Aniline tetramer conjugated N-doped graphene aerogel enabling efficient pH-universal aqueous supercapacitors

Aqueous supercapacitors have attracted enormous attention from academic and industry communities. However, the development of aqueous supercapacitors is limited by the lack of suitable negative electrode materials with a high energy density and superior cycle life. Here, we report an aniline tetramer conjugated N-doped graphene aerogel (AT-NGA) synthesized by a polymerization-hydrothermal method. AT was first prepared by chemical polymerization, and then AT-NGA was successfully synthesized by a hydrothermal method. AT-NGA has large specific capacitance, high cell voltage, and excellent cycling stability in all-pH aqueous electrolytes. The design could also be extended to other redox-active negative electrode materials for efficient pH-universal aqueous energy storage system applications. [Display omitted] The development of novel negative electrode (anode) materials for efficient aqueous supercapacitors (SCs) remains appealing yet significantly challenging. Here we propose an aniline tetramer conjugated nitrogen-doped graphene aerogel (AT−NGA) as the anode material, exhibiting a maximum capacitance of 699.1F g−1 under 1 A/g in 1 M H2SO4 as well as a long lifespan of 6,000 cycles at all pH levels. In particular, its capacitive contribution is 94.1 %, superior to the best pseudocapacitive materials known. To evaluate its pH-universality, we assembled three asymmetric SCs, namely, AT−NGA//1 M H2SO4//graphene aerogel, AT−NGA//1 M Na2SO4//NaMnO2-x and AT−NGA//1 M KOH//NiCoFe layered double hydroxide. The acid device delivers maximal energy and power densities of 35.8 mWh g−1 and 13.0 W/g, the neutral device achieves a maximal energy and power densities of 71.8 mWh g−1 and 33.0 W/g, and the base device exhibits a maximal energy and power densities of 48.2 mWh g−1 and 18.0 W/g, respectively. All the SCs display an outstanding cycling performance over 5,000 cycles (especially, 96 % capacitance retention for the acidic device after 12,000 cycles). Our design can also be expanded to prepare other redox-active anode materials for efficient aqueous SC applications.