Development of online diagnostic tools for polymer electrolyte fuel cells

Establishing a hydrogen economy is widely regarded by governmental institutions around the world as a key solution for reducing CO2 emissions. In this context, polymer electrolyte membrane fuel cells (PEMFCs) are the primary energy conversion technology for both mobile and stationary applications. However, deploying PEMFCs in such a critical role necessitates significant improvements in their durability. Prolonged use can subject PEMFCs to various faulty conditions, accelerating degradation mechanisms and significantly reducing their operational life and performance [1]. To mitigate these effects and maintain high efficiency over time, online diagnostic tools for continuous health monitoring of the cells are essential.

In this project, we propose a novel frequency response methodology called concentration-alternating frequency response analysis (CFRA). During CFRA experiments, a feed with a periodic concentration of oxygen and/or water is introduced to the cathode side of the cell at varying frequencies. Depending on the electric control applied—either voltastatic or galvanostatic—a periodic current or voltage is obtained as the output. By utilizing two different inputs and outputs, we can analyze four distinct input/output correlations in the frequency domain, each providing unique insights into system losses. The differences between EIS and CFRA are summarized in Figure 1.

The potential of this innovative technique was initially explored through theoretical investigations using a dynamic model of PEMFCs [2]. An experimental setup was subsequently designed and constructed to validate the simulation results and demonstrate the capability of CFRA [3-5]. Recently, we evaluated the performance of various frequency response methods employing electrical and non-electrical inputs for PEMFC diagnosis and assessed the quality of estimated parameters through identifiability analysis [6]. Our findings indicate that using water pressure inputs yields the most reliable parameter estimation (Figure 1). Consequently, employing this input for PEMFC diagnosis emerges as a promising approach.

Figure 1: The identifiability analysis reveals that CFRA, based on water perturbation as the input and voltage as the output, provides the most accurate parameters estimates related to mass transport in the cathode electrode and the Nafion electrolyte, yielding physically meaningful insights. Based on [6]. — **Figure 1:** The identifiability analysis reveals that CFRA, based on water perturbation as the input and voltage as the output, provides the most accurate parameters estimates related to mass transport in the cathode electrode and the Nafion electrolyte, yielding physically meaningful insights. Based on [6].

**Figure 1:** The identifiability analysis reveals that CFRA, based on water perturbation as the input and voltage as the output, provides the most accurate parameters estimates related to mass transport in the cathode electrode and the Nafion electrolyte, yielding physically meaningful insights. Based on [6].

Funding: MPI

Collaborations:

Prof. Sundmacher, MPI Magdeburg

Selected recent publications:

[1] Sorrentino, A., Sundmacher, K., & Vidaković-Koch, T. (2020) Polymer Electrolyte Fuel Cell Degradation Mechanisms and Their Diagnosis by Frequency Response Analysis Methods: A Review Energies, 13 (21), 5825 doi: 10.3390/en13215825.

[2] Sorrentino, A.; Vidaković-Koch, T.; Hanke-Rauschenbach, R.; Sundmacher, K. (2017) Concentration-alternating frequency response: A new method for studying polymer electrolyte membrane fuel cell dynamics Electrochimica Acta 243,53 - 64 doi: 10.1016/j.electacta.2017.04.150

[3] Sorrentino, A., Vidaković-Koch, T., & Sundmacher, K. (2019) Studying mass transport dynamics in polymer electrolyte membrane fuel cells using concentration-alternating frequency response analysis Journal of Power Sources, 412, 331–335 doi: 10.1016/j.jpowsour.2018.11.065.

[4] Sorrentino, A., Sundmacher, K., & Vidaković-Koch, T. (2019) A Guide to Concentration Alternating Frequency Response Analysis of Fuel Cells. Journal of Visualized Experiments - Environment, 154, e60129 doi: 10.3791/60129.

[5] Sorrentino, A., Sundmacher, K., & Vidaković-Koch, T. (2021) Decoupling oxygen and water transport dynamics in polymer electrolyte membrane fuel cells through frequency response methods based on partial pressure perturbations Electrochimica Acta, 390, 138788 doi: 10.1016/j.electacta.2021.138788.

[6] Sorrentino, A., Sundmacher, K., and Vidakovic-Koch, T. (2024) Assessment of frequency response techniques in diagnosing polymer electrolyte membrane fuel cells iScience, 27, 110254 doi: 10.1016/j.isci.2024.110254.