Hybrid Co(II) coordination polymer/CNT/GO electrodes for high energy asymmetric supercapacitor

Two-dimensional (2D) coordination polymers (CPs) have attracted significant attention in electrochemical energy storage because their layered architectures promote strong interfacial interactions with 1D and 2D carbon materials. Nevertheless, CPs often suffer from limited specific capacitance and poor structural stability. Integrating conductive carbon components can effectively overcome these drawbacks by leveraging synergistic effects to enhance overall charge storage capability. Herein, we report the solvothermal synthesis of a Co(II)-based coordination polymer, [Co(PDA)(H₂O)] ₙ (namely, MCo). The structure of MCo was elucidated by single-crystal X-ray diffraction (SC-XRD), revealing an hcb -type underlying net topology. Composite materials were subsequently fabricated by integrating MCo with multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO), designated as MCo/CNT and MCo/GO, respectively. The morphology and chemical composition of the resulting composites were characterized by FESEM, HR-TEM, and XPS analysis. Electrochemical analysis of symmetric supercapacitor (SSC) and asymmetric supercapacitor (ASC) devices showed that the ASC device has better specific capacitance (Sp.CP.). The specific capacitance of MCo, MCo/CNT 100, and MCo/GO 20 was calculated to be 14.54, 287.13, and 373.12 F g −1 at 0.5 A g −1 current density, respectively. The energy density and power density of MCo/GO 20 were calculated to be 132.6 Wh kg −1 and 400 W kg −1 at 0.5 A g −1 . The ASC device retained 68% capacitance after completion of 10,000 cycles of charging-discharging, demonstrating good cyclic stability. Furthermore, power-law analysis indicated a predominantly electric double-layer capacitance (EDLC) behavior with b-values ranging between 0.5 and 1. For practical demonstration, the ASC device successfully powered red, multicolor disco, and white LEDs, maintaining illumination for 120 s after a charging of 60 s. Additionally, an ASC flexible MCo/GO 20 device under PVA/KOH gel electrolyte showed sp. cp. of 461.03 F g −1 and energy density of 164.02 Wh kg −1 at a current density of 0.5 A g −1 with a capacitance retention of 87% at a current density of 6 A g −1 , after 5000th charge-discharge cycles. These results highlight the potential of MCo/GO 20 composites as a promising electrode material for next-generation supercapacitor application.