Application of additives for the electrodeposition of metals and alloys from ionic liquids

Ionic liquids (ILs) are considered a novel type of green electrolyte system due to their features of no proton interference, wide electrochemical window, low vapor pressure, good electrical conductivity, and low melting point. Metal and alloy electrodeposition from ILs can alleviate the shortcomings of traditional aqueous systems, such as the limited electrochemical window and easy interference from hydrogen evolution side reaction. Unlike high-temperature molten salts, ILs can be used for electrodepositing active metals and their alloys at low temperatures and in relatively mild conditions. The introduction of additives can change the electrochemical reduction potential of the active species in the ILs electrodeposition system, affect the electrochemical crystallization process of the electrodeposited grains, and significantly improve the microstructure and performance of the deposited layer. This review summarizes the research progress of additives for the electrodeposition of active metals, transition metals, and noble metals and their alloys from ILs. It systematically analyzes the mechanism, utility, and limitations of current additives during the electrodeposition process and prospects the future research directions of additives for the metal and alloy electrodeposition from ILs.