Structure-reactivity relationships for bimetallic electrodes
Bimetallic (electro-)catalysts are well known for their high activity, e.g., in fuel cell reactions. This project aims at a fundamental quantitative understanding of well defined, elementary electrochemical / electrocatalytic reactions and simple processes on nanostructured bimetallic electrode surfaces as model systems for bimetallic electrocatalysts, based on the concept of local reactivities of individual bimetallic nanostructures (atomic ensembles). Accordingly, the central task of this project is the identification, characterization and theoretical understanding of the electrochemical / -catalytic properties of individual bimetallic nanostructures of well defined composition and structure. Emphasis lies on (laterally) inhomogeneous surfaces such as stepped / kinked surfaces and in
particular mixed surfaces, e.g., surface alloys and their interaction with species like H, OH, O$_2$, CO, methanol etc. in oxidation or reduction reactions.
This objective shall be reached by a combination of experiment and theory. Nanostructured electrode surfaces with known types and densities of specific structural elements, which had been determined by atomic resolution scanning tunnelling microscopy, are prepared by ultrahigh vacuum techniques. Local reactivities are determined by correlation of the electrochemical / -catalytic characteristics of different electrode surfaces with systematically varied concentration of the respective structural element, e.g., by poisoning active bifunctional step sites by a string of inert metal. The results are compared with results of density functional theory calculations of adsorption / reaction processes, performed on appropriate model systems including the electrochemical environment. Kinetic Monte Carlo simulations of the overall reaction, with the energy parameters from the DFT calculations as input, are used to verify the underlying concepts and thus establish this approach as a general scheme for the understanding of (electro-)catalytic processes on inhomogeneous electrodes and catalysts.
A second important aspect of the project is the proper description of the metal-electrolyte interface at bimetallic electrodes, including the role of the surface inhomogeneities and of adsorbed species (anions, H, OH). This shall be investigated theoretically and in spectroscopic model studies.
The combined experimental / theoretical work in this project shall allow us to
- decide on the validity of the "local reactivity'' concept for describing the electrochemical / electrocatalytic properties of bimetallic surfaces, which underlies most mechanistic pictures, to
- identify possible differences therein between processes at the solid|gas and solid|liquid interfaces, to
- map out trends in the electrochemical properties and electrocatalytic activities of specific structural elements, and to
- identify contributions from different effects such as electronic ligand / strain effects, geometric ensemble effects or bifunctional effects.
- Prof. Dr. Rolf Jürgen Behm
- Inst. of Surface Chemistry and Catalysis
- Albert-Einstein-Allee 47
- D-89069 Ulm
- Telephone: +49 (0)731/50 25450
- Telefax: 0731/50 25452
- E-Mail: juergen.behm(at)uni-ulm.de
- Prof. Dr. Axel Groß
- Inst. of Theoretical Chemistry
- Ulm University
- Albert-Einstein-Allee 11
- D-89069 Ulm
- Telephone: +49 (0)731/50 22810
- Telefax: +49 (0)731/50 22819
- E-Mail: axel.gross(at)uni-ulm.de