Benzoate Acid-Dependent Lattice Dimension of Co-MOFs and MOF-Derived CoS2@CNTs with Tunable Pore Diameters for Supercapacitors

Herein three novel cobalt metal-organic frameworks (Co-MOFs) with similar ingredients, Co (bib) (o-bdc) ∞ (1), Co2 (bib) 2 (m-bdc) 2∞ (2), and Co (bib) (p-bdc) (H2O) (H2O) 0. 5∞ (3), have been synthesized from the reaction of cobalt nitrate with 1, 4-bis (imidazol-1-yl) benzene (bib) and structure-related aromatic acids (1, 2-benzenedicarboxylic acid = o-bdc, 1, 3-benzenedicarboxylic acid = m-bdc, and 1, 4-benzenedicarboxylic acid = p-bdc) by the solvothermal method. It is aimed to perform systematic research on the relationship among the conformation of benzoate acid, lattice dimension of Co-MOF, and pore diameter of MOF-derived carbon composite. Through the precursor strategy, Co-MOFs 1-3 have been utilized to synthesize porous cobalt@carbon nanotube composites (Co@CNTs). After the in situ gas-sulfurization, secondary composites CoS2@CNTs were successfully obtained, which kept similar morphologies of corresponding Co@CNTs without destroying previous highly dispersed structures. Co-MOFs and two series of composites (Co@CNTs and CoS2@CNTs) have been well characterized. Topology and Brunauer-Emmett-Teller analyses elucidate that the bdc2- ion could control the pore diameters of MOF-derived carbon composites by adjusting the lattice dimension of Co-MOFs. The systematic studies on electrochemical properties demonstrate that (p) -CoS2@CNT possesses hierarchical morphology, moderate specific surface area, proper pore diameter distribution, and high graphitization, which lead to remarkable specific capacitances (839 F g-1 at 5 mV s-1 and 825 F g-1 at 0. 5 A g-1) in 2 M potassium hydroxide solution. In addition, the (p) -CoS2@CNT electrode exhibits good electrochemical stability and still retains 82. 9% of initial specific capacitance at the current density of 1 A g-1 after 5000 cycles.