Integration of Polypyrrole Electrode into Piezoelectric PVDF Energy Harvester with Improved Adhesion and Over-Oxidation Resistance

Abstract

Smart textiles for wearable devices require flexibility and a lightweight, so in this study, a soft polypyrrole (PPy) electrode system was integrated into a piezoelectric polyvinylidenefluoride (PVDF) energy harvester. The PVDF energy harvester integrated with a PPy electrode had the piezoelectric output voltage of 4.24-4.56 V, while the PVDF energy harvester with an additional aluminum-foil electrode exhibited 2.57 V. Alkaline treatment and chemical vapor deposition with n-dodecyltrimethoxysilane (DTMS) were employed to improve the adhesion between the PVDF and PPy and the resistance to over-oxidation in aqueous solutions. The PVDF film modified by an alkaline treatment could have the improved adhesion via the introduction of polar functional groups to its surface, which was confirmed by the ultrasonication. The surface hydrophobicity of the PPy electrode was enhanced by the DTMS coating, resulting in the improvement of the resistance to over-oxidation with a water contact angle of 111°. Even with the hydrophobic coating, the electrodes remained electroconductive and continued to transfer an electric charge, maintaining the piezoelectricity of the PVDF film. The developed electrode-integrated energy harvester is expected to be applied to smart textiles because it offers the advantages of efficient piezoelectric generation, flexibility, and durability.

Keywords: durability; electroconductivity; electrode; energy harvester; flexibility; piezoelectricity; poly(vinylidene fluoride); polypyrrole.

Figure A1

FT-IR spectra of PVDF films treated with an NaOH solution for 0 min (UT), 60 min (A60), 120 min (A120), and 180 min (A180) for the range of 700–1400 cm⁻¹ (a), 1450–2000 cm⁻¹ (b), 1400–4000 cm⁻¹ (c).

Figure A2

Changes in the add-on (%) of a sample covered by only PPy polymerization (P) and a sample treated with an NaOH solution and followed by PPy polymerization (A120P) according to the ultrasonication duration.

Figure 1

Illustration of experiment procedure for polyvinylidenefluoride (PVDF) film.

Figure 2

Water contact angle and piezoelectric output voltage of the PVDF film treated with an NaOH solution.

Figure 3

FE-SEM images for untreated sample (UT) (a,b), polypyrrole coated PVDF film without alkaline treatment (P; c,d), polypyrrole coated PVDF film after alkaline treatment for 120 min (A120P; e,f), and hydrophobic coated PVDF film after alkaline treatment for 120 min and polypyrrole coating (A120PH; g,h).

Figure 4

Diagram of nucleation and growth mechanism and morphology of polypyrrole according to the hydrophilicity of substrates.

Figure 5

Water contact angle of an untreated sample (UT), a sample treated with an NaOH solution (A120), a sample treated with an NaOH solution and followed by PPy polymerization (A120P), and a sample treated with an NaOH solution and followed by PPy polymerization and hydrophobic coating (A120PH).

Figure 6

Surface resistivity of a sample treated with an NaOH solution and followed by PPy polymerization (A120P), and a sample treated with an NaOH solution and followed by PPy polymerization and hydrophobic coating (A120PH).

Figure 7

Piezoelectric output voltage of (a) a sample treated with an NaOH solution and followed by PPy polymerization (A120P) and (b) a sample treated with an NaOH solution and followed by PPy polymerization and hydrophobic coating (A120PH) and piezoelectric output current of (c) A120P and (d) A120PH (values on the upper left of each graph are average values of six samples in the peak to peak values).

Figure 8

Removal of PPy layer in (a) a sample covered by only PPy polymerization (P) and (b) a sample treated with an NaOH solution and followed by PPy polymerization (A120P) according to the duration of the ultrasonication.

Figure 9

Change of the surface resistivity of a sample covered by only PPy polymerization (P) and a sample treated with an NaOH solution and followed by PPy polymerization (A120P) according to the ultrasonication duration.

Figure 10

Surface resistivity of a sample treated with an NaOH solution and followed by PPy polymerization (A120P) and a sample treated with an NaOH solution and followed by PPy polymerization and hydrophobic coating (A120PH) by the duration of the immersion at water.