Theoretical and Experimental Investigations of Oxygen Activation Effect of Carbon Nanofibers Interacting with Polypyrrole

Abstract

Theoretical modeling calculations and experimental measurements were adopted to investigate the oxygen activation effect of carbon nanofibers (CNFs) interacting with polypyrrole (PPY). The CNF undergoes a hydrothermal oxidation process to form epoxy and hydroxyl groups containing carbon nanofibers (CNF-O). The oxygen activation effect of CNF on the electronic and electrochemical properties was investigated through the interfacial interaction between CNF-O and PPY. Theoretical modeling calculation discloses that CNF-O/PPY exhibits lower electronic bandgaps (0.64 eV), a higher density of states (10.039 states/eV), and a lower HOMO–LUMO molecular orbital energy gap (0.077 eV) than CNF/PPY (1.56 eV, 7.946 states/eV and 0.112 eV), presenting its superior electronic conductivity and electroactivity. The Mulliken population and charge density difference analysis disclose the stronger interface interaction of CNF-O/PPY caused by epoxy and hydroxyl groups. Cyclic voltammogram measurements reveal that CNF-O/PPY exhibits a higher response current and a higher specific capacitance (221.1–112.2 mF g−1) than CNF/PPY (57.6–24.2 mF g−1) at scan rates of 5–200 mV s−1. Electrochemical impendence spectrum measurements disclose that CNF-O/PPY exhibits a lower charge transfer resistance (0.097 Ω), a lower ohmic resistance (0.336 Ω), a lower Warburg impedance (317 Ω), and a higher double-layer capacitance (0.113 mF) than CNF/PPY (1.419 Ω, 9.668 Ω, 7865 Ω, and 0.015 mF). Both theoretical and experimental investigations prove that CNF-O/PPY presents an intensified intermolecular interaction rather than CNF/PPY. The promotive oxygen activation effect of CNF could contribute to improving the electronic and electrochemical properties of CNF-O/PPY.