Electroactive hydrogels have been considered as flexible solid-state supercapacitor electrode materials. Herein, a novel strategy has been proposed to directly prepare polyaniline (PANI) hydrogels from soluble PANI dispersion by self-crosslinking of molecules during the hydrothermal process. The PANI hydrogel single-electrode shows high specific capacitance (325 F g⁻¹) and superior rate capability. To achieve more excellent electrochemical performance, the graphene/PANI hydrogel (GPH7) is prepared using graphene oxide (GO) and soluble PANI dispersion. However, a slightly enhanced specific capacitance (375 F g⁻¹) is achieved for the GPH7 single-electrode, due to the strong interactions between GO and PANI molecules. It is of particular interest that the incorporation of m-phenylenediamine (mPD) into the GO and PANI system could protect the inherent conjugated structure of PANI, and thereby the as-prepared N-doped graphene/PANI hydrogels (GMPH7) show significantly improved specific capacitance (514.3 F g⁻¹). Moreover, the assembled flexible solid-state supercapacitors based on the PANI hydrogel, GPH7 and GMPH7 exhibit excellent areal specific capacitance (484, 519.2 and 584.7 mF cm⁻², respectively), approximately 100% capacitance retention after 2000 mechanical bending cycles and favorable energy density (42.96, 60.9 and 81.28 μW h cm⁻², respectively). Such hydrogel assembled supercapacitors with robust capacitive behavior and outstanding flexibility are promising for applications in flexible and wearable electronics.

Carbon cloth (CC) is widely used as a freestanding substrate for energy storage devices, due to its high conductivity, special porous network, and good mechanical flexibility. However, it is still challenging to fully utilize the space of CC to achieve a high mass loading of electroactive materials and ultimately fulfill high electrochemical performance. Herein, a new strategy is proposed to fill the gaps and voids in CC with a functionalized graphene hydrogel (FGH) through one-step hydrothermal treatment of oxidized CC submerged in a mixture of graphene oxide and p-phenylenediamine. The as-prepared FGH/functionalized CC is then adopted as a scaffold to load a lignosulfonate/polyaniline (Lig/PANI) hydrogel via in situ polymerization of aniline in the presence of lignosulfonate, and thereby an integrated textile (Lig/PANI/FGH/FCC) is obtained. The symmetric supercapacitor assembled with Lig/PANI/FGH/FCC electrodes and 1 M H₂SO₄ electrolyte shows a superior areal capacitance of 1223 mF cm⁻² and an energy density of 169.9 μW h cm⁻² at 2 mA cm⁻². Moreover, the assembled flexible all-solid-state supercapacitor presents competitive energy density (160.6 μW h cm⁻² at 1000 μW cm⁻²) and excellent flexibility. This design of anchoring a hierarchical porous conductive network in a macroscopic macropore framework paves a new avenue towards high mass loading and low interfacial resistance in macroporous material-based electrodes for high-performance energy storage devices.

Nitrogen-doped porous graphene/carbon (NPGC) framework electrode materials have been synthesized via chemical activation of graphene oxide/polypyrrole (GOP) composites with KOH. The effects of the mass ratio of KOH/GOP and activation temperature on the electrochemical performance of NPGC have been discussed. It is found that the NPGC prepared by activating GOP (GO : Py = 1 : 40) with 3.5 times mass of KOH at 650 °C (NPGC650) exhibits the highest specific capacitance of 405 F g⁻¹ at a current density of 0.2 A g⁻¹. Particularly, the specific capacitance still remains at 249 F g⁻¹ even at a current density as high as 10 A g⁻¹. Moreover, 96% of the capacitance can be retained after 1000 cycles even under a high operation current of 10 A g⁻¹. The present work provides a novel strategy to synthesize NGPC electrode material for supercapacitors.

To extend the applications of supercapacitors, it is important and challenging to develop structural/stiff supercapacitors with excellent mechanical and electrochemical performance. In this work, high performance double-crosslinked network functionalized graphene/polyaniline stiff hydrogels (DN-PGH/PANI_PA) have been successfully synthesized by polymerization of aniline in a confined functionalized graphene (PGH) hydrogel framework. A unique polyaniline (PANI) morphology with a combination of nanodot protrusions and nanofibers is obtained, where nanodot protrusions are tightly anchored to graphene walls and nanofiber crosslinked graphene sheets. The as-prepared DN-PGH/PANI_PA hydrogel, consisting of a continuous conductive closely combined double-crosslinked network and PANI nanofibers, together with a high crystallization degree of the PANI structure, is both stiff and mechanically robust with a high tensile strength of 1.39 MPa at a small ruptured elongation of 0.42%. Meanwhile, the DN-PGH/PANI_PA stiff hydrogels are assembled into symmetric supercapacitors and achieve a superior areal specific capacitance of 3488.3 mF cm⁻² and a volumetric specific capacitance of 872 F cm⁻³, remarkable rate capability, and excellent cycling stability, resulting in a notable energy density of 155 μW h cm⁻² at 200 μW cm⁻² and an outstanding power density of 20 015 μW cm⁻² at 67.5 μW h cm⁻². This novel double-crosslinked network design strategy establishes a promising approach towards the development of other stiff electrode materials as high performance structural supercapacitors.