Organic xerogels combined with iron and nitrogen as PGM-free catalysts for the oxygen reduction reaction.

Platinum-group-metal free catalysts have been widely studied in the last decade as an alternative to Pt, employed in fuel cells. Several carbon precursors have been investigated as carbon matrix for iron-nitrogen-carbon (Fe–N–C) catalysts, characterized by a large amount of micropores, fundamental to create Fe-N x -C active sites. Nonetheless, it is also acknowledged that wider pores are needed to facilitate mass transfer of oxygen/water (reagent/product of fuel cells) towards/from the active sites. Organic xerogels are known as easily tunable materials, that allow doping with a variety of heteroatoms. The present manuscript presents an investigation on the use of organic xerogels combined with iron and nitrogen in a single-step to obtain Fe–N-CXG electro-catalysts for the oxygen reduction reaction (ORR) of proton exchange membrane fuel cells. Several features of both organic xerogels and catalysts on the ORR activity are assessed: the textural properties of the organic xerogel, the iron loading of the Fe–N–C catalysts and the effect of acid-leaching of the catalysts. The present study proves the feasibility of using organic xerogels as carbon precursor to obtain PGM-free catalysts in an easy manner and scalable single-step synthesis. Catalysts obtained from organic xerogels synthesized at mildly acid pHs (5.8 and 6), with a nominal iron loading of 2 wt%, and subjected to two sets of acid leaching/thermal treatments, present enhanced catalytic activity towards the ORR. • Organic carbon xerogels are investigated as carbon matrix for Fe–N–C catalysts. • One-step and template-free synthesis of Fe–N–C catalysts is proposed. • Balanced iron doping creates enough active sites without impacting porosity. • Acid/thermal treatments enhance catalysts improving chemical properties. • High mesopore volume organic xerogels (pH 5.8) yield highly active ORR catalysts. [ABSTRACT FROM AUTHOR]