Ammonia Synthesis via Nitric Oxide Electrochemical Reduction on OH-MXenes: A Universal Descriptor

Currently, the electrochemical synthesis of NH3 by direct NO reduction has emerged as an alternative to the Haber–Bosch process. In this respect, developing new yet efficient catalysts with their known mechanisms is crucial to enhancing the synthesis performance. Because OH-functionalized MXenes (OH-MXenes in abbreviation) have some unique surface structures, they have attracted widespread interest in the field of the NO reduction reaction (NORR). This study utilized density functional theory (DFT) calculations to examine NO activation, NORR activity, and catalyst regeneration on 33 different OH-MXenes. It is found that the surface H atoms act as the active species for NO adsorption and are involved in the NORR on most OH-MXenes. In addition, the calculated results on Gibbs free energy show that the NORR on OH-MXenes is spontaneous with the third hydrogenation step during catalyst regeneration as the potential determining step. Moreover, combining OH-MXenes data with our previous research on the NORR performance of H-MXenes reveals a strong correlation between |Ev−ENO|2|ENO| and ΔGPDS on the surface H involved systems. This work not only deepens our understanding of the crucial role of surface H in NORR but also provides a basis for the high-throughput screening of catalysts for NH3 synthesis.