B/N co-doped porous carbon nanosheets with high B/N doping contents and excellent supercapacitor performance

Despite the important advances on B/N co-doped porous carbons (BNCs), integrating high B/N-doping content and hierarchical porosity into carbon nanosheets remains a challenging task for supercapacitor application. Herein, we report a novel BNC nanosheet with both expected properties through one-step H3BO3-mediated carbonization/activation of a newly-developed N/O-rich polymer (DPP). In such a mixture system, an in-suit crossing-linked DPP@H3BO3 composite is formed due to the formation of multiple intermolecular hydrogen bonds between the H3BO3 and the ester groups of DPP. The improved thermal stability for such a composite enables the fixation of more B-/N-bearing species in the carbon skeleton during carbonization. Particularly the nanosheet-like BNC-850 shows a rather high B/N content (6.63/7.27 at.%), a large SBET value (766.5 m2 g−1), and a hierarchical porosity, all of which are in favor of electrochemical performance in both aqueous supercapacitors and zinc-ion capacitors (ZICs). In 6 M KOH electrolyte, the BNC-850 electrodes deliver an impressive capacitance of 341.5 F g−1 at 0.5 A g−1, a high capacitance retention of 79.2 % at 20 A g−1, and a good cycling stability (95 % capacitance retention over 10,000 cycles at 5 A g−1). The energy density of BNC-850-based ZICs is as high as 126.0 Wh kg−1 at 459.0 W kg−1, exhibiting an outstanding superiority compared to the reported carbon-based ZICs. This work offers a facile strategy for accessing BNCs with high B/N-doping contents, and highlights the importance of such materials in high-energy-density ZICs.