The carbon yield was about 40.2% at a phosphoric acid/carbon
ratio of 0.25:1, which increased gradually and stabilized at high
range. The same trend has been observed in the chemical activation of carbons (Qasem et al., 2004; Haimour and Emeish, 2006). This phenomenon indicated that if there was not sufficient phosphoric
acid participating in the activation, the carbon precursor would be
heavily consumed without effective development of the pore structure,
implying that phosphoric acid also acted to protect the carbon
skeleton.