Electrocatalytic Reduction of Nitrate Using Magnéli Phase TiO₂ Reactive Electrochemical Membranes Doped with Pd-Based Catalysts

This research focused on synthesis, characterization, and application of point-of-use catalytic reactive electrochemical membranes (REMs) for electrocatalytic NO 3 – reduction. Deposition of Pd–Cu and Pd–In catalysts to the REMs produced catalytic REMs (i.e., Pd–Cu/REM and Pd–In/REM) that were active for NO 3 – reduction. Optimal performance was achieved with a Pd–Cu/REM and upstream counter electrode, which reduced NO 3 – from 1.0 mM to below the EPAs regulatory MCL (700 μM) in a single pass through the REM (residence time ∼2 s), obtaining product selectivity of <2% toward NO 2 – /NH 3 . Nitrate reduction was not affected by dissolved oxygen and carbonate species and only slightly decreased in a surface water sample due to Ca 2+ and Mg 2+ scaling. Energy consumption to treat surface water was 1.1 to 1.3 kWh mol –1 for 1 mM NO 3 – concentrations, and decreased to 0.19 and 0.12 kWh mol –1 for 10 and 100 mM NaNO 3 solutions, respectively. Electrocatalytic reduction kinetics were shown to be an order of magnitude higher than catalytic NO 3 – reduction kinetics. Conversion of up to 67% of NO 3 –, with low NO 2 – (0.7—11 μM) and NH 3 formation (<10 μM), and low energy consumption obtained in this study suggest that Pd–Cu/REMs are a promising technology for distributed water treatment.