Keynote Speaker
Prof. Dr. Tobias Cramer
Quantitative Imaging of Electroswelling in Organic Mixed Ionic Electronic Conductors
Tobias Cramer *
Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna, Italy
Ionic transport and accumulation into active layers of electrodes is of crucial relevance for energy storage and energy conversion processes. Organic mixed ionic electronic conductors (OMIECs) are a well characterized model system that exhibits a 3D electrified interface. As a result, unconventional properties emerge such as volumetric capacitance or strong electroswelling. Electroswelling allows to achieve volume changes and mechanical actuation controlled by small electrical potentials. The electroswelling effect is exploited in electrochemical actuators with low-voltage drive, nanoscale precision and miniaturization, with applications in soft robotics, soft micromechanical devices or actuated biomedical devices. However, electroswelling can also trigger delamination in OMIECs thin film devices used for sensors or electrochemical energy storage and puts their long-term stability at risk.
To investigate ionic transport and accumulation at the microscale, we introduce a novel type of modulated electrochemically controlled AFM experiment (mEC-AFM) that combines local surface strain measurements with electrochemical impedance spectroscopy. We test the experiment on OMIEC covered microelectrodes and obtain multidimensional spectroscopic data that explains the relevant processes and their timescales in electroswelling. Combining the technique with the PinPoint imaging mode, we record high resolution maps that report the local amplitude and phase of electroswelling on soft polymer thin films. The data demonstrate that electroswelling in PEDOT:PSS used as OMIEC material is driven by the volume of hydrated ions entering the thin film and does not depend on slower diffusive processes.[1] In more complex materials such as PPY-DBS ionic transport is further hindered and the multidimensional spectroscopic data allows for in-depth profiling of ionic transport and swelling properties.
Figure: Schematic showing the modulated EC-AFM experiment and the recorded data traces. The techniques allow to map electroswelling in mixed ionic and electronic conductors with nanoscale resolution.
[1] F. Bonafe et al. Adv. Sci. 2024, https://doi.org/10.1002/advs.202308746
Keywords: Modulated Electrochemically Controlled Atomic Force Microscopy (mEC-AFM), electroswelling, Organic Mixed Ionic Electronic Conductors