Copper nanowires decorated with TiO_2−x from MXene for enhanced electrocatalytic nitrogen oxidation into nitrate under vacuum assistance

The green synthesis of nitrate (NO₃⁻) via electrocatalytic nitrogen oxidation reaction (NOR) is a promising strategy for artificial nitrogen fixation, which shows great advantages than traditional nitrate synthesis based on Haber–Bosch and Ostwald processes. But the poor N₂ absorption, high bond energy of N≡N (941 kJ·mol⁻¹), and competing multi-electron-transfer oxygen evolution reaction (OER) limit the activity and selectivity. Herein, we fabricated MXene-derived irregular TiO_2−x nanoparticles anchored Cu nanowires (Cu-NWs) electrode for efficient electrocatalytic nitrogen oxidation, which exhibits a NO₃⁻ yield of 62.50 μg·h⁻¹·mg_cat⁻¹ and a Faradaic efficiency (FE) of 22.04%, and a significantly enhanced NO₃⁻ yield of 92.63 μg·h⁻¹·mg_cat⁻¹, and a FE of 40.58% under vacuum assistance. The TiO_2−x/Cu-NWs electrode also shows excellent reproducibility and stability under optimal experimental conditions. Moreover, a Zn-N₂ reaction device was assembled with TiO_2−x/Cu-NWs as an anode and Zn plate as a cathode, obtaining an extremely high NO₃⁻ yield of 156.25 µg·h⁻¹·mg_cat⁻¹. The Zn-nitrate battery shows an open circuit voltage (OCV) of 1.35 V. This work provides novel strategies for enhancing the performance of ambient N₂ oxidation to obtain higher NO₃⁻ yield.