Effect of fuel impurities on polymer electrolyte fuel cells

Abstract

This dissertation describes experimental investigations on the contamination of polymer electrolyte fuel cells (PEFCs) with fuel impurities. The content includes a comprehensive literature review, experimental evaluation of impact of impurities on PEFCs, electrochemical characterization on contamination mechanisms, and evaluation of the effect of impurities on mechanical properties of the membrane-electrode assemblies (MEAs). Long term stability test and cyclic contamination-recovery test are used to evaluate the PEFC tolerance to various impurities and the recovery strategies following the contamination. Cyclic voltammetry and electrochemical impedance spectroscopy are used to characterize any electrochemical changes due to contamination, and help to understand the contamination mechanisms. A hydrogen pump cell with application of reference electrodes is used to characterize contamination separately on two electrodes. Tensile test is used to evaluate the role of contaminants on mechanical properties of MEAs in axial direction. The major scientific contribution of the work includes the characterization of the effect of formic acid impurity; providing experimental evidence that ammonia contaminates both the membrane and the catalyst layers; characterizing ammonia contamination on the anode; and investigating variations of water uptake and mechanical properties of Nafion^® 212 membranes due to contamination with ammonium.