As an attractive alternative to the Haber−Bosch process, electrochemical process for nitrate (NO3−) reduction to ammonia (NH3) has made great strides in the development of advanced electrocatalysts to suppress the unavoidable H2 evolution reaction (HER) and side production of N2. However, isochronous NH3 separation and recovery from the mother liquor, especially wastewaters, is awfully neglected in state-of-the-art electrochemical system. Here, we designed electrochemical three-phase interfaces constructed by the CoP cathode and flat-sheet gas membrane to achieve NO3− reduction to ammonia and simultaneous NH3 recovery in the form of (NH4)2SO4 from wastewaters. A partial current density for ammonia yield and its recovery rate was 37.3 mA cm−2 and 306 gNH3−N m−2 d−1, respectively, accompanying 100% NO3− removal and 99.7% NH3 extraction. By favoring the originally unfavored side reaction HER, it served as the driving force for NH3 separation from the wastewater through gas stripping and membrane separation at the three-phase interfaces. Unexpectedly, the timely NH3 separation could also promote the reduction of NO3− to ammonia due to the release of much more active sites. From these, we envision that present electrochemical process can be routinely employed as effective strategy to address energy and environmental issues with NH3 recovery from NO3− wastewater.

Favoring the unfavored: Electrochemically selective ammonia extraction from nitrate by coupling electron- and phase-transfer reactions at a three-phase interface

ACS Fall 2021

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