Contamination of Membrane-Electrode Assemblies by Ammonia in Polymer Electrolyte Fuel Cells

Contamination of polymer electrolyte fuel cell (PEFC) membranes and catalyst layers with ammonia (NH3) is studied experimentally and computationally. Cyclic voltammetry (CV) scans and electrochemical impedance spectroscopy (EIS) analyses show that trace amounts of ammonia can significantly contaminate both the polymer electrolyte membrane (PEM) and the catalyst layers. The results show that the catalyst layer contamination can be reversed under certain conditions, while the membrane recovery tends to be much slower, and permanent effects of ammonia contamination is observed. We have also developed a model that predicts the transport and distribution of ammonium (formed upon reaction of ammonia with proton) and the impact of ammonium on the cell performance due to the apparent decrease in membrane proton conductivity. The model incorporates the Nernst-Planck equations to describe the multi-component cation transport through the membrane. With the model predictions, we are able to differentiate between the performance loss due to increased internal resistance and that due to the poisoning of the catalyst layers. Mechanisms of contamination of the polymer electrolyte and catalyst layers, and performance degradation of the PEFC are also postulated. Figure 1 shows the performance of a PEFC with 25 cm2 active area during contamination and recovery with 25 ppm NH3. It is clearly visible that a trace amount of NH3 in H2 can cause a serious decay of the cell performance, which makes agreement with the findings before. 1-3 However, the cell internal resistance increase can only contribute little to the total performance loss. EIS performed during the contamination process shows that the electrodes might be seriously poisoned by NH3 o