(509ab) The Effect of N* Coverage on the Electrocatalytic Oxidation of Ammonia on Pt(111): Insights from Theory

The electrocatalytic oxidation of ammonia (NH₃) has a fundamental role in different technologies, ranging from environmental remediation to fuel cells (FC) for energy production [1].

Pt-based electrocatalysts are generally characterized by easy deactivation. This has been attributed to the high activation energy barrier associated with the N–N bond formation [2-3]. A detailed mechanistic study on different close-packed transition metals surfaces was presented by Herron et al. [2] and more recently by Elnabawy et al. [4], by means of Density Functional Theory (DFT) calculations. They concluded that on Pt(111) the reaction proceeds through the coupling of co-adsorbed NH_x (x= 1–2) species and N* acts as a surface poison. Independently, atomic N* has been found to be the most abundant reaction intermediate on Pt(111), with coverage close to 0.6 ML [5]. The presence of co-adsorbed N* can dramatically change the energetic landscape of the electrocatalytic reaction mechanism. In this study, periodic DFT calculations were used to assess the effect of N* coverage on the NH₃ electro-oxidation reaction on a model Pt(111) extended surface. We demonstrate that the presence of N* adatoms has a profound effect on the activation energy barriers associated with N–N bond formation steps, apparently leading to easier N₂ evolution.

[1] Gottesfeld S., J. Electrochem. Soc., 116, 15, J3405, (2018).

[2] Herron J A., Ferrin, P., Mavrikakis M., J. Phys. Chem. C, 119, 14692, (2005).

[3] Rosca V., Koper M. T. M., Phys. Chem. Chem. Phys., 8, 2513–2524 (2006).

[4] Elnabawy A., Herron J. A., Karraker S., Mavrikakis M., J. Catal. (2021), in press.

[5] Gootzen, J. F. E., Wonders, A. H., Visscher, W., van Santen, R. A., van Veen, J. A. R., Electrochim. Acta, 43, 1851 (1998).