CeO2 Nanoparticles Boosted Fe-N-C Sites Derived from Dual Metal Organic Frameworks toward Highly Active and Durable Oxygen Reduction Reaction

The durability improvement of Fe-N-C electrocatalysts toward acidic oxygen reduction reaction (ORR) remains a grand challenge. H2O2 seriously degrades Fe-N-C sites, which account for a major origin of the low durability. Herein, the growth of hemin decorated zeolitic imidazole framework (hemin-ZIF 8) on preformed Ce-1,3,5-benzenecarboxylic acid (Ce-BTC) metal organic frameworks (MOFs) is reported. Interestingly, the resultant dual MOFs appear to be Ce-BTC nanorods decorated with many hemin-ZIF 8 dodecahedral nanocrystals, well resembling rice panicles. After pyrolysis, CeO2 nanoparticles are evenly distributed in carbonized nanorods and abundant Fe-N-C sites are embedded in shrunk dodecahedra, labeled as Fe-N-C-CeO2. Fe-N-C-CeO2 exhibits a high ORR activity in terms of a half wave potential (E-1/2) of 0.800 V (vs RHE). The high ORR activity is closely correlated with the well exposure of Fe-N-C sites. In addition, the presence of CeO2 leads to a low H2O2 yield of Fe-N-C-CeO2 (2.3%), much lower than that of Fe-N-C (4.3%) by itself in the absence of CeO2. After 5000 potential cycling, the E-1/2 of Fe-N-C-CeO2 degrades 15 mV superior to that of Fe-N-C (42 mV). Moreover, a single cell with Fe-N-C-CeO2 as cathode degrades much slower than that of Fe-N-C (28 000 s vs 7200 s) during chronoamperometric measurements.