Graphene oxide, a two-dimensional aromatic scaffold decorated by oxygen-containing functional groups, possesses rich chemical properties and may present a green alternative to precious metal catalysts. Graphene oxide-based carbocatalysis has recently been demonstrated for aerobic oxidative reactions. However, its widespread application is hindered by the need for high catalyst loadings. Here we report a simple chemical treatment that can create and enlarge the defects in graphene oxide and impart on it enhanced catalytic activities for the oxidative coupling of amines to imines (up to 98% yield at 5 wt% catalyst loading, under solvent-free, open-air conditions). This study examines the origin of the enhanced catalytic activity, which can be linked to the synergistic effect of carboxylic acid groups and unpaired electrons at the edge defects. The discovery of a simple chemical processing step to synthesize highly active graphene oxide allows the premise of industrial-scale carbocatalysis to be explored.

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Graphene oxide (GO) sheets are emerging as a new class of carbocatalysts. Conventionally, researchers exfoliate graphite oxide into submicrometer-sized, water-dispersible flakes to produce these sheets. The presence of oxygen functional groups on the aromatic scaffold of GO allows these sheets to mediate ionic and nonionic interactions with a wide range of molecules. GO shows remarkable catalytic properties on its own and when hybridized with a second material. It is a perfect platform for molecular engineering. This Account examines the different classes of synthetic transformations catalyzed by GO and correlates its reactivity with chemical properties. First, we raise the question of whether GO behaves as a reactant or catalyst during oxidation. Due to its myriad oxygen atoms, GO can function as an oxidant during anaerobic oxidation and become reduced at the end of the first catalytic cycle. However, partially reduced GO can continue to activate molecular oxygen during aerobic oxidation. Most importantly, we can enhance the conversion and selectivity by engineering the morphology and functionalities on the G/GO scaffold. GO can also be hybridized with organic dyes or organocatalysts. The photosensitization by dyes and facile charge transfer across the graphene interface produce synergistic effects that enhance catalytic conversion. Using GO as a building block in supramolecular chemistry, we can extend the scope of functionalities in GO hybrids. The presence of epoxy and hydroxyl functional groups on either side of the GO sheet imparts bifunctional properties that allow it to act as a structural node within metal-organic frameworks (MOFs). For example, known homogeneous molecular catalysts can be anchored on the GO surface by employing them as scaffolds linking organometallic nodes. We have demonstrated that porphyrin building blocks with GO can lead to facile four-electron oxygen transfer reactions. We have also evaluated the advantages and disadvantages of GO as a catalytic material relative to other types of catalysts, both metallic and nonmetallic. Researchers would like to increase the potency of GO catalysts because many catalytic reactions currently require high loading of GO. Further research is also needed to identify a low-cost and environmentally friendly method for the synthesis of GO.

Lithium−sulfur (Li−S) batteries suffer from multiple complex and often interwoven issues, such as the low electronic conductivity of sulfur and Li 2 S/Li 2 S 2 , shuttle effect, and sluggish electrochemical kinetics of lithium polysulfides (LiPSs). Guided by theoretical calculations, a multifunctional catalyst of isolated single-atom nickel in an optimal Ni−N 5 active moiety incorporated in hollow nitrogen-doped porous carbon (Ni−N 5 /HNPC) is constructed and acts as an ideal host for a sulfur cathode. The host improved electrical conductivity, enhanced physical-chemical dual restricting capability toward LiPSs, and, more importantly, boosted the redox reaction kinetics by the Ni−N 5 active moiety. Therefore, the Ni−N 5 /HNPC/S cathode exhibits superior rate performance, long-term cycling stability, and good areal capacity at high sulfur loading. This work highlights the important role of the coordination number of active centers in single-atom catalysts and provides a strategy to design a hollow nanoarchitecture with single-atom active sites for high-performance Li−S batteries.

Single Fe atom dispersed carbon nanostructures show promising oxygen reduction reaction (ORR) activities for renewable energy applications. Nevertheless, the microenvironment of the single Fe atoms needs to be further engineered to optimize the catalytic performance, which is challenging. In this work, we develop a NaCltemplate pyrolysis method to fabricate single Fe atom catalysts with atomically dispersed Fe−heteroatom (N, S) bridge sites anchored on carbon nanosheets. The N and S coordinated Fe atomic sites (FeN 3 S) are found to induce charge redistribution, lowering the binding strength of oxygenated reaction intermediates and leading to fast reaction kinetics and good oxygen reduction activity. Our work provides an effective method to regulate the microenvironment of single-atom catalysts for optimizing electrocatalytic performance.