In situ-decorated heterocomposites derived from Zn(ii)-based coordination polymer for asymmetric supercapacitor applications†

Abstract

Enhancing charge storage and balancing energy and power densities in a supercapacitor requires a hybrid approach. To this end, a material with high porosity, good crystalline stability, and an adjustable framework could be integrated with a 2D defect-containing material that has a large surface area. A hydrothermally synthesized Zn(II)-based coordination polymer, [Zn(IPA)₂(2-MI)₂]_n (MZ) [IPA: isophthalic acid, 2MI: 2-methylimidazole], and in situ fabricated heterocomposites with MZ anchored on graphene oxide (GO) and reduced graphene oxide (RGO) interlayer sheets are presented here. MZ and its heterocomposites were characterized using spectroscopic (SC-XRD for MZ, UV-visible, FT-IR, PXRD with Rietveld refinement, and XPS) and nanoscopic (FE-SEM with EDX, and HR-TEM) techniques to confirm their structural compositions. The topological underlying net of MZ shows the uninodal 2C1 net topology. The synergistic effect between MZ and GO/RGO delivered good supercapacitance (SC) properties. Three electrode-based electrochemical analysis (1 M KCl, 1 M KOH, 1 M Na₂SO₄) revealed that GMZ23 and RGMZ11 exhibited better performance in 1 M KCl aqueous electrolyte than MZ. Furthermore, symmetric (SSC) and asymmetric supercapacitor (ASC) devices were designed and tested. The RGMZ11 ASC device provided the specific capacitance (Sp. Cp.) of 154.53 F g⁻¹ (specific capacity-247.48 C g⁻¹), the energy density (E. D.) of 54.99 W h kg⁻¹, and the power density (P. D.) of 160 W kg⁻¹ at a 0.2 A g⁻¹ current density in 1 M TEABF₄ (DMSO) electrolyte. Up to 75% of the capacitance of RGMZ11 was retained after 10 000 charge–discharge cycles at a current density of 5 A g⁻¹. Moreover, the capacitive and diffusion-controlled processes were examined using the Dunn method and it was found that the optimized device follows a diffusion-controlled process at lower scan rate. The optimized RGMZ11 was successfully utilized to make a multi-color disco LED and a red LED glow. The above study suggests that the RGMZ11 heterocomposite shows good performance for SC applications.