Improving Fuel Cell Performance of FeN_<i>x</i>-Based Catalysts by Introducing Graphitic Microdomains in the Carbon Matrix.

Abstract

Breaking the known activity-stability trade-off is essential for the broad implementation of Fe-N-C catalysts in fuel cells. Here, we report the development of an atomically dispersed Fe-N-C catalyst with highly active FeN_<i>x</i> sites on carbon support with dispersed graphitic microdomains (FeN_<i>x</i>-Gmd), which were generated during the Fe₃C-catalyzed graphitization. The introduction of graphitic microdomain makes the FeN_<i>x</i>-Gmd exhibit outstanding oxygen reduction reaction activity when used as a cathode catalyst in practical fuel cells, with impressive peak power densities of 1.06 and 0.55 W cm^-2 under 150 kPa_abs H₂/O₂ and H₂/air, respectively. Both power densities proved that the FeN_<i>x</i>-Gmd were among the top five best-reported non-PGM-based catalysts. Theoretical calculations suggested the FeN_<i>x</i> sites supported on carbon structure with fewer defects, corresponding to a higher graphitic degree, showing higher activity compared to the one with more defects. Moreover, the improvement in catalyst activity does not compromise stability since graphitic microdomains enhanced the corrosion resistance of the carbon support. As a result, after 10000 cycles of accelerated stability test, the FeN_<i>x</i>-Gmd can still deliver a peak power density of 0.79 W cm^-2 in the H₂/O₂ test, which was even higher than many catalysts at the initial stage. Unlike the reported strategy of reducing the ratio of more active but less stable pyrrolic N-coordinated Fe (S1) sites, this study provided an alternative pathway for breaking the activity-stability trade-off of the Fe-N-C catalyst without significantly reducing the ratio of S1 sites.