Metal-Organic Frameworks for Electrocatalytic Nitrate-to-Ammonia Conversion: A Review.

This review takes a structure mechanism perspective on active site dynamics and charge transfer pathways governing ammonia selectivity in metal-organic frameworks (MOFs). This review aims to summarize the progress of MOF-based electrocatalysts for nitrate to ammonia conversion, with a focus on structural characteristics, charge transfer behavior, and catalytic activity. The basic principles of nitrate reduction reaction (NO3 -RR) such as reaction thermodynamics, reduction process, and important activity descriptors are presented. The recent developments on pristine MOFs, conductive MOFs, MOF-derived materials and hybrid architectures are summarized and the roles of metal centers, ligand functionalization, defect engineering, heterometallic interactions and interfacial coupling in controlling nitrate adsorption, intermediate stabilization and hydrogenation processes in MOFs are highlighted. Representative MOF based systems achieve NH3 Faradaic efficiencies (FEs) up to about 99% with production rates near 22.5 mg h-1 cm-2 and nitrate conversion approaching 99%. The contribution of theoretical calculations and operando characterization techniques toward understanding reaction mechanisms is discussed. Key bottlenecks include low-intrinsic conductivity, limited structural stability under reducing conditions, uncertain identification of the true active phase during reconstruction, and inconsistent testing protocols across studies. Finally, the current limitations and future research directions for developing stable, conductive, and practically relevant MOF-based NO3 -RR catalysts are critically evaluated.