GQD-assisted MnO6 octahedra engineering in CuMnO2 for high-performance coin-cell supercapacitors

Abstract

The growing demand for sustainable energy solutions has accelerated research on advanced supercapacitive electrode materials. This study explores the role of graphene quantum dot (GQD) incorporation within CuMnO₂ in tailoring morphology and energy storage performance. Here, different degrees of MnO₆ octahedron distortion in the CuMnO₂ nanostructure are achieved depending on the GQD concentration during the hydrothermal reaction. Due to the d-band centre modification and charge redistribution, the optimally tuned CuMnO₂/GQD nanostructure exhibits a 213% increase in specific capacitance (∼771.0 F g⁻¹ at 7.0 A g⁻¹) compared to its pristine counterpart in 3.0 M KOH. The fabricated symmetric aqueous coin-cell supercapacitor shows a specific capacitance of ∼145.0 F g⁻¹ at 1.0 A g⁻¹ and an energy density of 34.2 W h kg⁻¹ at a power density of 650 W kg⁻¹. We confirmed the repeatability of the charging/discharging process over 5000 cycles of operation, with 67% capacitance retention and 98% coulombic efficiency. However, an aqueous asymmetric coin-cell supercapacitor with an activated carbon anode exhibits robust performance with high specific capacitance (∼147.0 F g⁻¹ at 2.0 A g⁻¹) and high energy (∼40 W h kg⁻¹) and power (∼1398 W kg⁻¹) densities. It also maintains ∼71% capacity retention and 100% coulombic efficiency after 5000 cycles. Real-world applicability is demonstrated by operating commercial LEDs, highlighting their potential as high-performance electrode materials for pseudocapacitive energy storage systems.