Electrochemically Reduced Ultra-high Mass Loading Three-Dimensional Carbon Nanofiber Network: A Reproducible and Stable Cell Voltage of 2.0 V and High Energy Density Symmetric Supercapacitor

Commercial supercapacitors need high mass loading of more than 10 mg cm-2 and a high working potential window to resolve the low energy density concern. Herein, we have demonstrated a thick, ultrahigh mass loading (35 mg cm-2), and wide cell voltage electrochemically reduced layer-by-layer three-dimensional carbon nanofiber network (LBL 3D-CNFs) electrode via electrospinning, sodium borohydride treatment, carbonization, and electro-reduction techniques. During the electro-reduction technique, Na+ is adsorbed onto the various defect sites of LBL 3D-CNFs, which properly inhibit the formation of intermediate HER (hydrogen evolution reaction) product, leading to a wide cell voltage, whereas, the LBL 3D-CNFs network evokes an opportunity for storing a greater number of charges, resulting in astonishing electrochemical performances. A reproducible and stable cell voltage of 2.0 V symmetric supercapacitors is constructed and demonstrated. The as-constructed device can deliver areal energy output of 1922 µWh cm-2, at a power density of 3979 µW cm-2 equal to the gravimetric energy density of 27 Wh kg-1, and outstanding cyclic durability of 97.4 % after 20 000 GCD cycles. These record-breaking performances would make our device one of the most promising candidates for industrial point of view.