Surface Modified Ruthenium Nanoparticles:  Structural Investigation and Surface Analysis of a Novel Catalyst for Oxygen Reduction

Abstract

Ruthenium catalysts modified by selenium are of interest as a methanol insensitive oxygen reduction catalyst in a polymer electrolyte membrane fuel cell for mobile application. To elucidate the structural and chemical features of unsupported and carbon supported ruthenium nanoparticles prepared by thermolysis of Ru 3 (CO) 12 in an organic solvent with and without the presence of dissolved selenium, different bulk and surface sensitive methods such as transmission electron microscopy, X-ray diffractometry, thermogravimetry coupled with mass spectrometry, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure analysis were performed. It was found that the as-grown catalytic particles prepared without Se and handled under ambient conditions are distinguished by a ruthenium core of 4 nm size, the surface of which is covered by an amorphous ruthenium oxide/hydroxide and metal organic residues from the process of synthesis. In the presence of Se, Ru-Se and Se-O bondings have additionally been found at the surface. After heat treatment at 900 °C under vacuum, organic residues and ruthenium oxides could be removed. The particles have grown to a size of about 10 nm, the surfaces of which are covered by Ru-Se and Ru-SeO 3 units. The as-grown and heat-treated catalysts were characterized electrochemically by cyclovoltammetry, rotating disk electrode with and without methanol in the electrolyte, and rotating ring disk electrode measurements to quantify H 2 O 2 production. As expected from structural analysis, best results have been obtained with heat-treated, Se-modified ruthenium catalysts. It is proposed that in the heat-treated samples an interaction between Se 2-, [Se 2 ] 2-, and SeO 3 2decorating the surface of the ruthenium particles is responsible for the improved oxygen reduction process.

On the Structure of Carbon‐Supported Selenium‐Modified Ruthenium Nanoparticles as Electrocatalysts for Oxygen Reduction in Fuel Cells

“…Therefore, we hypothesize a structural model assuming firmly interacting Se that only partially decorates the surface of primary Ru core particles. [13] This assumption is also supported by structural considerations: 2.5-nm hcp Ru particles consist of about 580 atoms. Around 275 of these atoms (45 % of the total) belong to the surface, that is, they are coordinated by less than 12 neighbors.…”

“…On the other hand, RuSe 2 (the only described stoichiometric RuSe compound) is thermally stable only up to 950 8C. [13] Therefore, when annealing the samples, this temperature must not be exceeded. [12] To quantify the Se loss during annealing, the Se/Ru mass ratio of all catalysts was determined via neutron activation analysis (NAA).…”

Carbon‐Supported, Selenium‐Modified Ruthenium–Molybdenum Catalysts for Oxygen Reduction in Acidic Media

“…[20] Figure 8 a shows a 70 mV loss in E 1/2 after 1000 cycles. Potential cycling leads to a loss of Se and, hence, loss of activity.…”

Die Struktur von selenmodifizierten Rutheniumnanopartikeln auf einem Kohleträger – Elektrokatalysatoren für die Sauerstoffreduktion in Brennstoffzellen

“…Wir schlagen daher ein Strukturmodell vor, das zwar eine starke Ru-Se-Wechselwirkung annimmt, ungeachtet dessen aber nur von einer oberflächlichen Dekorierung der Ru-Nanopartikel mit Se ausgeht. [13] Dieses Modell wird auch durch stöchiometrische Über-legungen gestützt: So besteht ein hcp-Ru-Nanopartikel mit 2.5 nm Durchmesser aus ca. Diese Überlegungen lassen eine komplexe Verteilung des Se auf den Ru-Partikeln vermuten, die mit dem Röntgen-kleinwinkelstreuungsverfahren ASAXS untersucht wurde.…”