This study investigates the dynamic restructuring of nickel sulfides (NiS) for the electrocatalytic hydrogen evolution reaction (HER) in alkaline media. Using operando X-ray absorption spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy, the researchers found that NiS undergoes an in-situ phase transition to form a mixed phase of Ni₂S₂ and NiO, creating highly active dual sites at the Ni₂S₂/NiO interface. The interfacial Ni sites act as active sites for water dissociation and OH⁻ adsorption, while the interfacial S sites facilitate H⁺ adsorption and H₂ evolution. This transformation results in an overpotential of only 95 ± 8 mV at a current density of 10 mA cm⁻². The study highlights the dynamic nature of transition metal chalcogenides and the importance of controlling working conditions to achieve enhanced catalytic performance. The findings provide insights into the underlying catalytic mechanisms and offer a potential route for developing cost-effective and efficient electrocatalysts for alkaline HER.This study investigates the dynamic restructuring of nickel sulfides (NiS) for the electrocatalytic hydrogen evolution reaction (HER) in alkaline media. Using operando X-ray absorption spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy, the researchers found that NiS undergoes an in-situ phase transition to form a mixed phase of Ni₂S₂ and NiO, creating highly active dual sites at the Ni₂S₂/NiO interface. The interfacial Ni sites act as active sites for water dissociation and OH⁻ adsorption, while the interfacial S sites facilitate H⁺ adsorption and H₂ evolution. This transformation results in an overpotential of only 95 ± 8 mV at a current density of 10 mA cm⁻². The study highlights the dynamic nature of transition metal chalcogenides and the importance of controlling working conditions to achieve enhanced catalytic performance. The findings provide insights into the underlying catalytic mechanisms and offer a potential route for developing cost-effective and efficient electrocatalysts for alkaline HER.