Convenient and large-scale synthesis of nitrogen-rich hierarchical porous carbon spheres for supercapacitors and CO₂ capture

Highlights: • Convenient and large-scale synthesis route for N-doped hierarchical porous carbon sphere. • The resultant own spherical morphology, tunable hierarchical porosity, high surface area. • The optimal material exhibits a high CO₂ capture capacity of 4.23 mmol g⁻¹. • It shows a large voltage window of 1.8 V for symmetric cell in 0.5 M Na₂SO₄. - Abstract: Herein, considering the great potential of nitrogen-doped hierarchical porous carbons in energy storage and CO₂ capture, we designed a convenient and easily large-scale production strategy for preparing nitrogen-doped hierarchical porous carbon sphere (NHPCS) materials. In this synthesis route, spherical resorcinol-formaldehyde (RF) resins were selected as carbon precursor, and then the ZnCl₂-impregnated RF resin spheres were carbonized in a NH₃ atmosphere at a temperature range of 600–800 °C. During the one-step heat-treatment process, nitrogen atom could be efficiently incorporated into the carbon skeleton, and the interconnected and hierarchical pore structure with different micro/mesopore proportion could be generated and tuned by adjusting the activating agent ZnCl₂ dosage and carbonization temperature. The resultant nitrogen-doped hierarchical porous carbon sphere materials exhibited a satisfactory charge storage capacity, and the optimal sample of NHPCS-2-8 with a high mesopore proportion obtained at 800 °C with a ZnCl₂/RF mass ratio of 2:1 presented a specific capacitance of 273.8 F g⁻¹ at a current density of 0.5 A g⁻¹. More importantly, the assembled NHPCS-2-8-based symmetric capacitor displayed a high energy density of 17.2 Wh kg⁻¹ at a power density of 178.9 W kg⁻¹ within a voltage window of 0 ∼ 1.8 V in 0.5 M Na₂SO₄ aqueous electrolyte. In addition, the CO₂ capture application of these NHPCS materials was also explored, and the optimal sample of NHPCS-0-8 with a large micropore proportion prepared at 800 °C exhibited an exceptional CO₂ uptake capacity at ambient pressures of up to 4.23 mmol g⁻¹ at 0 °C.