Dr. Anna Mechler - Electrocatalysis
|B.Sc. (Applied Science)||Bergische Universität Wuppertal (2005-2008)|
|M.Sc. (Materialwissenschaften) ||Universität Osnabrück (2008-2010)|
|Promotion||MPI für Eisenforschung, IMPRS SurMat / Ruhr-Universität Bochum (2011-2014)|
|Postdoc||Université Montpellier, Frankreich (2014-2015)|
|Postdoc||MPI CEC, Heterogene Reaktionen (2016)|
|Gruppenleiterin||MPI CEC (seit 2017)|
In our group we investigate electrocatalytic active materials that facilitate the conversion of electrical energy to chemical energy and vice versa. For the storage of excess electrical energy, as for example from sustainable energy sources, water electrolysis is a feasible technique to generate hydrogen (and oxygen), where the energy is stored in chemical bonds. Here we focus on the rate-limiting oxygen evolution reaction in alkaline media. The advantage of alkaline media is the higher stability of non-noble materials, as for instance functionalized carbon materials as produced by the "Carbon Synthesis and Application" group (Dr. Saskia Heumann).
On the other hand we study catalysts for the reverse reaction, i.e. the oxygen reduction reaction. This reaction takes place on the cathode of a fuel cell, therefore enabling the re-conversion to electrical energy. Also here we use materials based on carbon, doped with iron or other transition metals to boost their activity. In addition hybrid materials of the combination of these non-precious metal catalysts with low amounts of precious metals are investigated to find possible synergies of these different material classes.
For a proper analysis we develop new experimental techniques, including for example an electrochemical flow cell coupled to an inductively coupled plasma optical emission spectrometer (ICP-OES) to characterize the stability of various catalyst materials. This cell also enables the implementation of further in situ techniques to improve our knowledge of material property changes during the electrochemical reaction.
For standard electrochemical testing we use several complementary setups that help us to address different aspects of electrocatalytic material properties.
1. Rotating (ring) disc electrodes (R(R)DE)
For rotating disc electrode studies powder catalysts are dispersed in an ink and then drop-casted onto a disc-shaped support. These supporting materials can vary from glassy carbon, gold or titanium. By the in-house fabrication of electrode tips we can produce a high variety of tips that are in some cases even exchangeable between different setups. Due to the small dimensions of the tips they are additionally suitable for post-mortem characterization as for example by optical microscopy, SEM, or IR/Raman.
From the MANGAN Project we are equipped with a RDE setup that is identical to that installed at 13 collaboration partners. The electrochemical cell is made out of peek connected to a thermostat, so that also measurements at controlled and elevated temperatures are possible. The rotator and potentiostat are from AutoLab and are managed via the Nova software environment, also equipped with an electrochemical impedance module. In this setup especially measurements for the MANGAN project according to the predefined standard procedure are performed, but the standardized format also facilitates studies on the influence of several experimental parameters.
Additional we have two R(R)DE test stations with rotators by PINE instruments. The electrochemical tests are run with a Biologic VMP 3 potentiostat. These setups allow the use of ring-disc-electrodes for the detection of reaction products like oxygen or hydrogen peroxide on the ring. They are also typically run under a controlled gas atmosphere and due to the closed cell-design can even be operated with e.g. H2 and CO, as for example necessary for CO-stripping experiments.
2. Electrochemical Flow Cell + ICP-OES
With this setup, financed by MAXNET Energy, we can comprehensively characterize the catalyst performance. By combining an electrochemical ﬂow cell (EFC) with a Clark electrochemical oxygen sensor and inductively coupled plasma−optical emission spectrometry (ICP-OES) we cannot only address the electrocatalytic activity and stability, but also monitor metal ions in the electrolyte as well as oxygen content. This allows for a quantitative transient analysis of catalyst corrosion products such as dissolved metal species during an electrochemical stress test as well as to monitor changes of the electrolyte composition (for example of impurities). The oxygen sensor allows accessing the faradaic efficiency and its changes by catalyst corrosion.