Carbonized electrospun Ni-doped zeolitic imidazolate framework-9-embedded polyacrylonitrile/poly(methyl methacrylate) fibers as freestanding supercapacitor electrodes

Abstract

This paper presents a surface-morphology modification strategy designed to enhance the energy density of supercapacitors by broadening the operational potential window. A freestanding supercapacitor electrode is synthesized by electrospinning a Ni salt, zeolitic imidazolate framework, polyacrylonitrile, and poly(methyl methacrylate) (PMMA) as a sacrificial template. The resulting PMMA-modified Co/carbon nanofibers have a high density of electrochemically active sites and good ion-transfer kinetics. The thermal decomposition of PMMA results in the growth of Ni–Co/CoOx-embedded carbon nanotubes, accompanied by an increase in the electrochemically active surface area from 158 to 233 m2·g−1. The optimized electrode, prepared with 1.6 wt% PMMA, has an operational potential window of 1.5 V, energy density of 283.4 μWh·cm−2, areal capacitance of 906.9 mF·cm−2 at a current density of 1 mA·cm−2, and capacitance retention of 98.9% after 10,000 charge–discharge cycles. The energy-storage mechanism of the fabricated system encompasses double-layer capacitance with significant pseudocapacitive contributions. Furthermore, flexible pouch-like supercapacitors assembled using the optimal electrode maintain ∼83.8% of the original capacitance upon 90° bending.