(699b) Predicting Adsorption Properties on Bimetallic Alloys As a Function of Local Morphology and Atomic Composition

Authors: 
Choksi, T. S., Stanford University
Roling, L., Stanford University
Abild-Pedersen, F., SLAC National Accelerator Laboratory
Bimetallic nanoparticles are widely used in catalytic and energy applications because they present a tunable configurational space together with synergistic effects between component metals which influences adsorption energies. These energies function as thermochemical reactivity descriptors in DFT derived screening models which have successfully designed bimetallic catalysts for numerous catalytic applications [1]-[5]. While current paradigms correlate surface adsorption to reactivity trends through a forward design approach, they lack a site-by-site resolution in descriptor space, hindering their capability of predicting active sites with atomic level precision. Incorporating such specificity enhances flexibility in materials space through targeted engineering of active sites, while simultaneously explicitly accounting for surface segregation phenomena that affects the stability of bimetallic catalysts.

Employing adsorption site stability as a descriptor, we predict adsorption energies of catalytically relevant descriptors like OH*, CH*, CH3* and CO* on generic bimetallic alloys of Ag, Au, Cu, Ir, Pd, Pt, and Rh at a site-by-site resolution, across a broad morphological and compositional design space. We build this framework by extending recently postulated scaling relations between metal atoms and metal-adsorbate complexes for monometallic systems [6] to bimetallic alloys. We observe linear correlations between the inherent stability of a surface binding site and the adsorption energies of metal-adsorbate complexes. These correlations are determined from a limited set of slab-based DFT calculations, for fixed binding site compositions, while varying the chemical ordering of nearest-neighbor metal atoms. We directly estimate molecular adsorption energies from the scaling trend, while systematically quantifying the effects of modifications in morphology and chemical ordering on adsorption strengths. Slopes and intercepts of the scaling lines are discussed in the context of the d-band theory. We examine the versatility of our model by predicting adsorption energies of OH* on top and bridge sites of 147 atom cuboctahedral PtAu nano-alloys in varying coordination and compositional environments. When integrated with a coordination-based model that directly estimates adsorption site stability [7], scaling relations predict adsorption energies within 0.12 eV, validating our paradigm. Finally. we discuss potential applications of our approach towards nano-engineering active sites with atomic resolution, to discover the next generation of bimetallic catalysts.

References

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