Mitigated Start-Up of PEMFC in Real Automotive Conditions: Local Experimental Investigation and Development of a New Accelerated Stress Test Protocol

This study combines local electrochemical diagnostics with ex situ analysis to investigate degradation mechanism associated to start-up/shut-down (SU/SD) of PEMFC and mitigation strategies adopted in automotive stacks. Local degradation resulting from repeated SU/SD was analyzed with and without mitigation strategies by means of a macro-segmented cell setup provided with Reference Hydrogen Electrodes (RHEs) at both anode and cathode to measure local electrodes potential and current. Accelerated Stress Test (AST) for start-up with and without mitigation strategies are proposed and validated. A ten-fold acceleration of performance loss due to un-mitigated SU/SD has been calculated with respect to AST for catalyst support. Under mitigated SU/SD, instead, a strong degradation was observed as localized at cathode inlet region (i.e. -38% ECSA loss and -22 mV voltage loss after 200 cycles) due to local potentials transient reaching up to 1.5 V vs RHE. These localized stress conditions were additionally reproduced in a zero-gradient and a new AST protocol (named start-up AST) was proposed to mimic the potential profile observed upon SU/SD cycling. Representativeness of the start-up AST for real world degradation was confirmed up to 200 cycles. Platinum dissolution and diffusion/precipitation within the polymer electrolyte was shown to be the dominant mechanism affecting performance loss.

Automated summary

This study investigates degradation mechanisms associated with start-up/shut-down of PEMFC in automotive stacks by combining local electrochemical diagnostics and ex situ analysis. The study found that un-mitigated SU/SD can lead to a ten-fold acceleration of performance loss, while mitigated degradation was observed to be localized at the cathode inlet region. Platinum dissolution and diffusion/precipitation within the polymer electrolyte were identified as the dominant mechanisms affecting performance loss.