Enhanced energy density in electric double layer capacitors using metal-organic framework as filler in biodegradable poly(vinyl) alcohol-based solid-state electrolytes

The essential factor in developing high-energy density electric double layer capacitors (EDLC) is enhancing the electrolyte's performance and the device's voltage. Hence, solid polymer electrolytes (SPEs) are regarded as attractive prospects for energy storage device applications due to their flexibility, interfacial compatibility, and processability. However, their poor ionic conductivity and weak resistance to dendrites constrain their practical use. In this work, a novel SPE consists of biodegradable polyvinyl alcohol (PVA) doped with functional filler using iron based metal organic framework (Fe-BTC-MOF), and sodium hexafluorophosphate (NaPF₆) as the dopant salt is explored to address the aforementioned limitations. The interaction between these three materials is investigated by Fourier transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) deconvolution shows that the Fe-BTC-MOF reduces the crystallinity percentage from ∼35 % to ∼29 %. For the electrical performance, the synergistic effect of Fe-BTC-MOF and the sodium salt significantly enhances room temperature ionic conductivity to 1.56 × 10⁻⁴ S/cm when 3 wt% of MOF is added. The linear sweep voltammetry (LSV) shows high electrochemical stability up to 3.33 V. Finally, the Fe-BTC-MOF/PVA/sodium salt SPE is utilized as the electrolyte in the fabrication of AC//SPE//AC EDLC that exhibits specific capacitance, C_sp of 55.0 F/g at 0.1 mA/cm², as obtained from GCD, over 1200 cycles. The solid-state EDLC also recorded an excellent energy density of 17.2 W h kg⁻¹ and power density of 935.9 W/kg, along with favorable cyclability of 85 % coulombic efficiency and 80 % capacitance retention, making this supercapacitor a feasible candidate for grid-scale energy storage.