Fundamental Investigation of Oxygen Reduction Reaction on Rhodium Sulfide-Based Chalcogenides

• Published in: Journal of physical chemistry. C 2009-04, Vol.113 (17), p.6955-6968
• Main Authors: Ziegelbauer, Joseph M, Gatewood, Daniel, Gullá, Andrea F, Guinel, Maxime J.-F, Ernst, Frank, Ramaker, David E, Mukerjee, Sanjeev
• Format: Article
• Language: English
• Subjects: ABSORPTION SPECTROSCOPY; ADSORPTION; C: Nanops and Nanostructures; CATALYSTS; CHALCOGENIDES; COMMUNICATIONS; DISSOLUTION; ELECTROCATALYSTS; ELECTRONS; HEATING; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MICROANALYSIS; national synchrotron light source; OXYGEN; RHODIUM; RHODIUM SULFIDES; SEGREGATION; SPECTRA; WATER; X-RAY DIFFRACTION
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp809296x

Synchrotron-based X-ray absorption spectroscopy (XAS), including the surface-specific ΔXANES technique, is used to investigate the active reaction site for water activation and the oxygen reduction reaction (ORR) on the novel, mixed-phase chalcogenide electrocatalyst Rh x S y /C (De Nora). The specific adsorption of water, OH, and O as a function of overpotential is reported. This study builds on a prior communication based solely on interpreting the XAS spectra of Rh x S y with respect to the metallic Rh3S4 phase. Here, a more extensive overview of the electrocatalysis is provided on Rh x S y /C, the thermally grown Rh2S3/C and Rh3S4/C preferential phases and a standard 30 wt % Rh/C electrocatalyst, including results obtained by X-ray diffraction (XRD), XAS, high-resolution transmission electron imaging, microanalysis, and electrochemical investigations. Heating of the Rh x S y catalysts to prepare the two preferential phases causes Rh segregation and the formation of Rh metal particles, and immersion in TFMSA causes S dissolution and the formation of a Rh skin on the Rh x S y samples. It is shown that some Rh−Rh interactions are needed to carry out the ORR. This is present on the Rh6 moieties in both the Rh3S4 and Rh x S y catalysts, but a partial Rh skin (present from acid dissolution) is also contributing to the ORR observed on Rh x S y . This to our knowledge is the first time a reaction site in a multiphase inorganic framework structure has been investigated in terms of electrocatalytic pathway for oxygen reduction.