Principles of Operation
1.2.1.1 DMFC Components
The core of the present DMFCsis a polymer electrolyte ion exchange membrane. The electrodes (anode and cathode) are in intimate contact with the membrane faces (Figure 1.1). The electrodes usually consist of three layers: catalytic layer, diffusion layer and backing layer. The catalytic layer is composed of a mixture of catalyst and ionomer and it is characterized by a mixed electronic-ionic conductivity. The catalysts are often based on carbon supported or unsupported PtRu and Pt materials at the anode and cathode, respectively. The membrane as well as the ionomer consist, in most cases, of a perfluorosulfonic acid polymer. The diffusion layer is usually a mixture of carbon and polytetrafluoroethylene (Teflon) with hydrophobic properties necessary to transport oxygen molecules to the catalytic sites at the cathode or to favor the escape of CO2 from the anode. The overall thickness of a membrane and electrode assembly (MEA) is generally smaller than one millimeter. Several cells are usually connected in series to form a fuel cell stack that is integrated in a system which contains the auxiliaries, allowing stack operation and delivery of the electrical
power to the external load.
DMFC Operation Mode