Scalable green synthesis of hierarchically porous carbon microspheres by spray pyrolysis for high-performance supercapacitors

Designing carbon materials with optimized hierarchical pore structures is crucial to realize high-performance electrical double-layer capacitors (EDLCs) with enhanced energy and power densities. Therefore, the development of the suitable synthesis strategies for hierarchically porous carbon (HPC) materials with a higher productivity has attracted significant interest. Here, a facile, economic, scalable, and environmentally friendly method to synthesize hierarchical pore-structured carbon materials by spray pyrolysis without the use of heavy metal salts is presented. A spray solution containing sucrose, NaCl, and H₂SO₄ is aerosolized by an ultrasonic nebulizer and undergoes pyrolysis to produce NaCl-templated carbon microspheres, followed by an activation step and washing to obtain HPC. Endowed with a specific surface area up to 1704 m² g⁻¹ and pore volume of 1.81 cm³ g⁻¹, the resulting carbon contains an interconnected micro/mesoporous network, which provides efficient ion transport channels with a short diffusion length and small ionic resistance. Moreover, it exhibits a specific capacitance of 102 F g⁻¹ at a current density of 30 A g⁻¹ with a retention of 92% over 10,000 cycles at 10 A g⁻¹ as an electrode in an organic-electrolyte-based EDLC. In contrast, the sheer microporous carbon does not exhibit EDLC behavior at a high rate. The proposed synthesis technique paves the way for cheap scalable syntheses of carbon materials with desired pore structures by spray pyrolysis, which may inspire further studies for various applications including energy storage, where carbon materials with high specific surface areas and yields are of significance.