Polypyrrole Nanofoam/Carbon Nanotube Multilayered Electrode for Flexible Electrochemical Capacitors

Polypyrrole (PPy)-based electrochemical energy storage electrodes have been widely investigated due to their desired pseudocapacitive charge storage capabilities. However, with the rigid and powdery nature of PPy, its utilization in flexible supercapacitor electrodes has been hindered. Herein, a surface-modified thermoplastic polyurethane (TPU) was utilized as the flexible substrate. It was coated with a thin surface layer of carbon nanotubes (CNTs), which provide the desired electrical conductivity and create a better interface with the PPy nanofoam (PPyNF) active structures. The fabrication process involved the exposed CNT from the TPU surface, which serves as a high-surface-area, conducting carbon layer suitable for in situ polymerization of PPyNF. With the formation of porous PPyNF on the TPU/CNT flexible substrate, the structural flexibility was retained, while a conducting network of porous pseudocapacitive material for charge storage was provided. The as-fabricated TPU/CNT/PPyNF electrodes demonstrated an areal capacitance of 712 mF/cm2 at a scanning rate of 5 mV/s and a retained capacity of 85% after 10 000 charge/discharge cycles. The retained flexibility and charge storage capability during bending were tested to show that 98.5% of capacity was retained even at a large bending angle of 90°.