R&D on lifetime of hydrogen fuel cells

1. INTRODUCTION
The reduction of greenhouse gas emissions and the emerging political focus on hydro-gen as a clean energy carrier are accelerating research into sustainable hydrogen produc-tion and use. Fuel cells (FCs) are a promising technology for sustainable energy produc-tion as they run on environmentally friendly fuels such as renewable green hydrogen (European Union, 2021). They are defined as electrochemical cells in which the chem-ical energy of a supplied fuel (gas or liquid) is directly converted into electricity (Hacker & Mitsushima, 2018). Efficiency, lifetime and sustainability of the entire process chain play an important role.
For use as power supply in electric vehicles, polymer electrolyte fuel cells (PEFCs) are seen as a viable option. The combination of long ranges and fast charging makes this technology particularly attractive. As part of the roll out of PEFC technology, the un-derstanding, prediction and prevention of FC durability limiting issues is critical (Kocher et al., 2021). A reduction of lifetime is often caused by the degradation of key components in the heart of the fuel cell (Bodner et al., 2018). The membrane electrode assembly (MEA) consists of anode, cathode and polymer electrolyte membrane (Fig. 1).
Aging in PEFCs is a complex process, dependent on nearly all system factors and is therefore complex to simulate or extrapolate. However, the commercial application of fuel cells dictates the requirement of lifetime predictions. Therefore, multiple ap-proaches can be used, the most common of which are accelerated stress tests (ASTs).
The performance and lifetime of a PEFC are dependent on several factors. When an abnormal or undesired condition occurs, the system performance usually degrades, sys-tem stability is impacted and the lifetime decreases. The duration and frequency of oc-currence of these abnormal conditions has a great influence on the impact and severity. To determine the effect of specific conditions, they can be replicated in test procedures with their impact on individual fuel cell parameter being monitored. This gives a close-to-application insight into real life degradation mechanisms.
2. METHODS AND EVALUATION
2.1 Accelerated Stress Tests
In order to determine stability and durability of a system or system component, specific testing procedures are applied. Depending on the aim, ASTs can be designed for differ-ent purposes, applications and use case profiles.
One commonly utilised vulnerability of fuel cells is that towards start up and shut down conditions. For such tests, harmonised cycle profiles and test conditions are available from the U.S. DoE (The US Department of Energy (DOE), 2013) or the European Joint Research Centre (JRC) (Tsotridis et al., 2015). The start up is particularly critical. A representation can be found below. In
Fig. 2, the test cell is flushed with nitrogen during the heating-up phase to the operating temperature of 80 °C. The cathode is supplied with air. After the operating temperature is reached, hydrogen is introduced in the anode, which immediately leads to a voltage peak and the electric current increases. The ageing process during the start-up procedure can be repeated as often as desired with the aid of a simulated load protocol and the effects of different operating parameters can thus be determined.
LITERATURE
Bodner, M., Senn, J., & Hacker, V. (2018). Degradation Mechanisms and Their Lifetime. Fuel Cells and Hydrogen: From Fundamentals to Applied Research, 139–154. https://doi.org/10.1016/B978-0-12-811459-9.00007-4
European Union. (2021). DELIVERING THE EUROPEAN GREEN DEAL: THE DECISIVE DECADE - architecture. July, 2021. https://doi.org/10.2775/352471
Hacker, V., & Mitsushima, S. (2018). Fuel Cells and Hydrogen. In Fuel Cells and Hydrogen: From Fundamentals to Applied Research. Elsevier. https://doi.org/10.1016/C2016-0-01053-7
Kocher, K., Kolar, S., Ladreiter, W., & Hacker, V. (2021). Cold start behavior and freeze characteristics of a polymer electrolyte membrane fuel cell. Fuel Cells, 21(4), 363–372. https://doi.org/10.1002/fuce.202000106
Ladreiter, W. (2020). Startup and Shutdown Strategies with Oxygen Consumption for Polymer Electrolyte Fuel Cells. Technical University Graz.
The US Department of Energy (DOE). (2013). Fuel Cell Tech Team Accelerated Stress Test and Polarization Curve Protocols for PEM Fuel Cells. U. S. Dept. of Energy. http://web.anl.gov/PCS/acsfuel/preprint archive/Files/49_2_Philadelphia_10
Tsotridis, G., Pilenga, A., Marco, G., & Malkow, T. (2015). EU harmonised test protocols for PEMFC MEA testing in single cell configuration for automotive applications. In EUR, Scientific and technical research series (Vol. 27632).

https://doi.org/10.2790/54653