Wang et al. developed a hierarchically porous nitrogen-doped carbon nanosheets (PNCNs) derived from grapefruit peels for supercapacitor studies . The grape fruit peels were activated, and carbonized using KOH at 700 ˚C. PNCNs showed the SBET of 1760 m 2 g -1 with microporous feature. The XPS studies of activated PNCNs showed O, and N heteroatoms with 15.83%, and 1.5%, respectively. The electrochemical performances of PNCNs electrode were analysed using 1 M H2SO4, and exhibited the specific capacitance of 311 F g -1 at 0.1 A g -1 , and 5.95% degradation was observed after 10000 cycles. The PNCNs electrode showed the higher energy density of 17.7 Wh Kg -1 at a power density of 1100 W Kg -1 compared to DCGPs electrode (0.77 Wh Kg -1 at the same power density) as evident from the Ragone plot (Fig. ). Further, a symmetric supercapacitor cell was assembled in 1 M Na2SO4 aqueous electrolyte which delivered a high energy density of 34.05 Wh Kg -1 at a power density of 180 W Kg -1 , and also retained 14.25 Wh Kg -1 even at a high-power density of 5400 W Kg -1 . The high supercapacitive performances were attributed to the high effective SBET, well developed hierarchical porous structure, combining double layer, Faradaic contributions, and heteroatom doping effects. Zhao et al. designed the B and N co-doped porous carbon tube bundle (B/N-PCTB) electrode materials derived from the dandelion fluff biomass using KOH activation for high-volumetric-energy-density supercapacitor . As calculated from the BET analysis, the porous carbon-tube bundle (PCTBs) showed the SBET of 1432 m 2 g -1 , which is much higher than that of CTBs without activation (536 m 2 g -1 ). Further, the SBET of the N-PCTBs, B-PCTBs, and B/N-PCTBs were determined as 1428, 1419, and 1420 m 2 g -1 , which are almost similar to that of PCTBs without heteroatom doping. The SBET values indicated that the doping of heteroatom did not change the SBET of porous carbon tube bundles. The XPS studies exhibited the presence of heteroatoms O, N, and B with at% of 5.18, 2.2, and 4.6%, respectively with higher B content, which is probably due to the role of boron atoms as electron acceptors, and anchoring sites, whereas nitrogen atoms containing poly-electrons provided more binding sites for B atoms. The CV curves of CTBS and PCTBS demonstrated the DELC behaviour, and the heteroatom-doped carbon materials indicated the existence of pseudocapacitive nature as shown in Fig. . The B/N-PCTB electrode with the active material of 2.5 mg cm -2 , showed the specific capacitance of 355 F g -1 at 1 A g -1 current density. The electrode recorded the capacitance retention of 82.3%, and a specific capacitance of 292 F g -1 at 20 A g -1 , which was found to be much superior to those of the B-PCTBs (261 F g -1 at 20 A g -1 , 77.9% capacitance retention), N-PCTBs (214 F g -1 at 20 A g -1 , 71.8% capacitance retention), PCTBs (198 F g -1 at 20 A g -1 , 69.2% capacitance retention), and CTBs (38 F g -1 at 20 A g -1 , 58.5% capacitance retention). Further, the B/N-PCTB electrode exhibited the specific capacitance of 216 F g -1 with a high loading mass of 40 mg cm -2 . The B/N-PCTB electrode displayed improved specific capacitance value while compared with the unitary heteroatom doped PCTBs, due to the synergistic effect of B and N atoms. Moreover, the -COOH, and -OH oxygen-containing functional groups has played a viable role on improving the wettability as well as the pseudocapacitance behaviour. The symmetric cell assembly was fabricated with the B/N-PCTB active material loading of 80 mg cm -2 (cathode: 40 mg cm -2 ; anode: 40 mg cm -2 ) as anode and cathode electrodes in 1 M Na2SO4, which performed a high volumetric energy density of 12.15 W h L -1 at the power density of 699.84 W L -1 , suggested the high supercapacitor performance of porous carbon tube bundle material.