SFG Study of the Potential-Dependent Adsorption of the p-Toluenesulfonate Anion at an Activated Carbon/Propylene Carbonate Interface

Abstract

Sum frequency generation spectroscopy has been used to characterise the potential dependent adsorption of the p-toluenesulfonate anion at the activated carbon/propylene carbonate interface of the commercial carbon YP50F. Spectra recorded from the interface between YP50F and a 1 M tetraethylammonium p-toluenesulfonate in propylene carbonate solution showed no ordered anion adsorption without an applied potential. In contrast, there is clear evidence of increasingly ordered anion adsorption with applied potential. Furthermore there is evidence of hysteresis such that the anion remains adsorbed when the applied potential was decreased back to 0 V. Significant reversal of polarity was required before the anion signal was lost. Changes to the propylene carbonate solvent peaks during the electrochemical cycle were also observed. The data indicate that the positive electrode charges either via a counter-ion adsorption mechanism or via an ion-exchange mechanism.

Stark Tuning Rates of Organic Carbonates Used in Electrochemical Energy Storage Devices

“…These findings lend a tractable metric to quantify the electrostatic forces at electrode interfaces under dynamic , or resting , potentials. From a technological standpoint, a thorough understanding of the field at the electrode/electrolyte junction may ultimately lead to new design principles for energy storage materials in a manner similar to that proposed recently by Leung et al.…”

“…These findings lend a tractable metric to quantify the electrostatic forces at electrode interfaces under dynamic 30,31 or resting 71,80 potentials. From a technological standpoint, a thorough understanding of the field at the electrode/ electrolyte junction may ultimately lead to new design principles for energy storage materials in a manner similar to that proposed recently by Leung electrochemical stability window for archetypal lithium ion battery electrolyte solvents by controlling the electrostatics at the liquid/solid junction using dipole-modified interfaces.…”

“…28 It is worth noting that this treatment relies on knowing the vibrational reporter's sensitivity to electric fields under the conditions described by the Onsager model 29 (isotropic dielectric surrounding a molecule) as well as both the refractive index and dielectric of the molecule of interest. Results separately published by Grey et al 30 and Somorjai et al 31 reveal shifts in the vibrational frequency of the C−H stretch of carbonate electrolyte solvents at capacitor and battery electrode interfaces under an applied voltage. Such results highlight the importance of the model proposed by Dawlaty in the context of energy materials.…”

Adsorption of 4-n-Nonylphenol, Carvacrol, and Ethanol onto Iron Oxide from Nonaqueous Hydrocarbon Solvents

“…Sum frequency generation vibrational spectroscopy [sum frequency generation (SFG)] is a surface-specific technique where a vibrational infrared (IR) spectrum is obtained in situ from molecules in solution at an interface. − The spectrum is collected by spatially and temporally overlapping a visible laser beam, with fixed frequency, and an IR laser beam, with tunable frequency, onto the interface of interest to generate a reflected laser beam with frequency equal to the sum of the two incident beams. This configuration gives rise to a nonlinear optical phenomenon whereby there is no signal from centrosymmetric environments . Hence, no signal is generated from a bulk isotropic material.…”

“…This configuration gives rise to a nonlinear optical phenomenon whereby there is no signal from centrosymmetric environments. 17 Hence, no signal is generated from a bulk isotropic material. However, at an interface, the center of symmetry is broken and an SFG signal is obtained.…”