(509ai) First-Principles Analysis of Coverage, Ensemble, and Solvation Effects on Selectivity Trends in NO Electroreduction on Pt3Sn Alloys

Nitrogen cycle electrochemistry is an upcoming area of interest in the chemical and environmental engineering communities, with applications ranging from removal of nitrates from wastewater streams to the development of fundamental understanding of NO electrochemistry. In spite of a significant amount of fundamental research for this chemistry on single crystal surfaces, however, the mechanistic details of the reactions are not fully known.

In this work, we begin by describing a detailed analysis of the reaction mechanism of NO electroreduction on PtSn alloys. These alloys are of interest because they have been experimentally shown to be selective to products such as hydroxylamine (NH₂OH) in acidic solutions, which is a more valuable product compared to NH₃, the only product formed on pure platinum surfaces. In spite of this interest, however, little is known about the structural and electronic features of the PtSn that cause this selectivity change.

To elucidate these features, we make use of periodic Density Function Theory calculations combined with theoretical electrochemistry analyses. We first present our analysis for low coverages of NO present on the Pt₃Sn(111) surface and derive preliminary conclusions about the reaction mechanism. Subsequently, we introduce an in-house graph theory based tool to efficiently estimate higher coverage structures of adsorbed NO on the Pt₃Sn(111) surface, and we extend the kinetic analysis to the limit of higher NO coverages, resembling the state of a real catalyst under continuous reaction conditions. Further, we compare the mechanistic insights for NO electrochemical reduction on Pt-Sn alloys with that on Pt(111) and Pt(100) surfaces, to understand the role of ‘Sn’ in promoting the selectivity to NH₂OH. We close by suggesting design strategies to tune the selectivity of NO electroreduction to desired products, including N₂ and hydroxylamine, on other transition metals and alloys.