Rational design of MnO2-nanosheets-decroated hierarchical porous carbon nanofiber frameworks as high-performance supercapacitor electrode materials

Abstract

A hierarchical structure is proved to be important for the improvement of electrochemical performances of MnO2-based electrode materials used in supercapacitors. However, the rational design of materials’ structure and its real performance served as electrode materials are still facing challenges. Herein, hierarchical porous carbon nanofibers using ZIF-8 nanoparticles as pore templates are designed to provide one-dimensional hollow frameworks for the growth of ultrathin MnO2 nanosheets (referred as HPCNF/MnO2). The as-prepared HPCNF/MnO2 samples have a hierarchical coaxial core-shell structure, with HPCNFs as the core and MnO2 sheets as the shell. The novel nanostructure of this hybrid provides abundant electrochemical active sites for Faradic reactions and short diffusion channels for ions/electron transport. The utilization of HPCNF/MnO2 active material with such a structure can be significantly enhanced, especially at the high current density. When evaluated as electrode materials, HPCNF/MnO2 exhibits a specific capacitance of 269 F g−1 at 0.5 A g−1 (308 F g−1 for MnO2), a high capacitive retention of 98% even after 5000 cycles at 50 mV s−1 by cyclic voltammetry (86.7% capacitance retention at 1 A g−1 after 2000 cycles) and a rate capability of 58% from 0.5 to 10 A g−1. Especially at the current density of 10 A g−1, the specific capacitance of HPCNF/MnO2 has increased by 133% compared with that of non-porous carbon fiber/MnO2 composites, demonstrating a great superiority of hierarchical porous carbon nanofibers as frameworks to support pseudocapacitive materials.