Study On The Stability Of Membrane Electrode Assembly For Proton Exchange Membrane Fuel Cell

Membrane electrode assembly (MEA) is one of the key components of proton exchange membrane fuel cells (PEMFCs). It is most likely to ultimately dictate the stack life, and has great significant effect on the commercialization of the PEMFC. As the commercialization of the fuel ceils approaches, it becomes even more significant to investigate its stability.With the aim to investigate the MEA's stability of a PEMFC under different operating conditions, the performance is carried out on a hydrogen/air single cell at atmospheric pressure. A 300 h short life-test of PEMFC at constant discharge current of 500 mA/cm~2 is conducted. In addition, two same single cells are continuously operated for 300 h in the dynamic operating conditions. The voltage responses and polarization curves are evaluated to compare the stability during the short life-test under constant current and two dynamic load (100-500 mA/cm~2 and 0-500 mA/cm~2) conditions, respectively. Cyclic voltammetry, electrochemical impedance spectra and linear sweep voltammetry are used to monitor the changes of the cell performance in situ and analyze the degradation of the cell. The results of SEM, TEM, and XRD characterizations obtained before and after the life-test are also compared, and the possible reasons of the degradation are discussed from microcosmic perspective.As a result, the extent of PEMFC degradation as well as the decay rate varies with load conditions, the performance loss of the cell at 0-500 mA/cm~2 pulse load condition is most pronounced and the cell at constant discharge current of 500 mA/cm~2 degrades little. The cell performance degradation is caused by many factors, such as the loss of catalyst electrochemical active surface area in cathode side, the increase of the electrochemistry resistance or the ohmic resistance, changes of electrodes structure, process of catalysts particles growth/agglomeration, dissolution, or migration etc. The performance degradation can be timely mitigated or partly recovered by using a potential sweep, which is a good method to eliminate the adsorbed intermediated species on the catalyst surface.In addition, influence of the metal ions on the performance of PEMFC is studied. The results show that under the same concentration of metal ions solution, the degradation of PEMFC performance caused by the contaminated membrane is more serious than that caused by contaminated catalyst layer. The effect of contaminated membrane on cell performance is more serious than that of contaminated catalyst under the same contamination extent. A small quantity of metal ions has little influence on the hydrophilic and hydrophibic of the electrode gas diffusion layer.A series of in situ methods are used and developed, which can reflect the change of catalyst active areas and the various polarization processes in the whole PEMFC. An accelerated testing method is put forward, namely, pulse loading accelerating the performance degradation.