Investigation of the complex interplay between structure and stability of carbon materials in electrochemical systems using the vanadium flow battery as example - CarboDeg

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Carbon materials are of paramount importance in devices for electrochemical energy conversion, such as batteries or fuel cells. In particular, when used as electrode materials, their properties are decisive for the efficiency of the conversion process. While tremendous effort is invested into the development of materials with high activity for the respective conversion process, the stability of the materials is considered to a far less amount, and mainly phenomenologically. The suggested project aims at closing this gap. In a more fundamental oriented study, the stability of carbon materials in aqueous electrochemical systems shall be investigated under varying conditions, and a molecular picture on the processes relevant for degradation and ageing shall be obtained. The project focusses on two central strategies to establish robust correlations: first, well-defined materials of increasing complexity will be chosen for these investigations with the aim of bridging the gap between model substrates like highly oriented graphite on the one hand and more practical materials such as carbon blacks on the other. Using well-defined model substrates allows to separate the various mechanisms of ageing/degradation, which might happen in parallel at more complex materials and would thus be inseparable. Second, powerful in situ-techniques are planned, in particular in situ-Raman spectroscopy and in situ-infrared spectroscopy. These techniques allow for a clear correlation of electrochemical stress and resulting ageing- and degradation phenomena. It is the combination of well-defined and characterised materials on the one hand and the use of in situ techniques on the other, that allows for a robust correlation between carbon structure (including surface chemistry), electrochemical stress and resulting ageing and degradation. It is planned to both carry out the investigations independent of a specific application to come to general conclusions and to transfer the gained knowledge on a system of high practical relevance, namely the vanadium flow battery. In the medium term, it is expected that the obtained results contribute to the development of reliable, long term stable materials for electrochemical energy conversion.