Fe/N/S-composited hierarchically porous carbons with optimized surface functionality, composition and nanoarchitecture as electrocatalysts for oxygen reduction reaction

- Fe/N/S-composited hierarchically porous carbon materials are realized with PAD as enriched N source.
- FeSO4/PDA ratio plays a promotion role on improving Fe(x)/N/S-PAD's ORR activity.
- Fe(1.5)/N/S-PAD with a trace Fe content down to 1.0 wt.% shows the best catalytic ORR activity.
- The stability during ORR in corrosive alkaline/acidic media for 5000 continuous cycles is achieved.
- The porous structure and surface functionality influences ORR performance greatly.

Non-precious Fe/N/S-composited hierarchically porous carbon materials (Fe(x)/N/S-PAD, PAD: poly(acrylamide-co-diallyldimethyl ammonium chlor), x: the weight ratio of FeSO4 7H2O/PAD) are synthesized using a facile silica colloid template approach with FeSO4 7H2O as Fe and S sources, and PAD as N source, respectively. A simultaneous creation of porous structures and surface functionalities (Fe, N and S) of such catalysts is realized just by simply tuning the weight ratio of FeSO4 7H2O and PAD in the synthetic precursors. As a result, a series of catalyst samples with high oxygen reduction reaction (ORR) activity/stability are obtained, demonstrating the promotion role of FeSO4/PAD ratio in synthesizing high-performing catalysts. Particularly, a catalyst (Fe(1.5)/N/S-PAD) with a trace Fe content down to 1.0 wt.% is tested to be superior to a commercial Pt/C catalyst in alkaline media and exhibits impressive ORR performance in acidic media. Combined with characterization results such as TEM, Raman spectra, BET and XPS analysis, it is found that the well-defined micro- and meso-porous structure play the key role in enhancing catalytic ORR performance rather than the final total N contents in the carbon. Regarding the stability of such a catalyst, test using cyclic voltammetry for 5000 cycles in O2-saturated solution shows a negligible degradation rate when compared with Pt/C one, suggesting that this catalyst could be used for catalyzing the high-performing cathode ORR in proton-exchange membrane fuel cells, alkaline fuel cells and metal-air batteries.

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