Thread electrodes with polypyrrole nanowires for solid state supercapacitors

Supercapacitor with favorable power density and short charging time has attracted tremendous attention. However, its energy-storing capability is still far less than the battery's. Pseudocapacitive materials such as polypyrrole exhibit great potential in the high-capacitance devices. Here, pyrrole was in-situ polymerized on the hollow polyurethane thread (PPy/HPU), then the PPy/HPU acted as working electrode for the electrochemical polymerization of pyrrole to construct PPy nanowires on its outer surface (EPPy-PPy/HPU thread). EPPy-PPy/HPU electrode with abundant PPy nanowires exhibits higher slope value of ΔJ/2 vs. scan rates (1.43 mF cm−1) than the PPy/HPU's one (0.327 mF cm−1), indicating its larger active area for electrochemical reaction. Thus, EPPy-PPy/HPU performs a superior capacitance (475.9–221.3 mF cm−2 at 0.25–1.00 mA cm−2) than the PPy/HPU (249.1–92.5 mF cm−2). Two EPPy-PPy/HPU electrodes were penetrated by PVA/H2SO4 gel electrolyte to assemble a solid-state supercapacitor (SSC), which presents a dominant diffusion-controlled capacitance, good rate capability (only falling from 36.25 to 29.5 mF cm−1) and stable energy density (0.915–1.286 μWh cm−1). This fiber-shaped SSC has great potential in the application of wearable energy storage devices.