NaBH4-assisted reconstruction of binary micro-domains on a Cu electrode for the selective production of green ammonia

Abstract

It is of both ecological and economic benefit to convert the pollutant nitrate (NO₃⁻) into valuable NH₃ via electrochemical nitrate reduction (NO₃RR) technology. Here, a grain-assembled Cu₂O–Cu nanowires/copper foam (Cu₂O–Cu NWs/CF) electrode for NO₃RR was developed via a NaBH₄-assisted reconstruction process. The optimized Cu₂O–Cu NWs/CF showed a superb NH₃ yield of 318.46 μmol h⁻¹ cm⁻² with a faradaic efficiency up to 98.53%, surpassing the performance of other Cu electrodes. The grain-assembled Cu₂O–Cu NWs/CF with larger surface areas caused more NO₂⁻ to be further converted into NH₃, and thus, the selectivity toward NH₃ remained near 100% in consecutive recycling. More importantly, in situ ATR-FTIR spectroscopy and density functional theory (DFT) calculations were executed for real-time tracking of the NO₃RR intermediates and for exploring the catalytic mechanism over the Cu electrode. The vital intermediate *NO, which is involved in the NH₃ selectivity, was hydrogenated to form *NOH with a much lower ΔG at Cu₂O–Cu sites (0.096 eV) than Cu–Cu₂O sites (0.617 eV). The Cu phase in the Cu₂O–Cu NWs/CF predominated in the NO₃RR, whereas Cu₂O phase favored the dissociation of H₂O into H* for deoxygenation and hydrogenation in NO₃RR. This work developed an advanced Cu electrode assembly for selective NH₃ production and shed light on the tandem mechanism at binary domains in NO₃RR catalysis.