Impacts of Catalyst Ink Composition and Wet Film Thickness on Fuel Cell Catalyst Layers Fabricated by Direct Film Coating Method

Abstract

Utilizing a direct film coating method (DFCM), such as doctor blade coating, offers a promising approach for efficient and scalable catalyst layer (CL) production for fuel cells. To further widen the understanding of lab-scale DFCM, the present research investigates how different Pt-based catalyst ink formulations coated via doctor blade coating with varying blade gap thickness (BGT) affect the CL quality and catalyst loading. In total, 120 CL samples were prepared by coating 20 different catalyst ink formulations with varying solids content, ionomer-to-carbon (I/C) ratio, and water-to-isopropanol solvent ratio with BGTs of 75, 125, and 200 μm. Inspection of these samples showed that the solvent ratio affects the coating uniformity, with the most uniform films achieved with a ratio of 1.67 or greater. Furthermore, increasing the I/C ratio for a given solids content ink formulation decreases the Pt loading, whereas an I/C ratio above or below 1.0 reduces cell performance due to mass transport or proton conductivity impacts, respectively. In addition, a relationship factor and equations are presented to estimate the solid weight and catalyst loading of the fabricated CL based on the ink formulation and BGT. Overall, this work provides important guidance for lab-scale DFCM fabrication of industrially relevant CLs.