Surface amorphization and functionalization of a NiFeOOH electrocatalyst for a robust seawater electrolyzer†

Hydrogen production of seawater electrolysis has attracted considerable interest due to the abundant seawater resources. However, the chloride ions (Cl⁻) in seawater not only corrode the electrodes but also cause side reactions, severely impacting the electrode efficiency and stability of the oxygen evolution reaction (OER) in seawater electrolysis. These challenges are the key factors limiting the development of seawater electrolysis technology. Here, we developed a surface-functionalized high-performance catalyst, which not only resists Cl⁻ corrosion using surface-functionalized ions, but also improves the OER activity by surface amorphization. The designed catalyst (Ru_0.1-NiFeOOH/PO₄³⁻) is composed of Ru_0.1-NiFeOOH and surface phosphate. On the one hand, a small amount of Ru doping can increase the surface amorphization of NiFeOOH and thus improve the catalytic activity. On the other hand, the phosphates on Ru_0.1-NiFeOOH are resistant to Cl⁻ corrosion, which in turn improves the electrode stability. This catalyst demonstrates robust performance operation over 1000 h in alkaline seawater solutions at an industrial current density of 0.5 A cm⁻². The anion exchange membrane seawater electrolyzer assembled with Ru_0.1-NiFeOOH/PO₄³⁻ only needs 1.6 V to achieve 0.5 A cm⁻² when powered by sustainable solar energy. The electrolyzer efficiency is 75.1% at 0.5 A cm⁻², which is superior to the 2030 technical target of 65% set by the U.S. DOE and most reported work. This work offers a new perspective for designing efficient and stable catalysts and is of great significance for advancing seawater electrolysis technology.