Manufacture of Robust Catalyst Layers for the DMFC

Catalyst layers for direct methanol fuel cells (DMFC) must possess a complex structure in order to provide protonic and electronic conductivity as well as access to reactants at all reactive sites. This involves a highly porous structure, which is often mechanically instable, especially when mass production processes are utilized. A feasible process should provide a catalyst layer in one coating step and must include relatively fast drying of the catalyst ink. In the present work, different types of additives are used to provide such an ink. Inorganic particles that arc much larger than the catalyst particles provide dimensional stability in the catalyst layer. Depending on their structure and surface, they can also be used to influence the porosity or hydrophobicity of the layers, and thus to optimize performance. Gel forming polymers are used to adjust the viscosity of the inks and since they also act as a binder, they help to stabilize the catalyst layers. These effects can be obtained by using minimal quantities of polymers, thus avoiding problems such as pore clogging or the deactivation of catalyst surfaces. As a result, catalyst inks can be adjusted to suit coating techniques such as knife-coating or screen-printing. Also, catalyst layers are mechanically stable, thus avoiding long-term degradation due to crack formation or delamination.