Remarkable capacitive enhancement of templated carbon materials by the redox additive electrolyte of p-phenylenediamine

Abstract

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 m² g⁻¹ and large total pore volume of 2.27 cm³ g⁻¹. To further improve the electrochemical performance, p-phenylenediamine (PPD, as redox-additive) of 5, 10, and 15 mmol L⁻¹ is introduced into the 6 mol L⁻¹ 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⁻¹ at 2 A g⁻¹, respectively, which are greatly higher than that of 325 F g⁻¹ for the case of the pristine P-3 : 1 sample when measured at 6 mol L⁻¹ 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.