Identifying Active Site in NiCo Sulfide Catalyst for Sulfion-Oxidation-Assisted Water Electrolysis

Hydrogen production through electrolysis of water is limited by the sluggish oxygen evolution reaction (OER), whereas substituting the OER with recyclable electrochemical sulfion oxidation reaction (SOR) offers a sustainable strategy. However, insufficient understanding of the SOR mechanism still hinders the development of efficient and stable catalysts. Here, nickel cobalt sulfide (S-NiCo) nanoneedle array has been used as efficient electrocatalyst for alkaline OER and SOR, whereas trace Ru nanocluster on S-NiCo substrate (Ru@S-NiCo) could efficiently electrocatalyze the alkaline hydrogen evolution reaction. The S-NiCo catalyst with heterointerface exhibits an OER overpotential ( η ) of 270 mV at 100 mA/cm 2 , and in situ electrochemical Raman measurement confirms that the real active species is the oxyhydroxide (Ni/Co–OOH). In particular, SOR displays an ultralow potential of 0.27 V at 100 mA/cm 2 and operates stably for 100 h. Theoretical calculations uncover that the truly active species of Ni 3 S 2 and Co 9 S 8 synergistically oxidize sulfion stepwise to short-chain polysulfides and S 8 . In addition, the electrocatalytic coupling is compared to the traditional water splitting. This work provides a new insight for design hydrogen production system assembled with Ru@S-NiCo and S-NiCo, which substantially reduces the cell voltage by 1.146 V at 100 mA/cm 2 and saves over 70.5% of power consumption by enabling efficient and durable multipurpose catalysts, thus realizing energy-efficient hydrogen generation and environmentally friendly sulfion recycling.