Abstract Due to low rate of Oxygen Reduction Reaction (ORR) in PEMFC and its dependence to the microstructure, the type and size of the catalyst particles, cathode catalyst layer (CCL) is an important component in PEMFC. Therefore optimization of the nanostructure of CCL is an effective factor on the PEMFC performance. CCL made of carbon supported Pt nanoparticles and Nafion. Oxygen transports through the void volumes of the CCL in order to reach the Pt surface. So optimization of void volumes which formed of micro and nano pores is an effective factor in enhancing the PEMFC performance. The electrode substrate is another important factor on the PEMFC performance because of providing the support of the electrode electrochemical reaction. In this project, Ballard and Toray (TGP) substrate electrode was compared. Result indicated that with increasing gas humidity from 30% to 100%, Ballard substrate show the higher performance than Toray substrate. It can be explained Ballard substrate have larger pore diameter because of lower bulk density. So gas transport through the Ballard substrate improves at high humidity gas. In this study, the effect of Pt nanoparticle, Nafion and carbon loading in CCL on the PEMFC performance was investigated. With changing in Pt, carbon or Nafion loading, void volumes of catalyst layer were determined and the PEMFCs performance were investigated. Crystal structure and size of Pt nanoparticles (Pt/c 30wt.%) were characterized by the X-ray diffraction (XRD) technique. CCL microstructure was investigated by the Scanning Electron Microscopy (SEM) technique. According to respective equations, void volumes of CCLs were calculated. CCLs thickness was eva‎luated between 15-17 µm by SEM. According to XRD results, the crystal structure of the Pt particles was face centered cubic (fcc) and the particle size 3.6 nm were calculated. Void volume of the CCLs decrease from 26.8% to 19.1% with increasing the Nafion loading from 25% to 31%. By changing the Pt loading of 0.48 to 0.85 (mg.cm-2) CCL void volume was not significantly changed. The results showed that the void volume is affected by Nafion loadings. Because of high density of Pt, with the increasing the Pt loading void volumes of CCLs were significantly changed. Keywords: PEMFC, Catalyst Layer, Structure, Catalyst Layer porosity, Nafion loading

محمد ژياني

بيژن نجفي , پيمان صاحب سرا