A Microelectrode Cell Investigation of the Pt/Ionomer Interface

Polymer-electrolyte fuel cells (PEFCs) are an emerging technology for renewable energy conversion and storage. One of the most pressing concerns in bringing PEFCs to market is cost, driven primarily by the platinum (Pt) catalyst used in the cathode and anode catalyst layers. However, reducing the amount of Pt used also introduces unexplained local oxygen mass-transport resistances in the catalyst layers. Therefore, it is critical to understand mass-transport resistances at the Pt/ionomer interface so they can be mitigated. In this work, the Pt/ionomer interface is studied using a custom microelectrode cell, an idealized, controllable model system for the electrified interfaces within the PEFC catalyst layer. We describe a novel micro-cell that is robust and allows simple and dynamic relative-humidity and temperature control. New results are presented for the mass-transport parameters of hydrogen and oxygen gas in Nafion 211 as a function of membrane water content and temperature. A 2D continuum transport numerical model separates membrane diffusivity and solubility from one transient current experiment. Extension of the micro-cell to study thin ionomer films is introduced.