Catalyst layers contact angle measurement

Contact angle measurements on the CL may also be useful in the characterization of catalyst layer degradation in a fuel cell. Yu et al. [19] found that the contact angle of a degraded CL became smaller compared to that of an unused catalyst layer, indicating more hydrophilic behavior accompan3dng degradation. 

Figure 326 Time-dependent contact angle of a catalyst layer with wetting process (A) 0 s, i.e., the first attachment of the water droplet at the catalyst layer surface with a contact angle of 148.7° (B) 60 s, the measured contact angle is 147.8° (C) 100 s, the measured contact angle is 146.2°. (For color version of this figure, the reader is referred to the online version of this book.)...

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. 

In mercury intrusion porosimetry, mercury surroimds the sample and application of differential pressure on mercury forces it into the pores. Mercury does not wet hydrophilic and hydrophobic pores and cannot enter these pores spontaneously owing to a small contact angle. Application of pressure on mercury can force it into the pores. The measured intrusion volume is equal to the pore volume and the differential intrusion pressure is related to pore diameter as given in Equation 8.43, where o and 0 are the surface tension and contact angle of mercury, respectively. Mercury porosimetry is valuable in determining the pore structure of the catalyst layer, especially for gas diffusion electrodes, where the distribution of gas and liquid phase pores is essential for the optimization of performance. 

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