Electrochemical pressure impedance spectroscopy for transport characterization in electrochemical cells

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Electrochemical pressure impedance spectroscopy (EPIS) shows a high sensitivity towards transport processes in cells with gaseous reactants (Grübl, Bessler et al. 2016). This novel technique is based on analyzing the dynamic current/voltage/pressure behavior by either current excitation/pressure detection or pressure excitation/voltage detection with frequencies in the range of 100 Hz to 1 mHz. For polymer electrolyte membrane fuel cells (PEMFC), EPIS is expected to allow the observation of flow and mass transport phenomena with high accuracy. These phenomena, covering gas transport in the gas diffusion layers and the catalyst support as well as evacuation of the produced water, govern the cell performance at high-current operation. The diversity of transport phenomena, their coupling with electrochemistry and temperature, and dependence on structural properties such as pore sizes and size distributions makes understanding and modeling difficult. With conventional techniques, in particular electrochemical impedance spectroscopy (EIS), transport phenomena are difficult to be distinguished from each other and their signal may be (partially) masked by charge-transfer processes.The key hypothesis governing the present proposal is that EPIS can significantly increase measurement sensitivity and accuracy of transport-related phenomena in PEMFCs. We therefore propose a combined experimental and modeling study of EPIS for PEMFCs. A single-cell setup with pressure excitation and detection will be developed and operated by CNRS - Université de Lorraine (CNRS, France). A dynamic multi-physics model will be developed and used for data analysis by Offenburg University of Applied Sciences (HSO, Germany). The primary goal of the study is the development and evaluation of EPIS for PEMFC diagnosis. In addition, the investigation is expected to bring a significant contribution on understanding, characterization and quantification of the different transport phenomena involving gases and liquid water in the cell. Finally, the use of low-cost pressure excitation and/or detection equipment such as a loudspeaker and/or pressure sensors will be tested, for the sake of significant reduction in the cost of the overall diagnosis technique. Our vision is that EPIS can become a standard diagnosis tool in everyday lab practice complementing EIS with limited add-on effort (financially and technically) but strongly enhanced output.The three-year project will consist in continuous interaction between the two partners, CNRS being in charge of the experimental part and generation of data, HSO working on model development and data interpretation. The work packages include a preparative phase for experiments and models; the development and the use of the EPIS tool covering the measurement device and the simulation tool; interpretation of the results; and evaluation and assessment of the EPIS technique.