In Situ STM Study of the Surface Structure, Dissolution, and Early Stages of Electrochemical Oxidation of the Ag(111) Electrode

Abstract

The surface structural modifications induced by underpotential anodic oxidation have been studied at the Ag(111)/0.1 M NaOH(aq) interface by in situ electrochemical scanning tunneling microscopy. For E pzc ≤ E ≤ −0.1 V/SHE, no specific surface structure results from the adsorption of hydroxide ions, indicating the formation of a weakly bonded and mobile layer of adsorbed hydroxide species. For −0.05 ≤ E ≤ 0.05 V/SHE, the Ag(111) surface undergoes reconstruction. The terraces become completely covered by irregularly arranged protrusions assigned to nuclei of a 2D layer similar to silver oxide and separated by non-reconstructed regions with adsorbed hydroxide. The 2D oxide islands consist of one reconstructed layer of silver embedded between two layers of subsurface species (oxide) and surface species (oxide and/or hydroxide). Atomic resolution evidences an enlarged Ag−Ag distance consistent with the growth of one monolayer of Ag2O(111). Long-range structural ordering is improved by reducing the rate of reconstruction in the adsorbed layer. Grains assigned to 3D silver oxide nuclei were also observed and possibly result from the aggregation of Ag atoms ejected from the surface lattice during the surface reconstruction. For E = 0.15 V/SHE, dissolution occurs and is strongly influenced by the irregular structure of the reconstructed surface. 2D pits are initiated on the terraces at the less resistant and non-reconstructed sites of the surface. They propagate by preferential dissolution of the topmost metal plane at the newly created step edges. 3D pits initiate and propagate in the second metal plane by the same mechanism. Dissolution is blocked by the ordered regions of the 2D silver oxide monolayer and by 3D oxide nuclei.

Impedance study on the capacitance of silver electrode oxidised in alkaline electrolyte

“…Therefore, presented conclusions about relation between C dlm and C dlox values are valid regardless of the selected specific C dl value. Ag oxidation and dissolution may lead to the surface roughening, as already pointed out in [8,21,22,29,30,67]. Comparative measurements carried out after completing the Ag oxidation experiments described later in the text showed an increase in C dlm in HER region by 2.0 ± 0.5 times (α = 0.919-0.942 and Q = (7.34-6.17) · 10…”

“…electrochemical quartz crystal microbalance [22,23], XPS [15] and ellipsometric [76][77][78] measurements. The silver oxidation in an alkaline environment can be accompanied by a dissolution of the electrode [22,23,38,67,72,[77][78][79], and Ag 2 O itself may undergo a dissolution as well [22,79]. Thus, apart from the reduction of the solid oxide [22], the charge of peak (C) may also contain a contribution from reduction of soluble Ag species formed during the electrode oxidation [24,[70][71][72]77].…”

“…7 can be analysed in terms of the oxide thickness influence on Q(CPE ox ) and indicates that the latter parameter decreases from 9.96 · 10 as low as 0.7-0.8, the Q(CPE ox ) cannot be identified as the pure capacitance. [8,22,29,30,67,77]; their independence on the oxide thickness may indicate that for the sufficiently thick oxide, the surface roughness becomes practically constant. It is likely that the surface roughening takes place mainly at the initial stages of the oxide formation, when significant sections of the metallic Ag surface are exposed to the electrolyte or the oxide is very thin.…”

Adsorption layers and passive oxide films on metals

“…[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] For ag (111) in 0.1 M NaOH(aq), OH-induced surface reconstruction has been evidenced by ecsTM in the potential range preceding the growth of 3D anodic oxides occurring at E ≥ 0.3 V/SHE. 61,62 However, surface reconstruction requires a potential (e > -0.1 V/sHe) higher than that (~-0.45 V) above which anodic peaks assigned to OH -adsorption are measured by cyclic voltammetry 56,58,60 and the formation of OH lads species is confirmed by in situ raman spectroscopy and ex situ XPs data. 52,59,60 The ecsTM images measured in the potential range of -0.45 £ E £ -0.1 V reveal atomically smooth terraces and no superstructure ( Fig.…”

Use of Local Electrochemical Methods (SECM, EC-STM) and AFM to Differentiate Microstructural Effects (EBSD) on Very Pure Copper

“…Till now corrosion was often consider as a purely chemical interaction with an exclusive dependence on compositional effects, while ignoring microstructural and crystallographic properties of the metal surface [4][5][6][7][8][9][10][11]. Some recent literature data, however, suggest an important effect of microstructural elements such as grain size, crystallographic orientation and grain boundary characteristics features on the electrochemical behavior [12][13][14][15][16][17][18][19][20][21][22].…”