Structural Tuning of a Flexible and Porous Polypyrrole Film by a Template-Assisted Method for Enhanced Capacitance for Supercapacitor Applications

Constructing a rational electrode structure for supercapacitors is critical to accelerate the electrochemical kinetics process and thus promote the capacitance. Focusing on the flexible supercapacitor electrode, we synthesized a three-dimensional (3D) porous polypyrrole (PPy) film using a modified vapor phase polymerization method with the use of a porous template (CaCO3). The porous design provided the PPy film with an improved surface area and pore volume. The porous PPy film electrode was studied as a binder-free electrode for supercapacitors. It was found that the abundant interpenetrated pores created by the CaCO3 templates within the 3D framework are beneficial to overcoming the diffusion-controlled limit in the overall electrochemical process. It was revealed by electrochemical investigation that a more pseudocapacitive contribution than diffusion-controlled process contribution was observed in the total charge in the redox reaction. The galvanostatic charge/discharge (GCD) measurements showed that the optimized 3D porous PPy film electrode delivered a high capacitance of 313.6 F g–1 and an areal capacitance of 98.0 mF cm–2 at 1.0 A g–1 in a three-electrode configuration, which is nearly three times that of the dense counterpart electrode synthesized in the absence of the CaCO3 template. A specific capacitance of 62.5 F g–1 at 0.5 A g–1 and 31.1 F g–1 at 10 A g–1 was obtained in a symmetric capacitor device. In addition, the porous structure provided the PPy film with the attractive capability of accommodating the volume change during the doping/dedoping process. This is essential for the PPy film to maintain a long cycling life in a practical operation for a supercapacitor. It turned out that a high capacitance retention up to 81.3% after 10,000 GCD cycles was obtained for the symmetric supercapacitor device with the 3D porous PPy electrode (57.1% capacitive retention was observed for the dense PPy electrode). The strategy and the insight analysis are expected to provide valuable guidance for the design and the synthesis of flexible and wearable film electrodes with high performance.