Solvation-Induced Onsager Reaction Field Rather than Double Layer Field Controls CO2 Reduction on Gold

<div><p>The selectivity and activity of the carbon dioxide reduction reaction (CO2R) are sensitive functions of the electrolyte cation. By measuring the vibrational Stark shift of in-situ generated CO on Au in the presence of alkali cations, we quantify the total electric field present during turnover and deconvolute this field into contributions from 1) the electrochemical Stern layer and 2) the Onsager, or solvation-induced, reaction field. The magnitude of the Onsager field is shown to be on the same order as the Stern layer field (∼10 MV/cm) but follows an opposite trend with cation, increasing from Li⁺< Na⁺< K⁺< Rb⁺≈Cs⁺. Contrary to theoretical reports,CO₂R kinetics are not correlated with the Stern field but instead are controlled by the strength of the Onsager reaction field with Cs⁺ as an exception. Spectra of interfacial water as a function of cation show that Cs⁺ induces a change in the interfacial water structure correlated with a dramatic drop in CO₂R activity, highlighting the importance of cation-dependent interfacial water structure on reaction kinetics. These findings show that both the Onsager reaction field and interfacial solvation structure must be explicitly considered for accurate modeling of CO₂R reaction kinetics.</p><br></div>

Solvation-Induced Onsager Reaction Field Rather than Double Layer Field Controls CO2 Reduction on Gold

<div><p>The selectivity and activity of the carbon dioxide reduction reaction (CO2R) are sensitive functions of the electrolyte cation. By measuring the vibrational Stark shift of in-situ generated CO on Au in the presence of alkali cations, we quantify the total electric field present during turnover and deconvolute this field into contributions from 1) the electrochemical Stern layer and 2) the Onsager, or solvation-induced, reaction field. The magnitude of the Onsager field is shown to be on the same order as the Stern layer field (∼10 MV/cm) but follows an opposite trend with cation, increasing from Li⁺< Na⁺< K⁺< Rb⁺≈Cs⁺. Contrary to theoretical reports,CO₂R kinetics are not correlated with the Stern field but instead are controlled by the strength of the Onsager reaction field with Cs⁺ as an exception. Spectra of interfacial water as a function of cation show that Cs⁺ induces a change in the interfacial water structure correlated with a dramatic drop in CO₂R activity, highlighting the importance of cation-dependent interfacial water structure on reaction kinetics. These findings show that both the Onsager reaction field and interfacial solvation structure must be explicitly considered for accurate modeling of CO₂R reaction kinetics.</p><br></div>

Solvation-Induced Onsager Reaction Field Rather than Double Layer Field Controls CO2 Reduction on Gold

<div><p>The selectivity and activity of the carbon dioxide reduction reaction (CO2R) are sensitive functions of the electrolyte cation. By measuring the vibrational Stark shift of in-situ generated CO on Au in the presence of alkali cations, we quantify the total electric field present during turnover and deconvolute this field into contributions from 1) the electrochemical Stern layer and 2) the Onsager, or solvation-induced, reaction field. The magnitude of the Onsager field is shown to be on the same order as the Stern layer field (∼10 MV/cm) but follows an opposite trend with cation, increasing from Li⁺< Na⁺< K⁺< Rb⁺≈Cs⁺. Contrary to theoretical reports,CO₂R kinetics are not correlated with the Stern field but instead are controlled by the strength of the Onsager reaction field with Cs⁺ as an exception. Spectra of interfacial water as a function of cation show that Cs⁺ induces a change in the interfacial water structure correlated with a dramatic drop in CO₂R activity, highlighting the importance of cation-dependent interfacial water structure on reaction kinetics. These findings show that both the Onsager reaction field and interfacial solvation structure must be explicitly considered for accurate modeling of CO₂R reaction kinetics.</p><br></div>

The role of solute polarity on methanol–silica interfacial solvation: a molecular dynamics study

PMFs of 1,3-propanediol and n-pentane at the methanol–silica interface.

A cosolvent surfactant mechanism affects polymer collapse in miscible good solvents

The coil–globule transition of aqueous polymers is of profound significance in understanding the structure and function of responsive soft matter. In particular, the remarkable effect of amphiphilic cosolvents (e.g., alcohols) that leads to both swelling and collapse of stimuli-responsive polymers has been hotly debated in the literature, often with contradictory mechanisms proposed. Using molecular dynamics simulations, we herein demonstrate that alcohols reduce the free energy cost of creating a repulsive polymer–solvent interface via a surfactant-like mechanism which surprisingly drives polymer collapse at low alcohol concentrations. This hitherto neglected role of interfacial solvation thermodynamics is common to all coil–globule transitions, and rationalizes the experimentally observed effects of higher alcohols and polymer molecular weight on the coil-to-globule transition of thermoresponsive polymers. Polymer–(co)solvent attractive interactions reinforce or compensate this mechanism and it is this interplay which drives polymer swelling or collapse.