Synthesis and characterization of nanofiber-type hydrophobic organic materials as electrodes for improved performance of PVDF-based piezoelectric nanogenerators

Poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives are synthesized by oxidative polymerization using sodium dodecyl sulfate (SDS) as an anionic surfactant dopant. The resulting polymeric materials featuring nanofiber-type one-dimensional (1D) structures are identified as poly(2‐butyl‐2,3‐dihydrothieno[3,4‐b][1,4]dioxine:dodecyl sulfate (PEDOT-C ₄ :DS) and poly(2‐hexyl‐2,3‐dihydrothieno[3,4‐b][1,4]dioxine:dodecyl sulfate (PEDOT-C ₆ :DS). The ratio of the DS anion doped into PEDOT-C ₄ :DS and PEDOT-C ₆ :DS is 0.16 and 0.23, respectively. The contact angle of water on the PEDOT-C ₄ :DS and PEDOT-C ₆ :DS films is 76.6° and 87.7° respectively, showing hydrophobic properties similar to that with water on PVDF. It facilitated the fully uniform film formation due to excellent surface matching. Peeling force of PEDOT-C ₄ :DS and PEDOT-C ₆ :DS is stronger than the one of PEDOT:PSS‐CNT composite. GIWAX analysis showed that PEDOT-C ₄ :DS formed the highly ordered edge-on structure and PEDOT-C ₆ :DS formed the bimodal orientation consisting of edge-on structure mainly and face-on structure slightly. The electrical conductivity (σ _{PEDOT‐C4:DS} =50.0 S cm ⁻¹ ) of PEDOT-C ₄ :DS is 41.7 times higher than that of PEDOT:PSS (σ _PEDOT:PSS =1.2 S cm ⁻¹ ). The output signals (maximum voltages/currents) of piezoelectric nanogenerators (PNGs, electrode/PVDF/electrode) using these materials as electrodes are PNG-1 (PEDOT:PSS‐CNT composite) 1.25 V/128.5 nA, PNG-2 (PEDOT-C ₄ :DS) 1.54 V/166.0 nA, and PNG-3 (PEDOT-C ₆ :DS) 1.49 V/159.0 nA. Of these, PNG-2 & PNG-3 show maximum piezoelectric output power of 63.0 nW and 59.9 nW at 9 MΩ compared to PNG-1 (41.0 nW at 10 MΩ). They are enhanced up to 53.7%. The excellent surface matching between a piezoelectric active material and an electrode material leads to high output power.