(389a) Understanding the Importance of High Coverages in Electro-Catalysed Reduction of NO on Pt-Sn Alloys

Nitrogen cycle electrochemistry is an emerging 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, and even basic information such as the nature of the rate-limiting step is not understood.

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 underlie this selectivity.

To elucidate these features, we make use of periodic Density Function Theory calculations combined with theoretical electrochemistry analyses. We briefly review some results elucidating the mechanistic insights of NO electrochemical reduction on Pt(111)^[1] and Pt(100)^[2] surfaces. Next, we 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 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. Then, we discuss the sensitivity of the mechanistic predictions to different electrochemical reaction barrier estimation techniques, and 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.

References:

1. Clayborne, A., Chun, H.-J., Rankin, R. B. & Greeley, J. Angew. Chem. 127, 8373–8376 (2015).

2. Chun, H.-J., Apaja, V., Clayborne, A., Honkala, K. & Greeley, J. ACS Catal. 3869–3882 (2017).