Green synthesis of zeolitic imidazolate framework-67 (ZIF-67) coatings for high-performance supercapacitors using bio-derived solvents

Abstract

Zeolitic imidazolate frameworks (ZIFs) are promising for energy storage due to their high surface area, tunable porosity, and chemical stability. However, their synthesis typically uses toxic solvents like N,N-dimethylformamide (DMF), hindering their widespread adoption. This study explores sustainable alternatives by using bio-derived solvents for the electrochemical synthesis of ZIF-67 coatings. In the present article, our group have systematically investigated ethyl lactate, dimethyl isosorbide, 2-methyltetrahydrofuran, and cyclopentyl methyl ether as solvents for electrodepositing ZIF-67. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that 2-methyltetrahydrofuran and cyclopentyl methyl ether yielded highly crystalline ZIF-67 coatings with well-defined rhombic dodecahedral crystals (2–3.5 µm). When integrated into a two-electrode supercapacitor, ZIF-67 coatings synthesized with these two solvents demonstrated significantly higher specific capacitances than other bio-derived solvents. These findings highlight 2-methyltetrahydrofuran and cyclopentyl methyl ether as viable green solvents for producing ZIF-67 coating, paving the way for environmentally friendly supercapacitors.