Selective Reduction of Aqueous Nitrate to Ammonium with an Electropolymerized Chromium Molecular Catalyst

Abstract

Nitrate (NO 3 − ) is a common nitrogen-containing contaminant in agricultural, industrial, and low-level nuclear wastewater that causes significant environmental damage. In this work, we report a bioinspired Cr-based molecular catalyst incorporated into a redox polymer that selectively and efficiently reduces aqueous NO 3 − to ammonium (NH 4 + ), a desirable value-added fertilizer component and industrial precursor, at rates of ∼0.36 mmol NH 4 + mg cat −1 h −1 with >90% Faradaic efficiency for NH 4 + . The NO 3 − reduction reaction occurs through a cascade catalysis mechanism involving the stepwise reduction of NO 3 − to NH 4 + via observed NO 2 − and NH 2 OH intermediates. To our knowledge, this is one of the first examples of a molecular catalyst, homogeneous or heterogenized, that is reported to reduce aqueous NO 3− to NH 4 + with rates and Faradaic efficiencies comparable to those of state-of-the-art solid-state electrocatalysts. This work highlights a promising and previously unexplored area of electrocatalyst research using polymer−catalyst composites containing complexes with oxophilic transition metal active sites for electrochemical nitrate remediation with nutrient recovery.

Metal Doped Unconventional Phase IrNi Nanobranches: Tunable Electrochemical Nitrate Reduction Performance and Pollutants Upcycling

“…Currently, advanced electrocatalysts play a significant role in achieving high selectivity, high productivity, and high energy efficiency toward NH 3 , as nitrate reduction is a quite complex reaction process that involves nine protons and eight electrons. Compared with the nonmetal catalysts and molecular catalysts with adjustable active centers, , metal-based catalysts display superior nitrate reduction performance owing to their high intrinsic activity and abundant catalytically active sites. Among all metal elements, copper (Cu) presents strong affinity toward nitrate due to d -orbital electrons, and Cu is highly effective in promoting nitrate-to-nitrite conversion .…”