Rational engineering of triple-hierarchical pores in carbon nanospheres for superior organic supercapacitive storage

Abstract

Porous carbon stands out as the most promising electrode material for supercapacitors, whereas a well-designed porous architecture is the key to enhancing supercapacitive performance. This is particularly crucial for organic electrolytes, where larger ion sizes and slower diffusion kinetics require not only electrostatic adsorption but also additional mesoporous and macroporous pathways to enhance ion transport. However, the inherent trade-off between micropore formation and mesopore/macropore development remains challenging to reconcile through conventional templating and activation strategies. Herein, we propose a copolymer soft-template carbonization and physical activation strategy to synthesize nitrogen-doped activated hierarchically porous carbon nanospheres (AHPCN-X) featuring a tri-modal pore distribution. By employing self-assembled copolymers to construct spherical architectures with abundant meso-/macropores, followed by CO₂ activation to regulate the formation of microporous structures and small mesopores within the porous framework, the optimized AHPCN-3 electrode demonstrates outstanding capacitive performance in organic electrolytes, achieving excellent capacitance and rate performance, attributed to the synergistic effects of balanced micropores (charge storage) and mesopores (ion transport), as well as a few macropores (electrolyte reservoir). Furthermore, the assembled symmetric supercapacitor delivers outstanding energy and power densities (41.5 W h kg⁻¹ and 19.5 kW kg⁻¹, respectively), coupled with remarkable cycling stability (89% capacitance retention after 20 000 cycles). This study demonstrates that constructing hierarchical porosity in carbon-based materials is an effective strategy to improve supercapacitor performance.