One-Step Synthetic Strategy of Hybrid Materials from Bimetallic Metal-Organic Frameworks for Supercapacitor Applications

This work reports a facile one-step method for the synthesis of new hybrid porous materials using bimetallic NiCo-MOF-74 as the starting precursor. By controlling the calcination atmosphere and temperature, the bimetallic NiCo-MOF-74 particles can be converted into a series of hybrid materials consisting of carbon, metal, and metal oxides. The direct carbonization of the bimetallic NiCo-MOF-74 particles at 800 °C under N₂ atmosphere results in the formation of graphitic carbon/Ni_xCo_1-x composites (termed NC-800). In contrast, the heat treatment of NiCo-MOF-74 in air at 350 °C (termed NC-350) yields Ni_xCo_1-x/Ni_xCo_1-xO composites (with a small trace of carbon) as the product. When evaluated as electrode materials for supercapacitors, NC-800 and NC-350 exhibit high specific capacitances of 715 and 513 F g^-1, respectively, at a high current density of 1 A g^-1. Furthermore, these hybrid materials also show good cycling stability with no visible degradation in their specific capacitance after 2,500 cycles. The excellent electrochemical performance of these hybrid materials may be attributed to (i) the synergistic effect of the graphitic carbon and binary mixed metals which can enhance the electrical conductivity of the composites, (ii) the presence of mesopores which can facilitate easy diffusion of electrolyte, and (iii) their large surface area and pore volume which can provide significantly more electroactive sites. The outstanding electrochemical properties of these MOF-derived hybrid materials indicate their promising potential as electrode materials for high-performance supercapacitors.