Maximum Noble‐Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum

Abstract

Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria "nanopocket", which binds Pt(2+) so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.

Surface sites on Pt–CeO2mixed oxide catalysts probed by CO adsorption: a synchrotron radiation photoelectron spectroscopy study

“…Two samples containing 12% and 25% of Pt in the Pt-CeO 2 oxide film were prepared on a well-ordered CeO 2 5 The Pt concentration of 12% and 25% in the volume of the mixed layers was achieved by using Pt/Ce deposition rate ratios of 1/7 and 1/3, respectively. The deposition rate ratios were determined from the ratios of nominal thicknesses of Pt to CeO 2 deposited during the same period of time.…”

“…Recently, we demonstrated that nanostructured cerium oxide films expose {100} nanofacets 8 which can stabilize Pt atoms in the form of Pt 2+ ions. 5 The {100} nanofacets expose square oxygen pockets in which Pt 2+ ions are strongly bound. The adsorption energy of Pt 2+ in the square oxygen pockets estimated by density functional calculations is large and explains the outstanding thermal stability of the Pt-CeO 2 films.…”

“…The adsorption energy of Pt 2+ in the square oxygen pockets estimated by density functional calculations is large and explains the outstanding thermal stability of the Pt-CeO 2 films. 5 In order to maintain this high stability, the number of Pt atoms in the Pt-CeO 2 films must not exceed the number of available square oxygen pocket sites. However, thermal treatment of the films often triggers restructuring of the catalyst, which may lead to a decrease in the density of the stable sites.…”

“…magnetron sputtering, [11][12][13] and co-deposition of Pt and Ce in the oxygen atmosphere. 5 The composition and thermal stability of these materials depend strongly on the surface structure and Pt concentration. 5 Often formation of Pt 2+ is also accompanied by generation of Pt 4+ and Pt 0 species.…”

“…5 The composition and thermal stability of these materials depend strongly on the surface structure and Pt concentration. 5 Often formation of Pt 2+ is also accompanied by generation of Pt 4+ and Pt 0 species. Therefore, analysis of surface sites is important to understand and tune the stability of Pt-CeO 2 films.…”