Synthesis of Ultrahigh Surface Area of Nitrogen‐Doped Porous Carbon Materials from Alginic‐Based Protic Polyanion Ionic Liquids for High‐Performance Supercapacitors

Carbon materials with a high specific surface area, large pore size, high electrical conductivity, and high chemical stability are regarded as promising electrode materials for supercapacitors. With the advantages of using ionic liquids precursors and biomass‐based precursors for the synthesis of carbon materials, nitrogen‐doped porous activated carbon materials with an ultrahigh surface area (up to 3638 m 2 g −1 ), a desirable pore size (up to 2.44 nm), and a high content of 10.38 at % oxygen and 1.14 at % nitrogen are prepared from alginic‐based protic polyanion ionic liquids (APPILs) using the KOH activation method. The specific structural properties of the as‐prepared carbon materials can be tuned by the nature of organic bases in the APPILs and carbonization conditions. When used as electrode materials for symmetric supercapacitors in 6 m KOH electrolytes, the obtained carbon material shows a significantly high gravimetric capacitance of up to 354 F g −1 at a current density of 0.1 A g −1 . Moreover, the assembled supercapacitor delivers a relatively high energy density of 12.3 W h kg −1 and a power density of 26 W kg −1 , as well as a high cycling stability of 95% capacitance retention after 10 000 cycles.