Bioinspired Interfacial Hydration Engineering via Metal-Organic Frameworks for Efficient Nitrate-To-Ammonia...

Electrocatalytic nitrate reduction to ammonia (eNO₃RR) offers a promising pathway for sustainable ammonia synthesis but is severely impeded by sluggish proton-coupled electron transfer kinetics and competitive hydrogen evolution, particularly at industrially relevant current densities in neutral media. Herein, we report a bioinspired interfacial hydration engineering strategy by constructing a UiO-66-NH₂ metal-organic framework overlayers on copper electrodes to boost eNO₃RR activity and selectivity. The optimized UiO-66-NH₂@Cu electrode exhibits exceptional performance, achieving a Faradaic efficiency of 98.6% and an ammonia yield rate of 5.02 mmol cm^-2 h^-1, and sustaining an ammonia partial current density exceeding 1 A cm^-2. Combining in situ spectroscopy and molecular dynamics simulations, we elucidate that the UiO-66-NH₂ overlayer reconstructs the interfacial hydration structure and promotes the accumulation of hydrated potassium ions (K⁺·H₂O) within the electrical double layer. Density functional theory calculations reveal that UiO-66-NH₂ effectively adsorbs K⁺·H₂O complexes, leading to preferential interfacial accumulation of this hydrated cation. Crucially, these hydrated cations function as superior proton donors compared to bulk water, significantly lowering the activation barrier for the rate-determining ^*NO₃ to ^*NHO₃ step. This work highlights the interfacial hydration microenvironment in modulating proton-coupled electron transfer, and provides a generalizable design paradigm for efficient electrosynthesis through microenvironment engineering.