Experimental investigation and numerical simulation of the electrolyte loss in a HT-PEM fuel cell

Abstract

In this work, long and short term degradation experiments concerning the electrolyte loss in a HT-PEM fuel cell based on the membrane system PBI/phosphoric acid were conducted. Particular emphasis was placed on the ionic conductivity which was investigated in-situ at regular intervals during the degradation test by means of electrochemical impedance spectroscopy (EIS) measurements. The long term test was executed over 4600 h including constant load and start-stop cycling operation. During the start-stop cycling operation at 150 °C, the load was intermitted for 680 times, cooled down to 60 °C, purged with nitrogen and heated up to the operating temperature of 150 °C, and operated for one hour at 0.2 Acm−2, before the cycle started all over again. Additionally, a special short term water stress test was developed to provoke acid leaching and to exclude aging effects of the catalyst to determine the effects of the electrolyte loss. Within 90 h, 59 water stress periods were performed, yielding a similar performance degradation as the long term test with respect to the membrane conductivity. The second part of this work concerns itself with the numerical simulation of the electrolyte loss in HTPEM fuel cells. The experimental results of the first part of this work were the basis to relate the electrolyte/phosphoric acid content in the membrane with predictable operating characteristics of the investigated fuel cell. It was found that a reduction of the phosphoric acid content within the membrane can explain the effects observed in the water stress experiment without the need to adopt further simulation parameters.