High-ammonia selective metal–organic framework–derived Co-doped Fe/Fe ₂O ₃ catalysts for electrochemical nitrate reduction

Significance

Electrochemical reduction of nitrate pollution in water into value-added ammonium is essential for modern agriculture and industry and represents a potentially sustainable strategy to replace the traditional Haber–Bosch process. However, the nitrate reduction reaction (NO ₃ ⁻RR) process under ambient conditions often suffers from low selectivity. Here, we developed a strategy of tuning an electronic structure for preparing cobalt-doped Fe@Fe ₂O ₃ electrocatalysts. Cobalt doping tunes the Fe d-band center, thereby modulating the adsorption energies of intermediates and suppressing hydrogen production. Therefore, the electrocatalysts exhibit superior NO ₃ ⁻RR activity with a high nitrate removal capacity (100.8 mg N g _cat ⁻¹ h ⁻¹), NH ₃ selectivity (99.0 ± 0.1%), and faradaic efficiency (85.2 ± 0.6%). This strategy provides an approach to design advanced materials for NO ₃ ⁻RR.

Abstract

Ammonia (NH ₃) is an ideal carbon-free power source in the future sustainable hydrogen economy for growing energy demand. The electrochemical nitrate reduction reaction (NO ₃ ⁻RR) is a promising approach for nitrate removal and NH ₃ production at ambient conditions, but efficient electrocatalysts are lacking. Here, we present a metal–organic framework (MOF)–derived cobalt-doped Fe@Fe ₂O ₃ (Co-Fe@Fe ₂O ₃) NO ₃ ⁻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, NH ₃ 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@Fe ₂O ₃ 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.