Effect of textures on oxygen reduction electrocatalysis by self-supporting carbons containing multiple iron species from a universal template synthesis

Abstract

Self-supporting porous carbons containing multiple iron species were synthesized through confined carbonization, alkali etching and final anneal by utilizing varied mesoporous silicas, polymerized aniline and iron chloride as the hard template, carbon/nitrogen and iron precursors, respectively. The duplicated carbons containing multiple iron species have mesoporous structures with large pore diameters, pore volumes and specific surface areas. Consequently, all samples showed excellent electrocatalytic activity toward oxygen reduction reaction (ORR) in 0.1 M KOH via 4-electron pathway. The activity order followed PANI-Fe-HT2(MCF) > PANI-Fe-HT2(MCM-48) ≈ PANI-Fe-HT2(KIT-6) > PANI-Fe-HT2(SBA-15) > PANI-Fe-HT2(MCM-41), suggesting that the three dimensional (3D) interconnected mesoporous structures of hard templates are generally more favorable for fabricating high-performing Fe-N-C materials. The highest onset potential (E_onset) and half-wave potential (E_1/2) obtained for the PANI-Fe-HT2(MCF) were 0.99 and 0.86 V, respectively, which even slightly surpass those of Pt/C, probably shedding light on the additional activity contribution of the unique pore structure duplicated from the MCF. The PANI-Fe-HT2(MCF)-based zinc-air battery (ZAB) delivered impressive power density (116.26 mW cm^-2) and specific capacity (788 mAh g_Zn^-1) as well, completely rivaling the Pt/C-based ZAB. The universal method will hold great promise for exploiting efficient Fe-N-C materials in their practical device applications.