Chemical blowing strategy synthesis of nitrogen-rich porous graphitized carbon nanosheets: Morphology, pore structure and supercapacitor application

Herein, we proposed a cost-efficient strategy to prepare nitrogen-doped porous graphitized carbon nanosheets, i.e. urea-assisted chemical blowing via foaming starch into the bubble networks of starch-derived polymers combining catalytic graphitization and subsequent KOH activation. In this synthesis route, starch acts as carbon precursor and foaming agent to build a bubble network of polymer, urea acts as nitrogen source and blowing agent to further blow bubble to form N-doped sheet-like carbons with ultrathin structure, γ-Fe2O3 serves as a graphitization catalyst precursor to generate highly graphitized framework. Importantly, the thickness of sheets, the nitrogen content and the graphitization degree can be simply tuned by adjusting the mass ratio of urea/γ-Fe2O3/KOH. The optimal sample exhibited uniform sheet-like morphology with a thickness of ∼80 nm, a high surface area of 2129.8 m2 g−1, and a large pore volume of 0.97 cm3 g−1. Acting as an electrode for supercapacitor in 6 M KOH electrolyte, it presented a high specific capacitance of 337.6 F g−1 at 0.5 A g−1. Moreover, the two-electrode symmetric cell was assembled in 1 M TEABF4/AN, and displayed a high energy density of 27.5 Wh kg−1 as well as an excellent cycling stability with 87.6% retention after 5000 cycles.