The release of nitrate to the environment from wastewater effluent and agricultural runoff contributes to groundwater contamination, harmful algal blooms, and disruption of biogeochemical nitrogen flows. Nitrate conversion via electrochemical reduction can eliminate the production of concentrated waste streams while avoiding the addition of reductant or hole scavenger chemicals. However, major challenges for nitrate removal from water via electrochemical conversion involve reducing the use of expensive precious metal electrocatalysts while also improving the reaction activity and selectivity, stability, and mass transport of nitrate to electrocatalyst active sites. The use of electrochemical membranes (EMs) as multifunctional porous flow-through electrodes could potentially address these challenges based on improved mass transport and altered kinetics under flow conditions within membrane pores.  Conductive membranes were fabricated using polymers combined with carbonaceous materials such as carbon nanotubes and water as a solvent. The EMs showed significantly higher nitrate removal efficiency during electrified filtration compared to flow-by mode. The small pore sizes in the membrane reduced the diffusional boundary layer by several orders of magnitude with respect to flow-by mode, overcoming diffusional mass transport limitations. During electro-filtration, the nitrate conversion activity was easily controlled by tuning the permeate flow rate, regardless of applied potential. These enhancements and tunability demonstrate key advantages of employing membranes with pore sizes of &lt; 1 µm as flow-through electrodes compared to conventional 2D electrodes and 3D electrodes with larger pore sizes. Additionally, the EMs demonstrated tunable levels of nitrate removal with product selectivity to N<sub>2</sub> of over 80% and without showing loss of stability over a period of at least 8 h. The mechanically-flexible membranes provide an advanced electrochemical water treatment architecture involving inexpensive materials and green synthesis methods. Beyond the environmental impacts of closing the nitrogen loop by converting nitrate into N<sub>2</sub>, selective nitrate reduction to ammonia may provide opportunities for recovery as fertilizer or carbon-free renewable energy storage.

Nitrate reduction enhancements using electrified membrane filtration

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