The potassium hydroxide-urea synergy in improving the capacitive energy-storage performance of agar-derived carbon aerogels

The electrochemical performance of biomass-derived carbon materials is strongly correlated to the chemical compositions and processing conditions. In this work, we demonstrate a crosslinker-free sol-gel method to synthesize N-doped porous carbon aerogels from agar hydrogels. The most significant distinction of our method from the existing carbon-production protocols is the involvement of potassium hydroxide (KOH) and urea, the two structure and composition modifiers. We establish the correlations between the dual modifiers and the physical and electrochemical properties of the resultant carbon aerogels as supercapacitor electrodes. Specifically, electrochemical tests reveal that both KOH and urea are indispensable to obtain carbon aerogels with surface areas surpassing 2000 m(2)/g and a gravimetric capacitance approaching 400 F/g at 0.5 A/g. The capacitance remains among the top of the porous carbon supercapacitor electrodes reported in the literature. In addition, the carbon aerogels are highly robust with only 4% capacitance loss after 10000 consecutive charge-discharge cycles. We expect the incorporation of KOH and urea in organic carbon precursors is effective and general in elevating the capacitance and rate capability of biomass-derived carbons, and will greatly enrich the material tool box for designing electrochemical devices including supercapacitors, batteries and fuel cells. (C) 2019 Elsevier Ltd. All rights reserved.