A distinctive unconventional tandem pathway for nitrate-to-ammonia was achieved via [6 + 2]-electron transfer processes of “HNO₃ → *NH₂OH” and “NH₂OH → NH₃” on Co,Fe dual-site conjugated metal organic frameworks.

Abstract

The electrochemical nitrate-to-ammonia reduction reaction (NO₃RR) 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 NO₃RR via an unconventional [6 + 2] electron-transfer tandem pathway. Unlike the traditional [2 + 6] tandem pathway, the Fe sites predominantly reduce NO₃₋ to *NH₂OH intermediate, which subsequently spills over onto the Co sites for further protonation. This unconventional tandem pathway effectively avoids the release of NO₂₋ and guarantees selective NH₃ production. The CoFe-cMOFs achieve 94.3% NH₃-producing Faradaic efficiency with a yield rate of 14.1 mg h⁻¹ cm⁻² in neutral electrolyte. The Zn-NO₃ ⁻ battery prototype incorporating CoFe-cMOFs exhibits 3.6 mW cm⁻² peak power density with stable NH₃ production. This work proposes a mechanistic breakthrough in tandem pathway regulation for selective electrochemical ammonia synthesis.