Predictive Theoretical Model for the Selective Electroreduction of Nitrate to Ammonia
Tong Mou, Yuting Wang, Péter Deák, Huan Li, Jun Long, Xiaoyan Fu, Bin Zhang, Thomas Frauenheim, Jianping Xiao
Abstract
The electrochemical reduction of nitrate (eNO3RR) emerges as a promising route for decentralized ammonia synthesis. However, the competitive production of nitrite at low overpotentials is a challenging issue. Herein, using the combination of density functional theory and microkinetic modeling, we show that the selectivity for NH3 surpasses that of NO2– at −0.66 VRHE, which nicely reproduced the experimental value on titania. NH2OH* → NH2* is the kinetically controlling step at a low overpotential for NH3 generation, while NO2* → HNO2 has the highest barrier to producing nitrite. Based on these mechanistic insights, we suggest that ΔG1 (NH2OH* → NH2*) – ΔG2 (NO2* → HNO2) can serve as a descriptor to predict the S(NO2–)/S(NH3) crossover potential. Such a model is verified by the experimental results on Ag, Cu, TiO2–x, Fe3O4, and Fe-MoS2 and can be extended to the Au catalyst. Thus, this work sheds light on the rational design of catalysts that are simultaneously energy-efficient and selective to NH3.