Effect of Ball-Milling on the Oxygen Reduction Reaction Activity of Iron and Nitrogen Co-doped Carbide-Derived Carbon Catalysts in Acid Media

Iron- and nitrogen-doped carbon-based catalysts are one of the most promising alternatives to platinum-group metal-based ones currently used in the fuel cell industry. Here, we study the effect of ball-milling conditions and compositions of catalyst precursors comprising a silicon carbide-derived carbon (CDC) on the properties of the final catalysts, most importantly their activity toward the oxygen reduction reaction (ORR). Ball-milling rates from 100 to 800 rpm were investigated with 400 rpm proving to be the optimum value. The effect of 1,10-phenanthroline-to-iron ratio in the precursor mixture was also studied, with a 12/1 molar ratio leading to the highest activity. Finally, ZnCl2 addition to the precursor mixture was explored as a pore former during pyrolysis. A ZnCl2-to-CDC mass ratio of 1 resulted in the highest ORR activity. Fe-57 Mossbauer spectroscopy reveals that the iron is atomically dispersed as Fe-N-x moieties. The most active catalyst showed a kinetic current density of 4.6 mA cm(-2) at 0.8 V vs RHE in rotating disk electrode tests and a current density of 18.6 mA cm(-2) at 0.8 V in a single-cell proton exchange membrane fuel cell.