Highly Efficient Electrochemical Nitrate Reduction to Ammonia in Strong Acid Conditions with Fe2M‐Trinuclear‐Cluster Metal–Organic Frameworks

Efficient, direct, electrocatalytic ammonia production from nitrate in a strong acid environment is possible by using the efficient electron proton conduction capability of the dinitrogen ligand and the metal active site in an Fe-based trinuclear cluster metal–organic framework (MOF).

Abstract

Nitrate-containing industrial wastewater poses a serious threat to the global food security and public health safety. As compared to the traditional microbial denitrification, electrocatalytic nitrate reduction shows better sustainability with ultrahigh energy efficiency and the production of high-value ammonia (NH₃). However, nitrate-containing wastewater from most industrial processes, such as mining, metallurgy, and petrochemical engineering, is generally acidic, which contradicts the typical neutral/alkaline working conditions for both denitrifying bacteria and the state-of-the-art inorganic electrocatalysts, leading to the demand for pre-neutralization and the problematic hydrogen evaluation reaction (HER) competition and catalyst dissolution. Here, we report a series of Fe₂M (M=Fe, Co, Ni, Zn) trinuclear cluster metal–organic frameworks (MOFs) that enable the highly efficient electrocatalytic nitrate reduction to ammonium under strong acidic conditions with excellent stability. In pH=1 electrolyte, the Fe₂Co-MOF demonstrates the NH₃ yield rate of 20653.5 μg h⁻¹ mg⁻¹ _site with 90.55 % NH₃-Faradaic efficiency (FE), 98.5 % NH₃-selectivity and up to 75 hr of electrocatalytic stability. Additionally, successful nitrate reduction in high-acidic conditions directly produce the ammonium sulfate as nitrogen fertilizer, avoiding the subsequent aqueous ammonia extraction and preventing the ammonia spillage loss. This series of cluster-based MOF structures provide new insights into the design principles of high-performance nitrate reduction catalysts under environmentally-relevant wastewater conditions.

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