Realizing Unconventional Tandem Nitrate Reduction for Efficient Ammonia Electrosynthesis Enabled by Co, Fe Dual-Site Conjugated Metal Organic Frameworks.

The electrochemical nitrate-to-ammonia reduction reaction (NORR) offers a sustainable route for carbon-neutral chemical synthesis, while the intricate multi-electron/proton transfer processes and unstable intermediates pose significant challenges in attaining high selectivity and efficiency. This study demonstrates a Co, Fe bimetallic conjugated metal organic frameworks (CoFe-cMOFs) that enable efficient NORR via an unconventional [6 + 2] electron-transfer tandem pathway. Unlike the traditional [2 + 6] tandem pathway, the Fe sites predominantly reduce NO to *NHOH intermediate, which subsequently spills over onto the Co sites for further protonation. This unconventional tandem pathway effectively avoids the release of NO and guarantees selective NH production. The CoFe-cMOFs achieve 94.3% NH-producing Faradaic efficiency with a yield rate of 14.1 mg h cm in neutral electrolyte. The Zn-NO battery prototype incorporating CoFe-cMOFs exhibits 3.6 mW cm peak power density with stable NH production. This work proposes a mechanistic breakthrough in tandem pathway regulation for selective electrochemical ammonia synthesis.