Carbon anodes have been widely utilized for the fabrication of high-performance asymmetric supercapacitors. However, they generally suffer from unsatisfactory energy density due to low specific capacitance arising from inferior conductivity and insufficient ionic diffusion rate. Here a surface modification method is conducted after the annealing of ZIF-67 precursor to produce hydrophilic, porous and heteroatom-doped carbon foam. On top of enhanced area capacitance, widened voltage window of −1.3–0 V (vs saturated calomel electrode) can be achieved through electrochemical reduction to suppress the hydrogen evolution reaction. The optimized reduced porous carbon foam on carbon cloth exhibits a maximum area capacitance of 1049 mF/cm2 at an applied current density of 12 mA/cm2 with excellent capacitance retention of 98.4% after 6000 charge-discharge cycles at 15 mA/cm2. By well pairing with hierarchical MnO2/CC cathode, a 2.3 V asymmetric supercapacitor in neutral aqueous Na2SO4 electrolyte is assembled, which delivers an exceptional energy density of up to 10.07 mWh/cm3. The procedure in this paper for carbonaceous material to simultaneously achieve considerable capacitance and enlarged voltage window can open up a wider prospect toward design of anodes for high-performance aqueous supercapacitor.