Bioinspired Tandem Electrode for Selective Electrocatalytic Synthesis of Ammonia from Aqueous Nitrate.

The electrocatalytic nitrate reduction reaction (NO 3 RR) has recently emerged as a promising technique for readily converting aqueous nitrate (NO 3 - ) pollutants into valuable ammonia (NH 3 ). 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 NO 3 RR. There are several natural enzymes that incorporate molybdenum (Mo) and that can activate NO 3 - . Based on this, a cadmium (Cd) single-atom anchored Mo 2 TiC 2 T x electrocatalyst (referred to as Cd SA -Mo 2 TiC 2 T x ) through the NO 3 RR to generate NH 3 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 NH 3 yield rate of 48.5 mg h -1 cm -2 . Moreover, the conversion of NO 3 - to NH 3 on the Cd SA -Mo 2 TiC 2 T x surface was further revealed by operando attenuated total reflection Fourier-transform infrared spectroscopy and an electrochemical differential mass spectrometer. The electrocatalyst significantly outperformed Mo 2 TiC 2 T x as well as reported state-of-the-art catalysts. Density functional theory calculations revealed that Cd SA -Mo 2 TiC 2 T x decreased the ability of the d-p orbital to hybridize with NH 3 * 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 NO 3 RR but also provides examples of bio-inspired electrocatalysts for the synthesis of NH 3 .