Predictive Theoretical Model for the Selective Electroreduction of Nitrate to Ammonia

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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.
Funding Information
  • Ministry of Science and Technology of the People's Republic of China (2021YFA1500702)
  • Liaoning Revitalization Talents Program (XLYC1907099)
  • Deutsche Forschungsgemeinschaft (FR-2833/7)
  • National Natural Science Foundation of China (22172156, 91945302, U1930402)
  • Chinese Academy of Sciences (DNL202003, XDB36030200)

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