Aniline-substituted viologen-containing redox-active electrolytes for supercapacitors

Abstract

Supercapacitors using the electrolyte containing aniline-substituted viologen were fabricated, and the effects of the substitution number of the aniline group on viologen materials were studied. The electrolyte mainly comprised 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) imide, dimethyl ferrocene, and the aniline-substituted viologens. As-synthesized aniline monomer, aniline dimer, and aniline trimer were used to substitute into the nitrogen site of the viologen molecule. The areal capacitance value of aniline dimer substituted viologen was 5.81 mF/cm², while the values for aniline monomer and aniline trimer substituted viologens were 0.82 and 2.17 mF/cm², respectively. The electrochemical stability for 1000 cycles was 98.6%, 90.8%, and 20.3% for the aniline monomer, aniline dimer, and aniline trimer substituted viologens, respectively. Electrolytes with aniline dimer substituted viologen represented good performance and high stability. On the other hand, aniline monomer exhibited poor performance for the supercapacitor, and aniline trimer substituted viologen showed very low stability, originating from a low solubility to build electrolytes. From these results, the aniline dimer was the appropriate substituent for the viologen, and the proposed material is expected to play an important role in enhancing the performance of the organic supercapacitor.