A simple decagram-scale synthesis of an atomically dispersed, hierarchically porous Fe-N-C catalyst for acidic ORR

Carbons doped with iron and nitrogen (Fe-N-Cs) are highly promising electrocatalysts for energy conversion reactions in the oxygen, nitrogen and carbon cycles. Containing no platinum group metals, they nevertheless compete with platinum-based catalysts in crucial fuel cell reactions, such as oxygen reduction in acid. Yet deployment of Fe-N-Cs in fuel cells requires also a flow-enhancing pore structure, and a scalable synthesis procedure - a rarely-met combination of requirements. We now report such a simple synthesis of over 10 g of an Fe-N-C catalyst with high activity towards oxygen reduction in acid. Atomically-dispersed Fe-N 4 active sites were designed orthogonally and simultaneously with hierarchical micro-, meso- and macroporosity, by exploiting a dual role of magnesium ions during pyrolysis. Combining the "active site imprinting" and "self-templating" strategies in a single novel magnesium iminodiacetate precursor yielded a catalyst with high specific surface area (SSA > 1600 m 2 g −1 ), a flow-enhancing hierarchical porosity, and high relative abundance of the most desirable D1-type Fe-N 4 sites (43%, by Mössbauer spectroscopy at 4.2 K). Despite the relatively low iron contents, the catalysts feature halfwave potentials up to 0.70 V vs. RHE at pH 1 and a mass activity of 1.22 A g −1 at 0.8 V vs. RHE in RDE experiments. Thanks to the simple and scalable synthesis, this active and stable catalyst may serve as a workhorse in academic and industrial research into atomically-dispersed ORR electrocatalysis. A scalable synthesis of magnesium ion imprinted nitrogen-doped carbon allows for facile preparation of large quantities of Fe-N-C, for large-scale fuel cell research.