Novel nanostructured catalysts for the high-temperature electro-oxidation of small organic molecules

• Antragsteller: Professor Dr. Rolf Jürgen Behm
• Fachliche Zuordnung: Physikalische Chemie von Festkörpern und Oberflächen, Materialcharakterisierung
• Förderung: Förderung von 2010 bis 2014
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 164152250

• Erstellungsjahr: 2016

Zusammenfassung der Projektergebnisse

The main scientific findings of this project can be summarized as follows: First, we succeeded in developing a method that allows us to perform combined electrochemical and in situ spectroscopic measurements (ATR-FTIR spectroscopy and simultaneously Differential Electrochemical Mass Spectrometry (DEMS)) on structurally well-defined electrodes under continuous electrolyte transport conditions. This is based on the use of shape-selected nanocrystals, which are deposited on a conducting, but electrochemically inert substrate Au film that is sufficiently transparent for ATR-FTIRS. Different from the original plans, we stopped the work on modifying the samples and set-up such that similar measurements can be performed also at elevated, fuel cell relevant temperatures. This was decided after significant efforts, in order to keep time for studies using this set-up. Second, applying this approach we could derive detailed insights on the mechanism of model reactions such as the electrooxidation of formic acid or ethanol, which are potential candidates also for fuel cell applications. For formic acid oxidation on Pt and Au, we could demonstrate the key role played by HCOO-anions in solution and, specific for Au, of the reaction of a HCOO-derived adsorbate with HCOOH. This has to be reproduced by any mechanistic proposal. Although this does not resolve the debate on the nature of the adsorbed reaction intermediate, we could significantly reduce the number of reaction mechanisms compatible with these requirements. For ethanol oxidation, structural effects could be mapped out under enforced electrolyte transport (structure - activity correlations), where effects induced by readsorption and further reaction of byproducts can be neglected. Third, using novel, structurally well-defined bimetallic electrodes we could in a systematic way identify the nature of the resulting modifications of the electrochemical/-catalytic properties which were introduced by the second metal, as compared to the respective monometallic electrodes, and quantify the effects. This was demonstrated for Pt (Pd) monolayer film electrodes on a Au substrate and for PtxAg1-x (PdxAg1-x) bimetallic nanocrystals, using CO adsorption / CO electro-oxidation as test reaction. These data together with results of DFT based numerical studies performed in parallel allowed us to expand current concepts on bimetallic (electro-)catalysis, which can serve as basis for systematic tailoring of improved electrocatalysts. Last, but not least, a vivid collaboration with the group of the cooperation partner at the University of Alicante (Prof. Feliu) has been established, which will continue and extend also over this project.

Projektbezogene Publikationen (Auswahl)

• Controlled surface structure for in situ ATR-FTIRS studies using preferentially shaped Pt nanocrystals. Electrocatal. 2 (2011) 69-74
  S. Brimaud, Z. Jusys, R.J. Behm
  
• Electrodeposition of a Pt monolayer film: Using kinetic limitations for atomic layer epitaxy. J. Am. Chem. Soc.135 (2013) 11716-11719
  S. Brimaud, R.J. Behm
  
• Formic acid electrooxidation on noble metal electrodes: The role of pH, surface structure and anion adsorption, and their mechanistic implication. ChemElectroChem 1 (2014) 1075-1083
  S. Brimaud, J. Solla-Gullón, I. Weber, J.M. Feliu, R.J. Behm
  
• Shape-selected nanocrystals for in situ spectro-electrochemistry studies on structurally well-defined surfaces under controlled electrolyte transport: A combined in situ ATR-FTIR / online DEMS investigation of CO electrooxidation on Pt”. Beilstein J. Nanotechnol.5 (2014), vol. 5, pp. 735-746
  S. Brimaud, Z. Jusys, R.J. Behm
  
• Further insights into the formic acid oxidation mechanism on Platinum: pH and anion adsorption effects. Electrochim. Acta 180 (2015) 479-485
  J.V. Perales-Rondón, S Brimaud, J Solla-Gullón, E Herrero, R.J. Behm, J.M. Feliu
  
• Ethanol oxidation on shape-controlled platinum nanoparticles at different pH: A combined in situ IR spectroscopy and online mass spectrometry study. J. Electroanal. Chem. 763 (2016) 116-124
  C. Busó-Rogero, S. Brimaud, J Solla-Gullón, F.J. Vidal-Iglesias, E. Herrero, R.J. Behm, J.M. Feliu