Synthesis and electrochemical capacitive performances of novel hierarchically micro-meso-structured porous carbons fabricated using microporous rod-like hydroxyapatites as a template

Electrochemical capacitors (ECs) are attractive energy storage systems for applications with high power requirements. Porous carbons are the materials that are most frequently used for the electrodes in ECs, because of their large surface area, high conductivity, chemical inertness, low cost, and tunable pore structure. Here, novel hierarchically micro-meso-structured porous carbons were synthesized, using microporous rod-like hydroxyapatite nanoparticles as a template and sucrose as a carbon source. The morphology and surface properties of the as-prepared porous carbons were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller surface analysis. The electrochemical capacitive performances were evaluated in an aqueous solution of 1 mol·L^-1 H₂SO₄ using cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge/discharge tests. The resultant carbons showed a high surface area of more than 719.7 m²·g^-1, large pore volumes of more than 1.32 cm³·g^-1, and a disordered pore structure composed of randomly distributed micropores, collapsed mesopores, and interweaving rod-like mesopores that took the shape of the template. As the carbonization temperature was increased, the density of micropores and rod-like mesopores decreased, and a tri-modal pore size distribution appeared for the carbon sample carbonized at 900 ° C. Because of these unique characteristics, the electrode material originated from the porous carbon carbonized at 900 °C exhibited good electrochemical capacitive performances.