Activating biomass carbon with metallurgical slag by pyrolysis in molten salt for high-performance supercapacitors

Pyrolysis of sustainable biomass to advanced carbon materials for energy storage is key-enabling in energy and environmental sustainability. However, obtaining carbon materials with well-defined microstructure and composition for high-performance energy storage is extremely challenging. Herein, efficient activation of biomass carbon is realized by introducing extra metallurgical slag during pyrolysis of coconut shell in Na(2)CO(3)–K(2)CO(3) molten salt. The molten salt guides the formation of carbon with a hierarchical honeycomb-like nanostructure, while the metallurgical slag facilitates enhanced doping of the heteroatom species, conjointly contributing to the increase of the specific surface area of carbon materials from 424 m(2) g(−1) to 1451 m(2) g(−1) and the extension of the single N dopant to multiple dopants of N, P, Zn and Co. Such adequate tuning of the microstructure and composition in the pyrolysis product increases the capacitance for supercapacitors from 30 F g(−1) to 135 F g(−1) at 0.5 A g(−1). The results can provide new insights for the controllable upgradation of both biomass and waste industrial slag toward enhanced energy storage.