Durability Improvement of Pd Core-Pt Shell Structured Catalyst by Porous SiO₂Coating

Porous SiO 2 coating was investigated to suppress agglomeration of catalyst nanoparticles (NPs) and mitigate ECSA decay of carbon supported Pd core-Pt shell structured catalyst (Pt/Pd/C), which is a promising cathode catalyst for polymer electrolyte fuel cells because of its high Pt utilization and enhanced oxygen reduction reaction (ORR) activity. SiO 2 coating was formed onto the catalyst via a sol-gel route using 3-aminopropyltriethoxysilane (APTES) or 3-mercaptopropyltrimethoxysilane (MPTES) as a seed molecule prior to hydrolysis of tetraethoxysilane (TEOS). When APTES with an amino functional group (-NH 2 ) was used as the seed, SiO 2 was coated not only onto catalyst nanoparticles (NPs), but also onto carbon support. On the contrary, SiO 2 was selectively coated onto catalyst NPs when MPTES with a thiol functional group (-SH) was used as the seed. Cyclic voltammetry experiments revealed that -SH functional group much strongly adsorbed onto Pt and Pd surfaces than -NH 2 functional group did. SiO 2 coating formed by the MPTES seed well suppressed NPs' agglomeration and mitigated ECSA decay with less loading of SiO 2 coating, improving durability and ORR mass activity of Pt/Pd/C catalyst even after accelerated durability test performed at 80°C.