Temperature- and potential-dependent structure of the mercury-electrolyte interface

Abstract

The atomic-scale structure of the mercury-electrolyte (0.01 M NaF) interface was studied as a function of temperature and potential by x-ray reflectivity and x-ray diffuse scattering measurements. The capillary wave contribution is determined and removed from the data, giving access to the intrinsic surface-normal electron density profile at the interface, especially to the surface layering in the Hg phase. A temperature dependent roughness anomaly known from the Hg-air interface is found to persist also at the Hg-electrolyte interface. Additionally, a temperature dependence of the layering period was discovered. The increase in the layer spacing with increasing temperature is approximately four times lager than the increase expected from thermal expansion. Finally, the interface is found to broaden towards the electrolyte side as the potential becomes more negative, in agreement with the Schmickler-Henderson theory. Our results favor a model for the interface structure, which is different to the model formerly used in comparable studies.

Evidence for Facilitated Surface Transport during Ge Crystal Growth by Indium in Liquid Hg–In Alloys at Room Temperature

“…The detailed behavior is more easily discernible after normalizing the XRR data by the Fresnel reflectivity (Figure b,d). For the case of pure Hg, the XRR curves in 0.1 M NaB 4 O 7 strongly resemble those observed for the Hg/0.01 M NaF interface. , Specifically, R ( q z ) initially decreases up to q z = 1.2 Å –1 and then increases again toward the quasi-Bragg peak at q z = 2.22 Å –1 . Quantitative fits to the model described in the Experimental Section provide very similar structural parameters and electron density profiles as in NaF solution at the most negative potentials (see Figure b and Table S1 in the Supporting Information).…”

“…From these values, scattering length densities of 8.177 × 10 –5 Å –2 for Hg/0.1 M NaB 4 O 7 and 5.364 × 10 –5 Å –2 for Hg 0.3 In 0.7 /0.1 M NaB 4 O 7 are calculated, resulting in q c values of 0.064 and 0.052 Å –1 , respectively. R / R F at each q z is a function of the laterally averaged electron density, ⟨ρ e ( z )⟩, profile along the surface-normal according to the master equation. , R / R F values were fitted by a modification of the distorted crystal model, , which was previously employed for the interface between liquid Hg and NaF solution. , This first-layer model treats ⟨ρ e ( z )⟩ of the liquid electrolyte/liquid metal junction (normalized by the bulk metal density) as a function of three independent terms, with the first describing the electrolyte, the second representing an explicit atomic layer at the interface, and the third summation term representing the decaying atomic layering in the near-surface region of the liquid metal Here, z H 2 O and σ H 2 O describe the position and width of the electrolyte front; ρ f and σ f are the amplitude and root-mean-square displacement of the first layer, respectively; d is the atomic layer spacing after the second metal layer; z f is the position of the first layer; “ d – z f ” is the distance between the first and second liquid metal layers; and σ n is the root-mean displacement of the n th layer, which increases with z toward the liquid metal bulk and is given by , where σ i is the intrinsic width common to all subsurface layers and σ b describes the rate at which σ n increases. , …”

Nucleation and Growth of PbBrF Crystals at the Liquid Mercury–Electrolyte Interface Studied by Operando X-ray Scattering

“…Liquid mercury has low chemical reactivity and a wide double layer potential range, providing the opportunity to investigate growth at a clean, oxide-free liquid metal surface at well-defined potentials in the absence of other surface reactions. The liquid Hg electrode is atomically flat and exhibits stratification of atomic layers near its surface, 11,15 similar to those found at liquid metal−vapor interfaces. 16,17 By combining cyclic voltammetry with in situ XRR and XRD, we previously showed that reversible growth of an ultrathin PbBrF adlayer of well-defined thickness, followed by epitaxial deposition of three-dimensional (3D) PbBrF bulk crystallites, is observed at the mercury−electrolyte interface (Figure 1).…”

Effect of Concentration on the Interfacial and Bulk Structure of Ionic Liquids in Aqueous Solution

“…At larger distances from the interface, details of the specific interactions between the ions and the solid play a minor role. As for most other isotropic liquids, from the third layer on, interfacial profiles are quantitatively described by generic mean-field models. − In this regime, for most liquids, the structure at buried solid/liquid interfaces and the free surface is determined by bulk parameters, namely, the dominating length scale d b and the decay length ξ b of the bulk’s correlation function. − Indeed, X-ray reflectivity experiments indicate that for a wide range of commonly used anions and cations in this respect ILs do not behave differently compared to the mere of other standard liquids . ,− In neat bulk IL, Triolo et al showed that imidazolium-based ILs with cations featuring long aliphatic side chain exhibit long range density fluctuations in X-ray scattering that correlate with the length of the hydrocarbon chain. Similarly, Nishi et al , studied the gas/IL interface and showed that an ordered interfacial structure evolves because of interfacial pinning of bulk density fluctuations, without extended lateral ordering within the layering .…”