Dwivedi, J.; Bachmann, L. J.; Jeromin, A.; Kulkarni, S.; Noei, H.; Tanase, L. C.; Tiwari, A.; Schmidt Caldas, L.; Roldan Cuenya, B.; Stierle, A.; Keller, T. F.: Spectro-Microscopy of Individual Pt-Rh Core-Shell Nanoparticles During Competing Oxidation and Alloying. ACS Nano 19 (2025), p. 28516-28529
10.1021/acsnano.5c07668
Open Access Version
Abstract:
The surface chemical composition of supported single Pt–Rh core–shell nanoparticles was studied to understand the Rh behavior in oxidizing and reducing gas environments using spectro-microscopy with high spatial resolution. We combined in situ X-ray photoemission electron microscopy with ex situ scanning electron-, atomic force-, and scanning Auger-microscopy to distinguish Rh oxidation–reduction, dewetting–sintering, and alloying–segregation during the course of the experiment. A more than 20% higher Rh 3d5/2 oxide to metal photoemission intensity ratio for the Rh layer on top of the Pt-core was found as compared to the bare strontium titanate (STO) oxide catalyst support in close vicinity, where Rh/RhOx nanoparticles are forming. At elevated temperatures, Rh diffuses into the Pt particle, and this alloying at the Pt metal surface competes with Rh oxidation, whereas the Rh/RhOx nanoparticles on the STO support are observed to sinter under identical oxidizing and temperature environments. A nanoparticle facet-dependent analysis of selected Pt-core nanoparticles suggests that Rh oxidation is most advanced on a small nanoparticle with a low coordination top facet that we indexed by electron backscatter diffraction, demonstrating the strength of our correlative approach.