Strong Acid-Mediated Proton Transfer via Water Tunneling Fosters Hydrogen Evolution Reaction on MoS₂ Derivatives under Alkaline Conditions

The surface functionalization of chemically exfoliated MoS₂ (<i>CE</i>-MoS₂) nanoflakes with Brønsted-acid end-capped aryl fragments adds an additional level of complexity to the comprehension of the correlation between the electron-donating strength of covalently grafted organic groups (Hammett parameter) and the HER performance of these hybrids. MoS₂ nanoflakes decorated with aryl-sulfonic acids promote proton transfer via tunneling of H-species, where weaker benzoic acid groups fail. Thus, surface-engineered <i>CE</i>-MoS₂ bearing sulfonic-acid end-capped dangling arms acts as an electrocatalyst that boosts HER kinetics even under an alkaline environment, where water dissociation represents the bottleneck of the process. Density functional theory (DFT) calculations have been used to corroborate experimental evidence and speculate on the role of acidic moieties with respect to water molecule <i>tunneling</i> and dissociation at the surface of the functionalized chalcogenide. The study represents a significant advance in the development of pH-insensitive electrocatalysts for HER.