Porphyrin-assisted synthesis of hierarchical flower-like polypyrrole arrays based flexible electrode with high areal capacitance

Abstract Flexible free-standing electrode with special hierarchical structure have received widespread attentions due to the increased specific surface area, shortened transport path of electrolyte ions and accelerated ion transmission. Herein, for the first time, the flexible free-standing three-dimensional (3D) flower-like polypyrrole/5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin copper (II) (TF-PPy/Cu-TCPP) nanocomposite electrode with hierarchical PPy micro-flower arrays on the surface has been fabricated via the combination of electrophoretic deposition and electrochemical polymerization. The growth mechanism is involved in the following aspects. I) The wrinkled Cu-TCPP nanosheets provide abundant porous channels to facilitate the immersion of pyrrole molecules and uniform cross-linking of PPy. II) The rough surface of the PPy/Cu-TCPP composite film provides rough sites for the growth of hierarchical TF-PPy arrays under the assistance of H2 bubbles. The collaborative advantages of 3D conductive networks and the hierarchical TF-PPy arrayed on the rough surface of electrode facilitate the fast ion/electron transport for the enhanced electrochemical performances. The corresponding TF-PPy/Cu-TCPP electrode shows an areal capacitance of 593 mF cm−2 at 0.5 mA cm−2, which is superior to the PPy/Cu-TCPP electrode (351 mF cm−2) and the pristine PPy (287 mF cm−2). The symmetric supercapacitor exhibits the energy density of 5.94 μW h cm−2 at a highest power density of 25 μW cm−2. This work will further enrich the valuable design concepts of flexible free-standing electrode with hierarchical structure for energy storage and conversion.