Lattice Oxygen Activation and Chloride Repulsion Achieved by PO 4 3– /SO 4 2– Coadsorption on NiFe LDH Anodes for Ampere-Level Seawater Oxidation

Coupling renewable energy with seawater electrolysis for green hydrogen production represents a promising approach in energy storage and conversion. Yet, conventional anodic materials suffer from chloride corrosion and active-site blockage in seawater, causing rapid deactivation at high current densities. It is thus crucial to develop electrode materials with inherent corrosion resistance and high catalytic activity that can sustain operation at ampere-level currents in harsh seawater environments. In this work, we precisely engineered a NiFe layered double hydroxide (LDH) anode functionalized with adsorbed PO 4 3– and SO 4 2– anions. This modified catalyst demonstrates exceptional sustainability-relevant durability, operating continuously for over 140 h at an industrially relevant current density of 1100 mA cm –2 in an alkaline flow cell, while requiring an overpotential of only 201 mV to achieve 100 mA cm –2 . Compared to the unmodified sample, the catalyst demonstrates significantly enhanced activity and corrosion resistance. Further mechanistic insights into the oxygen evolution reaction (OER) were gained through in situ spectroscopy and electrochemical differential mass spectrometry (DEMS). In situ Raman spectroscopy captured the dynamic reconstruction of the electrode material, leading to the formation of a stable active phase identified as NiFeOOH/PO 4 3– /SO 4 2– . By combining in situ 18 O-isotope-labeled DEMS with ATR-FTIR spectroscopy, the compatibility between the conventional adsorbate evolution mechanism (AEM) and the lattice oxygen mechanism (LOM) during the OER was confirmed. The synergy of these two mechanisms was shown to further enhance the OER performance. The results establish that PO 4 3– /SO 4 2– adsorption plays a dual role: it electrostatically repels Cl – to mitigate corrosion, while simultaneously activating lattice oxygen to promote the LOM pathway, thereby improving surface reactivity. The anion adsorption strategy presented here offers valuable guidance for designing efficient and robust anode materials for seawater electrolysis.