Currently, seawater electrolysis is an effective technology for the large-scale production of green hydrogen, but the issues of poisoning active sites and catalyst corrosion caused by chloride ions in seawater urgently need to be addressed. This paper reports a non-precious metal cobalt sulfide with sulfur vacancies (v-Co₉S₈) catalyst, where the presence of sulfur vacancies can accelerate the formation of metal hydroxyl oxides and induce the generation of high-valent Co, enabling v-Co₉S₈ to exhibit long-term stability and excellent oxygen evolution reaction (OER) activity in seawater electrolysis. At the same time, the high-valent Co acts as a Lewis acid, providing stronger OH⁻ adsorption and Cl⁻ repulsion capabilities during the seawater OER process. Therefore, v-Co₉S₈ catalyst achieves an overpotential of only 420 mV at 1000 mA·cm⁻² in alkaline seawater. At the same time, the assembled alkaline seawater anion exchange membrane (AEM) electrolyzer operates stably for over 130 h under the condition of 500 mA·cm⁻². This work reports a mechanism where anion vacancy-induced metal sulfide reconstruction forms high-valent metals, which is expected to provide effective guidance for the development of seawater electrocatalysts.

The direct electrolysis of high-salinity water (e.g., seawater) presents significant potential for large-scale green hydrogen production. However, challenges such as corrosion and catalyst poisoning, driven by high concentrations of Cl⁻, severely impact the efficiency and stability of both oxygen evolution reaction and hydrogen evolution reaction, posing a major obstacle to their industrialization. Therefore, developing high-performance electrocatalysts with anti-corrosion and anti-poisoning properties is critical for achieving stable and efficient electrolysis in high-salinity environments, making this a prominent challenge in contemporary research. This review presents a thorough analysis of the challenges and advancements in the production of green hydrogen through seawater electrolysis. We compile various approaches to enhance the selectivity of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), as well as corrosion resistance in high-salinity water electrolysis. These approaches include improvements in catalyst intrinsic activity, electrolyte design and introduct protective barrier layers. Finally, the prospects for the development of seawater electrolysis for hydrogen production are presented.

The development of efficient oxygen reduction reaction (ORR) electrocatalysts that utilize seawater as an electrolyte is crucial for harnessing marine resources and advancing the application of zinc-air batteries (ZABs). Here, Er₂O₃-Pt electrocatalysts enriched oxygen vacancies were constructed by a one-step microwave method. Theoretical calculations indicate that the unique 4f orbitals of Er, in conjunction with the Pt 5d and O 2p orbitals, allow the 4f electrons to demonstrate a degree of mobility. This behavior provides flexible electronic states and optimizes the binding strength of oxygen intermediates in the ORR. In addition, quasi in-situ characterization has proven that the addition of Er and the mediation of the oxygen vacancies have enriched the electrons at Pt, effectively reducing the adsorption of Cl⁻ and preventing the poisoning of the active site of Pt. As a result, Er₂O₃-Pt with half-wave potentials (E_1/2) of 0.85 and 0.67 V in alkaline seawater and pure seawater, respectively, was used as a cathodic catalyst in alkaline seawater-based ZABs to obtain a maximum power density of 184.6 mW·cm^-2 and remarkable stability in pure seawater.

Seawater electrolysis could address the water scarcity issue and realize the grid-scale production of carbon-neutral hydrogen, while facing the challenge of high energy consumption and chloride corrosion. Thermodynamically more favorable hydrazine oxidation reaction (HzOR) assisted water electrolysis is efficiency for energy-saving and chlorine-free hydrogen production. Herein, the MoNi alloys supported on MoO₂ nanorods with enlarged hollow diameter on Ni foam (MoNi@NF) are synthesized, which is constructed by limiting the outward diffusion of Ni via annealing and thermal reduction of NiMoO₄ nanorods. When coupling HzOR and hydrogen evolution reaction (HER) by employing MoNi@NF as both anode and cathode in two-electrode seawater system, a low cell voltage of 0.54 V is required to achieve 1,000 mA·cm⁻² and with long-term durability for 100 h to keep above 100 mA·cm⁻² and nearly 100% Faradaic efficiency. It can save 2.94 W·h to generate per liter H₂ relative to alkaline seawater electrolysis with 37% lower energy equivalent input.