Investigation and Mitigation of Anode and Cathode Impurities to Improve Polymer Electrolyte Fuel Cell Performance

Due to an increasing demand for environment-friendly power production, polymer electrolyte fuel cells (PEFCs) are promising devices with their low operation temperature, zero-emission, high efficiency and smaller sizes. However, some challenges still exist in commercial applications. One of the issues is impurities in hydrogen (anode fuel) and air (cathode oxidant). The first objective of this thesis is to investigate the carbon monoxide (CO) poisoning and a mitigation method of high-level CO (1,000 and 10,000 ppm) in a platinum (Pt) catalyst layer using hydrogen (H2)/CO mixture as the inlet fuel. A one-dimensional transient model is developed including the species diffusion, the conservation of adsorbed species, and ionic and electronic charges. Oscillations in overpotential and coverage of adsorbed species are observed for 1,000 ppm CO level, while they are not detected for 10,000 ppm CO. Hence, behavior of oscillations throughout the catalyst layer thickness, and the reasons are explored for the lower concentration case. For 10,000 ppm CO, current density is pulsed from 0.1 to 2.5 A/cm2 for the CO removal from Pt sites. It is concluded that up to 92% of CO within the catalyst layer can be removed, and 70% of the catalyst layer length is CO-free following the current pulsing. In addition to CO poisoning, regular cleaning of pipeline and hardware is also significant in fuel cell operation to avoid the corrosion of components. An experimental and analytical study is implemented to select the appropriate cleaning agents in PEFCs. Screening tests for several cleansers are performed during the injection of samples into the cathode inlet. One proper agent has shown a fully recoverable and minimal effect on the performance and as such is determined as the best candidate. PEFC can still operate at ~0.4 V at constant current (1 A/cm2) even with a considerable flow rate (250 µl/min) of the selected cleanser. Detailed analysis of this cleanser is provided by curve fitting the electrochemical impedance spectroscopy data, and evaluation of binary gas diffusion coefficients. It is indicated that performance loss during sample exposure is mainly due to its adsorption on active Pt sites and increase in mass transfer resistance.