Insights into Solution Chemistry from High Pressure Electrochemistry

Swaddle, Thomas W.

doi:10.1002/9783527612628.ch05

Cited by 4 publications

(2 citation statements)

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“…Cation specificity has been observed in many physical properties, including surface interactions, − interfacial tension experiments, − critical coagulation concentration data of colloidal suspensions, , and protein structure and kinetics. , One particularly interesting phenomenon is the ability of spectator cations to affect the rates of chemical reactions, which has been observed across a broad range of systems, including both homogeneous ,,− and heterogeneous − ,− ,,,− ET processes. In this work, we narrow our focus to homogeneous ET in the limit of weak coupling, as exemplified by the well-studied self-exchange reaction between Fe 2+ and Fe 3+ complexes. − This class of ET reactions can be formalized in the general context of Marcus theory, enabling the physical origins of specific cation effect to be partially isolated and potentially even quantified.…”

Section: Introductionmentioning

confidence: 99%

“…, Cs + ). Experiments carried out over this same series of electrolyte solutions have shown that the change in ET rate trends with the change in cationic radius. ,,− By studying bulk electrolyte systems in the absence of any specific redox species, we can quantify the effect that different cations have on the collective molecular fluctuations that are known to drive ET reactions.…”

Section: Introductionmentioning

confidence: 99%

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The Influence of Spectator Cations on Solvent Reorganization Energy Is a Short-Range Effect

2021

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In this manuscript, we use classical molecular dynamics simulation to explore the origin of specific cation effects on the rates of bulk-phase aqueous electron transfer (ET) reactions. We consider 0.6 M solutions of Cl– and a series of different cations: Li+, Na+, K+, Rb+, and Cs+. We evaluate the collective electrostatic fluctuations that drive Marcus-like ET and find that they are essentially unaffected by changes in the cationic species. This finding implies that the structure making/breaking properties of various cations do not exert a significant influence on bulk-phase ET reactions. We evaluate the role of ion pairing in these specific cation effects and find, unsurprisingly, that model redox anions that are more highly charged tend to pair more effectively with spectator cations than their monovalent counterparts. We demonstrate that this ion pairing significantly affects local electrostatic fluctuations for the anionic redox species and thus conclude that ion pairing is one of the likely sources of rate-dependent cation effects in aqueous ET reactions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Influence of Spectator Cations on Solvent Reorganization Energy Is a Short-Range Effect

2021

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Electrochemistry at High Pressures: A Review

2004

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High pressure electrochemical studies are potentially dangerous and less immediately implemented than conventional investigations. Technical obstacles related to properties of the working electrode material, preparation of its surface, availability of suitable reference electrodes, and the need for specially designed high pressure equipment and cells may account for the relative lack of experimental data on electrochemistry at high pressures. However, despite the stringent requirements for system and equipment stability, significant developments have been made in recent years and the combination of electrochemical methods with high hydrostatic pressure has provided useful insights into the thermodynamics, kinetics, and other physico-chemical characteristics of a wide range of redox reactions. In addition to fundamental information, high pressure electrochemistry has also lead to a better understanding of a variety of processes under non-classical conditions with potential applications in today×s industrial environment from extraction and electrosynthesis in supercritical fluids to measurement of the pH at the bottom of the ocean. The purpose of this article is to detail the experimental pressurizing apparatus for electroanalytical measurements at high pressures and to review the relevant literature on the effect of pressure on electrode processes and on the properties of aqueous electrolyte solutions.

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The Decamethylferrocene(+/0) Electrode Reaction in Organic Solvents at Variable Pressure and Temperature

Matsumoto

Swaddle

2004

Inorg. Chem.

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Half-wave potentials E(1/2) relative to a Ag/Ag(+) electrode, mean diffusion coefficients D, and standard electrode reaction rate constants k(el) are reported for the decamethylferrocene(+/0) couple (DmFc(+/0)) in nine organic solvents at variable pressure and (for five solvents) temperature. Limited data on the ferrocene(+/0) (Fc(+/0)) and Fe(phen)(3)(3+/2+) electrode reactions are included for comparison. Although E(1/2) for DmFc(+/0) correlates only loosely with the reciprocal of the solvent dielectric constant epsilon at ambient pressure, its pressure dependence expressed as the volume of reaction Delta V(cell) is a linear function of Phi = (1/epsilon)( partial differential ln epsilon/ partial differential P)(T) (the Drude-Nernst relation). Interpretation of the temperature dependence data is made difficult by enthalpy-entropy compensation. Measurements of D for solutions containing 0.5 mol L(-1) tetrabutylammonium perchlorate (TBAP) at 25 degrees C and ambient pressure are inversely proportional to the viscosities eta of the pure solvents as expected from the Stokes-Einstein relation, despite the fact that increasing [TBAP] results in increased eta. The activation volume Delta V(diff)(++) for diffusion of DmFc(+/0) ranges from 7 to 17 cm(3) mol(-1) and generally increases with increasing eta and thus with increasing [TBAP]. The activation volumes Delta V(el)(++) for the electrode reactions of DmFc(+/0) and Fc(+/0) are all positive, equaling the corresponding Delta V(diff)(++) values within the experimental uncertainty and contrast sharply with the negative Delta V(ex)(++) values characteristic of the corresponding self-exchange reactions in homogeneous solution. These facts, together with the thermal activation parameters, point to solvent dynamical control of the electrode (but not the homogeneous self-exchange) reactions. The apparent radii of the electroactive species according to the Drude-Nernst and Stokes-Einstein relations cannot be satisfactorily related to their crystallographic radii and are better regarded as adjustable parameters with limited physical significance.

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Insights into Solution Chemistry from High Pressure Electrochemistry

Cited by 4 publications

References 89 publications

The Influence of Spectator Cations on Solvent Reorganization Energy Is a Short-Range Effect

The Influence of Spectator Cations on Solvent Reorganization Energy Is a Short-Range Effect

Electrochemistry at High Pressures: A Review

The Decamethylferrocene(+/0) Electrode Reaction in Organic Solvents at Variable Pressure and Temperature

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