Underpotential deposition of Te monolayers on Au surfaces from perchloric acid solution studied by chronocoulometry and EQCM


Nicic I., Liang J., Cammarata V., ALANYALIOĞLU M., Demir U., Shannon C.

Journal of Physical Chemistry B, vol.106, no.47, pp.12247-12252, 2002 (Scopus) identifier

  • Publication Type: Article / Article
  • Volume: 106 Issue: 47
  • Publication Date: 2002
  • Doi Number: 10.1021/jp026625w
  • Journal Name: Journal of Physical Chemistry B
  • Journal Indexes: Scopus
  • Page Numbers: pp.12247-12252
  • Bilecik Şeyh Edebali University Affiliated: No

Abstract

We report a study of the underpotential deposition (UPD) of Te monolayers onto Au electrodes from perchloric acid solution using electrochemical quartz microgravimetry (EQCM) and chronocoulometry. We find that tellurium(IV) oxide (as TeO32-, TeO2 or HTeO2+) is adsorbed onto Au at potentials positive of the UPD region. EQCM experiments, in which an Au electrode poised at +0.7 V in pure HClO4 electrolyte was monitored as a function of time before and after the addition of TeO2, showed a slow adsorption of a submonolayer of TeO2. Energy-dispersive X-ray (EDX) measurements confirm the presence of a Te-containing species on the surface. Two distinct reductive UPD features at approximately +0.400 V and -0.100 V vs Ag|AgCl were observed by cyclic voltammetry. EQCM measurements indicate that there is a small, reproducible mass decrease accompanying the first UPD wave, consistent with the loss of H2O from the surface as an adsorbed layer of HTeO2+ is reduced to a submonolayer of Te atoms. Chronocoulometry indicates a charge density of 160 μC/cm2 for the first UPD wave, which, when taken together with the mass change data, is consistent with the four-electron reduction of adsorbed HTeO2+ to Te. In addition, analysis of the current-time data indicates that this process occurs by a two-dimensional instantaneous nucleation and growth mechanism, resulting in an ordered overlayer with a fractional coverage of ca. 0.41. The second UPD peak results in the formation of a dense monolayer by reduction of HTeO2+ from solution. This process also appears to occur by a direct four-electron reduction and exhibits simple Langmuir adsorption behavior as evidenced by exponentially decaying current-time transients. The saturation coverage is approximately 0.9.