Investigation of ionomer hydration and local relative humidity in platinum and non-noble based catalyst layers in proton exchange membrane fuel cells using SAXS

Abstract

Although the proton exchange membrane fuel cell has been studied for many years, there is still no precise description of the internal operating conditions on a local scale, even though the concentration of water, or its content, in the components of the membrane-electrode assembly plays a major role in the transport of protons and gases, and therefore in performance and durability. In this work, small angle X-ray scattering operando measurements were performed on membrane-electrode assemblies containing different catalysts, and a data processing method was developed in order to extract the contribution of the ionomer, not only in the membrane, but also within the catalyst layers. Thus, the hydration of the ionomer within the membrane and the catalyst layers was quantified during the cell operation. Predictably, during current generation, water is produced, resulting in an increase in the amount of water in all components of the membrane-electrode assembly, and water concentration increases from anode to cathode. Crucially however, the employed method facilitates the determination of the current density at which saturation is reached within the catalyst layer.