Degradation in phosphoric acid doped polymer fuel cells: A 6000 h parametric investigation

• 6000 h test of PBI-based MEAs in subsequent steady state conditions.
• Estimation of MEAs voltage decay rates in the different operating conditions.
• Analysis of degradation with EIS, CV, LSV.
• Continuous MEA internal water transport monitoring.

This paper reports an experimental study of the degradation of single PBI-based high temperature MEAs doped with phosphoric acid. The study is carried out by operating the single MEAs for long periods in steady state, the degradation is quantified considering the voltage decay rate. Besides the most common operating condition suggested by the MEAs producer (T = 160 °C, i = 0.2 A cm−2, λH2=1.2λH2=1.2, λair = 2), the study also investigates higher operating temperature (T = 180 °C), higher current density (i = 0.4 A cm−2) and double air flow rate (λair = 4). A temperature of 180 °C accelerates the degradation of the MEA which increases from around 8 μV h−1 up to around 19 μV h−1. On the opposite side, operating the MEA at i = 0.4 A cm−2 reduces the voltage degradation rate down to 4 μV h−1 and increases the power output making this condition particularly interesting. EIS, CV and LSV are used to clarify the causes of degradation. A consistent increase in the charge transfer resistance is observed and is related to the loss of catalyst active area due to catalyst agglomeration, carbon corrosion and possible acid leaching. Concerning the electrolyte membrane, a slight decrease in the proton conductivity is measured, a major effect on degradation is played by the increasing gas crossover rate and by the short circuit current.