Double-Layer Capacitances Caused by Ion–Solvent Interaction in the Form of Langmuir-Typed Concentration Dependence

Abstract

Variations of the double layer capacitances (DLCs) at a platinum electrode with concentrations and kinds of salts in aqueous solutions were examined in the context of facilitating orientation of solvent dipoles. With an increase in ionic concentrations, the DLCs increased by ca. a half and then kept constant at concentrations over 1 mol dm−3. This increase was classically explained in terms of the Gouy–Chapman (GC) equation combined with the Stern model. Unfortunately, measured DLCs were neither satisfied with the Stern model nor the GC theory. Our model suggests that salts destroy hydrogen bonds at the electrode–solution interface to orient water dipoles toward the external electric field. A degree of the orientation depends on the interaction energy between the salt ion and a water dipole. The statistical mechanic calculation allowed us to derive an equation for the DLC as a function of salt concentration and the interaction energy. The equation took the Langmuir-type in the relation with the concentration. The interaction energy was obtained for eight kinds of salts. The energy showed a linear relation with the interaction energy of ion–solvent for viscosity, called the B-coefficient.

Promoting Cu-catalysed CO2 electroreduction to multicarbon products by tuning the activity of H2O

“…has shown that the double layer capacitance (a proxy for the surface coverage of ions) measured across a wide range of salts was saturated for concentrations > 1m because the cation coverage followed a Langmuir isotherm. [56][57][58] Furthermore, our own analysis of the double layer capacitance as a function of aw at −1.21 V vs NHE estimated from electrochemical impedance spectroscopy showed that the capacitance was nearly invariant across the entire range probed in this study (Figure S9). This suggested that the surface coverage of cations does not substantially increase with increasing electrolyte concentration because it was already saturated on the surface.…”

Promoting Cu Catalyzed CO2 electroreduction to multi-carbon products by tuning the activity of water

“…Studies across several salt types have shown that the double layer capacitance saturates for concentrations > 1m. 38 To provide credence to this, we performed impedance spectroscopy on Cu in CO 2 saturated electrolytes to determine the interfacial capacitance during CO 2 reduction (Figure S1). If the Na + coverage increased as a function of electrolyte concentration, then we would observe an increase in the interfacial capacitance.…”

Department of Electronics, Faculty of Information Science and Electronics Engineering, Kyushu University

“…This picture has succeeded in explaining and predicting the doublelayer properties, for example, the differential capacitance of mercury electrodes 6 , and the zeta potentials of various metal oxides and hydrophobic materials 12 . However, the Stern-Gouy-Chapman theory cannot explain the recent experimental data on the double-layer capacitances of polycrystal platinum or indium tin oxide electrodes [15][16][17] , although these studies did not seriously take into account the variation of the surface potential with the salt concentration.…”