Filter\nPaper-Derived Hierarchical Porous Carbon by\na Simple Molten Salt Strategy in Air for High-Performance Supercapacitors

Carbon\nmaterials are widely used as electrode materials for supercapacitors\ndue to their low cost and high porosity. The traditional preparation\nscheme requires the participation of inert gas, and the electrochemical\nperformance exhibited still leaves much to be desired. Here, a hierarchical\nporous structure with a large specific surface area is successfully\nconstructed through a simple molten salt strategy with low-cost filter\npaper as the precursor and urea as the nitrogen source. Molten salt\ncan function as both a sealant, maintaining the integrity of the prepared\ncarbon structure, and a template, facilitating the formation of pores\nwithin the carbon material. Incorporating nitrogen atoms into carbon\nmaterials creates additional electrochemical active sites, facilitating\nenhanced redox reactions and improving the electrochemical performance.\nThe prepared FPAC/Urea-3:4 (FPAC: filter paper-based activated carbon)\nhas an impressive large specific surface area of 1020 m<sup>2</sup> g<sup>–1</sup> and abundant heteroatom doping. In the three-electrode\nsystem, the specific capacitance of FPAC/Urea-3:4 can reach 230.8\nF g<sup>–1</sup> at 1 A g<sup>–1</sup>. The study also\ninvestigated the potential application of FPAC/Urea-3:4 in symmetric\nsupercapacitors, with an energy density of 7.4 Wh kg<sup>–1</sup> and a specific power of 125.3 W kg<sup>–1</sup>, and the\ndevice can light up an LED lamp. In addition, it also showed excellent\ncycle stability with a capacitance retention rate of up to 97.7% after\n5000 cycles. This study proposes an efficient and promising application\ntechnology for the preparation of porous carbon in air.