The electrochemical nitrogen reduction reaction (NRR), a contributor for producing ammonia under mild conditions sustainably, has recently attracted global research attention. Thus far, the design of highly efficient electrocatalysts to enhance NRR efficiency is a specific focus of the research. Among them, defect engineering of electrocatalysts is considered a significant way to improve electrocatalytic efficiency by regulating the electronic state and providing more active sites that can give electrocatalysts better physicochemical properties. Recently, metal–organic frameworks (MOFs), along with their derivatives, have captured immense interest in electrocatalytic reactions owing to not only their large surface area and high porosity but also the ability to create rich defects in their structures. Hence, they can provide plenty of exposed active sites for electron transfer, NN cleavage, and N2 adsorption to enhance NRR performance. Herein, the concept, the in situ characterizations techniques for defects, and the most common ways to create defects into MOFs have been summarized. Furthermore, the recent advances of MOF‐based electrocatalysts towards NRR have been recapitulated. Ultimately, the major challenges and outlook of defects in MOFs for NRR are proposed. This paper is anticipated to provide critical guidelines for optimizing NRR electrocatalysts.

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Selective hydrogenation of alkynes to alkenes remains challenging in the field of catalysis due to the ease of over-hydrogenated of alkynes to alkanes. Favorably, the incorporation of metal nanoparticles (MNPs) into metal-organic frameworks (MOFs) provides an opportunity to adjust the surface electronic properties of MNPs for selective hydrogenation of alkynes. Herein, we used different metal-O clusters of MOFs to regulate the electronic status of platinum nanoparticles (Pt NPs) toward overhydrogenation, semihydrogenation, and unhydrogenation of phenylacetylene. Specifically, Pt/Fe-O cluster-based MOFs are found to reduce the electronic density on Pt NPs and inhibit the overhydrogenation of styrene, leading to an 80% increase in selectivity toward a semihydrogenation product (styrene). Meanwhile, Cu-O cluster-based MOFs generate high oxidation states of Pt NPs and release Cu 2+ ions, which worked together to deactivate Pt NPs in the hydrogenation reaction entirely. Thus, our studies illustrate the critical role of metal-O clusters in governing chemical environments within MOFs for the precise control of selective hydrogenation of alkynes, thereby, offering appealing opportunities for designing MNPs/MOFs catalysts to prompt a variety of reactions.

The metal nodes, functionalized ligands, and uniform channels of metal–organic frameworks (MOFs) are typically utilized to regulate the catalytic properties of metal nanoparticles (MNPs). However, though the ligand functionalization could impact the properties of the metal nodes and channels, which might further regulate the catalytic activity and selectivity of MNPs, related research in the design of MNP/MOF catalysts was usually neglected. Herein, we synthesized a series of Pt@UiO-66 composites (Pt@UiO-66-NH2, Pt@UiO-66-SO3H, and Pt@UiO-66) with slightly different organic ligands, which enhanced steric hindrance and contributed to multipathway electron transfer in selective hydrogenation of linear citronellal. The selectivity toward citronellol was gradually improved along with the increased size of functional groups (hydrogen, amino groups, and sulfo groups) on organic ligands, which enhanced steric hindrance provided by channels. In addition, the X-ray photoelectron spectroscopy measurements also revealed that the electronic state of Pt NPs was regulated through multipathway electron transfer from Pt NPs to metal nodes, between organic ligands and Pt NPs/metal nodes. Our research proved that the ligand functionalization altered physiochemical properties of the channels and metal nodes, further together managing the catalytic performance of Pt NPs through enhanced steric hindrance and multi-pathway electron transfer.

Through encapsulating functional materials, metal–organic framework (MOF) composites show extraordinary potential in various fields due to the excellent synergistic effects between the host and guests. However, many attractive functional species,...

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