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As one of the most investigated conducting polymers, polyaniline (PANI) is considered to be of practical use in many applications. In this study, two new ionic liquids, 1-methylimidazolium hydrogen sulfate ([Hmim]HSO4) and 1-methyl-3-n-butylimidazopersulfate ([C4mim]2S2O8), which were synthesized from 1-methylimidazole ([Hmim]), were used as solvent and dopant, oxidizer, respectively, for in situ polymerization of aniline. Because of the application of the unique structure of ionic liquid, we obtained the ionic liquid–doped polyaniline (IL-PANI) with high solubility (25 mg mL−1 in dimethyl sulfoxide (DMSO)). And by adjusting the ratio of [C4mim]2S2O8 to aniline monomer, the preferred PANI nanofibers could be controlled to form a three-dimensional porous structure. It was found that the ion/electron transport channels could be formed inside the 3D structure. Thus, the redox reactions could occur both at the surface and inside the PANI electrode. Electrochemical characterization showed that the fabricated PANI electrode exhibited a specific capacitance of 489 F g−1 at a current density of 0.5 A g−1. Also, the capacity retention rate reached up to 81% after 4000 cycles investigated at 2 A g−1. In addition, a high-energy density of 80.2 Wh kg−1 was measured when [Hmim]HSO4 was used as an electrolyte. Thus, the present work suggested a new strategy for fabricating high-performance PANI electrode for supercapacitor applications.

Three-dimensional (3D) nanostructured conducting polymer hydrogels represent a group of high-performance electrochemical energy-storage materials. Here, we demonstrate a molecular self-assembly approach toward controlled synthesis of nanostructured polypyrrole (PPy) conducting hydrogels, which was "cross-linked" by a conjugated dopant molecule trypan blue (TB) to form a 3D network with controlled morphology. The protonated TB by ion bonding aligns the free sulfonic acid groups into a certain spatial structure. The sulfonic acid group and the PPy chain are arranged by a self-sorting mechanism to form a PPy nanofiber structure by electrostatic interaction and hydrogen bonding. It is found that PPy hydrogels doped with varying dopant concentrations and changing dopant molecules exhibited controllable morphology and tunable electrochemical properties. In addition, the conjugated TB dopants promoted interchain charge transport, resulting in higher electrical conductivity (3.3 S/cm) and pseudocapacitance for the TB-doped PPy, compared with PPy synthesized without TB. When used as supercapacitor electrodes, the TB-doped PPy hydrogel reaches maximal specific capacitance of 649 F/g at the current density 1 A/g. The result shows that PPy nanostructured hydrogels can be tuned for potential applications in next-generation energy-storage materials.

We reported a facile self-generated sacrificial template method for fabricating mesoporous three dimension NiCo2O4/graphene electrode material. Nickel, cobalt, and zinc ions dissolved in ethylene glycol reacted with potassium hydroxide solution to co-deposit onto graphene at 140 °C under atmospheric environment. With further addition of potassium hydroxide, zinc hydroxide as a self-generated sacrificial template was dissolved in situ, leading to the formation of mesoporous morphology. Structure and morphology characteristics were determined by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and N2 adsorption experiments. Electrochemical properties were analyzed by AC impedance spectroscopy, cycling voltammetry, and charge/discharge test in 2 M KOH. Results showed that the as—prepared NiCo2O4/graphene electrode possessed a large specific surface area of 281.4 m2 g−1, an ultrahigh specific capacity of 1024.99 and 662.12 C g−1 at current density of 1 and 50 A g−1 respectively, and a long-term cycling life of 10,000 charge/discharge tests.

A facile synthesis approach was successfully developed to synthesize mesoporous NiCo2S4 in ethylene glycol. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and N2 adsorption–desorption experiment were conducted to examine the morphology and microstructure of the as-prepared NiCo2S4. Furthermore, electrochemical measurements, including cyclic voltammetry, galvanostatic charge–discharge tests, and electrochemical impedance spectroscopy, were carried out in a three-electrode system to evaluate the electrochemical properties of the mesoporous NiCo2S4. The as-prepared NiCo2S4 possessed a high specific surface area of 223.6 m2 g−1 with a high specific capacity of 406 C g−1 at 0.5 A g−1. In addition, only a 6.3 % loss of specific capacity was observed at 5 A g−1 after 20,000 GCD cycles, suggesting a long life cycle.