Simultaneous gas expansion and nitrogen doping strategy to prepare licorice root residues-derived nitrogen doped porous carbon for supercapacitors

Abstract

Herein, licorice root residues-derived nitrogen doped porous carbon (NP-LRC) has been prepared via a green and scalable simultaneous gas expansion, activation and nitrogen doping strategy using ammonium chloride (NH₄Cl) and potassium hydroxide (KOH) as the mixed activating agent. The decomposition of NH₄Cl to produce ammonia (NH₃) gas can play a dual role of a gas expansion agent and nitrogen source, while the KOH acts as a typical pore-forming agent during the carbonization process. The obtained NP-LRC has a large specific surface area, developed mesoporous structure and high nitrogen doping content (∼4 wt%). As an electrode material for supercapacitors, the NP-LRC exhibits a high specific capacitance of 221 F g⁻¹ at 0.5 A g⁻¹ and excellent rate capability (80.5% capacitance retention even at 20 A g⁻¹). Moreover, the symmetric supercapacitor assembled based on the NP-LRC electrode material and 1 M Li₂SO₄ aqueous electrolyte exhibits an energy density of 11.7 W h kg⁻¹ at a high power density of 450 W kg⁻¹ operated in the voltage range of 1.8 V, and outstanding cyclability of 96% capacitance retention after 10 000 cycles.