MXene-polypyrrole electrodes for asymmetric supercapacitors

Despite the tremendous progress in the development and applications of flexible high-performance MXene-polypyrrole (PPy) composites for supercapacitor (SC) technology, current research in this area is limited to symmetric devices with low active mass loading (AML) and operating in limited voltage windows of 0.5–1 V in acidic electrolytes. Here, we propose an asymmetric SC device operating in a neutral 0.5 M Na2SO4 electrolyte in a voltage window of 1.7 V. We report high capacitance of 1.37 F cm−2 from the cyclic voltammetry (CV) data and 1.18 F cm−2 from the galvanostatic charge-discharge (GCD) data. A useful strategy is provided for the fabrication of MXene-PPy composites, which allows their application in negative electrodes and facilitates remarkable capacitive performance at AML of 40 mg cm−2. We optimize composition and performance of the negative electrodes and report high capacitance of 2.11 F cm−2 from CV data and 2.49 F cm−2 from GCD data, which is achieved at low electrode resistance.  One of the key factors for the enhanced negative electrode performance is the use a conceptually new strategy for in-situ PPy polymerization on the MXene surface, which is based on the application of an efficient catecholate-type dispersant for electrostatic dispersion of MXene. The adsorbed dispersant acts as an anionic dopant for PPy, promoting PPy polymerization on the MXene surface. PPy coated multiwalled carbon nanotubes (MCNT) are formed by in-situ polymerization of PPy on dispersed MCNT for charge storage in positive electrodes of the SC devices. The positive electrodes were designed to match capacitive properties of the negative electrodes in a complementary potential window.