In Situ Clustering of Single-Atom Copper Precatalysts in a Metal-Organic Framework for Efficient Electrocatalytic Nitrate-to-Ammonia Reduction

When serving as a precatalyst, metal-organic frameworks (MOF) usually incur uncontrollable framework collapse in electro-catalysis. Herein, we report an anticollapse MOF-supported single-atom Cu precatalyst for electrocatalytic nitrate-to-ammonia reduction reaction (NARR), which can be applied in the rechargeable ammonia energy storage (RAES) technology. In situ X-ray absorption spectroscopy (XAS) revealed the association of the formation of real catalytic sites with the in situ clustering of single-atom Cu during NARR. Notably, the noncollapse MOF can afford the confined space to prevent the excessive aggregation of Cu atoms, leading to uniform ultrasmall nanoclusters (ca. 4 nm). Moreover, it achieves a maximal Faradaic efficiency toward NH3 of 85.5%, a formation rate of NH3 of 66 mu mol h(-1) cm(-2), and a specific activity of 53.43 mg(NH3) h(-1) mg(Cu)(-1) in 5 mM NO3- solution. The specific activity is found to be at least 3.3 times higher than that of other reported Cu-based catalysts. Density function theory (DFT) calculation further confirms the size effect and the host-guest interaction in facilitating the NO3- activation and the reaction energy decrease. Besides, it also exhibits a high selectivity of ammonia-to-nitrate of 93.3%, displaying great potential in RAES technology.

Automated summary

A noncollapse metal-organic framework (MOF) supported single-atom Cu precatalyst has been developed for electrocatalytic nitrate-to-ammonia reduction reaction (NARR). The unique MOF structure prevents framework collapse and allows the formation of uniform ultrasmall nanoclusters, resulting in high catalytic activity and selectivity. Density function theory (DFT) calculation confirms the size effect and the host-guest interaction in facilitating the reaction.