Electrochemical properties of CoMn/C based on zeolite-like metal-organic frameworks

Herein, we report a systematic investigation of the synthesis methodology, structural characteristics, and electrochemical performance of CoMn/C metal-carbon nanocomposites derived via IR pyrolysis from manganese-substituted metal-organic frameworks (MOFs) exhibiting ZIF-67 topology. The MOF precursors were synthesized utilizing a chemical co-precipitation approach in aqueous media under ultrasonic treatment, with systematic variation of Co:Mn molar ratios ranging from 95:5 to 50:50, employing 2-methylimidazole as the organic linking agent. X-ray diffraction analysis coupled with electron microscopy investigations revealed that manganese incorporation into the cobalt sites is feasible up to a Co:Mn ratio of 70:30 while maintaining the intrinsic ZIF-67 crystalline architecture, concomitantly leading to a systematic reduction in crystallite dimensions from 36 to 21 nm and corresponding morphological modifications. The subsequent IR pyrolysis conducted within the temperature range of 500–700 °C yielded metal-carbon nanocomposites comprising homogeneously dispersed Co, MnO₂, and Mn₃O₄ nanoparticles within a porous carbonaceous matrix. Electrochemical characterization demonstrated optimal specific capacitance values of 336 F/g at 0.25 A/g current density for nanocomposites exhibiting Co:Mn ratio of 80:20, synthesized at the optimal pyrolysis temperature of 600 °C. The resultant materials exhibited exceptional cycling stability, maintaining capacitance retention exceeding 95 % through 1000 charge-discharge cycles, while demonstrating robust performance across a broad potential window up to 1.4 V in 6M KOH aqueous electrolyte. The enhanced specific capacitance values are attributed to the synergistic contribution of double-layer capacitance from the developed porous carbon framework and pseudocapacitive effects arising from reversible redox processes of metallic nanoparticles and their corresponding oxides. These findings elucidate the significant potential of Mn-substituted MOFs as precursors for the fabrication of high-performance electrode materials in symmetric supercapacitor applications, exhibiting superior electrochemical characteristics.