Abstract: Developing electrocatalysts with ingenious active site-environment interactions for robust oxygen evolution reaction in alkaline seawater is essential for sustainable hydrogen production under industrial conditions, yet remains a significant challenge. Herein, we present a high-entropy amorphous pyrophosphate, FeCoNiMnPO_x, that serves as a highly active and durable electrocatalyst for alkaline seawater oxidation at large current densities. Our strategy leverages spin-state engineering of active metal sites by modulating oxygen vacancy concentrations via magnetic superexchange interactions. We found that four-coordinated Fe sites in FeCoNiMnPO_x facilitate the highest spin state transition, boosting dense π-bonding with oxygen intermediates, resulting in a near-optimal activity descriptor of ΔG_O* - ΔG_OH* = 1.76 eV. Such an optimized catalyst achieves a low overpotential of 299 mV at 400 mA cm^-2 and exhibits exceptional stability, maintaining performance for over 1000 h at 500 mA cm^-2 in alkaline seawater. This exceptional stability stems from the formation of a robust hydrogen-bonded network of four-coordinated interfacial water, which effectively repels detrimental chloride ions, mitigating catalyst corrosion and ensuring long-term durability. This work underscores the critical role of spin-state engineering in electrocatalysis and provides a novel pathway for designing highly durable electrocatalysts towards sustainable hydrogen production from seawater.

Key words: Seawater electrolysis, High-entropy pyrophosphates, Spin engineering, Magnetic superexchange interaction, Hydrogen-bonded network