(i) as bags with a suitable size to trap and release flavin molecules, and (ii) offered curvature or bend surfaces to enhance the interaction opportunities toward electroactive sites for influential surface absorption, and charge transfer electrochemistry. As a result, the highest content of mesopores was obtained for CNT pyrolyzed at 1000 ˚C, and delivered the best performance in MFC. spacing was expanded, and the structure got more disordered after B, N co-doping. The results showed that the theoretical upper limit of boron content in B, N co-doped carbon could reach a maximum of 12 at%, thereby suggesting that B, and N co-doped material could be more stable, and accessible than those materials with only one heteroatom. The BN-CNFs exhibited the maximum SBET of 1585 m g -2 , while CNFs was about 741 m g -2 . The study concluded that doping of N has significantly reduced the formation energy of B doping. The B, N-CNFs was utilized for Na ion battery applications, and delivered a high reversible charge capacity of 691 mA h g -1 at 100 mA g -1 , and high-rate capability of 277 mA h g -1 after 1000 cycles. The highperformance Na ion battery is ascribed to the porous and 3D interconnected structure that facilitated the migration of Na ions, and dual-atom doping towards the creation of defect sties in CNFs, and also improved the electrochemical performance and electronic conducting. The S-CNFs were obtained via freeze-drying BC, and pyrolyzed at 800 ˚C under Ar atmosphere, and the obtained product was mixed with element sulfur, and carbonized at 500 ˚C. CNFs displayed the average diameter of 50 nm, with an interlayer spacing of 0.386 nm, which was found to increase for S-doped CNFs . This indicates the enlargement of interstitial spacing due to sulfur doping due to its larger covalent radius (102 ppm) than that of carbon atom . XPS studies demonstrated the doping of sulfur, and its partially covalent link with CNFs. CNFs, and S-CNFs showed the SBET of 465, and 669 m g -2 ,