Breathing Bimetallic MOF Confined Polyoxometalates for Hydration Layer Loosening and Electronic Redistribution Toward Efficient Nitrate Electroreduction and Zn-Nitrate Batteries.

The traditional Haber-Bosch method suffers from harsh conditions and high energy consumption, while electrocatalytic nitrate reduction to ammonia (ENRA) is a green route for ammonia synthesis and can serve as a cathode reaction for Zn-nitrate batteries. Its development is limited by sluggish intermediate hydrogenation and severe hydrogen evolution reaction (HER). Herein, we develop topology-engineered isomeric polyoxometalate (POM)-confined bimetallic metal-organic framework (MOF) electrocatalysts (NH2-MIL-53, -88, -101). Flexible NH2-MIL-88(FeNi) enables tight encapsulation of [PW12O40]3- (PW12) clusters via the "breathing effect", yielding PW12@NH2-MIL-88(FeNi) with synergistically modulated electronic distribution and proton transfer. Combined experimental and theoretical studies reveal that confined PW12 induces electronic redistribution over Fe/Ni centers, concurrently strengthening NO3 - adsorption on Fe and accelerating *NO2 hydrogenation on Ni. Beyond electronic effects, PW12 loosens the rigid hydration layer and forms conjugated acid-base pairs with MOF amino groups, promoting proton diffusion, boosting *NO2 hydrogenation, and suppressing HER. Thus, PW12@NH2-MIL-88(FeNi) achieves an NH3 yield rate of 20.1 mg h-1 mgcat. -1 with a Faradaic efficiency of 98.6% under neutral electrolytes. When used as a cathode in rechargeable Zn-nitrate batteries, it delivers a peak power density of 13.2 mW cm-2. This study establishes a generalizable paradigm for engineering interfacial proton transport and electronic properties via POM confinement in MOFs.