Self regulating phosphate reservoir electrodes for stable high current seawater electrolysis with reduced metal leaching

Alkaline seawater electrolysis offers a direct route for sustainable hydrogen production yet remains constrained by chloride induced corrosion. Metal-leaching. and voltage instability at industrial current density. This work introduces a self regulating phosphate reservoir strategy integrated within porous Ni–Fe–Co hydroxide nanosheet electrodes to stabilize the catalytic interface under realistic seawater conditions. The approach combines scalable electrodeposition with controlled phosphate incorporation to create an anion buffered surface that suppresses chloride ingress while preserving high catalytic activity. In alkaline natural seawater. The reservoir enabled electrodes deliver oxygen evolution reaction overpotentials of 232 mV at 10 mA cm − 2 and 369 mV at 500 mA cm − 2 with a Tafel slope of 41.2 mV dec −1 . Full cell operation achieves stable seawater splitting at 500 and 1000 mA cm − 2 for 1000 h with voltage drift limited to 28 mV and 49 mV. respectively. Faradaic efficiency remains 97% to 99% for H₂ and 96% to 98% for O₂ throughout long operation. Operando impedance reveals early interface conditioning followed by resistance stabilization. While post mortem analysis confirms phosphate retention more than 75% and chloride penetration constrained to under 200 nm. Total dissolved metal release remains under 112 ppb after 1000 h at 1000 mA cm − 2 . Techno economic analysis indicates specific energy consumption about 42 kWh kg − 1 H₂ at industrial current density with limited cost contribution from phosphate loading.