Aromatic Polyimides Containing Diaminobenzoic Acid as in Situ Porogen for Electrochemical Supercapacitors

A series of aromatic polyimides derived from 4,4'-hexafluoroisopropylidine diphthalic anhydride (6FDA), with different ratios of 2,4,6-trimethyl-1,3-phenylenediamine (DAM), and 3,5-diaminobenzoic acid (DABA) were investigated as carbon precursors for supercapacitors. The synthesized polymers were electrospun and subjected to thermal treatment which enhanced the stability of the polymer chains by cross-linking. The effect of the carboxylic moiety in DABA was further scrutinized in terms of its ability to act as an internal porogen to create pores upon thermal treatment including carbonization at 1000 degrees C. The specific capacitance of 6FDA-DABA and 6FDA-DAM-DABA (6FDD) was 89 F g(-1) for both, with energy densities of 22 and 20 Wh kg(-1), respectively, upon carbonization. Fiber mats were activated by CO2 to further increase the surface area to obtain enhanced electrochemical performance. Although all the polyimide-derived carbons exhibited remarkable improvement of electrochemical performance upon activation, the best was observed for 6FDA-DABA-derived electrodes, which had specific capacitance of 147 F g(-1) (at 10 mV s(-1)), an energy density of 68 Wh kg(-1), a power density of 3.4 kW kg(-1), and excellent capacitance retention of 96% after 3000 cycles.