Heterostructural Graphene Quantum Dot/MnO2 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)/MnO2 heterostructural electrodes to extend the potential window to 0–1.3 V for high‐performance aqueous supercapacitor. The GQD/MnO2 heterostructural electrode is fabricated by GQDs in situ formed on the surface of MnO2 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/MnO2 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/MnO2‐3//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. An in situ formed graphene quantum dot/MnO2 heterostructural electrode is fabricated via the formation of MnOC bonds in the interface during a plasma‐enhanced chemical vapor deposition process using CO2 as carbon source. It is found that the potential window can be extended to 1.3 V by a voltage drop in the heterostructural region, which exhibits superior specific capacitance and ultrahigh energy density.