Dual optimization strategy to construct hierarchical reticulated porous framework with enriched Fe-NX active species for the highly efficient oxygen reduction reaction

Abstract

Proton exchange membrane fuel cells (PEMFCs) are severely restricted by slow cathodic oxygen reduction reaction (ORR) kinetics and expensive noble metal platinum catalysts. In particular, the ORR serves as a key process in electrochemical conversion, which significantly impacts the overall performance of the related devices. Accordingly, we proposed a facile and novel dual-optimization strategy to construct abundant Fe-NX active site embedded hierarchical reticulated porous structure catalysts. Initially, an extensive encapsulated Fe and Fe–N complexes is created in Fe modified zeolitic-imidazolate-frameworks-8/graphene oxide (Fe-ZIF-8/GO) precursor, subsequently, the thermal melting and restructuring process fosters the structural transformation of the precursor to robust and open nano-porous frameworks. In the meanwhile, the encapsulated Fe in the pores of the precursors and the pre-existing Fe–N coordination structures are converted into new Fe-NX active sites. This approach realizes the dual optimization of Fe-NX active site density enhancement and utilization, making the optimal catalyst Fe and N-doped porous carbon/graphene nanosheets-1 (Fe-NPC/GNs-1) exhibits a half-wave potential (E1/2) of 0.771V under acidic medium, and E1/2 of 0.917 V toward the ORR in alkaline conditions. The activity and stability under alkaline conditions exceed even that of commercial Pt/C (with negligible potential decay after 10,000 cycles under alkaline conditions), and also showed its capacity to substitute platinum-based catalysts and the potential application in Zn−air batteries.