Coordination engineering of Ni single-atom catalysts on hierarchical porous carbon for desulfurization and hydrogen evolution electrocatalysis

Rational design of electrochemical sulfide oxidation reaction (SOR) catalysts is a prerequisite to fully recycling hydrogen (H₂) and elemental sulfur (S⁰) resources, realizing the bridge between environment and energy fields, as well as enlightening the optimization of metal‒sulfur battery applications. While transition metal catalysts often suffer from sulfur poisoning, single-atom catalysts (SACs) offer a promising solution, where the precise coordination environment of metal centers becomes a critical determinant of catalytic performance. Herein, for the first time, we develop a Ni single-atom catalyst for SOR with unique Ni-N₃O₁ coordination anchored on hierarchically porous carbon (Ni₁@HPC), which demonstrates remarkable advantages over conventional Ni-N₄ or Ni-O₄ configurations, exhibiting a superior SOR activity (0.37 V vs. RHE at 100 mA cm^-2) that surpasses reported carbon-based catalysts and is comparable to most metal-based catalysts. In situ Raman and density functional theory (DFT) results reveal that the HPC facilitates rapid product S⁰ desorption while the Ni-N₃O₁ coordination enables appropriate reactant sulfide (S^2-) adsorption, striking a critical balance between activity and stability that other coordination geometries fail to achieve. Additionally, the practical application of coupling hydrogen evolution reaction (HER) and SOR is realized on Ni₁@HPC with low power consumption, which is a promising alternative to the traditional overall water splitting (OWS) process. This work not only establishes a structure-activity relationship for single-atom catalysts in SOR but also provides a general strategy for optimizing metal coordination in electrocatalytic systems.