A bottom-up fabrication for sulphur (S), nitrogen (N) co-doped two-dimensional microporous carbon nanosheets for high-performance supercapacitors and H2, CO2 storage

Abstract

The synthesis of two-dimensional (2D) carbon sheets with sub-nanometer pore-rich microporous morphology and an understanding of the structure–performance relationship are important to develop an advanced device for supercapacitors and gas adsorption. 2D microporous carbon nanosheets with nanometer thickness allow easy mass/ion transport and overcome the problem faced by traditional porous materials. We report a bottom-up method to form 2D S, N-doped microporous carbon nanosheets from simple organic molecules for supercapacitor and gas adsorption applications. The optimized microporous carbon nanosheets prepared at 800 °C (p-CNS-800) possess an average-micropore size of ∼2.2 nm with plenty of sub-nanometer micropores (>1 nm) and provide a high surface area (2847.8 m² g⁻¹) and pore volume (1.32 cm⁻¹). These unique 2D microporous carbon nanosheets and optimal S, N doping allow easy ion diffusion, electron transport, and ion/gas storage. p-CNS-800 showed an ultra-high specific capacitance of 935 F g⁻¹ and 615 F g⁻¹ at 0.5 A g⁻¹ in 1 M H₂SO₄ and 6 M KOH, respectively. The symmetric (p-CNS-800//p-CNS-800) device delivers specific capacitances of 297.4 F g⁻¹ (H₂SO₄) and 296.12 F g⁻¹ (KOH) and 247.2 F g⁻¹ (Na₂SO₄) with excellent cycling stability. The symmetric device delivers an excellent energy density of 31.01 W h kg⁻¹ and a power density of 1720.36 W kg⁻¹. Moreover, S, N-doped 2D-nanosheets showed excellent H₂ and CO₂ uptake. The H₂ uptake of 2D microporous carbon sheets is 2.6 wt% at 77 K under 1 bar pressure whereas CO₂ uptakes are 5.5 mmol g⁻¹ and 2.75 mmol g⁻¹ at 273 and 298 K with selectivity for CO₂/N₂ and CO₂/CH₄ being 21.8 and 2.6 respectively.