Nanostructured Electrolytic Composites Based on Cobalt Alloys with Refractory Metals: Composition and Functional Properties

Abstract

AbstractThe ternary Co–Mo–W (Zr) and Co–Fe–Mo coatings with the total content of refractory metals of 30–40 wt%, Co–W–Zr alloys with that of 12–26 wt% and Co–Fe–Mo are deposited from pyrophosphate–citrate electrolytes in pulse regime. The composition of the coatings as well as the surface morphology is shown to depend on the current density. A uniformly cone-shaped developed surface characterizing the coatings is due to the tungsten and molybdenum incorporation, but molybdenum-containing ternary coatings differs by the network of shallow cracks. The X-ray diffraction patterns reflect the amorphous and crystalline structure of ternary alloys. Phases of α-Co, intermetallic compounds Co3Mo, Co7Mo3, Co7Mo6, and traces of metallic molybdenum were detected in the coatings Co–Mo–Zr. The phase composition of Co–Mo–W deposits differs by the emergence of Co7W6 phase and traces of metallic tungsten, and there no any metallic W in the phase composition of Co–W–Zr electrolytic alloys. The corrosion behavior of the ternary coatings in alkaline medium studied by EIS shows the Co–Mo–Zr alloys are characterized by the highest corrosion resistance among the materials studied, and the results are more reproducible. Such behavior is due to the presence on the surface stoichiometric zirconium oxide ZrO2 with high both electrical resistivity and chemical stability. The coatings Co–Mo–W(Zr) and Co–Fe–Mo containing metallic phases of Mo or W are characterized by higher corrosion resistance. The mechanism and kinetics of electrolytic oxidation of methanol on electrodes with electrolytic ternary alloys coatings is determined. Based on the experiments carried out, we can conclude that the reaction of (CH3OH)S → (HCHO)S is the limiting stage, and it allows us to provide the process cycling and prevent the formation of carbon dioxide. The obtained data are indicative of a rather high electrocatalytic activity of ternary alloys, in particular, Co–Mo–Zr, for the reaction of methanol oxidation in the alkaline medium. Such catalytic properties can be explained by a higher degree of the surface branching, and the synergetic effect of the metals, in particular cobalt, molybdenum, and zirconium that are characterized by the different stable oxidation states and the affinity to oxygen.