Slot-Die Coating: A New Preparation Method for Direct Methanol Fuel Cells Catalyst Layers

Manufacturing of catalyst layers is one of the key processing steps in making membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). The catalyst ink, which usually contains catalysts, ionomers, solvents, and additives, is generally applied to the substrate by a wet-coating technique. Established coating techniques which are used for manufacturing catalyst layers for fuel cells are knife-coating, screen-printing, and spraying. Slot-die coating is also an established coating technique, but not currently used for making fuel cell electrodes. For each coating technique the properties of the catalyst layer will depend on the properties of the coating technique and the properties of the substrate. Also each coating technique requires the catalyst ink to be adjusted to its specific rheological requirements. In this study, slot-die coating is developed as a new method for the continuous manufacture of catalyst layers for direct methanol fuel cells. The rheological demands for a homogeneous layer thickness are studied with model inks and a suitable catalyst ink is prepared. With this ink, decal electrodes are fabricated and CCM-type MEAs are made. Fuel cell tests show that the performance of the slot-die coated electrodes is comparable to electrodes made by knife-coating.