Mesoporous Thin-Film NiS₂ as an Idealized Pre-Electrocatalyst for a Hydrogen Evolution Reaction

Developing active, durable, and inexpensive electrocatalysts is critical for hydrogen production to meet ever-growing sustainable energy needs. Nickel sulfides offer significant potential as electrocatalysts for a hydrogen evolution reaction (HER); however, the active phase governing the electrochemical conversion is still under debate. We show that mesoporous thin-film NiS₂ synthesized by a novel soft-templating method without post-sulfurization exhibits superior HER activity in alkaline media after a preconditioning step that results in sulfur leaching, amorphization of the surface, and collapse of the mesoporous structure. A comparative analysis with crystalline NiS₂ reveals that partial hydroxylation of the under-coordinated Ni sites is responsible for the superior HER activity.