Impact of the Relative Humidity on the Performance Stability of Anion Exchange Membrane Fuel Cells Studied by Ion Chromatography

Abstract

Although substantial improvement of the performance of anion exchange membrane fuel cells (AEMFCs) was achieved, longevity is still the main challenge for the AEMFC technology, which is attributed to the degradation of the functional groups of applied membranes and ionomers. Contrary to ex situ material stability studies, we demonstrate here the application of ion chromatography to quantify the amounts of degradation products in the exhaust water during different fuel cell operation conditions on the example of trimethylbenzyl ammonium as a functional group. Higher amounts of degradation products were detected directly after equilibration and completion of polarization curves compared to performance stability measurements under constant load. Moreover, the performance stability dependent on the relative humidity of the anode and cathode feed gases was evaluated. Elevated losses of ionic groups were observed in the anode exhaust water at high humidity fuel cell operation, although higher degradation rates were determined for the cathode side by modeling the performance stability. In contrast, higher amounts of degradation products were detected in the cathode exhaust water under low humidity conditions. However, the mobility of water and degradation products under different fuel cell operation conditions impedes a detailed allocation of the observed degradation to one electrode. The demonstrated combination of in situ electrochemical measurements, corresponding ex situ degradation measurements, and modeling data gives comprehensive insights into the evaluation of the performance stability of anion exchange membrane materials under fuel cell operation, which could exceed ex situ durability experiments based on the membrane materials itself.