Facile Steam-Etching Approach to Increase the Active Site Density of an Ordered Porous Fe–N–C Catalyst to Boost Oxygen Reduction Reaction

Abstract

Developing facile and effective strategies to improve the active site density of transition-metal and nitrogen codoped carbon (M–N–C) catalysts for oxygen reduction reaction (ORR) remains a challenge. Herein, we propose ordered templates and a steam-etching synergetic approach to increase the active site density of Fe–N–C catalysts with interconnected ordered porous structures. The steam etching corrodes inactive amorphous carbon while active sites are well preserved. X-ray absorption fine structure and fitting result reveal the uniform distribution of atomically dispersed Fe–N4 active sites. The steam etching dramatically increases the active site density by 4.6 times, which is verified by the NO adsorption–reduction experiments. As a result, the ORR mass activity of the ordered macroporous Fe–N–C catalyst treated by steam etching at 800 °C (OM–Fe–N–C–steam–800) is 1.8 times higher than that of Ar-protected one. The proton-exchange membrane fuel cell employing the OM–Fe–N–C–steam–800 catalyst delivered an enhanced peak power density of 0.78 W cm–2 compared to that of Ar-protected counterpart (0.63 W cm–2).