Decoupling layer metal–organic frameworks via ligand regulation to achieve ultra-thin carbon nanosheets for oxygen reduction electrocatalysis

Abstract

2D imidazole MOFs are considered to be ideal carbon precursors for oxygen reduction reactions owing to their adjustable ligand components and durable coordination mode. Due to the massive electron delocalization in the lamella, the conjugative effect among 2D MOF layers immensely restricts the exposure of catalytic sites after carbonization, which makes the decoupling layer extremely important on the premise of ensuring activity. Herein, atomic thickness ultra-thin zinc-imidazole MOF precursors were prepared through a bottom-up ligand regulated strategy to achieve the aim of lamellar decoupling. The introduction of heterologous ligands excites stable delocalized electrons, resulting in a decrease in the interlayer force of 2D zinc-imidazole MOF precursors. Subsequent salt template-supported ammonia pyrolysis assisted the MOF-derived carbon sheets to grow along the transverse direction and optimize pore size distribution as did the doping nitrogen type. The MOF-derived carbon sheets demonstrated increasing mesopores and fringe graphitic N which could significantly promote the mass transfer and electron transfer speed during the oxygen reduction reaction. In addition, the obtained ultra-thin carbon delivered an outstanding onset potential (0.98 V vs. RHE) and durability (retaining 91% of the initial current after 12000 s of operation), showing tremendous commercial prospects in sustainable energy.