Atomically dispersed Fe–N4 sites activated 3D-on-2D derived porous carbon structure toward superior oxygen reduction reaction

Abstract

The oxygen reduction reaction (ORR) is a crucial step in the energy transformation devices, which requires the fabrication of a cost-effective and energy-efficient Fe single-atom catalyst (SAC) to substitute platinum. However, achieving a controllable synthesis of Fe SAC is a formidable challenge. In this study, a Fe SAC with a novel 3D-on-2D architecture was fabricated by coating 3D metal-organic frameworks (MOFs) over the surface of 2D reduced graphene oxide (rGO). In-situ combining MOF and rGO in a composite structure by adjusting their weight proportion is a key to preparing an active 3D-on-2D structured catalyst with FeN4 active sites. Thanks to the favorable conductivity of the 2D rGO-derived carbon structure and the 3D MOF structure exposing an enhanced density of FeN4 sites, FeNC@rGO-2 demonstrates exceptional ORR activity. It performs more effectively than commercial Pt/C, exhibiting excellent half-wave potentials of 0.887, 0.705, and 0.741 V in alkaline, neutral, and acidic solutions respectively. Impressively, FeNC@rGO-2 exhibits excellent stability and methanol tolerance. When FeNC@rGO-2 is assembled as cathode catalyst in Zinc-air batteries (ZAB) and microbial fuel cells (MFC), FeNC@rGO-2-ZAB reveals outstanding power density (393 mW cm−2) and good charge/discharge cycling stability. Amazingly, FeNC@rGO-2-MFC also shows superior power density (2810 ± 19 mW m−2) and efficiency of electron recovery. This study reveals that FeNC@rGO-2 has extremely high application value in energy conversion devices oriented for alkaline and neutral electrolytes.