Effect of Temperature Variation on the Under-Potential Deposition of Copper on Pt(111) in Aqueous H2SO4

The under-potential deposition of copper on Pt(111) from aqueous 0.05 M H2SO4 + 5 mM CuSO4 center dot 5H(2)O is studied in the 273 <= T <= 333 K range using cyclic voltammetry (CV). The CV transients always reveal two cathodic peaks (C-I and C-II) for the entire temperature range; there is only one anodic peak (A(I)) in the case of 273 <= T < 298 K and the second one appears in the case of T >= 298 K. In the case of 273 <= T < 298 K, the cathodic and anodic peaks shift toward lower potentials upon T increase, while in the case of T >= 298 K, there is no observable peak displacement. The charge density associated with the Cu-UPD deposition and stripping does not reveal any temperature-dependence. The results demonstrate that T variation does not lead to charge-density redistribution between the peaks, but the charge density of the first peak (C-I and A(I)) in the deposition-stripping profiles is always greater than that of the second peak (C-II and A(II)). The experimentally determined charge density associated with the Cu deposition and stripping is lower than the value expected for one epitaxial Cu-UPD layer on Pt(111). This difference is due to the coadsorption of anions that occurs concurrently with UPD Cu.