Electronic regulation of first-coordination-shell environments in Mn-based single-atom sites for electrochemical NO reduction: A density functional theory study

Abstract

Abstract： Ammonia is both a key basic chemical and an ideal hydrogen-storage material.Compared with the energy-consuming Haber-Bosch process, the electrochemical nitric oxide reduction reaction (NORR) is regarded as a feasible way to produce NH 3 at mild conditions, owing to its easy substrate activation, large solubility, and possible pollution resource utilization. In this work, we have performed spin-polarized density functional theory calculations to thoroughly explore ten MnA 2 B 2 coordination environments derived from the two-dimensional Mn 3 (HXBHYB) monolayer, aiming at uncovering how the first coordination layer tunes the stability, activity, and selectivity of the Mn-based single-atom sites toward the NORR. The screening based on the formation energy and dissolution potential indicates that the N/O-rich coordination environment can effectively maintain the thermodynamic stability and electrochemical durability of Mn sites. NO prefers to adopt N-end adsorption on all candidate configurations. The adsorption free energy of *NO shows a strong linear correlation with the interfacial charge transfer and Mn d-band center, which implies that the ligandinduced electronic effect is one of the important factors affecting substrate adsorption and activation. Among the stable configurations, both MnN 2 O 2 and MnO 4 passed the thermodynamic screening of the first step *NO → *HNO. However, MnN 2 O 2 has a relatively low limiting potential (-0.17 V vs. RHE), a more gentle main reaction pathway, and stronger ability to suppress the N 2 /N 2 O side reaction and HER. Thus, we find that the fine-tuning of electronic modulation within the first coordination sphere of two-dimensional manganesebased conductive MOFs provides the theoretical basis for the rational design of highly efficient and low-cost NORR catalysts.