Studies on Tubular MnO₂-Core/Carbon Nanofiber-Shell Electrodes for Electrochemical Capacitors

Abstract

The goal of this study is to design hollow carbon nanofibers containing MnO2 (PPMMn), in which the pores of the carbon nanofiber surface are utilized for ion diffusion to facilitate rapid MnO2 surface redox reactions. Electrochemical performance is optimized by controlling the growth of MnO2 on the inner or outer surfaces of carbon nanofibers by varying MnCl2 contents. Accessible specific surface areas and the hollow structure of PPMMn composites provide more active sites and internal spaces to enable electrolyte ion access. The energy storage capabilities of PPMMn in the assembled symmetrical supercapacitors provide excellent capacitive behavior with a maximum specific capacitance of 254 F g–1, a maximum energy density of 32 Wh kg–1, and long-term cycling stability (96% of the initial capacitance after 10,000 cycles). In addition, the cyclic voltammetry curves are nearly overlapped for the PPMMn electrode in a flat or bent state, and the PPMMn-based devices assembled in series successfully lit a commercial light-emitting diode. The study shows that PPMMn electrodes have excellent flexibilities and mechanical strengths and broad prospects in the energy storage field.