Abstract <p>Niobium-based superalloys are attracting attention as next-generation materials for turbine blades, prompting exploration of fabrication methods for oxidation-resistant films to improve their oxidation resistance. However, practical oxidation-resistant films have yet to be realized owing to trade-offs among coating adhesion, film density, and production rate. In this study, the electrochemical siliciding of pure niobium in molten fluoride was investigated. A NbSi₂ film was successfully formed on a pure niobium cathode by galvanostatic electrolysis in a molten LiF-KF-K₂SiF₆ electrolyte, together with the co-deposition of pure silicon. Lower cathode current density resulted in a thicker NbSi₂ film than that obtained at higher current density under the same charge passed. The concentration of K₂SiF₆ in the electrolyte did not significantly affect the thickness of the NbSi₂ film. In contrast, increasing the electrolyte temperature led to a thicker NbSi₂ film. The rate-determining step in film growth was the diffusion of silicon atoms in the solid electrode, rather than the transport of silicon ions in the molten electrolyte. The NbSi₂ film grew at a rate exceeding the average diffusion distance calculated using Einstein’s equation. Increasing the electrolysis time resulted in complete siliciding of a 50&#xa0;μm thick niobium cathode. The NbSi₂ film formed a mixed-oxide scale of SiO₂ and Nb₂O₅ upon oxidation at 1173&#xa0;K in air.</p> Graphical Abstract <p></p>