Regulating the spin configuration of FeNC catalysts with CeO2 to enhance their activity and stability in PEMFCs

The application of FeNC catalysts has been hindered by their instability due to the demetalization of the active sites and attacks by H2O2 and superoxide radicals. In this work, CeO2 was introduced into the active sites of single atom (SA)-based FeNC catalyst as a free radical scavenger, and the FeSA/CeO2-NC catalyst showed excellent performance and stability. The half-wave potential of the oxygen reduction reaction (ORR) on FeSA/CeO2-NC was up to 0.815 V vs RHE in acidic media with only 7% decrease after 50 000 s chronoamperometric test. The FeSA/CeO2-NC catalysts showed excellent H2-O2 fuel cell performance with a maximum peak power of 700 mW cm−2, outperforming the FeSA-NC catalyst (300 mW cm−2). DFT calculations revealed that the introduction of CeO2 resulted in a more uniform distribution of the density of states, with a bandgap significantly smaller than that of Fe-N4, thereby exhibiting superior electronic conductivity. Additionally, CeO2 effectively regulated the spin configuration of Fe-N4, transitioning from high spin to intermediate spin states, which facilitated the adsorption of oxygen-containing intermediates from Fe-N4. This work not only elucidated the synergistic mechanism between CeO2 and Fe-N4 sites but also provided new directions for developing non-precious metal ORR catalysts with both high activity and durability.