(382g) Bimetallic Alloys in Action: Adsorbate-Induced Surface Segregation and Ensemble Formation in Ni-Pt and Au-Pd Nanoparticles

Bimetallic alloys show great promise for applications in a wide range of technologies related to electrochemistry and heterogeneous catalysis. The alloyed nature of these materials supports the existence of surface phenomena and structural motifs not present in single-component materials, which can have a profound influence on their electrochemical and catalytic behaviors. Furthermore, the electrochemical environment, and in particular the presence of adsorbates, is capable of transforming the surface structure in operando, resulting in changes in functionality and performance. We have utilized density functional theory (DFT) calculations to bring to light the atomistic details behind adsorbate-induced surface segregation observed in in-situ X-ray absorption spectroscopy (XAS) studies of NiPt and AuPd nanoparticles at hydrogen underpotential deposition potentials. In the latter case (i.e. AuPd), our theoretical results point toward the existence of a further phenomenon: adsorbate-induced ensemble formation. Given the crucial role that the ensemble effect is already known to play in many reactions catalyzed by bimetallic alloys, our results reiterate the importance of taking the in operando structures of alloyed surfaces into account in the rational design of catalysts.