Double Layer Impedance in Mixtures of Acetonitrile and Water

Abstract

Double layer (DL) impedances were evaluated in mixed solutions of water and acetonitrile at various ratios in the polarized potential domain in order to find competitive orientation of the two solvent molecules on the platinum electrode. The DL capacitance at any ratio of the mixture shows the common power law of the ac‐frequency. The capacitance at molar fractions of water less than 0.2 increases linearly with the fraction, and reaches the value for aqueous solution. This variation indicates accumulation of water molecules on the electrode excluding acetonitrile molecules. It is modelled on the concept of the Langmuir‐type isotherm in which water and acetonitrile molecules have competitive interaction with the electrode. The experimental variations by the use of the isotherm yield the difference in the interaction energy, 6 kJ mol−1. The accumulation of water in the DL is supported by the formation of the adsorbed layer by insoluble ferrocene.

Quantitative Relation of the Frequency Dispersion of Double Layer Capacitances to Surface Roughness

“…The experimental results has demonstrated that the ionic distribution is not a source of the frequency dispersion [21,22,25,27,53]. The present concept in section 2 is close to broadening of the time constant of adsorption kinetics, if the adsorption kinetics is equivalent to eq 5 [29].…”

“…where λ is a constant, f = ω/2π, and Cp,1Hz is a value of C p at f = 1 Hz. eq 3 has been derived by solving the differential equation, λωC = dC/dt, which is obtained from the linearity of the Nyquist plot (Z 1 = dC/dtK, -Z 2 = ωC/K, K = (ωC) 2 + (dC/dt) 2 ), where λ is the inverse of the slope of the linearity [22,[25][26][27][28]. Carrying out the differentiation of dCp/dt by use of dt = dω -1 yields j = VωCp(i + λ).…”

Study on Preferential Solvation of Water by Electrochemical Method

“…By contrast, oxygen atoms interact more easily with gold atoms. From the point of adsorption energy, the adsorption energy of FcCH 2 OH in aqueous solvent was lower than that of FcCH 2 OH in anhydrous acetonitrile on the electrode . So the adsorbed FcCH 2 OH more easily desorb from the surface of electrode in aqueous solvent.…”

“…However, the effect of water always is ubiquitous but often overlooked as a background environment in the water and organic solvent. In fact, the preferential solvation of water plays an important role in electrochemical behavior of solute , hydrogen evolution reaction , double layer capacitance , the process of electronic transfer . Exploring preferential solvation of water by electrochemical methods would provide new insights into the effect of water in the field of electrochemical research.…”

“…In this work, FcCH 2 OH was used as solute to study the preferential solvation of water in the presence of trace water in acetonitrile. The additional water affects the structure of the acetonitrile solvent layer on the electrode surface and the selectivity of the solvation of FcCH 2 OH . Moreover, in the mixed solvent, there are other interaction forces between solvent and solvent, including hydrogen bond network between water molecules and water molecules, weak dipole‐dipole interaction between acetonitrile molecules and acetonitrile molecules, and hydrogen bond interaction between water molecules and acetonitrile molecules.…”