N₂ Electro-Activation over Ru using Operando Atom Probe Microscopy

Challenges in the development of green electricity and energy storage challenges are leading us to consider NH₃ as a promising future zero-carbon fuel. The N₂ reduction reaction to NH₃ using electricity is extensively investigated with single atom electrocatalysts (SACs) recently showing promising results. Due to their morphology, the application of an electrical potential on SACs materials results in local High External Electric Fields (HEEFs) over the single atoms. If those effects present promising outcomes according to theoretical calculations^1,2, the values of those HEEFs and the mechanisms involved remains largely unknown and unexplored. Atom Probe Microscopy (APM) such as Field Ion Microscopy (FIM) and Operando Atom Probe are ideal techniques to unravel those mechanisms at the nanoscale since they inherently rely on HEEFs for imaging. In this work, we will illustrate those capabilities with the room temperature N₂ dissociation over Ru case imaged at the nanoscale with FIM and OAP.We use the recently developed OAP technique³ to effectively measure this dissociation over a 0001-oriented Ru specimen. After fixing a constant HEEF between 13 and 17 V/nm and the temperature at 300K, 1.4x10^-7mbar N₂ pure gas is introduced in the analytic chamber. The HEEF either directly ionize N₂ or provoke its dissociation. Dissociated N(ads) are mainly detected over the Ru{1012} and Ru{2114} facets. The occurrence of one or the other processes is intimately linked to the local surface structures and the local HEEFs.<br/>FIM and OAP are capable to observe and estimate the HEEF necessary to trigger specific chemical reaction steps such as the N₂ dissociative adsorption (i.e. activation). With an accurate calculation of those HEEF, those values can be extrapolated to create new chemical and reactor system designed to perform N₂ activation at relatively low energy cost. In a context of electrification of chemical processes, APM can help pave the way to a deeper understanding of the physical laws involved in electrochemistry, as well as in chemistry in general.<br/><br/>Reference<br/><br/>[1] S.M.Kathmann, Phys.Chem.Chem.Phys. <b>23</b>, 23836 (2021).<br/>[2] M.L.Karahka&H.J.Kreuzer, Surf.Sci. <b>643</b>, 164(2016).<br/>[3] S.V.Lambeets <i>et al.</i> Top.Catal. 1606(2020)<br/><br/>&lt;!--![endif]----&gt;