The Ni₃S₂ bulk phase supports efficient oxygen reduction reaction (ORR) catalysis in pH neutral aqueous electrolytes. Here, we combine electrochemistry, surface spectroscopy, and high-resolution microscopy to show that Ni₃S₂ undergoes self-limiting oxidative surface restructuring under ORR conditions to form an amorphous surface film conformally coating the Ni₃S₂ crystallites. The surface film has a nominal NiS stoichiometry and is highly active for ORR catalysis. Density functional theory calculations suggest that, to a first approximation, the catalytic activity of nickel sulfides is determined by the Ni-S coordination numbers at surface-exposed sites through a simple geometric descriptor. In particular, Ni surface sites with three S nearest neighbors, formed via reconstruction of the Ni₃S₂ surface, provide an optimal energetic landscape for ORR catalysis. By providing a framework for understanding catalytic activity on reconstructed amorphous surface phases, the work enables the rational design of high-performance electrocatalysts based on kinetically labile, earth-abundant materials.

Ni ₃ S ₂本体相在pH中性水性电解质中支持有效的氧还原反应（ORR）催化。在这里，我们结合了电化学，表面光谱学和高分辨率显微镜技术，表明Ni ₃ S ₂在ORR条件下经历了自限氧化表面重构，形成了共形覆盖Ni ₃ S ₂的非晶表面膜。微晶。该表面膜具有标称的NiS化学计量，并且对ORR催化具有很高的活性。密度泛函理论计算表明，通过一个简单的几何描述词，一阶近似结果是，硫化镍的催化活性由表面暴露部位的Ni-S配位数确定。尤其是，通过重建Ni ₃ S ₂表面而形成的具有三个S最近邻的Ni表面位点为ORR催化提供了最佳的能量分布。通过提供一个框架，以了解在重构的无定形表面相上的催化活性，这项工作使基于动力学不稳定的，富含地球的材料的高性能电催化剂的合理设计成为可能。