Facile synthesis of nitrogen-doped carbon nanosheets with hierarchical porosity for high performance supercapacitors and lithium–sulfur batteries

Abstract

Magnesium citrate and potassium citrate are two commonly used food additives in our daily life. Herein, we prepared nitrogen-doped hierarchical porous carbon nanosheets (N-HPCNSs) through direct pyrolysis of their mixtures and subsequent NH₃ treatment. The as-prepared N-HPCNS shows hierarchical porosity (specific surface area of 1735 m² g⁻¹ and pore volume of 1.71 cm³ g⁻¹), and a moderate nitrogen doping of 1.7%. Moreover, it can be effectively applied in various energy storage/conversion systems. When used as supercapacitor electrodes, it shows a high specific capacitance of 128 F g⁻¹ in organic electrolytes and retains 45% of the original capacitance even at an ultrahigh current density of 100 A g⁻¹. It can also serve as an effective sulfur carrier in lithium–sulfur batteries. The N-HPCNS/sulfur cathode shows high discharge capacities of 1209 mA h g⁻¹ at 0.2C and 493 mA h g⁻¹ even at 4C. Over 500 charge/discharge cycles at 1C, it still retains a high discharge capacity of 486 mA h g⁻¹ with an ultralow capacity loss of 0.051% per cycle and a high average coulombic efficiency of 99.4%.