From supramolecular hydrogels to functional aerogels: a facile strategy to fabricate Fe3O4/N-doped graphene composites

Abstract

This manuscript introduces a simple method to fabricate hybrid aerogels with Fe₃O₄ nanocrystals/nitrogen-doped graphene (Fe₃O₄/N-GAs) through one-shot self-mineralization of ferrocenoyl phenylalanine/graphene oxide (Fc-F/GO) supramolecular hydrogels. We found that GO could trigger a sol–gel transition of Fc-F gelators below the critical gelation concentration and the electron microscopic results revealed that the self-assembled Fc-F fibrils tightly bound onto graphene sheets. Upon hydrothermal reaction, Fc moieties in these fibrils could be locally oxidized to Fe₃O₄ nanocrystals by GO, remaining on the top of reduced GO (RGO) sheets and therefore inhibiting the self-aggregation of graphene nanosheets. After drying, the remains of the supramolecular hybrid hydrogels are presented as the three-dimensional (3D) framework of ultra-thin graphene sheets on which Fe₃O₄ nanoparticles (NPs) are uniformly immobilized as single crystals. Since the new born Fe₃O₄ nanocrystals are closely anchored on the graphene sheets, the as-prepared Fe₃O₄/N-GAs complex shows excellent electrocatalytic activity for the oxygen reduction reaction (ORR, compared to commercial Pt/C). Notably, the Fc-F/GO supramolecular hydrogels act as multifunctional reagents, such as capping agents for preventing graphene nanosheets from stacking and Fe and N sources for Fe₃O₄/N-GAs. We expect that this intriguing strategy can provide a useful archetypical example in designing nonprecious metal oxides/carbon hybrid materials to serve as substitutes for noble metal catalysts.