“…The latter observation is suggestive of differences in the binding properties of the monovalent cations, with the high pH data in Figure (b) indicating adsorption to the negative α-alumina surface in the order Li + > Na + > K + ≈ Cs + . A similar binding sequence has been obtained in previous studies of γ-alumina substrates, , and other metal oxide minerals including titania, ,,, and hematite. , 2 The ζ potential behavior of α-alumina as a function of both the monovalent cation type and pH. The electrolyte concentration is (a) 0.01 mol dm -3 XNO 3 and (b) 1.0 mol dm -3 XNO 3 .…”
An electroacoustic technique has been used to monitor the binding of various monovalent inorganic ions
on α-alumina at different pHs, nondilute solids, and moderate to high (0.01−1.0 mol dm-3) electrolyte
concentrations. The ζ potential versus pH data show that NaNO3, KNO3, CsNO3, KBr, KCl, and KI are
indifferent electrolytes for the α-alumina surface. However, LiNO3 causes a significant change in the
isoelectric point of α-alumina, indicating that Li+ adsorbs in a specific manner to the surface over the range
of concentrations investigated. At high (1.0 mol dm-3) electrolyte concentrations, the monovalent cations
bind to the negative α-alumina surface in the order Li+ > Na+ > K+ ≈ Cs+. By contrast, the Br-, Cl-, I-,
and NO3
- anions adsorb to an almost identical extent over the entire range of concentrations and pH
conditions investigated. The cation binding sequence is consistent with the water “structure making−structure breaking” model first proposed by Gierst et al. and Bérubé and de Bruyn, which is based on
the hydration enthalpies of the ions and the heat of immersion of the colloidal substrate. The comparable
anion adsorption behavior is believed to arise because of the similar and/or low hydration enthalpies of
the anions, which lead to a similar anion−surface interaction in each case.
“…The latter observation is suggestive of differences in the binding properties of the monovalent cations, with the high pH data in Figure (b) indicating adsorption to the negative α-alumina surface in the order Li + > Na + > K + ≈ Cs + . A similar binding sequence has been obtained in previous studies of γ-alumina substrates, , and other metal oxide minerals including titania, ,,, and hematite. , 2 The ζ potential behavior of α-alumina as a function of both the monovalent cation type and pH. The electrolyte concentration is (a) 0.01 mol dm -3 XNO 3 and (b) 1.0 mol dm -3 XNO 3 .…”
An electroacoustic technique has been used to monitor the binding of various monovalent inorganic ions
on α-alumina at different pHs, nondilute solids, and moderate to high (0.01−1.0 mol dm-3) electrolyte
concentrations. The ζ potential versus pH data show that NaNO3, KNO3, CsNO3, KBr, KCl, and KI are
indifferent electrolytes for the α-alumina surface. However, LiNO3 causes a significant change in the
isoelectric point of α-alumina, indicating that Li+ adsorbs in a specific manner to the surface over the range
of concentrations investigated. At high (1.0 mol dm-3) electrolyte concentrations, the monovalent cations
bind to the negative α-alumina surface in the order Li+ > Na+ > K+ ≈ Cs+. By contrast, the Br-, Cl-, I-,
and NO3
- anions adsorb to an almost identical extent over the entire range of concentrations and pH
conditions investigated. The cation binding sequence is consistent with the water “structure making−structure breaking” model first proposed by Gierst et al. and Bérubé and de Bruyn, which is based on
the hydration enthalpies of the ions and the heat of immersion of the colloidal substrate. The comparable
anion adsorption behavior is believed to arise because of the similar and/or low hydration enthalpies of
the anions, which lead to a similar anion−surface interaction in each case.
“…However, judging by the best of the 10 SWOPT solutions we found a spacing of 1.3 Å between the hematite and the Cs + ions, which is consistent with the results by Nemšák et al [13]. These results are furthermore consistent with earlier studies of alkali adsorption on hematite [26,27] as well as different behavior between Na + and Cs + at the liquid/vapor interface [28,29]. SWOPT results, just like the analysis by Nemšák et al, indicate that Cs + ions are directly at the liquid/vapor interface -probably with a partial solvation shell -and Na + ions are excluded from this interface to a depth of ∼4 Å.…”
Section: Example 2: Si-mo Multilayer Mirrorsupporting
“…Analyzing differences in the RCs obtained for Cs and Na reveals that Cs + ions are on average a few angstroms farther from the hematite surface. This is consistent with the inverse lyotropic adsorption sequence (Li + 4 Na + 4 K + 4 Cs + ) based on indirect capacity measurements on different oxides [68][69][70][71] including Fe 2 O 3 , which can be explained by the ionic double-layer model. A more detailed quantitative analysis of the RCs of Na2p, Cs4d, Fe3p, as well as all the components in the O1s and C1s region, together with self-consistent optimization, further revealed the detailed concentration profile at this solid/ liquid interface, as shown in Fig.…”
Electrode/electrolyte interfaces play a vital role in various electrochemical systems, but in situ characterization of such buried interfaces remains a major challenge. Several efforts to develop techniques or to modify existing techniques to study such interfaces are showing great promise to overcome this challenge. Successful examples include electrochemical scanning tunneling microscopy (EC-STM), surface-sensitive vibrational spectroscopies, environmental transmission electron microscopy (E-TEM), and surface X-ray scattering. Other techniques such as X-ray core-level spectroscopies are element-specific and chemical-state-specific, and are being widely applied in materials science research. Herein we showcase four types of newly developed strategies to probe electrode/electrolyte interfaces in situ with X-ray core-level spectroscopies. These include the standing wave approach, the meniscus approach, and two liquid cell approaches based on X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy. These examples demonstrate that with proper modifications, many ultra-high-vacuum based techniques can be adapted to study buried electrode/electrolyte interfaces and provide interface-sensitive, element- and chemical-state-specific information, such as solute distribution, hydrogen-bonding network, and molecular reorientation. At present, each method has its own specific limitations, but all of them enable in situ and operando characterization of electrode/electrolyte interfaces that can provide important insights into a variety of electrochemical systems.
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