Grain boundary boosting the thermal stability of Pt/CeO2 thin films

Understanding how defect chemistry of oxide material influences the thermal stability of noble metal dopant ions plays an important role in designing high-performance heterogeneous catalytic systems. Here we use in-situ ambient-pressure X-ray photoemission spectroscopy (APXPS) to experimentally determine the role of grain boundary in the thermal stability of platinum doped cerium oxide (Pt/CeO2). The grain boundaries were introduced in Pt/CeO2 thin films by pulsed laser deposition without significantly change of the surface microstructure. The defect level was tuned by the strain field obtained using a highly/low mismatched substrate. The Pt/CeO2 thin film models having well defined crystallographic properties but different grain boundary structural defect levels provide an ideal platform for exploring the evolution of Pt--O--Ce bond with changing the temperature in reducing conditions. We have direct demonstration and explanation of the role of Ce3+ induced by grain boundaries in enhancing Pt2+ stability. We observe that the Pt2+--O--Ce3+ bond provides an ideal coordinated site for anchoring of Pt2+ ions and limits the further formation of oxygen vacancies during the reduction with H2. Our findings demonstrate the importance of grain boundary in the atomic-scale design of thermally stable catalytic active sites.