Facile fabrication of MnO 2 -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.