Dynamic state analysis of porous gas diffusion electrodes

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In sub-project 2, the macrokinetics of the alkaline oxygen reduction reaction (ORR) and the carbon dioxide reduction reaction (CO2RR) in silver-based gas diffusion electrodes (GDE) are investigated with model-based and experimental dynamic methods. A basic understanding of the limiting processes inside the electrodes will be generated for both reactions and compared. The complex interactions of species transport, phase equilibria and various electrochemical reaction steps render the analysis and identification of the processes in porous electrodes a challenging task. In case of GDEs for carbon dioxide reduction, chemical reactions and the competing hydrogen evolution reaction have to be considered in addition. It will be investigated how the potential, the chemical kinetics and the electrode design influence transport processes, species distribution as well as current density. Furthermore, the impact of single processes on performance and dynamic behaviour of the electrode will be elucidated.Quantitative dynamic models for the processes inside the electrode will be developed to answer these questions. The measurement data required for validation will be provided by the project partners and obtained in own experiments using differential electrochemical mass spectrometry. Dynamic techniques allow one to analyse processes individually and to determine their characteristic time constants, kinetic parameters, and their impact on the GDE performance. For the GDE with ORR, steps in potential and current density are particularly suitable dynamic input signals because of the prevalence of slow transport processes. The results from the other sub-projects such as detailed kinetics, local reaction conditions and electrolyte distribution inside the electrode are combined in the modelling to better understand the influence of individual processes on the overall GDE behaviour. Additionally, a model-based analysis of selected scenarios is conducted to draw conclusions for improving electrode design and operation conditions. Furthermore, dynamic and steady-state methods will be compared regarding their advantages and disadvantages for investigating GDE and the general suitability of dynamic methods for studying GDE will be evaluated using GDEs with both reactions.