Redox-Active Gel Electrolyte Combined with Branched Polyaniline Nanofibers Doped with Ferrous Ions for Ultra-High-Performance Flexible Supercapacitors.

Youtian Mo,Yanlin Xia,Wei Meng,Xusheng Du

doi:10.3390/polym11081357

Abstract

In this work, the effects of utilizing an Fe2+/Fe3+ redox-active electrolyte and Fe2+-doped polyaniline (PANI) electrode material on the performance of an assembled supercapacitor (SC) were studied. The concentration of the redox couple additive in the electrolyte of the SC was optimized to be 0.5 M. With the optimized concentration of 0.4 M Fe2+, the doped PANI branched nanofibers electropolymerized onto titanium mesh were much thinner, cleaner, and more branched than normal PANI. A specific capacitance (Cs) of 8468 F g−1 for the 0.4 M Fe2+/PANI electrode in the 1 M H2SO4 + 0.5 M Fe2+/Fe3+ gel electrolyte and an energy density of 218.1 Wh kg−1 at a power density of 1854.4 W kg−1 for the resultant SC were achieved, which were much higher than those of the conventional PANI electrode tested in a normal H2SO4 electrolyte (404 F g−1 and 24.9 Wh kg−1). These results are among the highest reported for PANI-based SCs in the literature so far and demonstrate the potential effectiveness of this strategy to improve the electrochemical performance of flexible SCs by modifying both the electrode and electrolyte.

Highlights

Supercapacitors (SCs) are attractive because of their high power, long periodicity, and environmental friendliness [1,2]
Fe2+ /Fe3+ redox-active additive into the electrolyte combined with the optimized electrode materials on the performance of SCs was studied in detail
It was found that the electroplating electrolyte containing Fe3+ and aniline were very unstable and PANI precipitate occurred in tens of minutes, possibly due to the chemical reaction between Fe3+ and the monomer, as FeCl3 was often used as an oxidant reagent for the chemical polymerization of PANI

Summary

Introduction

Supercapacitors (SCs) are attractive because of their high power, long periodicity, and environmental friendliness [1,2]. For the utilization of specific electrolytes, besides organic electrolytes (such as ionic liquids) with a widening working potential window, redox-active electrolytes were recently developed by adding redox additives to electrolytes [35] These redox media can afford additional capacitive contributions through their reversible electrochemical reactions and can improve the electrochemical performance of assembled symmetric/asymmetric SCs. Electrolytes with a variety of redox-active additions have been studied, such as H2 SO4 + FeBr3 and KCl + VOSO4 [36,37], H2 SO4. Various polyaniline material electrodes and redox-active electrolytes have been used in capacitors, little information on the capacitive performance of Fe2+ -doped PANI in an Fe3+ /Fe2+ active electrolyte is available so far. Fe2+ /Fe3+ redox-active additive into the electrolyte combined with the optimized electrode materials on the performance of SCs was studied in detail

Experimental

Characterization

Electrochemical Measurements

Results

Electrochemical

Conclusions