Electro- and Electroless Deposition of Rhenium from Reline Deep Eutectic Solvent

Abstract

Rhenium exhibits exclusive properties among refractory metals suitable for extreme applications, many of which require rhenium coatings rather than bulk metal. Recently, there is a renewed interest in using electrodeposition as a potential tool to achieve traditional and tailor-designed coatings. In this context, we report electrodeposition and electroless deposition of rhenium coatings using choline chloride: urea (Reline) deep eutectic solvent and evaluated the corrosion performance of the coatings. Voltammetric response of perrhenate ion in Reline DES indicates an irreversible charge transfer process and the diffusion coefficient was estimated to be in the order 10−6 cm2 s−1. Chronoamperometry analysis revealed rhenium deposition on glassy carbon electrode proceeds via instantaneous 3-D nucleation. Rhenium coatings achieved on copper and mild steel substrates under different galvanostatic and potentiostatic conditions exhibited superior corrosion resistance of ≤0.03 mmpy. FE-SEM and AFM microscopy analysis evidenced smoother deposits under galvanostatic conditions. XPS data confirms metallic nature of rhenium in the deposit with surface covered with oxides. Sub-micron electroless rhenium coatings were achieved on copper/nickel/mild steel substrates via galvanic exchange using spent rhenium electrolytes devoid of additional agents.