Improvement of energy storage characteristics by regulating the"mesoporous carbon/electrolyte"interface with heteroatom doping
Mesoporous carbon doped with multi-heteroatoms for preparing excellent electrode-materials is one of the effective strategies to enhance energy density of supercapacitors.Soybean protein is coagulated by using ferrous sulfate solution and carbonized under inert atmosphere to obtain mesoporous carbon doped with muti-heteroatoms(TFe).The microstructure,surface chemical properties,phase composition,pore structure,and specific surface area of the material are analyzed by using several instruments,such as scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),nitrogen adsorption-desorption analyses.Three electrode-system is adopted for testing electrochemical performance of TFe.Acetylene black,polytetrafluoroethylene,and TFe are mixed evenly and extruded to form a thin sheet.It is tightly pressed onto a stainless-steel sheet mesh(316L,150 mesh)as the working-electrode.A 304-stainless-steel sheet as the counter electrode,Ag/AgCl saturated potassium chloride as the reference electrode,and 6 mol L-1 KOH solution as the electrolyte.A protype supercapacitor is also assembled,activated carbon as the positive electrode material,TFe as the negative electrode material,glass fiber membrane as the separator,and 6 mol·L-1 KOH solution as the electrolyte.They are encapsulated into a CR2030 button-battery case.Performance of this asymmetric supercapacitor is tested by chronopotentiometric technique.Results show that the obtained carbon has a hierarchical pore structure with heteroatom-groups,such as iron,nitrogen,phosphorus,sulfur,and oxygen on its surface.Carbon in the material mainly exists in an amorphous state.The pore size of the material is mainly distributed around 3.7 nm,and its specific surface area is 276 m2·g-1.Iron and phosphorus existing as Fe2P on the mesoporous carbon,provides 58％of the electrochemical specific capacitance for the material,significantly improving the interface-compatibility between mesoporous carbon and aqueous electrolyte.In three-electrode system,6 mol·L-1 KOH electrolyte,electrochemical specific capacitance of mesoporous carbon composite increased by more than 150％,compared to that of undoped-mesoporous carbon.
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