Synthesis of a Three-Dimensional Interconnected Oxygen‑, Boron‑, Nitrogen‑, and Phosphorus Tetratomic-Doped Porous Carbon Network as Electrode Material for the Construction of a Superior Flexible Supercapacitor

To construct a high-performance next-generation carbon-based flexible supercapacitor, high porosity, large mass density, and high flexibility are three significant challenging goals. However, one side always affects another. Herein, high-density tetratomic-doped porous composite carbon derived from sustainable biomaterials is achieved via two-step processes of carbonization and acid-washing treatment. The assembled carbon-based electrodes are highly doped with various heteroatoms (B, O, N, and P) for 33.59 atom %, resulting in abundant porosity, high densities, high pseudocapacitive contribution for 84.5%, and superior volumetric capacitive performance. The fabricated flexible electrode exhibits high flexibility, high mass loading (316 mg cm–3), and remarkable tensile strength (44.6 MPa). Generally, the volumetric performance is key and a significant parameter to appraise the electrochemical characteristics of flexible supercapacitors within a limited space. The aqueous symmetric supercapacitor demonstrates a high volumetric energy density and an excellent power density of 2.08 mWh cm–3 and 498.4 mW cm–3, respectively, along with 99.6% capacitance retention after 20 000 cycles, making it competitive to even some pseudocapacitors.