Robust fused aromatic pyrazine-based two-dimensional network for stably cocooning iron nanoparticles as an oxygen reduction electrocatalyst

Abstract

Fused aromatic (FA) porous organic networks (PON) have unique properties including structural diversity, low density, thermal and chemical stability, and are gaining extensive attention in the scientific community. Here, we report a new FA-PON formed by polycondensation between triphenylene hexamine (TPH) and hexaketocyclohexanone (HKH) octahydrate. The structure and properties of the FA-PON were characterized by various techniques, which showed the chemical formula of the repeating unit to be C24N6 (C4N1), with good thermal and chemical stability. The hole-to-hole distance of the FA-PON was 0.994 nm and each hole contained 6 nitrogen atoms, allowing the efficient fixation and encapsulation of iron (Fe) nanoparticles, and formation of a durable indirect-contact catalyst for the oxygen reduction reaction (ORR). The Fe nanoparticles on the FA-PON (Fe@FA-PON) catalyst displayed high electrocatalytic activity with durability in both acidic and alkaline media. Moreover, the catalyst exhibited unusual ORR activity with a half wave potential of 0.884 V, which is a 38 mV positive shift compared to commercial platinum on activated carbon (Pt/C) catalyst in alkaline medium.