Spatially Resolved Electronic Alterations As Seen byin Situ195Pt and13CO NMR in Ru@Pt and Au@Pt Core–Shell Nanoparticles

Abstract

Pt-based core–shell (M@Pt where M stands for core element) nanoparticles (NPs) have recently been under increasing scrutiny in the fields of fuel cell and lithium air battery electrocatalysis due to their promising prospects in optimizing catalytic activity, reducing Pt loading and consequently lowering its cost. To achieve the latter, delineating spatially resolved local (surface) elemental distribution and associated variations in electronic properties under working condition (i.e., in situ) is arguably a prerequisite of fundamental importance in investigating electrocatalysis but unfortunately is still sorely missing. In this regard, in situ195Pt electrochemical NMR (EC-NMR) of Pt-based NPs is unique in terms of accessing such information, particularly the spatially resolved partition between the s- and d-like Fermi level local density of states (Ef-LDOS) modified by the core elements. In this paper, we report a comparative in situ195Pt EC-NMR investigation of Ru@Pt vs Au@Pt NPs which was complemented by in situ13C EC-NMR of the 13CO adsorbed on the respective NPs generated via dissociation of methanol and by ab initio DFT calculations. The obtained results showed opposing electronic effect between Ru vs Au cores: the former reduced substantially the s-like but not the d-like Ef-LDOS of the Pt shell while the latter did the opposite. According to recent quantum calculations, a reduction in d-like partition would weaken the Pt–O bond while a reduction in s-like partition would weaken the Pt–H bond, which is largely in agreement with experimental observations.