Electrochemically reconstructed copper-polypyrrole nanofiber network for remediating nitrate-containing water at neutral pH

As the main nitrogen-containing pollutant of agricultural and industrial wastewater, nitrate (NO3−) is obtainable from the natural nitrogen cycle and industrial emission. Recovering nitrogen (N) from nitrate-polluted wastewater to produce ammonia (NH3) is a promising route to mitigate pollution risks and create economic values. Since nitrate polluted wastewater always exists in acidic or neutral form, electrocatalytic nitrate conversion in neutral electrolytes is convenient for following treatments. Herein, we report an in-situ electrochemical reconstructed nanofiber-like Polypyrrole-Copper (PPy-Cu-E) 3D network for high-efficient NO3− reduction to NH3 in the neutral electrolyte (pH =7.5). In the presence of NO3−, the electrochemical reconstruction process endowed PPy-Cu-E with compactly arranged Cu nanocrystals on its nanofibers and remarkably improved electrochemical active surface area. In flow cell, the PPy-Cu-E achieved a high NH3 yield rate (0.588 mmol mgcat h−1) at a relatively low overpotential (−0.61 V vs. RHE) with 91.95 ± 1% Faradaic efficiency. By employing authentic electroplating wastewater (pH = 7.4) as a catholyte, 93 % of NO3−-N could be converted in 10 h. This work demonstrated the feasibility of high-yield electrocatalytic conversion from nitrate to ammonia under relatively low overpotential in neutral electrolytes and provided a promising method for N-recovery from nitrate wastes.