Selective Reduction of Aqueous Nitrate to Ammonium with an Electropolymerized Chromium Molecular Catalyst
Maiko J. Askari, Jeremy Kallick, Charles C. L. McCrory
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.