FOR 1376: Elementary Reaction Steps in Electrocatalysis: Theory Meets Experiment
Physics
Final Report Abstract
One long-term goal of the theoretical efforts of the Research Unit was to take the electrochemical environment at the electrode-electrolyte interfaces more realistically into account. This includes an appropriate modeling and description of the ion adsorption on the electrodes, the presence of the aequeous electrolyte, and the variation of the electrode potential. In a systematic approach, the adsorption of halides on metal electrodes was addressed using the concept of the computational hydrogen electrode. The structure of the water layers was modelled explicitly using ab initio molecular dynamics, but also implicitly as a polarizable continuum in order to avoid the high computational costs of the explicit statistical sampling. Based on these efforts, the importance of a proper consideration of the electrochemical environment in the theoretical modeling could be demonstrated using the electro-oxidation of methanol as an example, in particular as far as the selectivity in the electrocatalytic reaction is concerned, which was also addressed experimentally within the Research Unit. Thus the differences in the methanol oxidation in electrocatalysis and in gas-phase heterogeneous catalysis on Pt(111) could be explained. One of the most severe issues in electrocatalysis is the large overpotential associated with the oxygen reduction reaction (ORR) in acid media that severely limits the performance of fuel cells. In fact, the reaction of oxygen is faster in alkaline solutions, and catalyst materials that are less expensive than Pt can be used. A good OH-conducting membrane was missing for alkaline cells, but recently significant progress has been made in this respect. In a series of papers members of the Research Unit have elucidated the reaction mechanism of the ORR in alkaline media on gold and silver catalysts. Together with the progress with respect to a good membrane this has laid the foundation to further improve alkaline fuel cells. The research unit furthermore focused in close collaboration between theory and experiment on the electrocatalytic activity of nanostructured electrodes, in particular bimetallic electrodes and stepped electrodes. These comprehensive studies have allowed to disentangle coordination, composition and strain effects. Thus a more advanced understanding of the local reactivity of nanostructured electrodes has evolved which will be beneficial in the rational improvement of electrocatalysts.
