Dual-anion NiSSe electrocatalyst enabling sulfur-tolerant sulfion oxidation for energy-efficient hydrogen production

Replacing the oxygen evolution reaction (OER) with sulfion oxidation in aqueous media offers a promising route for energy-efficient hydrogen generation and simultaneous sulfide removal due to its significantly lower thermodynamic potential. However, practical application of the sulfion oxidation reaction (SOR) is limited by rapid catalyst deactivation caused by sulfur passivation. Herein, we report a dual-anion NiSSe electrocatalyst with a lamellar, pyrite-type structure that exhibits excellent sulfur tolerance and sustained catalytic activity. The optimized NiSSe catalyst achieves low operating potentials of 0.224 and 0.488 V versus the reversible hydrogen electrode (RHE) at current densities of 20 and 100 mA cm^-2, respectively, while retaining 98.2% of its activity after 35 h of continuous operation. Structural and spectroscopic analyses reveal that co-incorporation of sulfur and selenium modulates the electronic structure of Ni centers, generating intrinsically sulfur-resistant surface sites. In situ Raman and ultraviolet-visible (UV-vis) spectroscopy demonstrate that sulfion oxidation proceeds via soluble polysulfide intermediates, thereby limiting the formation of passivating surface sulfur. Post-reaction characterization confirms suppression of irreversible sulfur accumulation. Density functional theory (DFT) calculations further show that dual-anion NiSSe achieves an optimal balance between sulfion adsorption and S₈ desorption, resulting in accelerated SOR kinetics. This work establishes a general dual-anion engineering strategy for stabilizing electrocatalysts under sulfur-rich conditions and provides mechanistic insights for developing efficient SOR-coupled hydrogen production and sustainable sulfion conversion systems.