Boosting the supercapacitive performance of NiCo metal-organic frameworks via the synergistic effect of oxygen vacancies and bismuth decoration

To fulfill the escalating demand for next-generation energy storage systems, designing supercapacitors with superior specific capacity, prolonged durability is imperative. Nonetheless, the practical implementation of most metal-organic frameworks in electrochemical storage is frequently restricted by their inherent low electrical conductivity and insufficient accessible active sites. In this work, a synergistic strategy involving oxygen vacancies and bismuth decoration was successfully implemented to bolster the electrochemical performance of NiCo-MOF via a facile solvothermal synthesis followed by a precisely controlled NaBH 4 reduction process. The electronic structure and surface morphology were optimized through the simultaneous in-situ construction of a conductive Bi and the intentional introduction of oxygen vacancies, alongside mesopore creation. The resulting Bi@Ni 2 Co 1 -MOF-40 architecture delivered a remarkable specific capacity of 1559.7C g −1 at 1 A g −1 . It also presented outstanding rate performance and structural stability, maintaining 88.3% capacity retention following 5000 galvanostatic cycles at a high rate of 20 A g −1 . Furthermore, an asymmetric supercapacitor (ASC) configured with Bi@Ni 2 Co 1 -MOF-40 and activated carbon exhibited a specific capacitance of 252.8 F g −1 at a current density of 1 A g −1 within a wide voltage window of 0–1.5 V. The device delivered a maximum active-mass-normalized energy density of 79 Wh kg −1 at a power density of 750.4 W kg −1 . Experimental results demonstrate that metallic Bi accelerates interfacial charge transfer, while the rich oxygen vacancies substantially lower the energy barrier for electrolyte ion diffusion, leading to a high capacitive contribution of 76.03% at 100 mV s −1 . These synergistic effects are fundamental to its superior performance. This study highlights the remarkable charge storage capacity of defect-engineered Bi@Ni 2 Co 1 -MOF-40 heterostructures, making them exceptionally promising candidates for next-generation, high-performance supercapacitor electrodes.