Heterostructural Graphene Quantum Dot/MnO(2) Nanosheets toward High‐Potential Window Electrodes for High‐Performance Supercapacitors

The potential window of aqueous supercapacitors is limited by the theoretical value (≈1.23 V) and is usually lower than ≈1 V, which hinders further improvements for energy density. Here, a simple and scalable method is developed to fabricate unique graphene quantum dot (GQD)/MnO(2) heterostructural electrodes to extend the potential window to 0–1.3 V for high‐performance aqueous supercapacitor. The GQD/MnO(2) heterostructural electrode is fabricated by GQDs in situ formed on the surface of MnO(2) nanosheet arrays with good interface bonding by the formation of Mn—O—C bonds. Further, it is interesting to find that the potential window can be extended to 1.3 V by a potential drop in the built‐in electric field of the GQD/MnO(2) heterostructural region. Additionally, the specific capacitance up to 1170 F g(−1) at a scan rate of 5 mV s(−1) (1094 F g(−1) at 0–1 V) and cycle performance (92.7%@10 000 cycles) between 0 and 1.3 V are observed. A 2.3 V aqueous GQD/MnO(2)‐3//nitrogen‐doped graphene ASC is assembled, which exhibits the high energy density of 118 Wh kg(−1) at the power density of 923 W kg(−1). This work opens new opportunities for developing high‐voltage aqueous supercapacitors using in situ formed heterostructures to further increase energy density.