title: EQCM study of the [Au(III)Cl4](-)-[Au(I)Cl2](-)-Au(0) redox system in 1-ethyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquid.
abstract: The electrochemical behavior of the [Au(III)Cl(4)](-)-[Au(I)Cl(2)](-)-Au(0) redox system in room temperature ionic liquid (RTIL) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF(4)) has been investigated quantitatively using an in situ electrochemical quartz crystal microbalance (EQCM) technique based on a Pt film-coated quartz crystal electrode (Pt-QCE). A series of two-electron (2e) and one-electron (1e) reductions of the [Au(III)Cl(4)](-) to [Au(I)Cl(2)](-) and [Au(I)Cl(2)](-) to Au metal were recognized at the Pt surface. Besides, the disproportionation reaction of [Au(I)Cl(2)](-) (i.e., the 2e-reduction product of [Au(III)Cl(4)](-)) to [Au(III)Cl(4)](-) and Au metal was also observed. Electro-dissolution of the Au deposited on the Pt electrode through a 1e-oxidation reaction in the presence of chloride ions was also confirmed using the Pt-QCE based EQCM technique. A 2e-oxidation reaction of [Au(I)Cl(2)](-) (i.e., the dissolved product) to [Au(III)Cl(4)](-) along with the oxidation of Cl(-) ion on the Pt surface was also realized at high anodic potential. The results demonstrate that in situ EQCM technique is applicable and powerful in elucidating electrochemical surface phenomena accompanying a mass change in RTIL.
authors.affiliation: Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Oyama
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Mohammad Rezaur
authors.initials: MR
authors.lastname: Rahman
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Okajima
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohsaka
authors.forename: Noboru
authors.initials: N
authors.lastname: Oyama