Tandem Nitrate Electroreduction to Ammonia with Industrial-Level Current Density on Hierarchical Cu Nanowires Shelled with NiCo-Layered Double Hydroxide

Electrochemical conversion of industrial nitrate wastewater to valuable ammonia (NH3) is an attractive method for nitrate removal and NH3 production. However, the energy efficiency is limited by the high reaction overpotential and poor selectivity. Herein, we demonstrate a tandem electrode composed of hierarchical Cu nanowires shelled with NiCo-layered double hydroxide (NiCo LDH/Cu NW) that exhibits an industrial-relevant NH3 partial current density of 570 mA cm(-2) while maintaining a Faradaic efficiency of 94.25% through the nitrate reduction reaction (NO3RR). The practical application of the NO3RR route in simulated wastewater with different NO3- concentrations and in membrane electrode assembly is developed, which demonstrates great potential for industrial application. Furthermore, online differential electrochemical mass spectrometry, in situ Fourier transform infrared spectroscopy, and density functional theory calculations confirm the tandem catalysis mechanism of NiCo LDH/Cu NW, suggesting that the activity of catalysts for NO3RR could be attributed to the synergy effects, in which Cu nanowires would preferentially catalyze the reduction of NO3- to NO2- and then NiCo LDH catalyzes the reduction of NO2- to NH3.