Copper-nickel-MOF/nickel foam catalysts grown in situ for efficient electrochemical nitrate reduction to ammonia.

Abstract

Reducing nitrate (NO₃^-) in an aqueous solution to ammonia under ambient conditions can provide a green and sustainable NH₃-synthesis technology and mitigate global energy and pollution issues. In this work, a CuNi_0.75-1,3,5-benzenetricarboxylic acid/nickel foam (CuNi_0.75-MOF/NF) catalyst grown in situ was prepared via a one-pot method as an efficient cathode material for electrocatalytic nitrate reduction reaction (NO₃RR). The CuNi_0.75-MOF/NF catalyst exhibited excellent electrocatalytic NO₃RR performance at -1.0 V versus a reversible hydrogen electrode, achieving an outstanding faradaic efficiency of 95.88 % and an NH₃ yield of 51.78 mg h^-1 cm^-2. The ¹⁵N isotope labeling experiments confirmed that the sole source of N in the electrocatalytic NO₃RR was the NO₃^- in the electrolyte. The reaction pathway for the electrocatalytic NO₃RR was derived by in situ Fourier transform infrared spectroscopy and in situ differential electrochemical mass spectrometry. Density functional theory calculations revealed that the Ni element in the CuNi_0.75-MOF/NF catalyst had excellent O-H activation ability and strong *H adsorption capacity. These *H species were transferred from the Ni sites to the *NO adsorption intermediates located on the Cu sites, providing a continuous supply of *H to Cu, thereby promoting the formation of *NOH intermediates and enhancing the hydrogenation process of the electrocatalytic NO₃RR.