Enhanced pseudocapacitive performance of a Pb-based MOF/FCNT composite for high-stability supercapacitor applications: a step ahead towards energy storage

As society moves towards a low-carbon future, the global emphasis on efficient and sustainable energy storage platforms increases and has intensified the search for advanced electrode materials that offer high capacitance, fast charge-discharge capability, and long-term cycling stability. However, most conventional materials suffer from limited electrical conductivity, poor rate performance, or structural degradation over extended cycling. To address these limitations, a novel composite electrode material based on a Pb-based MOF (YK-2) and functionalized carbon nanotubes (FCNTs) was developed and systematically studied. A series of composites, YK-2@FCNT(5), YK-2@FCNT(10), and YK-2@FCNT(15), were successfully synthesized and thoroughly investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a three-electrode system. Among them, YK-2@FCNT(10) demonstrated the highest specific capacitance of 913.57 F g^-1 at 0.5 A g^-1, significantly outperforming the pristine YK-2 electrode. EIS analysis revealed a marked reduction in both solution and charge transfer resistance due to the incorporation of FCNTs, enhancing conductivity and ion diffusion. Dunn's method further confirmed a mixed charge storage mechanism with a <i>b</i>-value of 0.747, where the proportion of capacitive contribution rose significantly from 32.02% to 65.33% as the scan rate increased from 5 to 80 mV s^-1. Additionally, YK-2@FCNT(10) retained 92.87% of its initial capacitance even after 5000 consecutive charge-discharge cycles at 10 A g^-1, indicating excellent long-term electrochemical stability. Furthermore, a symmetrical supercapacitor device assembled using YK-2@FCNT(10) electrodes delivered a high specific capacitance of 216.9 F g^-1 at 0.5 A g^-1 and maintained an excellent cycling stability of 86.67% over 5000 cycles. The device also achieved a remarkable energy density of 30.12 Wh kg^-1 and a maximum power density of 4998.69 W kg^-1, confirming its strong potential for practical high-performance energy storage applications.