Capacitance behaviour of the ammoxidised coal Original Research Article

A possibility to obtain a new electrode material for supercapacitors by ammoxidation and activation of the hard carbon has been examined. Carbonization process of precursor material was conducted at temperature 700 °C after demineralization. Samples were activated with steam at the temperature 800 or 850 °C and controlled burn-off of ca. 50 wt%. Ammoxidation was carried out with ammonia and air mixture at 300 or 350 °C before carbonization as well as before or after activation. Active materials were characterized by porous structure, elemental and X-ray photoelectron spectroscopy analyses and electrochemical measurements in three-electrode Swagelok type capacitor. The capacitances ca. 175 F/g were obtained for activated carbon materials working as positive electrode in acidic condition (4 M H2SO4) if ammoxidation had been made before or after carbonization. However, in alkaline condition (7 M KOH), the best performance ca. 145 F/g was demonstrated by carbon material ammoxidized after activation if used as the negative electrode. The influence of the stage when ammoxidation is applied and thermal conditions of carbon modification on the porous and chemical structure of the samples as well as the resulting outcome in capacitance characteristics are discussed.