Porous carbon generation by burning starch-based intumescent flame retardants for supercapacitors

Exploring novel methods for preparing porous carbon is essential for developing electrode materials. Herein, a general strategy for preparing porous carbon via flame-burning carbonization of a three-in-one intumescent flame retardant (IFR) is proposed. The IFR comprising biomass (starch, agar, cotton fiber, and cottonseed meal as carbon sources), Zn3(BO3)2 (as an acid source) and K2CO3 (as a gas source) is carbonized directly by a flame gun in 5 min to prepare porous carbon. The carbon layer is formed by esterification, depolymerization, ring opening, polycondensation and aromatization. Concurrently, the molten state of the boron and potassium compounds prevents the carbon from burning out. Benefited from the doping, templating, and activating effects of Zn3(BO3)2 and K2CO3, the samples exhibit a layered porous structure and multi-heteroatom doping, demonstrating excellent capacitive properties. The starch-based K2CO3-glycol-DMSO deep eutectic solvent gel electrolyte is synthesized, and the fabricated solid-state capacitor exhibits high energy density (24.5 Wh kg−1), a large voltage window (2.2 V), and a wide temperature operating range (-25 °C to 75 °C). Moreover, the four types of IFRs are amenable to the proposed burning carbonization method, and it is expected that diverse carbon materials will be synthesized using other IFRs in the future.