Synergistic Enhancements of Niobium Metal–Organic Framework/V2CTx Composites with Graphene Quantum Dots for Energy Storage and Hydrogen Evolution

Abstract

MXenes have gained increasing attention due to their unique advantages, including exceptional electrical conductivity, tunable layer structures, and controllable interfacial chemistry. This study addresses these limitations by incorporating niobium metal–organic frameworks (Nb-MOF) onto vanadium carbide MXene (V₂CT_x) surfaces, enhancing energy storage and electrochemical water-splitting performance. Additionally, graphene quantum dots (GQDs) serve as dopants, significantly increasing the specific surface area and charge storage capacity. The optimized Nb-MOF/V₂CT_x@GQDs heterostructure exhibits a low hydrogen evolution reaction (HER) overpotential of 90.54 mV at 10 mA cm⁻², with a Tafel slope of 103.45 mV dec⁻¹, indicating enhanced charge transfer kinetics. For energy storage applications, the asymmetric Nb-MOF/V₂CT_x@GQDs//AC device achieves a high specific capacity of 320 C g⁻¹ at 2.0 A g⁻¹, an energy density (E_d) of 59 Wh kg⁻¹, and a power density (P_d) of 1800 W kg⁻¹, while maintaining 81.2% capacity retention and 87.5% Coulombic efficiency after 12 000 cycles. These findings demonstrate the synergistic effect of Nb-MOF and V₂CT_x, further enhanced by GQDs, establishing the composite as a promising material for next-generation energy storage and HER.