A Study of Molybdenum Coatings Underpotential Preparation in an Ionic Liquid System

Abstract

Electrodeposition of refractory metals is a challenging issue in the electroplating field owing to their low reduction potential. Electrodeposition of molybdenum in MoCl5-BMIMPF6 by a cyclic scanning regime was introduced in this paper. Ni-Mo and Pt/Ni-Mo deposits were prepared by underpotential deposition to induce the bulk deposition of molybdenum. The coatings were observed and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrochemical behavior of metallic molybdenum in ionic liquids was studied by cyclic voltammetry and chronoamperometry. The results show that the initial nucleation/growth process of molybdenum in MoCl5-BMIMPF6 follows three-dimensional progressive nucleation with diffusion-controlled growth, and the nucleation rate of molybdenum is slow in the ionic liquid system. The effects of supporting electrolytes and sputtering Pt/Ni electrodes were particularly studied. A yellow-brown uniform coating with more refined crystalline grains was obtained on the Ni surface by the addition of NaF due to its positive role in the mass transfer process and good complexing actions that promote nucleation. A gray-white coating with metallic luster was successfully fabricated on the surface of sputtered Pt/Ni because the substrate with a high work function is benign to molybdenum growth at a lower temperature and more positive potentials.