Printed PEDOT:PSS Trilayer: Mechanism Evaluation and Application in Energy Storage

Abstract

Combining ink-jet printing and one of the most stable electroactive materials, PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), is envisaged to pave the way for the mass production of soft electroactive materials. Despite its being a well-known electroactive material, widespread application of PEDOT:PSS also requires good understanding of its response. However, agreement on the interpretation of the material's activities, notably regarding actuation, is not unanimous. Our goal in this work is to study the behavior of trilayers with PEDOT:PSS electrodes printed on either side of a semi-interpenetrated polymer network membrane in propylene carbonate solutions of three different electrolytes, and to compare their electroactive, actuation, and energy storage behavior. The balance of apparent faradaic and non-faradaic processes in each case is discussed. The results show that the primarily cation-dominated response of the trilayers in the three electrolytes is actually remarkably different, with some rather uncommon outcomes. The different balance of the apparent charging mechanisms makes it possible to clearly select one electrolyte for potential actuation and another for energy storage application scenarios.

Keywords: PEDOT:PSS-IPN trilayer; energy storage; ink-jet printing; linear actuation; three different electrolytes.

Figure 1

SEM images of a cross section of PP–IPN trilayer (scale bar 100 µm), including an inset for the thickness estimation of different layers. (b) EDX spectroscopy line scan of elemental composition of the cross section (inset of a) showing carbon (C, black), sulfur (S, red), and oxygen (O, blue) relative content.

Figure 2

Isometric and isotonic ECMD measurements under cyclic voltammetry (1.0 to −0.6 V, 5 mV s⁻¹, 5th cycle) of PP–IPN trilayers in PC solutions of: EDMICF₃SO₃ (black), LiTFSI (red) and NaClO₄ (blue). Response as in (a) strain ε; (b) stress σ; (c) current density j against potential E (vs. Ag/AgCl (3M KCl)) with an inset for EDMICF₃SO₃ oxidation/reduction peaks.

Figure 3

Square wave potential step (1.0 to −0.6 V, 0.005 Hz, 3rd and 4th cycle) response of PP–IPN trilayers in EDMICF₃SO₃ (■, black), LiTFSI (●, red) and NaClO₄ (♦, blue) of (a) strain vs. time; (b) stress vs. time, with potential E (dotted); (c) strain vs. frequency; (d) the stress difference Δσ vs. frequency. The dotted lines in d show the linear fit, for orientation only.

Figure 4

Square wave potential steps (1.0 V to −0.6 V) response of PP–IPN trilayer in EDMICF₃SO₃ (■, black), LiTFSI (●, red) and NaClO₄ (♦, blue) in propylene carbonate. The charge densities at reduction (Figure S3b) were obtained at different applied frequencies by integrating the current density/time curves (Figure S3a, 0.005 Hz). The strain and stress differences against the charge density are shown in (a,b), respectively. The dashed lines are the linear fits, shown for orientation.

Figure 5

Stress response stability during square wave potential steps (0.1 Hz) for PP–IPN layers in EDMICF₃SO₃ (black, ■), LiTFSI (red, ●) and NaClO₄ (blue, ♦) in (a,a`): stress (blocking force) vs. time; (b) stress difference vs. cycle number.

Figure 6

(a) diffusion coefficients vs. frequency upon reduction in PP–IPN trilayers in EDMICF₃SO₃ (■, black), LiTFSI (●, red) and NaClO₄ (♦, blue) solutions. The strain rate ν_red^strain in (b) and the stress rate ν_red^stress in (c) against the diffusion coefficients upon reduction. The dashed lines symbolize the linear fits and are shown as visual guides.

Figure 7

Square wave current steps of PP–IPN trilayers showing in (a) the potential time evolution (3rd to 4th cycle) at 0.005 Hz and current ± 50 µA (dotted) and (b) the specific capacitance vs. frequency; and (c) the specific capacitance vs. cycle number in long term test at 0.1 Hz (± 1 mA). (EDMICF₃SO₃ (black, ■), LiTFSI (red, ●) and NaClO₄ (blue, ♦)).