posted on 2024-01-18, 08:03authored byYifan Ren, Shijie You, Ying Wang, Jianping Yang, Yanbiao Liu
The
electrocatalytic nitrate reduction reaction (NO3RR) has
recently emerged as a promising technique for readily converting
aqueous nitrate (NO3–) pollutants into
valuable ammonia (NH3). It is vital to thoroughly understand
the mechanism of the reaction to rationally design and construct advanced
electrocatalytic systems that can effectively and selectively drive
the NO3RR. There are several natural enzymes that incorporate
molybdenum (Mo) and that can activate NO3–. Based on this, a cadmium (Cd) single-atom anchored Mo2TiC2Tx electrocatalyst (referred
to as CdSA-Mo2TiC2Tx) through the NO3RR to generate NH3 was
rationally designed and demonstrated. In an H-type electrolysis cell
and at a current density of 42.5 mA cm–2, the electrocatalyst
had a Faradaic efficiency of >95% and an impressive NH3 yield rate of 48.5 mg h–1 cm–2. Moreover, the conversion of NO3– to
NH3 on the CdSA-Mo2TiC2Tx surface was further revealed by operando attenuated total reflection Fourier-transform
infrared spectroscopy and an electrochemical differential mass spectrometer.
The electrocatalyst significantly outperformed Mo2TiC2Tx as well as reported state-of-the-art
catalysts. Density functional theory calculations revealed that CdSA-Mo2TiC2Tx decreased the ability of the d-p orbital to hybridize
with NH3* intermediates, thereby decreasing the activation
energy of the potential-determining step. This work not only highlights
the application prospects of heavy metal single-atom catalysts in
the NO3RR but also provides examples of bio-inspired electrocatalysts
for the synthesis of NH3.