HYDROGEN ADSORPTION SURFACES, INTERFACES AND NANOSYSTEMS Weak hydrogen binding and easy H dissociation are key descriptors2 SYNCHROTRON SOLEIL HIGHLIGHTS 2020 in hydrogenation catalysis. On the o-Al13Co(010) and m-Al4 13Co(-201)4 surfaces, a spontaneous dissociation of H occurs on top of surface Co2 atoms. Figure 3 presents an overview of the hydrogen adsorption properties, obtained through potential energy surfaces. Atomic hydrogen is found to SIXS BEAMLINE be strongly bound to the surface, either on top of Al atoms located above subsurface Co atoms (o-Al13Co(010), Eads4 = -0.59 eV) or on top of Co Associated publication atoms (m-Al13Co(-201), Eads4 = -0.53 eV). This suggests that hydrogen Pseudo-2-Fold Surface of the AlCo dissociation is likely on these sites. Additional favorable adsorption sites Catalyst: Structure, Stability, and13 4 are found on top or in the vicinity of surface Co atoms, but with weaker Hydrogen Adsorption. adsorption energies, i.e. likely active for hydrogenation steps. All these sites are well connected to one another and it is reasonable to assume that the C. Chatelier, Y. Garreau, A. Vlad, diffusion of hydrogen atoms on this surface is facilitated. J. Ledieu, A. Resta, V. Fournée, M.-C. de Weerd, A. Coati & É. Gaudry. FIGURE 3 ACS Applied Materials & Interfaces, 12, 39787 (2020). References [1] M. Armbrüster etal. , Nat. Mater., 11, 690 (2012). [2] L. Piccolo et al., Sci. Tech. Adv. Mat., 20, 557 (2019). [3] É. Gaudry et al., Phys. Rev. B, 94, 165406 (2016). [4] É. Gaudry et al., J. Mater. Chem. A, 8, 7422 (2020). Corresponding author Émilie Gaudry Université de Lorraine, CNRS, Institut Jean Lamour (UMR 7198), 54011 Nancy, France emilie.gaudry@univ-lorraine.fr Captions FIGURE 1: SXRD reciprocal space maps: (top) In-plane map where the diffraction spots of the orthorhombic CONCLUSION phase are indexed with black circles. (bottom) Out-of- plane map (K = 2) where the position of the monoclinic The structure, stability and hydrogen adsorption properties of the o-Al Co diffraction spots are represented in green and red 13 4 circles (two twin domains). Facets present the m-(-201) pseudo-twofold surface have been investigated by a combination of orientation. experimental and theoretical techniques. A highly faceted surface morphology has been identified, similar to that of the d-AlNiCo (12110) and (10000) twofold FIGURE 2: Artist’s rendition of a o-(010) terrace and a quasicrystalline surfaces. Our surface model consists of a coexistence of both m-(-201) facet together with the associated reciprocal space (K = 2). Al and Co atoms are drawn in light blue flat terraces and facets, with a fairly denser and Co-enriched atomic surface and dark blue, respectively. structure. A wide diversity of favorable atomic hydrogen adsorption sites are FIGURE 3: Adsorption energy maps of hydrogen on (top) calculated at those surfaces, some of them being quite strongly bound to o-Al13Co4(010) and(bottom) m-Al13Co4(-201). Al and Co the surface, thus likely promoting H dissociation, while others interact more2 atoms are drawn in light blue and dark blue, respectively. weakly with the surface, and are possibly more active for hydrogenation steps. As already predicted for the pseudo-tenfold orientation [4], reaction conditions may modify the faceted structure of the pseudo-twofold surface identified under ultrahigh vacuum conditions. Further experimental and theoretical works are therefore needed. 27