NiMo-C Coatings Synthesized by Reactive Magnetron Sputtering for Application as a Catalyst for the Hydrogen Evolution Reaction in an Acidic Environment

This study examines the structure and properties of NiMo-C coatings synthesized via reactive magnetron sputtering of a NiMo alloy target in an argon/acetylene atmosphere. The coating structure evolves with carbon content from nanocrystalline, through amorphous to quasi-amorphous with a nanocolumnar structure. The nanostructure consists of metallic columns perpendicular to the substrate surrounded by an amorphous carbon shell. The coatings are evaluated for their potential use as catalytic materials in the hydrogen evolution reaction (HER) in an acidic environment. The medium carbon content coatings show optimal properties in this direction, i.e., high corrosion resistance in an acidic environment and good HER performance described by the Tafel slope and characteristic overpotentials. Even at the highest carbon content, 74 at. %, the Tafel slope does not increase substantially, which is more likely attributable to the distinctive nanocolumnar structure, ensuring the presence of catalytic centers in the form of metallic islands on the surface. At the highest current densities applied, a weak but visible correlation is observed between the characteristic overpotentials and the contact angle hysteresis derived from the wettability measurements.