An activation-free protocol for preparing porous carbon from calcium citrate and the capacitive performance

In this work, we demonstrate a simple and effective carbonization method to prepare porous carbon without any activation process, using calcium citrate as carbon source. The carbon products were well characterized by means of thermogravimetric analysis, X-ray diffraction pattern, field emission scanning electron microscopy and BET surface area measurement. It is found out that the carbonization temperature plays a crucial effect on the structures and electrochemical properties of the carbons. Because of the coexistence of major amount of mesopores and minor micropores towards the carbon at 700 °C, the sequences of capacitance values are: 700 °C > 800 °C > 600 °C. As a result, the maximum specific capacitance of the carbon at 700 °C reaches as much as 172 F g−1 at the current density of 1 mA cm−2, which corresponds to a BET surface area of 1072 m2 g−1, also confirming the nonlinear relationship between the specific surface area and the capacitance. Meanwhile, the maximum energy density and power density of the carbon at 700 °C are 24 Wh kg−1 and 6.7 kW kg−1, respectively. Owing to the high specific capacitance and good cycle stability, the present carbons are excellent electrode materials for high-rate electrochemical capacitors.

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► A simple carbonization method has been developed to prepare porous carbon.
► The carbonization temperature has a crucial effect on the capacitive properties.
► The carbons possess high BET surface areas and narrow PSD.
► The carbons possess high specific capacitance and excellent cycle stability.