Amorphous/crystalline Ni-Fe based electrodes with rich oxygen vacancies enable highly active oxygen evolution in seawater electrolysis.

To realize large-scale production of hydrogen through seawater electrolysis, it is highly crucial to engineer high-activity and robustly stable catalytic materials for oxygen evolution reaction (OER). Here, a facile etching growth strategy based on Ni foam (NF) is employed to fabricate an amorphous/crystalline Ni-Fe based electrode with rich oxygen vacancies as a promising OER electrocatalyst (a/c-NiFeOH@NF). Of note, the introduction of Fe induces the generation of plentiful Ni(Fe)OOH species, which can contribute to the remarkable OER behavior. Profiting from the favorable geometric microstructure of ultrathin nanosheets coupled with 3D open-pore architecture and regulated electronic state by increased oxygen vacancies and abundant crystalline-amorphous boundaries, the resulting a/c-NiFeOH@NF displays prominent electrocatalytic OER activity in pure alkaline solution and seawater, achieving impressive overpotentials of only 219 and 233 mV to reach 100 mA cm, respectively. More significantly, the electrode can keep stable operation without obvious attenuation for over 1200 h at 100 mA cm, demonstrating its exceptional corrosion resistance. Such robustness of this electrode surpasses those of almost all reported OER electrocatalysts. Furthermore, in a self-assembled seawater electrolyzer with a/c-NiFeOH@NF as the anode and l-RuP@NF as the cathode, a large current density of 500 mA cm is easily achieved at the voltage of 1.795 V at 65 °C. The work offers a novel paradigm for constructing low-cost, high-efficiency, and ultra-stable OER catalysts, which shows huge promise for industrial seawater electrolysis applications.