With the characteristics of safe and cost-effective, aqueous supercapacitors have been a research focus. But the narrow work voltage window greatly hinders the enhancement of energy density. The work voltage window is limited by the thermodynamic stable potential of water (1.23 V), such the limitation may be surpassed by increasing the over-potential of the hydrogen evolution reaction. Herein, the heteroatom-rich micropore carbon fiber fabric (CC) is modified by Na-containing functional groups. As negative electrode, Na-containing functional groups CC (Na-CC) exhibits the expanded negative potential window due to Na-containing functional groups inhibits the adsorption of H+ and the increased specific capacitance due to the enhanced surface area and 0 content. A 2.1 V aqueous carbon-based supercapacitor is assembled based on Na-CC (-) and CC (+), exhibiting the maximum energy density of 7 mWh cm(-3) and the power density of 900 mW cm(-3) as well as excellent cyclic stability of similar to 100% retention after 16000 cycles. The present work may provide the novel insight into the design of the safe and cost-effective aqueous high-voltage supercapacitors.