Tuning Carbon Contents and Further Capacitances of Coordination Polymer-Derived Carbonaceous Composites by Annealing Temperatures

In this article, one unusual coordination polymer [Co(bib)(1.5)(NO3)(2)(CHCl3)](infinity), named as CP-3-ZX, is assembled from ligand 1,4-bis(imidazol-1-yl)benzene (bib) and cobalt nitrate. In CP-3-ZX, the Co-II ion is connected by bib into one-dimensional (1D) double-track ladders, which are mutually packed to form tetragonal channels with a porosity of 23.9%. Subsequently, CP-3-ZX is employed as a precursor, and a sequence of Co3O4@C composites with various carbon contents is obtained through changing the annealing temperature. A moderate amount of carbon can enlarge the Brunauer-Emmett-Teller specific surface area, enhance the conductivity, and finally augment the capacitance of the carbonaceous material. An extensive comparison reveals that Co3O4@C-400, designated by setting the calcined temperature at 400 degrees C, has the highest specific capacitance of 317 F g(-1) because of the optimized carbon content among these Co3O4@C composites. Moreover, an asymmetric supercapacitor Co3O4@C-400//AC is fabricated using the positive electrode of Co3O4@C-400 and the negative electrode of activated carbon (AC). Co3O4@C-400//AC exhibits an energy density of 13.8 Wh kg(-1), and a retention of 82% after 5000 cycles indicates good cycling durability. Significantly, the 4 x 2 battery unit of Co3O4@C-400//AC can be utilized to run a time counter for 11 s and light a toy Christmas tree for more than 20 min. The outstanding propulsion competence proves that Co3O4@C-400 has tremendous applications in supercapacitors.