Capacitance Enhancement of Metal-Organic Framework (MOF) Materials by Their Morphology and Structural Formation

Three types of metal-organic framework (MOF) materials were designed, synthesized, characterized, and thoroughly evaluated for their specific capacitance. Imidazole, adenine, and a mixture of both compounds along with nickel were used to synthesize the three MOFs (Imz-MOF, Imz + Adn-MOF, and Adn-MOF). The synthesized materials were subjected to standard characterization techniques. The surface morphology of the materials was studied using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM) analyses. The Imz-MOF possesses a cubic structure, while Imz + Adn-MOF and Adn-MOF show a flake and mixed flake-like structures. The effect of the morphology and molecular structural formation was studied and explained systematically. The Brunauer-Emmett-Teller (BET) analysis was used to study the surface area and porous nature of the materials. The capacitance of the materials was evaluated using an electrochemical workstation with 3 M KOH as an electrolyte at various sweep rates and a galvanostatic charge-discharge (GCD) test at different current densities. The results show that the maximum efficiencies of Imz-MOF, Imz + Adn-MOF, and Adn-MOF were obtained at 407.42, 80, and 60 F g(-1) values, respectively. The materials demonstrated good recycling properties even after 5000 cycles. The higher capacitance of Imz-MOF could be attributed to the structural formation and the ligand-to-metal electron donation, which enhances the conductivity of the material. The imidazole group contributes to the material's conductivity and charge-transfer (CT) nature. Based on the capacitance performance results of the materials, it is confirmed that Imz-MOF possesses a superior efficiency over Imz + Adn-MOF and Adn-MOF.