Cation Effects on the Potentials of Zero Charge of Gold, Silver, and Mercury Electrodes

Bode, Donald D.; Andersen, Terrell N.; Eyring, Henry

doi:10.1149/1.2426510

Cited by 10 publications

(4 citation statements)

References 6 publications

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“…Cation-dependent kinetics of [Fe(CN) 6 ] 3– /[Fe(CN) 6 ] 4– in terms of the exchange current density and the reorganization energy can be attributed to cation-dependent solvation structures of [Fe(CN) 6 ] 3– /[Fe(CN) 6 ] 4– at the electrified interface. As similar cation-dependent kinetic current densities were found for RDE measurements collected from Pt (Figure S12) to those obtained from Au, the cation-dependent kinetics of [Fe(CN) 6 ] 3– /[Fe(CN) 6 ] 4– redox are unlikely derived from the positively charged interface, where Pt is expected to have less positive charge than Au near the equilibrium potential of [Fe(CN) 6 ] 3– /[Fe(CN) 6 ] 4– (∼0.9 V RHE ) due to the higher potential of zero charge of 0.72 V RHE on Pt, than 0.62 V RHE on Au . Of significance to note is that increasing the fraction of weakly H-bonded water and decreasing the fraction of strongly H-bonded water near the electrified interface were found to correlate with increasing exchange current density in the order of Li + < K + < Cs + in Figure and decrease with the reorganization energy of [Fe(CN) 6 ] 3– /[Fe(CN) 6 ] 4– redox in the order of Li + > K + > Cs + (Figure ), as shown in Figure f.…”

Section: Resultssupporting

confidence: 70%

“…The reverse trend was noted when the potential was reversed, as shown in Figure S14d–f. In addition, the peak intensity changes as a function of voltage were more pronounced for [Fe(CN) 6 ] 4– than [Fe(CN) 6 ] 3– , which can be attributed to the greater negative charge of [Fe(CN) 6 ] 4– and thus the greater electrostatic attraction to positively charged Au in the voltage range . Moreover, in situ SEIRAS spectra at 1.1 V RHE revealed increasing consumption of [Fe(CN) 6 ] 4– and production of [Fe(CN) 6 ] 3– in the order of Li + < K + < Cs + , as shown in Figure S14g, in agreement with faster kinetics on the same order (Figure ).…”

Section: Resultsmentioning

confidence: 94%

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Cation-Dependent Interfacial Structures and Kinetics for Outer-Sphere Electron-Transfer Reactions

et al. 2021

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The kinetics of aqueous outer-sphere electron-transfer (ET) reactions are determined in large part by noncovalent electrostatic interactions that originate from the surrounding electrolyte solution. In this work, we examine the role of spectator cations in modifying the rate of heterogeneous ET for an [Fe(CN)6]3–/[Fe(CN)6]4– redox pair. We combine the results of electrochemical measurement, in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), classical molecular dynamics simulation, and theoretical modeling to demonstrate how changing the identity of the spectator cation species over a series that includes Li+, Na+, K+, Rb+ to Cs+ influences the solvation properties and ET kinetics of the redox species. By analyzing the results in the context of the Marcus–Hush–Chidsey (MHC) theory, we find that the solvent reorganization energy increases systematically as the cationic radius decreases. The trend can be attributed to cation-dependent coordination environments of the redox species, whereby more cations of less charge density such as Cs+ than Li+ are present in the redox solvation shell in bulk and at the electrified interface, promoting weaker hydrogen bonds and lowering the effective interfacial static dielectric constant. We discuss the implications of these findings for enabling the tunability of reaction thermodynamics and rates in electrochemical processes.

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Section: Resultssupporting

confidence: 70%

Section: Resultsmentioning

confidence: 94%

Cation-Dependent Interfacial Structures and Kinetics for Outer-Sphere Electron-Transfer Reactions

et al. 2021

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“…This value is 0.3 V positive of the lowest overpotential examined in this study. Indeed, the potential range of HER data collection is well negative of the potential of zero charge of Au. − Consequently, the surface is negatively charged under these conditions and is expected to repel anions such as phosphate.…”

