Shuichiro Yamaguchi

EQCM Study of the [AuIIICl4]−−[AuICl2]−−Au(0) Redox System in 1-Ethyl-3-methylimidazolium Tetrafluoroborate Room-Temperature Ionic Liquid

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.

Scanning electrode quartz crystal analysis Application to metal coatings

Scanning electrode quartz crystal analysis (SEQCA) has been applied to the monitoring of quartz surfaces that are partially coated with gold. The lateral resolution for gold coatings is better than that for insulating coatings. The mass sensitivity in the centre region is better than that in the edge region. On the other hand, the lateral resolution is independent of the area and location of the gold coating. It may be possible to distinguish a conducting coating from an insulating one. Gold coatings can be located in NaCl solutions if the concentration is ⩽10 mM. The possibility of further improvement in lateral resolution is discussed.