Electrochemical Study of Ion Transfers Processes at the Interfaces between Water and Trifluorotoluene and Its Derivatives

Abstract

As one phase constituting of a liquid/liquid (L/L) interface, suitable organic solvents are of great significance for the study of electrochemistry at a L/L interface. In this work, the thermodynamic and kinetic parameters of simple ion transfer (IT) at the water/trifluorotoluene (W/TFT) interface were measured using micro-and nanopipettes voltammetry, respectively. In addition to the study of model ions, we have also explored some ions whose transfer potentials are close to the two ends of the potential window. Inspired by the work of the W/TFT interface, we also further developed two novel L/L interfaces and investigated various simple IT reactions based on the W/oand p-methylbenzotrifluoride (W/o-and p-MBTF) interfaces. The transfer potential and Gibbs energy of ITs across the W/o-and p-MBTF interface were determined by the analysis of the electrochemical voltametric curves. Special attention should be paid to that we can observe the IT peak or steady-state of tetraamyl ammonium (TAA + ) at W/o-and p-MBTF interfaces with no difficulty, which is rather challenging at other L/L interfaces. Compared to the classical W/1,2-dichloroethane (DCE) and W/ nitrobenzene (NB) interfaces, the W/TFT and its derivatives interfaces exhibit low toxicity, favourable stability, and wider potential windows, which can be better choices for replacing the traditional organic solvents in the electrochemical study at a L/L interface.

Observing Discrete Blocking Events at a Polarized Micro- or Submicro-Liquid/Liquid Interface

“…A wider PPW builds up, as displayed in Figure (compare black traces in panels A and B), when TFT instead of DCE is used as the oil phase. In Figure A, we can see that the standard (Δ o w ϕ°) and half-wave (Δ o w ϕ 1/2 ) IT potentials of ClO 4 – at the water/DCE interface are estimated as −0.170 and −0.181 V, respectively, using the Galvani potential scale suggested by Wandlowski et al Similarly, in Figure B, the Δ o w ϕ° and Δ o w ϕ 1/2 of ClO 4 – at the water/TFT interface are −0.159 and −0.136 V, respectively, according to the work reported by Shao and coworkers . The experimental steady-state currents for 10 mM ClO 4 – approximately reach −231 pA at −0.329 V in Figure A and −55.8 pA at −0.323 V in Figure B, respectively.…”

Boosting the cell voltage in biphasic flow batteries via Galvani potential difference

“…It has been well known since the 1970s that the interface between immiscible electrolyte solutions (ITIES) can be significantly polarized, resulting in Galvani potential differences of up to 0.7 V between phases. [12][13][14][15] For thermodynamic definition of the Galvani potential difference, see the ESI. † We have shown earlier that the redox potential difference between two redox couples is influenced by the Galvani potential difference between the two phases.…”

“…while for biphasic systems the additional term Df i 0 is included, [12][13][14][15] arising from the difference of solvation energy of species i between the two phases.…”

“…Liquid-liquid interfaces can be polarized electrochemically with an external power supply, but also chemically by partition of a common ion. [12][13][14][15] The degree of immiscibility between the two solvents is proportional to the generated Galvani potential difference by partition of salts. 19,20 The greater the difference in immiscibility between the organic and aqueous phases, the more pronounced the Galvani potential difference becomes with the same salt, as recently discussed in detail by Samec et al 19,20 This property opens up exciting possibilities for optimizing the performance of biphasic flow batteries, as the tailored selection of solvents and their immiscibility can be strategically engineered to enhance the overall voltage and energy output of the system.…”

“…The thermodynamics of partition of ions at the interface of two immiscible electrolytes (ITIES) is well understood. [12][13][14][15] As measurements between pure solutions would be difficult, all the available data focuses on mutually saturated solutions. The Galvani potential difference of the interface depends on the partitioning of different ions, and can be evaluated when the Gibbs energy of transfers of all the charged species from aqueous to organic phases are known.…”