Protonic and Electronic Conductivity in the Catalyst Layer

High protonic and electronic conductivity are highly desirable to optimize the CL structure with respect to high fuel cell performance. The measured fuel eell voltage ( ceii) alternatively expressed as Equation 21.33  

Hydrophobicity and hydrophilicity play complex and critical roles in both the gas diffusion layer and the eatalyst layer of a PEM fuel cell. A suitable hydrophobicity is necessary for better PEM fuel cell performance. If an electrode is too hydrophilic, the electrode is easily flooded by condensed water, resulting in a dramatic decrease in fuel eell performance. The hydrophobicity and hydrophilicity can be controlled by the ehoice of carbon, the ionomer/carbon ratios, the eontent of 

To date, there are two major types of catalyst layer fabrication techniques. One is to cast or spray the catalyst ink onto the gas diffusion layer to form a catalyzed GDL (CGDL), which is hydrophobic and has a thickness of about 20-50 pm the other is to deposit or spray catalyst ink onto the proton exchange membrane to form a catalyst coated membrane (CCM), a hydrophilic layer with a thickness of 5-10 pm. 

Yu and Ziegler [40] also employed an environmental scanning electron microscope (ESEM method) as a contact angle analysis tool to investigate hydrophobicity and hydrophilicity on inhomogeneous materials. They measured the contact angles of the catalyst layer before and after MEA evaluation, and found that the catalyst layer became more hydrophilic after MEA evaluation thus, this hydrophilic increase could be the cause of lower fuel cell performance. 

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