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Electrocatalytic nitrate reduction sustainably produces ammonia and alleviates water pollution, yet is still challenging due to the kinetic mismatch and hydrogen evolution competition. Cu/Cu2O heterojunction is proven effective to break the rate‐determining NO3−‐to‐NO2− step for efficient NH3 conversion, while it is unstable due to electrochemical reconstruction. Here we report a programmable pulsed electrolysis strategy to achieve reliable Cu/Cu2O structure, where Cu is oxidized to CuO during oxidation pulse, then regenerating Cu/Cu2O upon reduction. Alloying with Ni further modulates hydrogen adsorption, which transfers from Ni/Ni(OH)2 to N‐containing intermediates on Cu/Cu2O, promoting NH3 formation with a high NO3−‐to‐NH3 Faraday efficiency (88.0±1.6 %, pH 12) and NH3 yield rate (583.6±2.4 μmol cm−2 h−1) under optimal pulsed conditions. This work provides new insights to in situ electrochemically regulate catalysts for NO3−‐to‐NH3 conversion. [ABSTRACT FROM AUTHOR]

Electrocatalytic nitrate reduction sustainably produces ammonia and alleviates water pollution, yet is still challenging due to the kinetic mismatch and hydrogen evolution competition. Cu/Cu2O heterojunction is proven effective to break the rate‐determining NO3−‐to‐NO2− step for efficient NH3 conversion, while it is unstable due to electrochemical reconstruction. Here we report a programmable pulsed electrolysis strategy to achieve reliable Cu/Cu2O structure, where Cu is oxidized to CuO during oxidation pulse, then regenerating Cu/Cu2O upon reduction. Alloying with Ni further modulates hydrogen adsorption, which transfers from Ni/Ni(OH)2 to N‐containing intermediates on Cu/Cu2O, promoting NH3 formation with a high NO3−‐to‐NH3 Faraday efficiency (88.0±1.6 %, pH 12) and NH3 yield rate (583.6±2.4 μmol cm−2 h−1) under optimal pulsed conditions. This work provides new insights to in situ electrochemically regulate catalysts for NO3−‐to‐NH3 conversion. [ABSTRACT FROM AUTHOR]

Selective reduction of nitrate to N 2 is attractive but still a difficult challenge in the water treatment field. Herein, we established a flow-through electrochemical system packed with polymeric beads supported nZVI (nZVI@D201) for selective nitrate reduction. Consequently, efficient nitrate reduction in the flow mode was achieved on nZVI@D201 under electrochemical regulation with N 2 selectivity of up to 95% for at least 60 h. Otherwise, nZVI was gradually exhausted after 20 h, and the product was mainly the undesired NH 4 +. Through a series of comparative experiments, we clarified that the enhanced nitrate reduction on nZVI under electrochemical regulation was mainly attributed to electrons (from cathode) and active hydrogen ([H]) rather than the previously speculated H 2. Combining the characterizations of nZVI during nitrate reduction by X-ray diffraction and X-ray photoelectron spectrometry, we found that nitrate reduction under electrochemical regulation was mediated by nZVI along with the resultant Fe0@Fe x O y -Fe(II) structure and was sustained by electrons (from cathode) and [H] via the in situ reduction of Fe(III) back to Fe(II). Meanwhile, the undesirable product NH 4 + was efficiently oxidized to N 2 by the active chlorine generated on the anode. This study not only clarifies the mechanism of enhanced nitrate reduction on nZVI via electrochemical regulation but also advances the technological coupling of nZVI reduction with electrochemistry. Image 1 • Selective nitrate reduction was achieved in a flow-through electrochemical system. • Nitrate was reduced with N 2 selectivity up to 95% via electrochemical regulation. • Enhanced nitrate reduction was attributed to electrons (from cathode) and [H]. • The study advances technological coupling of nZVI reduction with electrochemistry. [ABSTRACT FROM AUTHOR]