High-ammonia selective metal-organic framework-derived Co-doped Fe/Fe₂O₃ catalysts for electrochemical nitrate reduction.

Abstract

Ammonia (NH₃) is an ideal carbon-free power source in the future sustainable hydrogen economy for growing energy demand. The electrochemical nitrate reduction reaction (NO₃^-RR) is a promising approach for nitrate removal and NH₃ production at ambient conditions, but efficient electrocatalysts are lacking. Here, we present a metal-organic framework (MOF)-derived cobalt-doped Fe@Fe₂O₃ (Co-Fe@Fe₂O₃) NO₃^-RR catalyst for electrochemical energy production. This catalyst has a nitrate removal capacity of 100.8 mg N g_cat^-1 h^-1 and an ammonium selectivity of 99.0 ± 0.1%, which was the highest among all reported research. In addition, NH₃ was produced at a rate of 1,505.9 μg h^-1 cm^-2, and the maximum faradaic efficiency was 85.2 ± 0.6%. Experimental and computational results reveal that the high performance of Co-Fe@Fe₂O₃ results from cobalt doping, which tunes the Fe d-band center, enabling the adsorption energies for intermediates to be modulated and suppressing hydrogen production. Thus, this study provides a strategy in the design of electrocatalysts in electrochemical nitrate reduction.