A New Process to Prepare Pt Alloy Nanoparticles
Pt alloy catalysts are potential candidates to replace pure Pt catalysts in fuel cells due to their higher activity. However, the activity and durability of the Pt alloys highly depend on the preparing method. The Pt alloys prepared by conventional impregnation method usually have large particle size, and element distribution in these particles is not uniform. Using polyol method Zhong et al. can obtain a mono-dispersed Pt alloy nanoparticles supported on carbon support with an average particle size smaller than 3 nm by controlling the annealing temperature lower than 700C (US Patent 7053021 B1 and US 7335245 B2). However, the capping agents were thermo-decomposed in an oxygen atmosphere in the above paten, which is not suitable for most of high active catalysts. In addition, the annealing temperature for Pt alloy catalysts in their process is too low to achieve good durability in a harsh fuel cell environment. In this invention, a modified post-treatment of Pt alloy catalysts prepared by the polyol method are proposed. The process of preparing Pt ternary and quaternary alloy nanoparticles in the US Patent 7053021 is adopted. After the nanoparticles are loaded on supports, the capping agents are carefully removed in an inert atmosphere (N2, Ar, etc.) by keeping the temperature at around 270C. After removing the capping agents and pre-annealed at 400C, the supported catalysts are further annealed at elevated temperatures up to 1200C (preferably 700-1000C) to improve the durability and activity.
- Avoid particle aggregation by minimizing the carbon and metal nanoparticles burning during the capping agents removal process.
- Improve the activity and durability of Pt alloy by increasing the annealing temperature.
U.S. 9,548,501; JP5657689B2; DE112009005450T5
Binghamton University RB332