Large Areal Mass, Mechanically Tough and Freestanding Electrode Based on Heteroatom‐doped Carbon Nanofibers for Flexible Supercapacitors

A flexible and freestanding supercapacitor electrode with a N,P‐co‐doped carbon nanofiber network (N,P‐CNFs)/graphene (GN) composite loaded on bacterial cellulose (BC) is first designed and fabricated in a simple, low‐cost, and effective approach. The porous structure and excellent mechanical properties make the BC paper an ideal substrate that shows a large areal mass of 8 mg cm −2 . As a result, the flexible N,P‐CNFs/GN/BC paper electrode shows appreciable areal capacitance (1990 mF cm −2 in KOH and 2588 mF cm −2 in H 2 SO 4 electrolytes) without sacrificing gravimetric capacitance (248.8 F g −1 and 323.5 F g −1 ), exhibits excellent cycling ability (without capacity loss after 20 000 cycles), and remarkable tensile strength (42.8 MPa). By direct coupling of two membrane electrodes, the symmetric supercapacitor delivers a prominent areal capacitance of 690 mF cm −2 in KOH and 898 mF cm −2 in H 2 SO 4 , and remarkable power/energy density (19.98 mW cm −2 /0.096 mW h cm −2 in KOH and 35.01 mW cm −2 /0.244 mW h cm −2 in H 2 SO 4 ). Additionally, it shows stable behavior in both bent and flat states. These results promote new opportunities for N,P‐CNFs/GN/BC paper electrodes as high areal performance, freestanding electrodes for flexible supercapacitors.