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A porous self-supporting titanium sheet electrode embedded with Cu sites was constructed by anodic oxidation combined with hydrothermal/pyrolysis strategy, and high ammonia yield rate and near 100 % Faradaic efficiency were achieved in the electrocatalytic conversion of nitrate. [Display omitted] • Anodic oxidation tandem hydrothermal/pyrolysis embed Cu sites in porous titanium sheets. • Ammonia yield rate and FE as high as 7292.43 μg h−1 cm−2 and 97.34 %, respectively. • Cu/PTS can efficiently catalyze eNitRR in complex water environments. • Operando ATR-FTIRAS measurements reveal the evolution of NO 3 − to NH 3. • Nitrate hazard concentration can be reduced below the limit value of WHO and US EPA. Electrochemical nitrate reduction synthesis of ammonia can use clean energy to convert low-value nitrate pollutants into high value-added ammonia yield. The development of eNitRR catalyst with high activity, high selectivity and stability is the key to achieve distributed small-scale production of nitrate. In this study, a self-supported catalyst (Cu/PTS) with high catalytic activity (for eNitRR) was constructed by anodic oxidation combined with hydrothermal/pyrolysis strategy to realize the embedding of Cu species on the substrate of porous titanium sheet. The ammonia production rate of Cu/PTS catalyzed eNitRR is as high as 7292.43 μg h−1 cm−2 (−1.0 V vs. RHE), the Faradaic efficiency is close to 100 %, reaching 97.34 %, and isotope labeling and Operando ATR-FTIRAS verified and revealed the fact that NO 3 − to NH 3 , respectively. Density functional theory calculations well reveal the roles of various components in Cu/PTS and reveal the factors for the enhancement of eNitRR performance. Thanks to the self-supporting characteristics of porous titanium sheet and the surface embedding of copper species, Cu/PTS not only have good electrochemical stability when catalyzing eNitRR, but also can drive eNitRR to operate efficiently in complex water environment. While realizing the purification of nitrate wastewater and the synthesis of ammonia, Cu/PTS can be used as a positive electrode to construct a nitrate–zinc battery to realize the dual functions of self-driven ammonia production and external power supply. [ABSTRACT FROM AUTHOR]

Through the chelation effect of 1,10-phenanthroline and the spatial confinement effect of polydopamine-derived nitrogen-doped hollow carbon spheres, sub-nanometer-scale copper active species were constructed, which realized the electrochemical reduction of nitrate to ammonia in a complex water environment and purified nitrate wastewater. [Display omitted] • Double confinement mechanism realizes sub-nanometer-scale copper preparation. • Ammonia yield rate and FE as high as 21413.5 μg h−1 mg cat. −1 and 92.07%, respectively. • CuCN/NHCSs can efficiently catalyze eNitRR in complex water environments. • Nitrate hazard concentration can be reduced below the limit value of WHO and US EPA. Electrochemical-nitrate-reduction-reaction (eNitRR) ammonia synthesis shows the vision of green ammonia synthesis and is also an effective way to purify nitrate wastewater. In this study, the complex of 1,10-phenanthroline and Cu2+ was adsorbed on the surface of polydopamine-derived nitrogen-doped-hollow-carbon-spheres, and sub-nanometer-scale copper species (CuCN/NHCSs) were obtained after heat treatment. Using CuCN/NHCSs as catalyst, the ammonia yield rate and Faradaic efficiency of eNitRR reached 21413.5 μg h−1 mg cat. −1 (−1.1 V vs RHE) and 91.08% (−0.9 V vs RHE), respectively. CuCN/NHCSs still have high catalytic activity for eNitRR even in complex water environments (such as acidity, alkalinity, coexisting ions). In the face of low concentration of nitrate in natural sewage, CuCN/NHCSs as a catalyst can reduce the concentration of NO 3 − to below the limits set by WHO and US EPA within 10 h, and achieve effective purification of nitrate sewage. DFT calculations show that both single-atom Cu sites and Cu atom cluster sites on NHCSs can promote the electrochemical conversion of NO 3 − to ammonia, so minimizing copper sites can maximize the unit activity. Furthermore, the simultaneous anchoring of Cu atom clusters and single-atom Cu in the carbon matrix is beneficial to lower the energy barrier of the potential-determining step of eNitRR. [ABSTRACT FROM AUTHOR]