PH'D defense M. Thimothée Drugeot

Abstract :

The Proton Exchange Membrane Fuel Cell is a promising "low carbon" technology to power electric vehicles. However, the shut-down and start-up phases have been identified as critical events because the existence of a transient H₂|Air front on the anode side causes the circulation of internal currents leading to huge degradation reactions within the cathode catalytic layer. The performance and ultimately the lifetime of the cell are thus strongly altered. Although these degradation mechanisms have been studied at small scale, the implementation of mitigation strategies at stack/system scale remains insufficient to meet the lifetime requirements. This thesis is therefore interested in understanding the degradation mechanisms and quantifying the performance losses at the representative scale of a state-of-the-art cell design as a function of shut-down and start-up conditions. This is achieved through:

• The development of accelerated ageing tests emulating a realistic profile of the cathode potential during the start-up phase in a 100 cm² single cell with a state-of-the-art fluidic design and cell core. A sensitivity study has been performed to evaluate the respective impact of the maximum potential reached, the duration of the front, the gas humidity and the temperature on the performance losses. Post-mortem analyses have also been conducted to characterize the evolution of the physicochemical and electrochemical properties of the active layer in relation to the degradation mechanisms.
• The transposition of the current by-pass mitigation strategies up to the short-stack scale. For this purpose, a series of tests has been developed to reproduce the start-up phase to compare two electrical architectures: the shunt resistance connection for the whole stack or for each cell individually. Local current density measurements have also been performed simultaneously to access the local and internal operation of the cells and thus to understand the differences in terms of protection of these architectures compared to the reference case without by-pass.

Jury members

Nadia YOUSFI-STEINER Professeure des Universités – Université Bourgogne Franche-Comté – Rapporteure
Gaël MARANZANA Professeur des Universités - Université de Lorraine – Rapporteur
Bruno AUVITY Professeur des Universités – Université de Nantes – Examinateur
Marian CHATENET Professeur des Universités – Université Grenoble Alpes – Examinateur
Yann BULTEL Professeur des universités – Université Grenoble Alpes – Directeur de Thèse
Eric PINTON Ingénieur de recherche – CEA Grenoble Liten – Invité (co-encadrant)
Fabrice MICOUD Ingénieur de recherche – CEA Grenoble Liten – Invité (co-encadrant)