Switching of the ion exchange behaviour of PEDOT thin films during a potential cycling: An electrochemical atomic force microscopy study

Thickness variations of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films placed under potential conditioning were measured with the help of electrochemical atomic force microscopy (EC-AFM). In this purpose, in-situ AFM operating in the contact mode was coupled with either cyclic voltammetry (CV) or advanced cyclic voltammetry (AdCV). A PEDOT functionnalized platinum electrode was used simultaneously as a sample for in-situ AFM measurements and a working electrode in a usual three electrode electrochemical setup. PEDOT films were electrodeposited with the help of the CV technique from lithium perchlorate aqueous solutions. From these EC-AFM investigations, brand new PEDOT films were found to be anion exchangers, in good agreement with conclusions of investigations reported in literature. Unexpectedly, PEDOT films having undergone a comprehensive electrochemical cycling (i.e. an electrochemical aging) in a potential range encompassing narrowly their redox process by using tens of CV or AdCV potential cycles behave as cation exchangers. Such observation strongly suggests that the electrochemo-mechanical and ion exchange behaviours of PEDOT can be both switched by simply using a potential cycling. Interestingly, the initial steps of this switching process were observed on a brand new PEDOT film during 26 consecutive CV scans. In the course of this process still ongoing at the end of the 26th cycle, a second swelling peak appears and grows progressively beside the initial swelling peak attributed to an anion exchange behaviour. This leads to a dual ion exchange behaviour for the resulting PEDOT film within the explored potential range. Indeed, this new swelling peak can be attributed to a cation exchange behaviour from the comparison of the potential dependant chronothicknograms and corresponding voltathicknograms with those obtained previously in this work. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Thickness variations of PEDOT thin films under potential conditioning were studied using electrochemical atomic force microscopy. The research showed that PEDOT films can switch from anion exchange behavior to cation exchange behavior through electrochemical aging, suggesting that ion exchange behaviors of PEDOT can be modulated by potential cycling.