Pre‐Polymerization and Pre‐Etching Dominated by Carbon Dots to Fabricate the Sub‐Nanometer Microporous Carbon for Supercapacitors

The self-templating method is a facile and low-cost strategy to synthesize porous carbon materials, but the obtained products usually have low yields, limited specific surface areas (SSAs), and broad pore size distributions. It is a great challenge for the self-templating method to prepare the sub-nanometer (0.5-1.0 nm) microporous carbon that is preferred for high-performance supercapacitors. In this study, carbon dots (CDs) are employed as the sole precursor to prepare porous carbon without using any activating agents. The obtained carbon materials have large SSA (2733.6 m² g^-1), high micropore area ratio (92.5%), high packing density (0.82 g cm^-3), high yield (12%), and concentrated sub-nanometer pore structure. The formation mechanism of such porous carbon and the unique functions of CDs as self-templates are interpreted by various characterizations. When used as electrodes for supercapacitors, this carbon material exhibits specific capacitance up to 639 F g^-1 and is compatible with electrolytes of wide pH values and enlarged voltage windows (1.3-1.7 V). The symmetric devices assembled by such material exhibit low self-discharge behaviors, excellent energy densities (15.9-44.1 Wh kg^-1), and good cycling performance even under the commercial-level mass loading (10 mg cm^-2) on electrodes.