B, N co-doped carbon nanosheets derived from graphene quantum dots: Improving the pseudocapacitive performance by efficient trapping nitrogen

B, N co-doped carbon nanosheets prepared by boric acid-assisted carbonization show an increased nitrogen content than the precursor graphene quantum dots, enabling high pseudocapacitance for supercapacitor electrodes. [Display omitted] •B, N co-doped carbon nanosheets are prepared by boric acid-assisted carbonization.•The nanosheets show an increased nitrogen content than the precursor GQDs.•The trapping of nitrogen is ascribed to the balance of positive and negative charges.•The nanosheets show high pseudocapacitance due to the highly doped structure. Doping heteroatoms especially nitrogen is widely applied for improving the capacitive energy storage performance of carbon materials. However, preserving nitrogen in carbon skeleton is still challenging because nitrogen species are unstable at high temperature. Herein, we develop a simple boric acid-assisted method for trapping nitrogen into carbon skeleton. Using the graphene quantum dots with an initial nitrogen content of 5.0 at.% as precursors, the B, N co-doped carbon nanosheets with an increased nitrogen content of 7.2 at.%, a boron content of 4.4 at.%, and a surface area of 817 m2 g−1 are prepared. Benefiting from the high heteroatom content, the nanosheets show a significantly improved capacitance of 257 F g−1 at 1 A g−1 and a good rate performance of 150 F g−1 at 50 A g−1. The pseudocapacitance contribution at 10 mV s−1 is as high as 48%. The assembled symmetric capacitor shows a superior cycle stability with no obvious fading after 10,000 cycles at 10 A g−1. Our work can help to understand the synergistic effect of heteroatoms for co-doping of carbon and broaden the avenue for designing functional carbon materials.