Role of Polarons in Single-Atom Catalysts: Case Study of Me1 [Au1, Pt1, and Rh1] on TiO2(110)

TL;DR

This study investigates how polarons influence the behavior and stability of single-atom catalysts on TiO2 surfaces, revealing different interaction mechanisms for Au, Pt, and Rh atoms through combined theoretical and experimental approaches.

Contribution

It provides a detailed analysis of polaron-adsorbate interactions on TiO2, highlighting the importance of charge transfer and local environment in single-atom catalysis, which was not fully understood before.

Findings

Pt and Au favor oxygen vacancy sites with strong charge transfer

Rh interacts weakly with polarons, leaving them largely unaffected

Adsorption configurations depend on polaron coupling and charge transfer mechanisms

Abstract

The local environment of metal-oxide supported single-atom catalysts plays a decisive role in the surface reactivity and related catalytic properties. The study of such systems is complicated by the presence of point defects on the surface, which are often associated with the localization of excess charge in the form of polarons. This can affect the stability, the electronic configuration, and the local geometry of the adsorbed adatoms. In this work, through the use of density functional theory and surface-sensitive experiments, we study the adsorption of Rh1, Pt1, and Au1 metals on the reduced TiO2(110) surface; a prototypical polaronic material. A systematic analysis of the adsorption configurations and oxidation states of the adsorbed metals reveals different types of couplings between adsorbates and polarons. As confirmed by scanning tunneling microscopy measurements, the favored Pt1 and Au1 adsorption at oxygen vacancy sites is associated with a strong electronic charge transfer from polaronic states to adatom orbitals, which results in a reduction of the adsorbed metal. In contrast, the Rh1 adatoms interact weakly with the excess charge, which leaves the polarons largely unaffected. Our results show that an accurate understanding of the properties of single-atom catalysts on oxide surfaces requires a careful account of the interplay between adatoms, vacancy sites, and polarons.