Special Operating Features of DMFC

The peripheral equipment needed for direct methanol fuel cells is largely analogous to that of polymer electrolyte membrane fuel cells. The mechanical basis of fuel cells and stacks on the whole consists of bipolar plates between which the sandwiched membrane-electrode assemblies are arranged. For the venting of heat, cooling plates with a circulating heat transfer agent are set up in a particular order between individual fuel cells in the stack. 

The major distinguishing features of direct methanol fuel cells relative to polymer electrolyte membrane fuel cells are 

Different provisions have been suggested to account for these special features. 

Considerable changes are needed in the anodic part of the membrane-electrode assemblies in order to accommodate the first two of the above-mentioned points. Instead of the porous gas diffusion layer that in polymer electrolyte membrane fuel cells ensures a uniform distribution of hydrogen across the surface, a gas-liquid diffusion layer that contains a set of hydrophilic as well as a set of hydrophobic pores is needed here. Through the hydrophilic pores, this layer must secure the unobstructed access of the aqueous methanol solution to the reaction zone and its uniform distribution. Through the hydrophobic pores, this layer must secure the unobstructed elimination of carbon dioxide, as the gaseous reaction product, from the reaction zone. Analogous changes must be made in the catalytically active anode layer of the membrane-electrode assemblies, where the gas is actually formed, and must be removed toward the gas-liquid diffusion layer. 

By introducing carefully determined amounts of Naflon and polytetrafluoroethy-lene into the gas-liquid diffusion layer and into the catalytically active layer, the ratio needed between hydrophilic and hydrophobic micropores is achieved. 

---