One-Step Synergistic Effect to Produce Two-Dimensional N-Doped Porous Carbon Nanosheets with Ultrahigh Porosity from Biomass for High-Performance Supercapacitors

Biomass is an ideal source for the preparation of electrode materials due to its abundant distribution, renewability, and low price. Carbon materials constructed by nitrogen doping can greatly improve the performance of electrode materials, provide additional pseudocapacitance, and expand the application of supercapacitors in practice. Nitrogen-doped walnut shell (WS) carbon materials were prepared by chemical cross-linking and KOH activation using WS and γ-polyglutamic acid as raw materials. The effects of the ratio for carbon and nitrogen source compounds and activation temperature on the morphology, pore structure, graphitization of the carbon materials, and their electrochemical properties were systematically investigated. Nitrogen-doped WS carbon materials possessed a unique 2D lamellar structure and a high specific surface area (1932 m2 g–1). The addition of heteroatoms increased the polarizability and conductivity of the carbon material and introduced additional pseudocapacitance as a result of the good electrochemical performance. At a current density of 0.5 A g–1, the specific capacitance of materials can reach 342.0 F g–1 with a capacitance retention rate of 73% (20 A g–1). After 8000 cycles, the capacitance loss is only 8%, providing excellent electrochemical performance.