Polypyrrole-Carbon Nanotube-FeOOH Composites for Negative Electrodes of Asymmetric Supercapacitors

For the first time, polypyrrole (PPy) coated carbon nanotubes (CNT) were combined with FeOOH to fabricate negative supercapacitor (SCP) electrodes. The synergistic effects of PPy-CNT and FeOOH resulted in enhanced electrochemical performance at high active mass loading of 37 mg cm−2 in a voltage window of −0.8–+0.1 V versus a saturated calomel electrode. Particle extraction through liquid-liquid interface (PELLI) was utilized for the agglomerate-free processing of FeOOH, which improved FeOOH mixing with PPy-CNT and contributed to the enhanced capacitive behavior of the composite. Tetradecylamine (TA) was found to be an efficient extractor for FeOOH. Cyclic voltammetry and impedance spectroscopy data at different electrode potentials provided an insight into the synergistic effects of PPy-CNT and FeOOH, and influence of PELLI on electrode performance. An areal capacitance of 4.5 F cm−2 and nearly ideal capacitive behavior were achieved at a low electrode impedance. The important finding was that capacitances of the negative PPy-CNT-FeOOH and positive MnO2-CNT electrodes can be matched in different voltage windows to fabricate advanced asymmetric devices, which exhibited promising electrochemical performance in a voltage window of 1.6 V at high active mass.