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Sulfion oxidation reaction holds great potential for replacing kinetically sluggish water oxidation to save power consumption and simultaneously purifying environmental sulfion-rich sewage. However, it is still challenged by the insufficient mechanism understanding and questionable stability caused by sulfur passivation. Here, it is demonstrated that bifunctional Co 3 S 4 nanowires for assembling hybrid seawater electrolyzer that combines anodic sulfion oxidation and cathodic seawater reduction with an ultra-low power consumption of 1.185 kWh m −3 H 2 under 100 mA cm −2 , saving energy consumption over 70% compared to the traditional water splitting system. Unlike water is oxidized into O 2 at high potentials under alkaline water splitting system, experiments combined with in situ characterizations uncover the stepwise oxidation of S 2− to short-chain polysulfides and then to value-added product of S 8 . Density functional theory calculations prove that Co 3 S 4 possesses reduced energy barriers in the rate-determining S 3 2− to S 4 − oxidation step and S 8 desorption step, promoting conversion of short-chain polysulfides and efficient desorption of S 8 . These findings reveal the catalytic mechanism of sulfion oxidation and inspire an economic approach toward the fabrication of bifunctional Co 3 S 4 for achieving energy-saving hydrogen production from seawater while rapidly disposing sulfion-rich sewage with boosted activity and stability.

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