Pulse and Pulse/Reverse Techniques for Electrodeposition of Rhenium and Refractory Metals

Abstract

Refractory metals possess unique properties including high melting points, high hardness at room temperature, chemical resistance, and high density. Electrodeposition of refractory metals is of interest as a scalable approach to apply uniform coatings to enable a wide range of applications in aerospace, nuclear, catalysis, biomedical fields. This talk will focus on pulse electrochemical variables to enable methods to electrodeposit high quality metallic rhenium (Re).Re has traditionally been difficult to deposit from aqueous solutions due to the over potential for hydrogen evolution and complex electrochemical reactions. Electrodeposition of rhenium usually occurs from the perrhenate ion (ReO4-) with an oxidation state of +7. The exact mechanism to reduce the perrhenate ion from +7 to metallic rhenium is still unknown. It is unlikely that the 7 electrons transfer in a single step, so reduction likely occurs through intermediate oxide species including ReO2, ReO3 and Re2O5. Combined with the hydrogen evolution reaction, Re coatings are generally deposited at low faradaic efficiency, are brittle, and limited in thickness (sub-micron). In our previous work, water-in-salt electrolytes and complexing additives have enabled resolution of some of the issues associated with this complexity and a range of deposit qualities, though cracking issues remain and coating quality issues still needed optimization.Herein, we present on the effects of pulsed electrochemical approaches to eliminate cracking in the film by balancing nucleation and growth and the competing hydrogen evolution reaction. A custom high-throughput cell was developed to rapidly screen parameters and explore time-dependent evolution of the electrodeposition processes.