Facile fabrication of MnO2-embedded 3-D porous polyaniline composite hydrogel for supercapacitor electrode with high loading

To obtain the promising pseudocapacitance of MnO2, the composite hydrogel of MnO2 and polyaniline (PANI) was fabricated using in situ polymerization of aniline hydrochloride in the aqueous solution containing commercial MnO2 nanoparticles and additives. Both scanning electron microscopy and transmission electron microscopy results indicated that the composite hydrogel exhibited a 3-D porous structure, within which MnO2 nanoparticles were uniformly embedded. The investigations of cyclic voltammetry, galvanostatic charge−discharge, and electrochemical impedance spectroscopy demonstrated superior supercapacitor (SC) performance of the hydrogel electrode even with high loading. The electrode with loading of 1.5 mg cm–2 showed a favorable specific capacitance (293 F g–1, 10 mV s–1), which only decreased to 258 F g–1 when the loading of the electrode was seven times higher (10.8 mg cm–2). Furthermore, the hydrogel electrode displayed good cycle stability in the acidic solution (81% capacitance retention after 1000 charge/discharge cycles). The favorable electrochemical performance of the composite hydrogel should be attributed to the fast electron/ion transport and good protection for MnO2 in the 3-D porous structure. Due to the facile one-pot synthesis and optimized nanostructure, it could be expected that MnO2-embedded 3-D porous PANI composite hydrogels have great application in the field of high-performance electrode with high loading for SCs.