Unlocking a Water Coordination Environment in Co-Based Metal-Organic Frameworks for Advanced Nitrate-to-Ammonia Electroreduction.

Electrochemical nitrate reduction to ammonia (e-NO3RR) offers a promising and sustainable alternative to the traditional Haber-Bosch process, enabling decentralized ammonia production under ambient conditions. However, the efficiency of e-NO3RR is limited by the sluggish reaction kinetics due to the high activation energy barriers, poor mass transport, and the weaker adsorption affinity of the catalyst surface. In this study, we report the design and synthesis of a stable three-dimensional cobalt-based metal-organic framework (HUST-38), constructed from benzene-1,4-dicarboxylate ligand and DABCO, featuring water coordination within its framework. Impressively, the as-prepared HUST-38 delivers a high NH3 Faradaic efficiency of 95.7% and a high NH3 yield rate of 13.38 mg h-1 mgcat-1 at -0.6 V vs RHE, significantly outperforming the control sample of HUST-39 (3.98 mg h-1 mgcat-1, nonwater coordination) and the mostly reported single-site solid electrocatalysts. Various in situ measurements disclose that the labile solvent coordination in HUST-38 promotes water molecule accessibility to the catalytically active metal centers, hence augmenting localized *H enrichment and enhancing NO3- reduction. The theoretical calculations further substantiate the essential function of metal coordination microenvironments in modulating the electrocatalytic process, specifically by reducing free energy barriers associated with key reaction intermediates and enhancing the adsorption and desorption kinetics of reactants and products, ultimately leading to improved electrocatalytic activity and efficiency. The present work provides a foundation for the structural design of metal organic frameworks to develop efficient electrocatalysts.