Development of online diagnostic tools for polymer electrolyte fuel cells

Establishing the hydrogen economy in society is considered by most of the world’s governmental institutions to be one of the main solutions for limiting CO₂ emissions. In this scenario, polymer electrolyte membrane fuel cells (PEMFC) represent the principal energy conversion technology used for both mobile and stationary applications. However, the employment of PEMFCs in such an important and challenging role requires a significant improvement in their durability [1]. Prolonged use can expose PEMFCs to several faulty conditions, which accelerate the action of different degradation mechanisms dramatically lowering operating life and performance. To avoid these effects and ensure long-lasting high efficiency, online diagnostic tools for continuous monitoring of the health status of the cell are essential. In this project we suggest a new frequency response methodology based on periodic concentration inputs so called concentration-alternating frequency response analysis (cFRA). During cFRA experiments, a feed characterized by a periodic concentration of oxygen and/or water is sent to the cathode side of the cell at different frequencies (Fig. 1-left). A periodic current or voltage is obtained as the output depending on the electric control applied to the cell, respectively voltastatic or galvanostatic. Since two different inputs and outputs are used, it is possible to analyze four distinct input/output correlations in the frequency domain, containing different information on losses in the system. The prospect of the novel technique was first theoretically investigated employing a dynamic model of PEMFCs [2]. Subsequently, an experimental setup was designed and constructed to validate the results of the simulations and prove the capability of cFRA (Fig. 1-right) [3-5]. The results of this study are summarized in Fig. 2. As the experimental and simulated curves indicate, EIS spectra detect the contributions of all the main dynamic processes occurring in the cell, i.e., charging of the double layer due to the electrochemical reactions, mass transport of oxygen in the cathode channel and electrode, and water sorption in the Nafion membrane. On the contrary, cFRA separately reveals the contribution of the oxygen mass transport or water sorption to the Nafion using, respectively, concentration of oxygen (Fig. 2-middle) and water (Fig. 2-right) as inputs.

Fig. 1: left - Schematic of EIS and cFRA experiments; right - Simplified scheme of the experimental setup designed to perform cFRA experiments — **Fig. 1:** left - Schematic of EIS and cFRA experiments; right - Simplified scheme of the experimental setup designed to perform cFRA experiments

**Fig. 1:** left - Schematic of EIS and cFRA experiments; right - Simplified scheme of the experimental setup designed to perform cFRA experiments

Fig. 2: Comparison between experimental (symbol-solid line) and simulated (solid line) EIS and cFRA spectra under galvanostatic conditions at three different steady states: left - EIS magnitude plot; middle - cFRA magnitude plot obtained by oxygen pressure input; right - cFRA magnitude plot obtained by water pressure input.

Fig. 2: Comparison between experimental (symbol-solid line) and simulated (solid line) EIS and cFRA spectra under galvanostatic conditions at three different steady states: left - EIS magnitude plot; middle - cFRA magnitude plot obtained by oxygen pressure input; right - cFRA magnitude plot obtained by water pressure input.

Funding: MPI

Collaborations:

Prof. Sundmacher, MPI Magdeburg

Selected recent publications:

[1] Sorrentino, A., Sundmacher, K., and Vidakovic-Koch, T., Polymer Electrolyte Fuel Cell Degradation Mechanisms and Their Diagnosis by Frequency Response Analysis Methods: A Review. Energies, 2020. 13(21): p. 5825.

[2] A. Sorrentino, T. Vidaković-Koch, R. Hanke-Rauschenbach, K. Sundmacher, “Concentration-alternating frequency response: A new method for studying polymer electrolyte membrane fuel cell dynamics”, Electrochim. Acta, 243 (2017) 53-64
[3] Sorrentino, A., Vidakovic-Koch, T., and Sundmacher, K., Studying mass transport dynamics in polymer electrolyte membrane fuel cells using concentration-alternating frequency response analysis. Journal of Power Sources, 2019. 412: p. 331-335.

[4] Sorrentino, A., Sundmacher, K., and Vidaković-Koch, T., A Guide to Concentration Alternating Frequency Response Analysis of Fuel Cells. JoVE, 2019(154): p. e60129.

[5] Sorrentino, A., Sundmacher, K., and Vidakovic-Koch, T., Decoupling oxygen and water transport dynamics in PEMFCs through frequency response methods based on partial pressure perturbations. Electrochimica Acta, 2021. 390: p. 138788.