Experimental and Theoretical Findings of the Concerted Effect of Dual Quantum Dots on a Graphene Matrix for Energy Storage Applications

The construction of composite electrode materials that exhibit superior energy and power densities has stirred rigorous research on supercapacitors. Herein, we have successfully designed nitrogen-doped carbon dots (CDs) and hematite dots (HtDs) functionalized reduced graphene (RG) hybrid ternary composites (RG@CDs/HtDs) by liquid exfoliation followed by the solvothermal method. The hybrid electrode material, RG@ CDs/HtDs, exhibits a high specific capacitance of 1566 F/g at a scan rate of 2 mV s-1 and excellent stability up to 10,000 cycles. The DFT calculations have been performed to investigate the capacitance enhancement in the hybrid structure. The enhanced quantum capacitance and intense electronic states near the Fermi level for the ternary structure RG@CDs/HtDs justify the superior charge storage. When HtDs and CDs are introduced into RG, charge transfers from the Fe 3d orbital to the C 2p orbital of RG occur. An asymmetric aqueous supercapacitor device has been fabricated using RG@CDs/HtDs as a cathode and Mn3O4/C as an anode. Remarkably, the assembled aqueous asymmetric supercapacitor operates in a stable and wide potential window of 2.5 V with an ultrahigh energy density (134 Wh kg-1) along with extraordinary rate capability and is stable at 10,000 cycles performance that was validated on powering of the red light-emitting diode (LED).

Automated summary

We successfully designed nitrogen-doped carbon dots (CDs) and hematite dots (HtDs) functionalized reduced graphene (RG) hybrid ternary composites (RG@CDs/HtDs), which exhibit high specific capacitance and excellent stability. The enhanced charge storage is justified by theoretical calculations and experimental results. Assembled in an asymmetric aqueous supercapacitor, RG@CDs/HtDs as a cathode and Mn3O4/C as an anode, it demonstrates stable operation, wide potential window, ultrahigh energy density, and extraordinary rate capability.