Porous carbon derived from sorghum stalk for symmetric supercapacitors

Abstract

Sorghum stalk based porous carbons (SSCs) have been synthesized through a simple carbonization method at 800 °C used sorghum stalk as carbon precursor and ZnCl₂ as activating agent. The morphology and structure of the SSCs are investigated by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption, Raman spectra and X-ray diffraction. Undergoes activation at optimal amount of zinc chloride (sorghum stalks to ZnCl₂ is 1 : 1), the resulting samples, labeled as SSC1.0 has a porous texture with high specific surface area and efficient ion diffusion channels (1354.7 m² g⁻¹ specific surface areas and 0.765 cm³ g⁻¹ pore volumes), and the sample also has superhydrophilicity characterized by water contact angles. As supercapacitor electrode, it can deliver 216.5 F g⁻¹ specific capacitance at 0.5 A g⁻¹, 75% capacitance retention even at 8 A g⁻¹ in 2 mol L⁻¹ KOH aqueous electrolyte and excellent cyclic stability with 92% capacitance retention after 5000 cycles at 5 A g⁻¹. Moreover, the assembled SSC1.0//SSC1.0 symmetric cell has wide voltage range of 1.8 V, and high energy density in 0.5 mol L⁻¹ Na₂SO₄ aqueous electrolyte.