Structure transitions between copper-sulphate and copper-chloride UPD phases on Au(111)

Abstract

Abstract. Structure transitions between copper UPD adlayers on Au(111)-(1 × 1) in sulfuric acid and chloride containing electrolyte were investigated by in situ scanning tunnelling microscopy. We demonstrate that co-adsorbed sulphate ions in the (√3 × √3)R30° UPD adlayer are replaced by chloride ions and, depending on the halide coverage, a commensurate (2 × 2) or a slightly distorted (5 × 5)-like Cu-Cl UPD adlayer are formed. The stability ranges of these phases are controlled both by the electrode potential and the Cl -concentration. Phase transitions between the three UPD phases were monitored by time-resolved in situ STM. The observed structure details were attributed to mechanisms based on two-dimensional nucleation and growth processes.

Underpotential deposition of Cu on Au(111) from neutral chloride containing electrolyte

“…The CVs of Cu-UPD at neutral pH as exemplified in Figure 1., parallel those of Cu deposition from acidic solution 31,48,62,64 with features, like at low pH, varying with chloride concentration. Since the structural quality of the substrate, i.e., terrace width and step density, also plays a role, additional sample to sample variations were seen in our experiments using flame annealed Au/mica substrates.…”

“…Therefore, we are unable to clearly correlate any specific feature in this region with structural transitions and chloride adsorption/desorption as done in studies at low pH. 31,62,64 Phenomenologically, peaks B/B', which vary in intensity from clearly discernible to vanishingly small, are in the potential range where phase transitions occur 62,64 and peak C is located in the region identified with chloride desorption. 31,62 Notably, with regard to the latter we did not observe a corresponding anodic peak which under acidic conditions indicates the readsorption of chloride.…”

“…The exact dimensions of the ordered structure have been reported to be potential dependent with a slight compression seen in STM images when moving in the cathodic direction. 31,64 Within the range of chloride concentrations examined (10 mM to 0.05 mM), the potential difference of peaks A and A' widens from 20 mV at high concentration ( Figure 1) to about 60 mV at low concentration with, in addition, a broadening of peak A. The structural quality of the substrate also affects the shape of the peaks up to the point where peak A' exhibits a shoulder or even a second peak.…”

“…12 Numerous studies have established the crucial role of the anion in the formation and structure of the UPD layer 10,12,32,34,38,[48][49][50][51][52][53][54][55][56][57][58][59][60] which is highlighted by the stabilising effects of the sulfate anion on the (√3×√3)R30° honeycomb structure 57 and the commensurate (1×1) structure of Cu on Au(111), 10 or the transition of a Cu-UPD layer on Au(111) from a (√3 x √3)R30° to a (5×5) structure upon the exchange of the sulfate by chloride. 31,37,38,50,[61][62][63][64] Notably, Cu-UPD has overwhelmingly been studied at pH ≤ 1 whereas studies employing less acidic conditions 43,48,65,66 or even neutral pH 67,68 are rather scarce. Here we present the structural characterisation of a Cu-UPD layer on Au(111) prepared from a neutral chloride containing solution.…”

New insight on the behavior of the irreversible adsorption and underpotential deposition of thallium on platinum (111) and vicinal surfaces in acid electrolytes

“…1 Also, the effects of anions on the UPD of metals plays an important role. [11][12][13][14][15][16] The applications of surfaces modified by metals are numerous: from the catalysis of the electro-oxidation of organic substances to the simulation of crystal nucleation and growth. 17, 18 The combination of electrochemical and spectroelectrochemical methods has produced interesting studies to of the structure of metallic and anion adsorbates.…”