Carbon nanotube-supported Pt catalysts (Pt/CNT) for the cathode in a polymer electrolyte fuel cell (PEFC) were covered with silica layers using tetraethoxysilane (TEOS) and also methyltriethoxysilane (MTEOS) to improve the catalyst durability under the severe conditions at the PEFC cathode. Both the silica-coated Pt/CNT catalysts had excellent durability for potential cycling between 0.6 and 1.0 V (vs RHE) in N 2 -purged 0.1 M HClO 4 electrolyte, while Pt/CNT without silica coating was significantly deactivated due to an increase of the Pt metal particle size. Silica-coated Pt/CNT prepared from MTEOS had similar activity for the oxygen reduction reaction as Pt/CNT without silica coating, whereas the silica coverage obtained with TEOS slightly reduced the catalytic activity of the Pt/CNT catalyst. The silica layers prepared from MTEOS are more hydrophobic than those prepared from TEOS due to the presence of methyl groups. In addition, the silica layers prepared from MTEOS have larger pores than those prepared from TEOS. The hydrophobic silica layers with larger pores in the silica-coated Pt/CNT do not inhibit the diffusion of the reactants (oxygen) and the discharge of the products (water) during the oxygen reduction reaction.
Carbon nanotube (CNT)-supported Pt metal nanoparticles were covered with silica layers by utilizing the
successive hydrolysis of 3-aminopropyl-triethoxysilane and tetraethoxysilane on CNTs with Pt hydroxide.
The CNT-supported Pt metal particles covered with silica layers (denoted as SiO2/Pt/CNT) were used as the
electrocatalysts. SiO2/Pt/CNT electrocatalysts showed a high stability for the repeated potential cycling
experiment, whereas Pt/CNT electrocatalysts were deactivated seriously for the experiment because of the
growth of Pt metal particles in size. The silica layers in SiO2/Pt/CNT prevent the dissolution of Pt metal
particles as well as the migration and agglomeration of Pt metal particles on the supports, which results in the
improvement of the stability of Pt/CNT electrocatalysts.
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