LAUSR

Electrolysis of costless and infinite seawater is a promising way toward grid‐scale hydrogen production without causing freshwater stress. Practical potential of this technology, however, is hindered by low energy efficiency and anode corrosion by the detrimental chlorine chemistry in seawater in addition to unaffordable electricity expense. Herein, energy‐saving hydrogen production is reported by chlorine‐free seawater splitting coupling sulfion oxidation. It yields hydrogen at a low cell voltage of 0.97 V, cutting the electricity consumption to 2.32 kWh per m3 H2 at 300 mA cm−2. Compared to alkaline water electrolysis, the energy expense is primarily saved by 60% with 50% lower energy equivalent input. Benefiting from the ultralow cell voltage, the hazardous chlorine chemistry is fully avoided without anode corrosion regardless of Cl− crossover. Meanwhile, it also allows fast degradation of S2− pollutant from the water body to value‐added sulfur with 80% efficiency, for further reducing hydrogen cost and protection of the ecosystem. Connecting such a hybrid seawater electrolyzer to a commercial solar cell can harvest the hydrogen from seawater with better sustainability. This work may offer new opportunities for low‐cost hydrogen production from the unlimited ocean resources with environmental protection.