**4. Conclusions**

Charging/discharging in PEDOT or any other conducting polymer is accompanied by ion flux in order to maintain a neutral net charge. PEDOT polymerized different potentials has been studied here in order to establish the effect of the polymerization potential on the ion mobility and the corresponding expansion. Depending on the given design, such findings are potentially applicable for use in linear (PEDOT-FF) or bending (PEDOT-BL) actuators. The mostly anion-dominated activity seen for PEDOT deposited at 1.0 V gradually shifted to increased cation involvement with increasing deposition potentials of 1.2 V and 1.5 V, which in turn led to the a shift from expansion upon oxidation to mixed and increasing expansion upon reduction. EDX spectroscopy confirmed that, upon reduction, an increasing PF6- anion content remained in PEDOT polymerized at higher potentials, calling for cation incorporation in order to maintain a neutral net charge. The SEM micrographs indicated that denser and less porous PEDOT networks were formed at higher polymerization potentials, which might be the main reason for lowered PF6 mobility. EQCM measurements confirmed that mixed ion activity (both cation and anions participation) processes accompanied charging/discharging. As mixed activity modes are undesirable in general, the extensive study of PEDOT here enables one to understand the factors behind ion mobility and to either choose polymerization potentials optimal for more controlled actuation or to make maximum use of the mixed activity by choosing conditions for equal expansion upon reduction and oxidation. Future applications of such devices, i.e., where one ion movement process dominates, include soft robotics and smart textiles.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/polym13152448/s1: Figure S1. Charge potential curves in cyclic voltammetry (± 1.0 V, TBAPF6-PC electrolyte) of PEDOT films made at EP 1.0 V (black curve), EP 1.2 V (red curve) and EP 1.5 V (blue curve) shown in a: for PEDOT-FF, in b: for PEDOT-BL and c: for EQCM measurements. The arrows indicate the start and end points of the 3rd cycle. Figure S2. Cyclic voltammetric (scan rate 10 mV s<sup>−</sup>1) in TBAPF6-PC electrolyte at ±1.0 V showing EQCM measurements of frequency f

against charge Q of PEDOT films on quartz crystals polymerized at a: EP 1.0 V, b: EP 1.2 V and c: EP 1.5 V. The arrows indicate the direction of the san (starting point −1.0 V).

**Author Contributions:** Conceptualization, T.T. and G.U.; Data curation, D.G.W. and B.K.V.; Formal analysis, R.K. and D.G.W.; Funding acquisition, G.U; Investigation, R.K., B.K.V. and T.T.; Methodology, D.G.W. and B.K.V.; Project administration, G.U.; Resources, T.T.; Software, D.G.W.; Supervision, G.U.; Validation, R.K.; Writing–original draft, R.K.; Writing–review & editing, T.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by DFG 428 and Estonian Research Council PRG-1084.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the Corresponding author.

**Acknowledgments:** The research was supported from DFG 428 Macromolecular networks (Freiburg, Germany) and the Estonian Research Council PRG-1084.

**Conflicts of Interest:** The authors declare no conflict of interest.
