Facile fabrication of hierarchical porous carbon based on extract separated from coal with outstanding electrochemical performance

Abstract

Due to the abundant accessible pores for ion storage, hierarchical short diffusion paths for ion transport, and high diffusion efficiency through macropores, newly developed hierarchical porous carbons (HPCs) have been attracting much attention as one of the most promising electrode materials for high-performance supercapacitors. However, the large-scale production and practical applications of HPCs are still big challenges. Herein, a novel kind of HPCs were directly synthesized from low-cost extracts of coal by coupling nano MgO template with in situ KOH activation strategy. During the formation of HPCs, nano-MgO not only serves as structure-directing agent to obtain nanosheet structure, but also plays a critical role in determining the porous system and rate performance of HPCs. The HPCs feature interconnected layered structure with developed hierarchical pore system, and have a high specific surface area up to 3347 m² g⁻¹. As electrodes for supercapacitors, the HPCs show a high capacitance of 346 F g⁻¹ at 0.5 A g⁻¹ in 6 M KOH, an excellent rate performance with capacitance remaining at 262 F g⁻¹ at 10 A g⁻¹ and a superior cycle stability with 92% capacitance retention after 5000 cycles at 5 A g⁻¹. The fine capacitive performances of HPCs are ascribed to hierarchical pore system, short paths for ion fast transport and 2D layered graphene sheets, make it a promising electrode candidate for high performance supercapacitors.