Tandem catalysis for nitrate reduction to ammonia boosted by CoFe-layered double hydroxide on Cu2+1O nanowires in neutral media

Abstract

Electrochemical conversion of nitrate (NO₃⁻) in wastewater to valuable ammonia (NH₃) under ambient conditions is a facile and competitive route for nitrate remediation. Cu-based catalysts are competitive candidates for the nitrate reduction reaction (NO₃RR) but still face low NH₃ faradaic efficiency and yield rate. Herein, we report a rational design of a tandem electrode, CoFe LDH/Cu₂₊₁O NWs, fabricated by Cu₂₊₁O nanowires (Cu₂₊₁O NWs) covered with CoFe-layered double hydroxide (LDH) that exhibits NH₃ faradaic efficiency and yield rate as high as 95.58% and 7.01 mg h⁻¹ cm⁻², respectively, under neutral conditions at −0.79 V vs. RHE. Combined with the in situ Fourier transform infrared spectroscopy and density functional theory calculations, the mechanism of NO₃RR was revealed, and the contribution of heterogeneous structures to the tandem nitrate reduction process was further explained. The NO₃⁻ was preferably reduced to *NO₂ on Cu₂₊₁O NWs, and then the heterostructure CoFe LDH was associated with the combination of *H and intermediates which advanced the production of NH₃. This work offers a new paradigm for constructing efficient, stable, and energy conservation transition metal composited electrocatalysts in the NO₃RR.