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

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//NaMnO_2-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.