Sustainable Ammonia Production via Nitric Oxide Electrochemical Reduction on H-MXenes: A DFT Study

Ammonia has gained more interest as a promising candidate to produce clean and renewable hydrogen energy in recent years. It is crucial to develop a new and efficient method for improving the performance of NH3 synthesis. Nowadays, electrochemical NH3 synthesis by direct NO reduction has become an alternative to the Haber–Bosch process. Herein, the performance of a NO reduction reaction (NORR) on 33 different H-functionalized MXenes (H-MXenes) has been investigated by the combination of density functional theory (DFT) calculations with the least absolute shrinkage and selection operator (LASSO) regression. Through surface Pourbaix diagrams and Gibbs free-energy calculations, the reaction mechanism and limiting potential (UL) of the NORR on the H-MXenes are investigated. The DFT calculations demonstrate that the surface H could regulate the strength of NO adsorption, lower the free energy of the elemental step, effectively reduce the limiting potential, and hence improve the NORR performance. Furthermore, the results on the LASSO regression indicate a good fitting between the expression consisting of the combined descriptors from 1D to 4D and the UL values from the DFT calculations. Moreover, |Gv−ENO|2|GNO| is regarded as human-readable NORR performance descriptors with R2 = 0.83. This work not only provides a deep insight into the important role of H-functionalization in NORR but also profits to understand the originals of the NORR activity for the high-throughput screening of NH3 synthesis catalysts.