF), to synergistically enhance Cl¯ resistance and OER activity in alkaline simulated seawater. The Fe‐NiNH/NF catalyst demonstrates exceptional performance, requiring only 320 mV overpotential at 100 mA cm −2 in KOH and NaCl solution, with a negligible 10 mV increase compared to pure KOH. When implemented in an alkaline anion exchange membrane water electrolyzer, the catalyst achieves 1.76 V cell voltage at 1 A cm −2 with 350‐h stability. Post‐reaction characterizations confirm the transformation of Fe‐NiNH/NF into Fe‐NiOOH with adsorbed NO 3 ¯. Theoretical calculations reveal that NO 3 ¯ forms an exclusionary layer via strong polarity and steric hindrance, electrostatically repelling Cl¯, and NO 3 ¯ and Fe 3+ collectively downshift the Ni d‐band center, weakening Cl¯ adsorption while optimizing intermediate binding.