Magnesium oxide scaffolded preparation of N, O self-doped biochar with super-hydrophilic surface for aqueous supercapacitor with desired energy density

To assemble electrochemical supercapacitor with attractive energy density, heteroatoms self-doped biochar with hydrophilic surface and natural pore system is prepared by pyrolyzing Flammulina velutipes (FV) pickled with Mg (CH3COO)(2) for the first time. The resultant biochar FVB-2-900 displays a super hydrophilicity. It also shows specific surface area of 1174.2 m(2)center dot g(-1) and pore volume up to 1.57 cm(3)center dot g(-1). Due to its N, O co-doped hydrophilic surface, the electrode based on it displays a specific capacitance of 470.5 F center dot g(-1) at current density of 0.5 A center dot g(-1) in three-electrode system. Its outstanding energy density of 18.0 Wh center dot kg(-1) is calculated at power density of 0.7004 kW center dot kg(-1) in the electrolyte 1.0 M H2SO4 for the assembled symmetric super-capacitor. Furthermore, a higher energy density of 26.1 Wh center dot kg(-1) at power density of 1.0 kW center dot kg(-1) is recorded in the electrolyte 1.0 M Na2SO4. It also exhibits a good cyclic stability of 100 % retention rate after 10,000 cycles at 5.0 A center dot g(-1). The simple synthesis process, outstanding property, and excellent electrochemical super-capacitor performance make the biochar FVB-2-900 a competitive candidate in the green energy storage.