Fenton Chemistry at Polarized Liquid-Liquid Interfaces for Interfacial Electropolymerization

Jönsson-Niedziółka, Martin

A sustainable future requires an energy sector led by renewable sources, especially energy conversion and storage (ECS). Advances in the design and synthesis of nanomaterials, like conducting polymers [1], are critical for future development. An example for this type of material is poly-(3,4-ethylenedioxythiophene) (PEDOT), ideally known for energy applications as a thin film due to its excellent properties (e.g., tunable conductivity, flexibility, and transparency) [2]. However, current manufacturing methods require additives, like surfactants, that affect their properties, leading to decreased performance [3].

The use of liquid-liquid interfaces continues to grow as a viable platform for nanomaterial film synthesis with impressive structural properties [4]. Since several such interfaces are electrochemically active [5], providing external stimulus at these interfaces can fine tune the electric field to enhance interfacial electrosynthesis or self-assembly. This has the potential to produce free-floating films that can be transferred to any solid support with ease for device fabrication. The ability to form thin films directly in a single step will eliminate the need for additives such as surfactants. To explore this, we have investigated the use of Fenton chemistry (H₂O₂ in the presence of a ferrous compound) as the oxidant to polymerize PEDOT at the liquid-liquid interface. This combination offers the advantages of interfacial electropolymerization with a “greener” oxidant.

We used cyclic voltammetry (CV) to study PEDOT formation at the interface under different pHs, molar ratios, and solvent conditions. Repetitive cycling at pH 1.5 - 2 (~10mM HCl) shows the growth of the electrical double layer with each successive cycle as a peak (around ca. -0.1 V vs Ag/AgCl) is growing accordingly until a blue material (PEDOT) is observed at the interface. This is liken to CVs observed for CP electropolymerization on typical solid electrodes [6]. However, this potentiodynamic method takes more than ~5 hours so we also explored chronoamperometry to hasten the film formation and control film thickness. Applying constant potential (ca. 1.25 V vs Ag/AgCl) allowed film formation even after ~60 mins, and the film thickness also varies with time. The properties of produced films were then characterized using electrochemistry, SEM, XPS, RAMAN, and ex-situ conductivity. As a proof-of-concept, we demonstrate that Fenton chemistry is a viable alternative to produce PEDOT at the liquid-liquid interface.

The latest results on PEDOT interfacial electropolymerization using Fenton chemistry and its characterization will be presented and discussed.

Literature:

[1] Q. Meng, et. al., Nano Energy, 2017, 36, 268–285. [2] M. N. Gueye, et. al., Chem. Mater., 2016, 28, 3462–3468. [3] A. Köhler and H. Bässler, Electron. Struct. Org. Semicond., 2015, 307–388. [4] J. Forth, et. al., Adv. Mater., 2019, 1806370, 1806370. [5] L. Rivier, et. al., Angew. Chemie Int. Ed., 2017, 56, 2324–2327. [6] J. Heinze, et al., Chem. Rev. 2010, 110 (8), 4724–4771