α-α Coupling-Dominated PPy Film with a Well-Conjugated Structure for Superlong Cycle Life Supercapacitors

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-β, or β-β 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.