Electrochemical Behavior of Silver Halogenocomplexes in an Amide-Type Ionic Liquid

Abstract

Silver halides, AgX (X = Cl–, Br–, and I–), are known to be typical poorly soluble salts in aqueous solution. AgX is also almost insoluble in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonly)amide (BMPTFSA). However, AgX has been known to dissolve in the media in the presence of X– by forming halogenocomplexes, [AgX n ](n–1)–. Dissolution of AgCl has been reported in basic chloroaluminate ionic liquids[1] and deep eutectic solvents containing Cl–. In these reports, however, electrochemical behavior of [AgX n ](n–1)– has not been studied in detail. We have already reported that some metal chlorides are soluble in BMPTFSA in the presence of Cl– and that electrodeposition of the metals is possible[2,3]. In the present study, dissolution of AgX has been investigated in BMPTFSA with addition of BMPX. Furthermore, electrodeposition of Ag and electrochemical preparation of Ag nanoparticles have been examined in the Lewis basic ionic liquids. AgX was found to dissolve in BMPTFSA containing 0.5 M BMPX. The dissolved species was determined to be [AgX3]2– by potentiometric technique. The deposition and dissolution of Ag were observed in cyclic voltammetry. The redox potential of [AgX3]2–/Ag was more negative than that of [Ag(TFSA)3]–/Ag and dependent on the kind of halide. The diffusion coefficient of [AgX3]2– was determined by chlonoamperometry. The initial stage of electrodeposition of Ag on a glassy carbon electrode was regarded as progressive. Potentiostatic cathodic reduction of [AgX3]2– resulted in deposition of Ag. The morphology of Ag deposits depended on the reduction potential. Formation of Ag nanoparticles dispersed in the ionic liquid was confirmed after potentiostatic cathodic reduction at a negative potential using transmission electron microscopy[2].