Local degradation phenomena in membrane electrode assemblies for heavy-duty application of PEMFCs

Kurzfassung

PEMFC is a key technology for the decarbonization of the transport sector. Hydrogen powered vehicles appear as most promising solution to maintain driving range and refueling time competitive to traditional combustion engine vehicles. Both aspects are of high importance for Heavy-Duty Vehicles (HDV), but also durability targets become more challenging. The targeted lifetime is anyway significantly higher for HDV with 30,000 h compared to Light-Duty Vehicles (LDV), such as passenger cars, with 7,000 h. Additionally, the required operating conditions are shifted towards higher cell voltage and cathode potential to assure high efficiency and towards high temperature to facilitate heat dissipation. Thus, operating conditions are more aggressive regarding material degradation in the used membrane electrode assembly (MEA). The presented work will demonstrate the importance to examine and understand occurring degradation mechanisms on different positions of an MEA in a PEMFC stack for HDV application. For example, the local operating conditions at the cathode near air inlet are typically characterized by a temperature of about 90 °C, 21% oxygen in the feed air and moderate relative humidity, while a temperature of about 105 °C, 9% oxygen and high relative humidity are present near air outlet. The impact of these conditions on the degradation behavior will be demonstrated by durability tests in a differential cell applying these conditions and a HDV relevant load cycle. In-depth analysis of the degradation mechanisms will be presented by a combination of electro-chemical in-situ und physico-chemical ex-situ measurements. Additionally, the impact of the used MEA component materials on the degradation behavior will be discussed based on the analysis of different MEAs. This aspect should provide a starting point for a material guideline regarding the development of robust MEAs for HDV application with increased lifetime and high efficiency.