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

Abstract

The under-potential deposition of copper on Pt(111) from aqueous 0.05 M H 2 SO 4 + 5 mM CuSO 4 ·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.