Electrodeposition of Copper at Well-Defined Pt(111) and Rh(111) Electrodes in Sulfuric Acid Solutions:  Studying with In Situ Scanning Tunneling Microscopy

Abstract

We report in situ scanning tunneling microscopy (STM) results of underpotential deposition (UPD) of copper at well-ordered Pt(111) and Rh(111) electrodes in sulfuric acid solutions. Cyclic voltammograms of Pt(111) at 1 mV/s in 0.05 M H2SO4 and 5 mM CuSO4 reveal two well-defined UPD peaks at 0.65 and 0.61 V, whereas one doublet UPD peak at 0.44 V is observed for Rh(111). Real-time STM imaging revealed that the two sharp UPD features for Pt(111) correspond to the formation of a ( 3 × 3)R30°structure and a disorder phase, respectively. A long-range ordered ( 3 × 7)oblique structure was imaged after a full monolayer of Cu was deposited, tentatively assigned to the (bi)sulfate anions lying atop the Cu adlayer. In contrast, a monolayer of Cu was deposited in a single step on Rh (111), where (bi)sulfate anions also actively participated in the process. In situ STM revealed a well-ordered ( 3 × 7)oblique structure throughout the deposition process, likely because of the coadsorbed (bi)sulfate anions. A series of timedependent in situ STM images were acquired to unveil the deposition processes of Cu. Deposition of Cu preferentially began at defect sites, particularly upper step ledges. Lateral growth and coalescence of Cu islands followed to cover nearly the whole surface. Decreasing potential to the bulk deposition region led to the formation of local Cu islands with a thickness of 4-5 layers of Cu, on which a well-ordered ( 3 × 7)oblique structure was still observed. All the STM results indicate that sulfate anions were heavily involved in the UPD processes of Cu at these two electrodes. The different adsorption energies of Cu adatoms on Pt and Rh electrodes also affect the deposition processes.

Sulfate and CO surface complexes formation with upd copper on Pd(111) and Pt(111) electrode surfaces: abnormal vibrational frequency shifts of CO and sulfate during upd processes

“…The appearance of the sharp band width seen in the m S-O 3 symmetric stretching band suggests the existence of two dimensional ordering of the surface complex on the electrode. This fact accords well with the result of in situ STM reported by Yau et al [22] and our group [8]. From the discussion above, the sulfate ion is not regarded as an adsorbate species during the upd process in the potential range of 600-650 mV in Fig.…”

“…Yau and coworkers reported in situ STM on upd copper on Pt(111) in sulfuric acid solution. They observed an ordered p 3 Â p 3 structure on a 1 Â 1 pseudomorphic upd copper surface on Pt(111) [22]. The results of Cu upd on a Pd(111) electrode were quite similar to those obtained on a Pt(111) electrode.…”

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.…”

Phase Transitions in Two‐dimensional Adlayers at Electrode Surfaces: Thermodynamics, Kinetics, and Structural Aspects

“…The UPD of Cu on Pt(hkl) has been studied by electrochemical techniques [375][376][377][378][379][380][381][382][383][384][385][386], electroreflectance [375], radioactive labeling [387,388], IR-spectroscopy [389,390], electrochemical quartz crystal microbalance (EQCM) [391], in situ STM [389,[392][393][394][395][396], and a variety of X-ray techniques [200,385,[397][398][399][400][401], as well as ex situ UHV-methods such as LEED, AES, and XPS [389,399,[402][403][404][405][406]. Figure 21 shows a slow scan voltammogram of Cu-UPD on a high-quality [390,395,396] and SXS [408], and is in agreement with ex situ XPS and LEED investigations [389,390,402].…”

“…Figure 21 shows a slow scan voltammogram of Cu-UPD on a high-quality [390,395,396] and SXS [408], and is in agreement with ex situ XPS and LEED investigations [389,390,402]. During the second UPD peak, B 2 , the sulfate ions are displaced from the honeycomb center, and a (1 × 1) pseudomorphic ML is formed with the Cu residing in the threefold hollow sites of the Pt surface, on top of which the sulfate ions arrange in a ( √ 3 × √ 7) pattern, θ = 0.20 [389, 396, 397.] The reverse processes take place during the dissolution of the UPD phase upon positive potential excursion.…”