Banana peel biomass-derived carbon and nitrogen-doped quantum dot/UiO-66 hybrid nanocomposites for high-performance asymmetric supercapacitors

Abstract

Supercapacitors are promising energy storage devices, yet their wide application is limited by low energy density. Similarly, UiO-66, a zirconium-based metal–organic framework (MOF), possesses a high surface area but suffers from poor electrical conductivity. To overcome these limitations, nitrogen-doped carbon quantum dots (NCQDs) derived from banana peel biomass were synthesised via a green hydrothermal approach and embedded into the UiO-66 framework. This integration preserved the MOF's structural integrity while the introduced nitrogen functionalities enhanced interfacial interactions, electrical conductivity and electron-transfer pathways. Consequently, the UiO-66/NCQDs hybrid exhibited lower charge-transfer resistance and superior redox activity compared with pristine UiO-66 and UiO-66/CQDs. In an asymmetric supercapacitor assembled with activated carbon, the hybrid electrode delivered a specific energy of 30.32 Wh kg−1 at a power density of 2449.38 W kg−1, retaining 93.45% of its capacitance after 4000 cycles. These findings demonstrate a sustainable strategy for engineering high-performance, biomass-derived MOF/QD energy storage devices.