Phase‐Selective NiCo Oxide Electrodes Enable Paired Electrochemical Conversion and Valorization of Nitrogen‐Containing Wastewaters

ABSTRACT Conventional wastewater treatment generally focuses on pollutant removal while consuming energy and recovering little chemical value. Here, we report a phase‐selective Ni‐Co oxide platform for paired electrochemical conversion of nitrogen‐containing contaminants, coupling cathodic acetonitrile (AN) hydrogenation to ethylamine (EA) with anodic hydrazine oxidation to N 2 . Annealing NiCo layered double hydroxide precursor under Ar and in air produces cubic NiCoO 2 and spinel NiCo 2 O 4 , respectively, which exhibit complementary catalytic preferences. NiCoO 2 achieves 90.4%–91.2% Faradaic efficiency toward EA over 50–200 mA cm −2 in 8 wt.% AN, whereas NiCo 2 O 4 approaches 100% Faradaic efficiency toward N 2 over the same current‐density range. Combined in situ spectroscopy and density functional theory calculations reveal that this catalytic complementarity arises from phase‐dependent reaction energetics: NiCoO 2 favors H‐assisted AN hydrogenation while enabling facile EA release, whereas NiCo 2 O 4 promotes hydrazine dehydrogenation and, critically, N 2 desorption and active‐site regeneration. A 100 cm 2 membrane‐electrode assembly maintains 88–93% EA Faradaic efficiency and stable paired operation for 120 h. The paired system was further demonstrated using separately collected industrial wastewaters, together with downstream EA recovery and a preliminary process‐level assessment. These results establish crystal‐phase regulation of reaction and product‐release energetics as a strategy for matching distinct electrode reactions within paired wastewater valorization.