High performance carbon nanotube based fiber-shaped supercapacitors using redox additives of polypyrrole and hydroquinone

Abstract

Fiber-shaped supercapacitors (FSSCs) have attractive applications in flexible devices. Here, we report a high performance carbon nanotube (CNT) based fiber-shaped supercapacitor by adding two redox additives simultaneously: polypyrrole (PPy) to the electrodes and hydroquinone (HQ) to the electrolyte. A core–shell CNT–PPy nanocomposite fiber was prepared by an electrochemical deposition method. In the FSSC with CNT–PPy electrodes, PPy provides pseudocapacitance due to its reversible dropping/de-dropping reactions in polyvinyl alcohol (PVA)/H₂SO₄ gel electrolyte. The capacitance of the CNT–PPy FSSC reaches 36 F g⁻¹ (127 mF cm⁻¹, 588 mF cm⁻², and 17 F cm⁻³), which is 7 times higher than that of the pure CNT FSSC. By adding HQ to the PVA/H₂SO₄ gel electrolyte in the CNT–PPy FSSC, the specific capacitance reaches 56 F g⁻¹ (202 mF cm⁻¹, 1168 mF cm⁻², and 42 F cm⁻³), which is 10 times higher than that of the pure CNT FSSC. HQ can enhance ion transfer of the gel electrolyte by the redox reaction of HQ and benzoquinone. PPy and HQ have synergistic effects on the FSSCs. The FSSCs with PPy and HQ also show high stability in the cyclic test for 2000 cycles, and good flexibility under bending, knotting, and tension.