Development of a highly active Fe[sbnd]N[sbnd]C catalyst with the preferential formation of atomic iron sites for oxygen reduction in alkaline and acidic electrolytes.

Fe N C catalyst containing abundant atomic Fe-N x sites is synthesized using a MgCl 2 -assisted synthesis approach. The catalyst delivered an excellent oxygen reduction activity in alkaline and acidic electrolytes with outstanding stability. [Display omitted] • Highly active Fe N C catalyst is synthesized by a simplified salt-assisted approach. • Only a single heat-treatment step is employed to produce a highly active catalyst. • The synthesized Fe N C catalyst consists of atomic Fe-N x sites exclusively. • Optimized catalyst delivers excellent ORR activity in acidic and alkaline media. Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesized via complicated routes involving multiple heat-treatment steps to form the desired Fe-N x sites. We herein developed a highly active Fe N C catalyst comprising of exclusive Fe-N x sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-N x centers, which yielded a high density of electrochemically accessible active sites (1.36 × 1019 sites g−1) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E 1/2) of 0.905 V RHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E 1/2 of 0.760 V RHE is achieved at a low loading level (0.29 mg cm−2). In PEMFC tests, a current density of 2.3 mA cm−2 is achieved at 0.90 V iR-free under H 2 –O 2 conditions, reflecting high kinetic activity of the optimized catalyst. [ABSTRACT FROM AUTHOR]