Integrating Carbon Dots with Porous Hydrogels to Produce Full Carbon Electrodes for Electric Double-Layer Capacitors

As a class of electrode materials for electric double-layer capacitors (EDLCs), carbon dots (CDs) are able to enlarge specific surface areas, fabricate hierarchical pores, and graft pseudocapacitive groups, leading to additional capacities and superior energy densities. In this work, the commercial polyacrylamide gel (PAMG) is used as a good host for CDs, which has continuously interconnected pores, a cross-linked network, and good swelling capacity so as to form continuous conductive carbon skeleton. After a one-step calcination–activation treatment, CDs are fused onto the final carbon architecture to form a series of porous carbon materials with specific functional groups. Different kinds of CDs, including the oxygen-doped, the nitrogen-doped, and the oxygen, nitrogen co-doped ones, are employed to prepare such carbon materials and tested, respectively. All of these materials have high specific surface areas, well-balanced pore size distributions, high conductivity, abundant superficial functional groups, and good wettability. When they are assembled as electrodes in EDLC, they exhibit remarkable performances, such as specific capacitance of 401–483 F g–1, rate stability over 75% (1–30 A g–1), energy density of 17–23 Wh kg–1, and cycling life of nearly 100%. These results prove that our method, calcination–activation on the CDs–porous (hydro)gel composites, is a universal route of preparing good carbon electrode materials for electrochemical energy storage.