Nile Blue Functionalized Graphene Aerogel as a Pseudocapacitive Negative Electrode Material across the Full pH Range

The pursuit of new negative electrode materials for redox supercapacitors with a high capacitance, boosted energy, and high rate capability is still a tremendous challenge. Herein, we report a Nile Blue conjugated graphene aerogel (NB–GA) as a negative electrode material with excellent pseudocapacitive performance (with specific capacitance of up to 483 F g^–1 at 1 A g^–1) in all acidic, neutral, and alkaline aqueous electrolytes. The contribution from capacitive charge storage represents 93.4% of the total charge, surpassing the best pseudocapacitors known. To assess the feasibility of NB–GA as a negative electrode material across the full pH range, we fabricated three devices, namely, a symmetric NB–GA||NB–GA device in an acidic (1.0 M H₂SO₄) electrolyte, an NB–GA||MnO₂ device in a pH-neutral (1.0 M Na₂SO₄) electrolyte, and an NB–GA||LDH (LDH = Ni–Co–Fe layered double hydroxide) device in an alkaline (1.0 M KOH) electrolyte. The NB–GA||NB–GA device exhibits a maximum specific energy of 22.1 Wh kg^–1 and a specific power of up to 8.1 kW kg^–1; the NB–GA||MnO₂ device displays a maximum specific energy of 55.5 Wh kg^–1 and a specific power of up to 14.9 kW kg^–1, and the NB–GA||LDH device shows a maximum specific energy of 108.5 Wh kg^–1 and a specific power of up to 25.1 kW kg^–1. All the devices maintain excellent stability over 5000 charge–discharge cycles. The outstanding pseudocapacitive performances of the NB–GA nanocomposites render them a highly promising negative electrode material across the entire pH range.