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

Abstract

ABSTRACT 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 (NH 2 ‐MIL‐53, ‐88, ‐101). Flexible NH 2 ‐MIL‐88(FeNi) enables tight encapsulation of [PW 12 O 40 ] 3− (PW 12 ) clusters via the “breathing effect”, yielding PW 12 @NH 2 ‐MIL‐88(FeNi) with synergistically modulated electronic distribution and proton transfer. Combined experimental and theoretical studies reveal that confined PW 12 induces electronic redistribution over Fe/Ni centers, concurrently strengthening NO 3 − adsorption on Fe and accelerating *NO 2 hydrogenation on Ni. Beyond electronic effects, PW 12 loosens the rigid hydration layer and forms conjugated acid‐base pairs with MOF amino groups, promoting proton diffusion, boosting *NO 2 hydrogenation, and suppressing HER. Thus, PW 12 @NH 2 ‐MIL‐88(FeNi) achieves an NH 3 yield rate of 20.1 mg h −1 mg cat. −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.