In Situ EXAFS Study To Probe Active Centers of Ru Chalcogenide Electrocatalysts During Oxygen Reduction Reaction

Abstract

Novel cluster Ru chalcogenide materials Mo x Ru y Se z and Ru x Te y were studied in situ using EXAFS in the transmission mode during the oxygen reduction reaction. Reversible changes in the structure of the active center were revealed for the electrochemical reaction as a function of the applied electrode potential. The shift of the potential in the anodic direction from 0.08 to 0.78 V versus rhe (reference hydrogen electrode) in the presence of oxygen resulted in an increase of the Ru-O and simultaneous decrease of the Ru-Ru coordination numbers in the first coordination shell of Ru. Along with the variation of the coordination numbers, we observed reversible changes of the coordination distances: a decrease of the Ru-O and an increase of the Ru-Ru distance with the positive polarization. These changes witness the distortion of the catalytic center upon oxygen adsorption. A tentative mechanism of oxygen activation on Ru x X y cluster materials is proposed on the basis of the in situ EXAFS data.

What Can We Learn in Electrocatalysis, from Nanoparticulated Precious and/or Non-Precious Catalytic Centers Interacting with Their Support?

“…This phenomenon was associated to the coordination of Selenium atoms over the ruthenium atoms surface. As revealed by EXAFS analysis [79,80] the closest Ru-Ru averaged distance was 2.64 Å (corresponding to the hcp phase of metallic ruthenium) and that of the metal chalcogenide Ru-Se was 2.43 Å. It is worth noting that the calculated Debye-Waller parameters were a factor of 2 higher for the Ru-Se coordination distance than for Ru-Ru.…”

New Concepts in the Chemistry and Engineering of Low‐Temperature Fuel Cells

“…To take full advantage of these powerful tools, methods must be developed to rapidly screen and identify materials of interest [188]. Indeed, (1) the synthesis of new Ptbased catalysts [156], (2) the increasing role of Pt additives [156,189,190], and (3) the emergence of Pt-free catalysts [69,70,73,74,[191][192][193][194], have proved to be essential in the development of increasingly better fuel cell systems. Fuel cell scientists may now use many of the methods developed since the 1970s or so, including both the ex situ ultra-high-vacuum methods [195,196] and in situ infrared (IR) spectroscopy, nuclear magnetic resonance (NMR), and synchrotron X-ray methods [194,[197][198][199][200][201][202][203][204][205].…”

“…To address this challenge, researchers are exploring methanol-tolerant cathode catalysts for MR-DMFCs as well as for conventional, PEM-based DMFC designs, to alleviate the adverse effects of methanol crossover. Ruthenium-selenium (Ru-Se)-based chalcogenides are among the most promising methanol-resistant oxygen reduction catalysts [69][70][71][72][73][74][75][76][77][78]. Despite displaying excellent methanol tolerance and substantial oxygen reduction activity (although still quite lower than that of Pt), other studies indicate that Ru-Se-based catalysts may not be sufficiently stable for extended use in operating fuel cells [79].…”

“…Many Pt-free oxygen reduction catalysts have been explored, including Rubased chalcogenides (see Section 19.2.2) [66,[69][70][71][72][73][74][75][76][77][78], metal oxides [178,179], transition carbides [180], cobalt-polypyrrole-carbon composites [181], enzymes [120,121], and pyrolized porphyrins [66,81,[182][183][184][185], but none have shown the necessary electrocatalytic activity, stability under acidic conditions, and durability to replace Pt-based catalysts in fuel cell systems. However, quite recently, Lefevre et al reported on the development of Fe/N/C catalysts that demonstrate high oxygen reduction activity equivalent to that of Pt/C [184,185].…”

Elektrokatalyse in Brennstoffzellen und Elektrolyseuren: Kohlenstoff‐Nanoröhren‐basierte Katalysatoren und neuartige Untersuchungsmethoden

“…Als Aktivkomponente für die Sauerstoffreduktion werden in der HCl-Elektrolyse jedoch nicht Platin, sondern ein Rhodiumsulfid [10,11] sowie RuSe-Verbindungen untersucht [12,13]. Insbesondere Rh x S y -Verbindungen haben sich unter den korrosiven Bedingungen der HCl-Elektrolyse als wesentlich stabiler erwiesen als Pt, das vor allem im Fall einer Zellabschaltung durch aus dem Anodenraum übertretendes Chlorid/Chlor angegriffen wird [2,14].…”