A Comparative Study of Hydroxide Adsorption on the (111), (110), and (100) Faces of Silver with Cyclic Voltammetry, Ex Situ Electron Diffraction, and In Situ Second Harmonic Generation

Abstract

Hydroxide adsorption on the (111), (110), and (100) faces of silver electrodes from mixed NaOH/NaF solution is studied using cyclic voltammetry and in situ second harmonic generation (SHG). Cyclic voltammograms for the three low index silver planes in alkaline electrolytes are for the first time compared. They show two pairs of anodic and cathodic peaks in the potential interval below the equilibrium Ag/Ag(2)O potential. These are attributed to the specific adsorption of hydroxide ions followed by submonolayer oxide formation. The differences in the cyclic voltammograms for the (111), (110), and (100) planes are attributed to different (i) work functions, (ii) surface atomic densities, and (iii) corrugation potentials for these surfaces. Ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) show that disordered adlayers are formed on Ag(111) and Ag(100), in contrast to Ag(110), where ordered structures are produced in the region of the first pair of current peaks. In the region of the second pair of peaks, LEED indicates disordered oxide phases on each crystal plane and RHEED shows the presence of small islands of c(2 x 2) structure at some potentials on (110) and (100). SHG measurements were performed (i) in the potential scan mode at constant rotational angle and (ii) at constant potential as a function of the rotational angle. The isotropic (for the (111), (110), and (100) planes) and anisotropic (for the (110) and (111) planes) contributions to the SHG intensity were calculated by fitting the experimental data and are discussed in terms of their dependence on the charge density at the interface, on hydroxide adsorption, and on submonolayer oxide formation.

Sum-Frequency Spectroscopy of Molecular Adsorbates on Low-Index Ag Surfaces: Effects of Azimuthal Rotation

“…and 8 show SFG spectra in the CN-stretch region of CBT-modified Ag(111) or Ag(110) surfaces. The SFG spectra of CBT on Ag(100) surface (not shown) exhibited little orientational dependence, as expected from the isotropic surface nonlinear susceptibility tensor for 4-fold symmetry, 19,47 and from previous SHG measurements. 19 In Figures 7 and 8 the spectra have a single resonance near 2230 cm -1 due to the CN-stretch of CBT plus a NR background which, as described by eq 3, mimics the spectrum of the femtosecond IR pulses.…”

“…The SFG spectra of CBT on Ag(100) surface (not shown) exhibited little orientational dependence, as expected from the isotropic surface nonlinear susceptibility tensor for 4-fold symmetry, 19,47 and from previous SHG measurements. 19 In Figures 7 and 8 the spectra have a single resonance near 2230 cm -1 due to the CN-stretch of CBT plus a NR background which, as described by eq 3, mimics the spectrum of the femtosecond IR pulses. The IR pulses were tuned so that the resonance appeared near the flat part at the spectral peak, which maximized the R intensity and made the fitting procedure most accurate.…”

Enhanced antimicrobial activity with faceted silver nanostructures

“…Therefore, the enhanced activity of the faceted nanostructures strongly suggests that surface morphologies might actually play a dominant role in the determination of the antimicrobial activity. As triangular nanoprisms, nanotetrahedra, and nanodecahedra are faceted predominantly by highly reactive {111} surfaces, these nanostructures exhibit an exceptionally strong affinity to sulfur-containing membrane proteins and oxygen-containing functional groups of lipopolysaccharide molecules which constitute 25 and 75 % of cell wall surfaces, respectively [21,50,51]. This would allow these highly faceted silver nanostructures to efficiently localize to E. coli cell walls, penetrate the outer membrane, and release silver ions into the periplasmic space.…”

“…This study indicates that the activity is highly dependent on surface structure and suggests that the silver {111} facet is most favorable for antimicrobial applications due to its high atom density. This surface structure not only increases the likelihood of silver atoms binding to bacterial cell membrane and cell wall constituents but also enhances dissolution rate of silver atoms from the nanoparticle surface via oxidation by molecular oxygen and hydroxide molecules as evidenced by cyclic voltammetry studies comparing the dissolution between different silver facets [21]. Given the evidence, nanostructures with predominantly {111} faceted surfaces warrant further investigation to shed light on the nature of their enhanced antimicrobial activity.…”

Fundamentals of Electrocatalysis

“…This step has a clear voltammetric signature for Pt (111) in alkaline and acidic aqueous electrolytes of weakly adsorbing anions (e.g. HClO 4 ) [13], Au(111) [120] in neutral and alkaline electrolytes and Ag(hkl) in alkaline electrolytes [121,122]. The reversible nature of OH adsorption on Pt (111) is reflected by mirror-like anodic and cathodic peaks.…”