RESUMO
As the electrode of a supercapacitor, polypyrrole (PPy) inevitably suffers from structural rupture during repeated doping/dedoping processes and releases low practical capacitance due to the large amount of aggregation or cross-linking in PPy chains. The coupling mode (α-α, α-ß, or ß-ß coupling) of pyrroles is critical to the conjugated structure, the conductivity, and cycling stability of PPy. Here, we prepared an α-α coupling-dominated PPy film via simple frozen interfacial polymerization. The PPy film with a nanostructure exposes more electrochemical active sites for the electrode, which can enhance the practical capacitance. The high proportion of the α-α coupling mode results in a high degree of large π-conjugation and a planar structure that can effectively improve the reversible ion transport efficiency and promote uniform stress distribution during the charge and discharge process. The assembled symmetric water-based supercapacitor delivers a high specific capacitance of 267.1 F g-1 at 1 A g-1 and 266.7 F g-1 at 5 A g-1 and exhibits an outstanding cycling performance of above 200 F g-1 even after 60,000 cycles.
RESUMO
As a kind of energy storage device, a flexible supercapacitor has the characteristics of high capacity, fast charge/discharge rate, good stability, portability and softness. Conductive polymer polypyrrole (PPy) can be used as an electrode material for supercapacitors due to its environmental friendliness, simple synthesis process, good conductivity and potential for large-scale production. However, pristine PPy inevitably suffers from structural rupture due to repeated doping/de-doping during charge and discharge processes, which in turn impairs its cycle stability. In general, compounding with flexible substrates like soft carbon materials, cellulose or nylon fabric, is a good strategy to weaken the inner stress and restrain the structure pulverization of PPy. Herein, cellulose is utilized as a soft substrate to compound with PPy based on the electrochemical oxidation of polypyrrole. The interfacial electrodeposition method can successfully obtain a smooth, uniform and flexible PPy/cellulose composite film, which shows good conductivity. The assembled symmetric supercapacitor with PPy/cellulose film has an optimized specific capacitance of 256.1 mF cm-2, even after 10,000 cycles at a current density of 1 mA cm-2. Furthermore, there is no significant capacitance loss even after 180° bending of the device. This work provides a new means to prepare flexible, low-cost, environmentally friendly and high-performance electrode materials for energy conversion and storage systems.
