Changes in Proton and Electron Transfer Resistance in Cathode Catalyst Layer of PEM Fuel Cell By Carbon Corrosion

Abstract

The structural robustness of the catalyst layer controlled by the morphology of the carbon support is closely related to the durability of the fuel cell. Electrochemical corrosion of the carbon support leads to the structural collapse of the cathode catalyst layer, decreasing the catalyst layer thickness. The collapse of the catalyst layer causes the increase in the oxygen diffusion resistance, which has been accepted as the major mechanism of the performance degradation of the fuel cell by carbon corrosion. However, little attention has been paid on the possibility of the damage of proton and electron pathway in the cathode catalyst layer by carbon corrosion and the resultant performance decay by the pathway damage. In this study, we introduce the fuel cell performance degradation mechanism in terms of the changes in proton and electron transfer resistance that is induced by the structural change of the cathode catalyst layer by carbon corrosion. Two types of cathode catalyst layer were prepared by adding electrically conductive carbon nanoparticles (Vulcan carbon) and electrically nonconductive silica nanoparticles into the typical Pt/C catalyst layer, respectively, as a model catalyst layer. The cathode catalyst layer consisted of a Pt/C (TEC10E50E) catalyst and long-side chain (Nafion IEC 1.00) ionomer binder. The electrolyte membrane was NRE211 (25 μm). Membrane electrode assemblies (MEAs) were fabricated by decal transfer process and their electrochemical characteristics were measured in a single cell. The accelerated stress test of the carbon corrosion was evaluated by applying a high potential of 1.4 V, and the change of the characteristics of the MEA was confirmed through electrochemical evaluation, before and after the carbon corrosion. The addition of nanoparticles to the cathode catalyst layer enhanced the structural stability of the catalyst layer regardless of the type of nanoparticles, which led to better durability in the catalyst layers added with nanoparticles after carbon corrosion. After carbon corrosion test, the cathode catalyst layer added with nanoparticles revealed a smaller decrease of catalyst layer thickness and a less increase of ohmic resistance than that of the catalyst layer without the nanoparticles. The different behavior of ohmic resistance change between the catalyst layers with and without the nanoparticles was closely related to the degree of damage in electron pathway in the cathode catalyst layer by carbon corrosion. The degree of proton resistance change in the catalyst layer was also dependent on the presence and the type of nanoparticles added to the catalyst layers.