Development of a highly active FeNC catalyst with the preferential formation of atomic iron sites for oxygen reduction in alkaline and acidic electrolytes.

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 synthesizedviacomplicated routes involving multiple heat-treatment steps to form the desired Fe-N sites. We herein developed a highly active FeNC catalyst comprising of exclusive Fe-N 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 centers, which yielded a high density of electrochemically accessible active sites (1.36 × 10 sites g) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E) of 0.905 V in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E of 0.760 V is achieved at a low loading level (0.29 mg cm). In PEMFC tests, a current density of 2.3 mA cm is achieved at 0.90 V under H-O conditions, reflecting high kinetic activity of the optimized catalyst.