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

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 Mo₂TiC₂T electrocatalyst (referred to as Cd_SA-Mo₂TiC₂T) 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 Cd_SA-Mo₂TiC₂T surface was further revealed by operando attenuated total reflection Fourier-transform infrared spectroscopy and an electrochemical differential mass spectrometer. The electrocatalyst significantly outperformed Mo₂TiC₂T as well as reported state-of-the-art catalysts. Density functional theory calculations revealed that Cd_SA-Mo₂TiC₂T 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.