Low-temperature fuel cells consist of various components with dižerent functions, determined by their bulk and surface properties. Important bulk properties are, for example, the porosity, hardness, and conductivity of the GDL material, which is important for transport processes in the cell, the ionic conductivity of the membrane material, the leakage rate of the membrane material, the conductivity and tightness of the bipolar plates, and the elasticity of the sealing materials. Surface properties are also very important. še chemical composition of a few atomic layers determines the catalytic properties of catalysts and the surface composition of the GDL material-for example, the ratio of PTFE in the covered and uncovered areas of the carbon structure-determines the GDL’s hydrophobic/hydrophilic behavior. šis means that the ratio of carbon to PTFE in the GDL in the bulk is not relevant. A further example of an important surface property is the surface composition of the bipolar plates, which has a signiœcant in›uence on the degradation or corrosion of this component and on the contact resistance.