Polyformamidine-Derived Non-Noble Metal Electrocatalysts for Efficient Oxygen Reduction Reaction

A facile approach for the template-free synthesis of highly active non-noble metal based oxygen reduction reaction (ORR) electrocatalysts is presented. Porous Fe-N-C/Fe/Fe3C composite materials are obtained by pyrolysis of defined precursor mixtures of polyformamidine (PFA) and FeCl3 as nitrogen-rich carbon and iron sources, respectively. Selection of pyrolysis temperature (700-1100 degrees C) and FeCl3 loading (5-30 wt%) yields materials with differing surface areas, porosity, graphitization degree, nitrogen and iron content, as well as ORR activity. While the ORR activity of Fe-free materials is limited (i.e., synthesized from pure PFA), a huge increase in activity is observed for catalysts containing Fe, revealing the participation of the metal dopant in the construction of active electrocatalytic sites. Further activity improvement is achieved via acid-leaching and repeated pyrolysis, a result which is attributed to the creation of new active sites located at the surface of the porous nitrogen-doped carbon by dissolution of the Fe and Fe3C nanophases. The best performing catalyst, which was synthesized with a low Fe loading (i.e., 5 wt%) and at a pyrolysis temperature of 900 degrees C, exhibits high activity, excellent H2O selectivity, extended stability, in both basic and acidic media as well as a remarkable tolerance toward methanol.