Section: Resultsmentioning

confidence: 97%

Donor-Dependent Promotion of Interfacial Proton-Coupled Electron Transfer in Aqueous Electrocatalysis

et al. 2019

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Efficient interfacial electrocatalysis requires rapid concerted proton−electron transfer (CPET) at the electrode surface, a process for which there is little mechanistic understanding. In aqueous media, multiple proton donors coexist, adding to the mechanistic complexity. Herein, we examine the rate of the hydrogen evolution reaction (HER) on Au, a proxy for CPET to Au, as a function of the concentration of exogenous phosphate and borate proton donors. We find that the reaction order in phosphate is 0.6, whereas the reaction order in borate is close to 0, indicating that phosphate, unlike borate, can outcompete water as a proton donor for interfacial CPET. Promotion in phosphate is substantial; the rate of the HER on Au in saturated potassium phosphate at pH 6.8 is identical to the rate of the HER on Au at pH 1. Additionally, we demonstrate that buffer-promoted CPET is a phenomenon that extends beyond Au to an Earth-abundant catalyst, NiS x . Kinetic data indicate that interfacial CPET cannot be viewed as a simple bimolecular reaction between the donor and a surface site, but that it first requires the formation of a preassociation complex embedded in the double layer. Our results emphasize that both the proton donor and the donor's environment control the rate of interfacial CPET and consequently have profound effects on the rate of heterogeneous electrocatalysis.

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“…As the KOH concentration increases, these are replaced by OH-ions which are attracted to the electrode (positive charge) and increase the dlc. [At the potentials used here the silver electrode is almost lv anodic to its potential of zero charge (8).] The OH-and the K + ions are hydrated.…”

Section: Double Layer Capacicance~the Foregoing Resultsmentioning

confidence: 99%

Silver Oxide Electrode Processes

Dirkse¹,

DeWit²,

Shoemaker³

1967

J. Electrochem. Soc.

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The cathodic and anodic overvoltages at a silver electrode were measured in a range of KOH concentrations of 20-45%. The values of these overvoltages undergo a change in 30-35% KOH. Similar changes or maxima or minima have been observed for other phenomena in KOH solutions, e.g., double layercapacitance. An attempt to account for these changes is made in terms of ion-pair association in concentrations greater than 35% KOH. This association is due to insufficient solvent for the normal hydration of the ions.Occasionally, in studying various phenomena taking place in alkaline solutions, it has been observed that these phenomena have a maximum or a minimum value at about 30-35% KOH. For example, the hydrogen overvoltage at a zinc electrode shows a minimum at about 10M in both KOH and NaOH (1) ; the parameters associated with the anodic passivation of zinc have a maximum at about 9M KOH (2); and the rate of decomposition of silver oxide dissolved in KOH solutions has a minimum at 7-9M KOH (3). Sometimes these maxima or minima can be explained in terms of the net effect of increasing OH-ion concentration and increasing viscosity (or decreasing mobility) as the KOH or NaOH concentration increases. However, this does not offer a satisfactory explanation for all these phenomena. Consequently, the work reported here was undertaken with a twofold objective: (a) to see whether any silver electrode processes exhibited maxima or minima; and (b) to seek an explanation for any such phenomena. Similar work on the zinc electrode is also in progress at our Laboratory. ExperimentalThe method selected to look for maxima and minima involved the use of the sine wave tester described by Kordesch and Marko (4). The IR-free overvoltage of the silver electrode was measured as the current was increased anodically and then as it was increased cathodically. The silver electrode was a piece of silver foil of which only a circular area of 0.32 cm 2 was exposed to the electrolyte. The counter electrode was a sintered Ag-Ag20 plate, 4 x 5 cm; the reference electrode in most runs was Hg/HgO/OH-. The OHconcentration was the same in the cell as in the reference electrode.Readings were taken at 1-min intervals during each run. A typical set of results is given on Fig. 1. The anodic run was carried out first. Then the electrode was allowed to remain on open circuit for about an hour before the cathodic run was made. During the open-circuit period some of the AgO may have de-O ._c d -300 o uJ -600 --9 w u~ --O ~ ] 0.1 0.2 03 0.5 I 2 rno.Fig. 1. Current-voltage curve for a silver electrode in 20% KOH at room temperature. The reference electrode is AgO/Ag20; C) anodic; 9 cathodic.composed to Ag20, and some Ag20 may have dissolved off the electrode. Figure 2 shows the pattern of the open-circuit voltage after the anodic run was terminated. The voltage holds at the AgO/Ag20 level for some time and then, because of decomposition of at least the surface layer of AgO, falls to the Ag20/Ag level. The cathodic run was begun only after the opencircuit voltage h...

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Cation Effects on the Potentials of Zero Charge of Gold, Silver, and Mercury Electrodes

Cited by 10 publications

References 6 publications

Cation-Dependent Interfacial Structures and Kinetics for Outer-Sphere Electron-Transfer Reactions

Cation-Dependent Interfacial Structures and Kinetics for Outer-Sphere Electron-Transfer Reactions

Donor-Dependent Promotion of Interfacial Proton-Coupled Electron Transfer in Aqueous Electrocatalysis

Silver Oxide Electrode Processes

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