Ruthenium Electrodeposition from Water-in-Salt Electrolytes and the Influence of Tetrabutylammonium

Abstract

The use of water-in-salt electrolytes is evaluated for the electrodeposition of metallic ruthenium. The mechanisms of proton reduction inhibition by concentrated LiCl and dilute tetrabutylammonium is evaluated. Concentrated LiCl is found to disrupt the hydrogen bonding network within the solution bulk, whereas TBA is found to adsorb onto the electrode surface, blocking proton access. Ruthenium exists as a different complexed species in water-in-salt electrolytes vs dilute aqueous electrolytes, leading to a −300 mV shift in the deposition onset potential. Greater current efficiencies of Ru deposition can be obtained when depositing at proton overpotentials by the use of water-in-salt electrolytes, and TBA can offer further improvements. The grain structure and resistivities of Ru thin films are studied.