Electrochemically induced transformations of ruthenium(III) trichloride microcrystals in salt solutions

G. Inzelt, Z. Puskás, K. Németh, I. Varga

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Ruthenium (III) trichlorid solid crystals have been mechanically attached to gold surfaces and studied by cyclic electrochemical quartz crystal microbalance measurements in the presence of aqueous solutions of different concentrations containing M+Cl-, where M +=H+, Li+, Na+, K+, Rb+, Cs+. The RuCl3 and the complexes formed during the electrochemical transformations show two or more reduction and reoxidation pairs of waves, depending on the experimental conditions (concentration, scan rate, and potential range). The voltammetric peaks are shifted into the direction of higher potentials with increasing electrolyte concentrations except at very high concentrations when the peaks belong to the first reduction/reoxidation processes move oppositely. The mass change was reversible, during reduction mass increase, while during oxidation mass decrease occurred at medium electrolyte concentrations in two, more or less distinct steps. At high or low concentrations the mass excursions are more complex involving different mass increase/decrease regions as a function of potential which vary with the potential range of the measurements. The peak potentials and the electrochemical activity strongly depend on the nature of the cations and pH. It is related to the formation of complexes in different compositions. The mass change decreases with increasing electrolyte concentrations attesting the important role of the water activity and the transport of solvent molecules. It was concluded that in dilute solutions during the first reduction step M + ions enter the surface layer. The strongly hydrated Li+ ions transfer water molecules into the microcrystals, while simultaneously with the incorporation of K+, Rb+, and Cs+ ions H2O molecules leave the surface layer. The opposite transport of ions and solvent molecules occur during oxidation. In the course of further reduction the incorporation of all ions studied except that of Cs+ ions is accompanied with water sorption. The number of sorbed water molecules is proportional to the hydration number of these ions. A reaction scheme is proposed in which M+ m-3[RuIIICl m (H2O) n ]3-m • xH2O (m≥3) and [RuIIICl m (H2O) n ] 3-m (Cl-)3-m • xH2O (m≤3) type complexes are reduced to the respective-or depending on the electrolyte concentration higher or lower-Ru(II)chloro complexes resulting in mixed valence compounds (phases). Taking into account the layered structure of RuCl 3 the electrochemical reduction can be explained as an intercalation reaction in that mixed valence intercalation phases with a general formula M x +(H2O) y [RuCl3] x- are formed from RuCl3•x H2O. The reduction/reoxidation waves are related to the redox transformations of Ru(III) to Ru(II) sites, while the composition of the polynuclear complexes and the structure of microcrystals change.

Original languageEnglish
Pages (from-to)823-835
Number of pages13
JournalJournal of Solid State Electrochemistry
Volume9
Issue number12
DOIs
Publication statusPublished - Dec 2005

Fingerprint

Microcrystals
Ruthenium
microcrystals
ruthenium
Salts
chlorides
Ions
salts
Electrolytes
Molecules
electrolytes
ions
Water
Intercalation
molecules
intercalation
water
surface layers
Oxidation
valence

Keywords

  • Electrochemical quartz crystal microbalance
  • Intercalation
  • Microcrystals
  • Ruthenium(III) chloride
  • Solid state electrochemistry

ASJC Scopus subject areas

  • Electrochemistry
  • Electrical and Electronic Engineering
  • Chemical Engineering (miscellaneous)
  • Physics and Astronomy (miscellaneous)
  • Materials Science (miscellaneous)

Cite this

Electrochemically induced transformations of ruthenium(III) trichloride microcrystals in salt solutions. / Inzelt, G.; Puskás, Z.; Németh, K.; Varga, I.

In: Journal of Solid State Electrochemistry, Vol. 9, No. 12, 12.2005, p. 823-835.

Research output: Contribution to journalArticle

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