Electrosynthesized Fe-based, Cu-based and Fe-Cu Metal-Organic Framework Systems for Supercapacitor Applications

Abstract

A novel electrochemical method was successfully developed for the synthesis of monometallic MIL-100(Fe), HKUST-1 and Fe-Cu metal-organic framework (MOF) systems under mild conditions and short reaction times. X-ray diffraction confirmed the successful formation of the parent frameworks, showing strong agreement with simulated patterns from the literature. Structural analysis of the Fe-Cu MOF systems revealed the coexistence of Fe-based and Cu-based MOF phases, forming physical phase mixtures. Textural characterisation by N₂ adsorption-desorption measurements revealed high surface areas of 1,044 m²·g⁻¹ for MIL-100(Fe), 781 m²·g⁻¹ for HKUST-1 and up to 800 m²·g⁻¹ for selected Fe-Cu MOF systems. The electrochemical performance of MIL-100(Fe), HKUST-1 and Fe-Cu(3.75/15) system was evaluated using galvanostatic charge-discharge and cyclic voltammetry in a three-electrode configuration with conductive catalytic inks. All materials displayed hybrid supercapacitor behaviour, combining electric double-layer capacitance and pseudocapacitive contributions. The Fe-Cu MOF system (Fe-Cu(3.75/15)) demonstrated enhanced electrochemical performance, achieving a specific capacitance of 1,073 F·g⁻¹, an energy density of 205 Wh·kg⁻¹ at 1 A·g⁻¹, and a power density of 3,632 W·kg⁻¹ at 5 A·g⁻¹. The improved performance is attributed to the coexistence of Fe- and Cu-based MOF phases, which promote complementary redox activity and charge storage mechanisms. These results highlight the potential of electrochemically synthesised MOF phase mixtures as promising materials for high-performance supercapacitor applications.