Hierarchical porous carbon spheres derived from larch sawdust via spray pyrolysis and soft-templating method for supercapacitors

Abstract

Hierarchical porous carbon spheres (PCSs) with a tunable pore structure were prepared from larch sawdust via spray pyrolysis and a soft-templating method. Decomposition of the soft template, i.e., Pluronic F127, in the carbonization step led to formation of a hierarchical porous structure with mesopores and macropores. Swelling of the core, presumably predominantly of the poly(propylene oxide) component, was induced by evaporation of water. This led to the generation of ultra-large mesopores and macropores. The surface morphology and pore structure of the carbon spheres were controlled by varying the F127 concentration. The PCSs morphologies changed from smooth to rough with increasing addition of F127, and the particle sizes became more uniform. When the content of F127 reached 0.075 (ratio of F127/larch-based resin), the prepared PCSs (PCSs-0.075) had structural integrity, a high surface area (760.3 m2 g−1), and a large pore volume (0.59 cm3 g−1), and contained a combination of micropores, macropores, and mesopores. X-ray diffraction and Raman spectroscopy showed that addition of F127 had little effect on the graphitic degree of the samples. Because of its hierarchical pore structure and high surface area, the optimized sample, i.e., PCSs-0.075, gave an excellent electrochemical performance as an electrode material for supercapacitors, with a specific capacitance of 338.8 F g−1 at 0.2 A g−1 and a good rate capability (165.1 F g−1 at 5 A g−1) in 6 M KOH solution. These PCSs with mesopores and macropores, which facilitate penetration of ions into pores, are promising as efficient electrode materials for supercapacitors.