Deciphering Dynamic Surface of PtRu Alloy Nanocatalysts to Revisit Their Synergistic Effects During the Electrooxidation

Correlating dynamic structural transformation of catalysts with the surface intermediate species under operating conditions is critical for updating the understanding of structure-performance relationships. Here, we probe the electrochemical potential-dependent surface structures and adsorbed intermediates on PtRu binary alloy nanocatalysts to revisit its synergistic mechanisms for CO electrooxidation enhanced activity. In-situ spectral characteristics by using modified shell-isolated nanoparticle-enhanced Raman spectroscopy, show that in acidic solution, when the potential is positively scanned from 0.1 V to 1.5 V relative to reversible hydrogen electrode (RHE), the surface of the alloy catalyst evolves from metallic PtRu to adsorbed oxygen gradually covering and accumulating on Ru sites (denoted as PtRuOx, x <= 2), forming segregated RuO2, and finally forming a three-dimensional oxide layer (denoted as 3D PtRuO4). Moreover, molecular evidence associated with periodic density functional theory calculations reveals that electronic effects promote ruthenium to become more oxidizable and oxophilic. In particular, we found here that *O and *OH at surface RuOx sites are highly efficient CO oxidation active species in comparison to the same entities adsorbed on metallic Ru sites. This work sheds light on the complex surface dynamic process of practical Pt-based binary nanocatalysts and improves the understanding of synergistic mechanism for the development of fuel cell devices.