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A straightforward multitemplate carbonization method for producing nanoporous carbons has been implemented using magnesium citrate as the carbon source and magnesium powder as the template. Notably, the crystallinities of the carbon materials were greatly enhanced with increasing carbonization temperatures. Sample C-4:1–900 obtained by carbonizing the mixture of magnesium citrate and Mg powder (in a mass ratio of 4:1) at 900 °C exhibited a large BET surface area of 1972.1 m2 g–1 and a high pore volume of 4.78 cm3 g–1, thereby resulting in the best electrochemical behaviors. It delivered a large specific capacitance of 236.5 F g–1 at 1 A g–1 when measured in a three-electrode system. Additionally, in a two-electrode system, the energy density was 15 Wh kg–1 for a power density of 0.5 W kg–1, when measured at an operating temperature of 80 °C.

Nanoporous carbon materials with hierarchical porosities have been produced via a template carbonization method, in which potassium citrate (or gelatin) serves as the carbon precursor and Mg(OH) 2 powder as the hard template. The P-3 : 1 sample derived from potassium citrate and Mg(OH) 2 (with a mass ratio of 3 : 1 at 800 C) possesses high BET surface area of 1894.7 m 2 g À1 and large total pore volume of 2.27 cm 3 g À1 . To further improve the electrochemical performance, p-phenylenediamine (PPD, as redox-additive) of 5, 10, and 15 mmol L À1 is introduced into the 6 mol L À1 KOH as the mixed electrolyte, forming P-3 : 1-5/10/15 samples. Interestingly, the specific capacitances toward the P-3 : 1-5/10/15 samples have been greatly enhanced up to 579.2, 712.8 and 852.3 F g À1 at 2 A g À1 , respectively, which are greatly higher than that of 325 F g À1 for the case of the pristine P-3 : 1 sample when measured at 6 mol L À1 KOH electrolyte.Furthermore, the P-3 : 1-15 sample delivers high capacitance retention of 70.5% even after 5000 charge-discharge cycles. What's more, the synthesis method has been readily extended for the case of gelatin and Mg(OH) 2 , and a similar electrochemical trend in the cases of the P-3 : 1-5/10/15 samples also occurs.

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