Graphitization induced by KOH etching for the fabrication of hierarchical porous graphitic carbon sheets for high performance supercapacitors

Abstract

Porous graphitic carbons are promising candidates for energy conversion and storage. At present, it is highly desired but remains challenging to construct high-surface-area hierarchical porous graphitic carbons. Herein, graphitic carbon nanosheets with hierarchical pores are easily fabricated from a multifunctional carbonaceous precursor (pentaerythritol melamine phosphate or PMP). The PMP carbonaceous precursor can be readily converted into a 3D macroporous scaffold enclosed by carbon nanosheets via chemical foaming without any sacrificial templates and special drying procedures. Then a subsequent potassium hydroxide chemical activation process dramatically increases the surface area (up to 3853 m² g⁻¹) and porosity (up to 2.79 cm³ g⁻¹). Simultaneously, graphitization of the carbon nanosheets was promoted with increased aromaticity and size of the polyaromatic units via breaking the phosphate ester bonds with KOH etching at a temperature as low as 800 °C. The resulting porous graphitic carbon nanosheets are constructed with an interconnected continuous three-dimensional network surrounded by predominantly multilayer sp²-bonded carbon with a dense nanometer scale pore structure. Due to such synergistic features, the resulting porous graphitic carbon nanosheets deliver 188 F g⁻¹ specific capacitance and excellent rate performance in nonaqueous electrolytes.