Gas Phase‐Heat Absorption‐Condensate Phase Stepwise Flame Retardant Strategy to Prepare Coal Tar Pitch‐Based Porous Carbon for Supercapacitor

Abstract Porous carbon is widely used in energy storage‐conversion systems, and the question of how to explore an efficient strategy for preparation is very significant. Herein, the flame retardant capability of (NH 4 ) 2 SO 4 /Mg(OH) 2 that contains gas phase‐heat absorption‐condensate phase components is assisted to carbonize coal tar pitch in air and obtain the porous carbon. The mechanism of stepwise inflaming retarding is systematically investigated. In the carbonization process in a muffle furnace, (NH 4 ) 2 SO 4 decomposes releasing gases at below 400 °C to act as the role of gas phase flame retardant. Mg(OH) 2 starts to decompose at ≥ 400 °C, and it has the effect of heat absorption and condensed phase flame retardation (MgSO 4 and MgO). What's more, the flame retardant also serves as an N, S source and template. The obtained porous carbon possesses an ultrahigh carbon yield of 56.9 wt.%, hierarchical pore structure, and multi‐heteroatoms doping. It can still reach up to 244.7 F g −1 even loaded 20 mg of active material. In addition, the (NH 4 ) 2 SO 4 /agar gel electrolyte is synthesized, and the fabricated flexible ammonium ion capacitor exhibits a superior energy density of 40.8 Wh kg −1 . This work uncovers a new way to construct porous carbon, which is expected to synthesize more carbon materials using other carbon sources.