Examination of Underpotential Deposition of Copper on Pt(111) Electrodes in Hydrochloric Acid Solutions with in Situ Scanning Tunneling Microscopy

Abstract

In situ scanning tunneling microscopy (STM) has been used to examine underpotential deposition (UPD) of Cu at Pt(111) electrodes in the solutions of 0.01 M HCl and 1 mM Cu(ClO4)2. Cyclic voltammetry reveals two well-defined features at 0.72 and 0.55 V (vs RHE), where a tailing phenomenon is noted for the former peak. In situ STM imaging reveals a disorder-to-ordered transition of the adlayer, as the electrochemical potential of Pt(111) was stepped from 0.8 to 0.7 V to facilitate the deposition of a sub-monolayer of Cu adatoms. The ordered adlattice can be approximately characterized as (4 × 4), whose irregular intensity modulation of the STM atomic features indicates its incommensuratity. Toward the end of the first UPD feature, deposition of Cu continues, resulting in reconstruction of the (4 × 4) adlattice to (√7×√7)R19.1°. The latter structure is then stable toward further negative potential stepping to the end of the second UPD wave. In situ STM imaging turns fuzzy when the electrochemical potential of Pt(111) is made more negative to the Nernst value. Varying the operation parameters of the STM can result in atomic structures of not only the upper layer of chloride but also the lower metallic adlayer or the Pt(111) substrate.

Revealing the elemental-specific growth dynamics of Pt–Cu multipods by scanning transmission electron microscopy and chemical mapping

“…† and 0.340 V for Cu 2+ /Cu versus reversible hydrogen electrode), and then the as-formed Pt induces the reduction of Cu 2+ ions by taking advantage of Cu UPD, resulting in the formation of the Pt-Cu alloy by co-reduction of the Pt and Cu precursors. 31,[40][41][42] The decrease of Pt content in stage 2 indicates that the reduction rate of Pt 2+ ions is slower than that of Cu 2+ ions, which can be attributed to two possible reasons. One is that the addition of Br À ions and the amine group has a stronger complexing with Pt 2+ ions than Cu 2+ ions, resulting in the slower reduction rate of Pt 2+ ions relative to Cu 2+ ions.…”

In Situ Scanning Tunneling Microscopy Imaging Self-Assembled Monolayers of Mercaptoacetic Acid and Cupric Ion on Au(111) Electrode

“…We explain this result by citing incomplete reduction of Cu 2+ ions to Cu 0 in the UPD regime and their coordination to MAA could make them more difficult to be reduced. 21,22 Furthermore, Cu deposition could be further impeded by the need of MAA to segregate on the Cu deposit. These issues might be responsible for the broad peak shape of C2.…”

In situ scanning tunneling microscopy study of cobalt thin film electrodeposited on Pt(111) electrode

“…The Pt(1 1 1) electrode was immersed from the quenching tube with a thin film of water on top, which protected this Pt electrode from adsorption of contaminants in the ambient. The STM cell was equipped with a Pt counter and a Pt quasi-reference electrodes [27][28][29]. All potentials reported here are converted into a scale of a Ag/AgCl electrode.…”