Beneficial effects of phosphoric acid as an additive in the preparation of activated carbon fibers from Nomex aramid fibers by physical activation

Activated carbon fibers (ACFs) were prepared by CO2 activation of chars obtained by pyrolyzing Nomex [poly (m-phenylene isophthalamide)], either alone or pre-impregnated with phosphoric acid (impregnation ratio of 7 wt.% H3PO4). The resulting materials were characterized by elemental analysis, X-ray diffraction, SEM-EDX, thermogravimetry and N2 (77 K) and CO2 (273 K) adsorption. Nomex impregnation with phosphoric acid produced an increase in the char yield in pyrolysis (64.1 vs. 53 wt.% without impregnation) and enhanced the reactivity during activation by an almost sevenfold factor. ACFs with BET surface areas as high as 1300 m2 g−1 at burn-off degrees of the order of 40% are obtained from both nonimpregnated and impregnated Nomex.