Spectroelectrochemical Evidence of Interconnected Charge and Ion Transfer in Ultrathin Membranes Modulated by a Redox Conducting Polymer.

Alexander Wiorek,Yujie Liu,Maria Cuartero,Gaston A Crespo

doi:10.1021/acs.analchem.0c03124

Abstract

Previous publications have demonstrated the tuning of ion-transfer (IT) processes across ion-selective membranes (ISMs) with thicknesses in the nanometer order by modulating the oxidation state of a film of a conducting polymer, such as poly(3-octylthiophene) [POT], that is in back-side contact. Attempts on the theoretical description of this charge transfer (CT)–IT system have considered the Nernst equation for the CT, while there is no empirical evidence confirming this behavior. We present herein the first experimental characterization of the CT in POT films involved in different CT–IT systems. We take advantage of the absorbance change in the POT film while being oxidized, to monitor the CT linked to nonassisted and assisted ITs at the sample–ISM interface, from one to three ionophores, therefore promoting a change in the nature and number of the ITs. The CT is visualized as an independent sigmoid in different potential ranges according to the assigned IT. Herein, we have proposed a simple calculation of the empirical CT utilizing the mathematical Sigmoidal–Boltzmann model. The identification of the physical meaning of the mathematical definition of CT opens up new possibilities for the design of sensors with superior analytical features (mainly in terms of selectivity) and the calculation of apparent binding constants in the ISM.

Highlights

The ion-selective membrane (ISM) is a vivid element of many successful sensing concepts and attracts the attention of different research profiles from fundamental aspects to applied science.[1]
Spectroelectrochemistry is introduced to investigate the role of POT assisting different IT processes across nanometersized ISMs with an increasing number of ionophores
We aim at demonstrating for the first time how the nature and number of ITs occurring at the sample−ISM interface dictate the dynamic POT+/POT0 conversion

Summary

■ INTRODUCTION

The ion-selective membrane (ISM) is a vivid element of many successful sensing concepts and attracts the attention of different research profiles from fundamental aspects to applied science.[1]. Where EC0 T is the standard redox potential of the POT oxidation process, R is the gas constant, T is the absolute temperature, nPOT is the average number of electrons transferred at the electrode surface from POT0 to POT+, A is the active area of the electrode, and δPOT is the thickness of the POT film. We present the first experimental approach to individually follow the CT in POT films coupled to IT(s) in different ISMs comprising no ionophore, one ionophore (for potassium ion), two ionophores (for lithium and potassium ions), and three ionophores (for lithium, sodium, and potassium ions). We have functionalized regular indium tin oxide (ITO) glass electrodes with a layer of electropolymerized POT and different spin-coated nanometer-sized ISMs on the top. The reader is referred to the Supporting Information

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES