Architecture engineering and electronic modulation strategy of copper oxide for boosting nitrate-to-ammonia conversion

Electrocatalytic nitrate reduction (NO3RR) offers a promising strategy for the dual purpose of wastewater denitrification and sustainable ammonia (NH3) production. However, the process involves complex multi-electron and proton-coupled steps, often leading to undesired byproducts. The development of catalysts that can simultaneously deliver high activity and selectivity remains a pressing challenge. Herein, we report a molybdenum-doped copper oxide (Mo0.5-CuO NNs) catalyst featuring a three-dimensional (3D) network structure composed of interwoven one-dimensional nanoneedles. In 0.5 M K2SO4 electrolyte with 50 mM NO3−, the Mo0.5-CuO NNs exhibit exceptional NO3RR performance, achieving an NH3 yield of 23.15 mg h−1 mgcat−1 and Faradaic efficiency (FE) of 97.9% at −0.55 V vs. RHE, with NO2− selectivity suppressed to just 2.17%. Mechanistic investigations from in situ Fourier transform infrared spectroscopy (FTIR) identify a higher proportion of “free water” molecules on the Mo-doped CuO surface than on pristine CuO across all applied potentials. Further kinetic isotope effect experiments combined with density functional theory calculations confirm that Mo doping effectively facilitates the water dissociation process, thereby enabling enhanced proton supply. These findings suggest that the synergistic effect between the 3D network architecture and Mo-induced electronic modulation is identified as the key to achieving both high NH3 yield and high selectivity.