Browsing by Author "Hoang, Annie"

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    Nanoengineering of Bimetallic Materials for Electrocatalytic Applications
    (2019-11) Hoang, Annie; Birss, Viola; Shi, Yujun; Kibria, Md. Golam; Thangadurai, V.
    Fuel cells are electrochemical devices that cleanly convert fuel into electricity. However, the high cost of the catalyst materials and the lack of hydrogen fueling stations have led to the need for less costly catalysts, as well as the use of liquid fuels (e.g., ethanol, a highly accessible and renewable fuel for direct ethanol fuel cells (DEFCs)). In this work, Ru@Pt core@shell nanoparticles (NPs, 3-6 nm) supported on Vulcan Carbon (VC) powder were produced by two synthesis methods, and then compared for their catalysis towards the ethanol oxidation reaction (EOR). A stabilizer-based synthesis (Method I) produced NPs in a colloidal solution, prior to attaching the NPs to the carbon support. Method II was a stabilizer-free synthesis, involving nucleating Ru NPs on carbon, followed by thermal annealing, and then Pt shell deposition. Both synthesis methods successfully achieved Ru@Pt core@shell formation, although Method II generated larger and less agglomerated NPs that were also more crystalline after thermal annealing. Without annealing, the Method II Pt shell was not as uniform on the Ru cores as desired. These Ru@Pt core@shell NPs were examined for their activity towards the EOR in acidic conditions at room and elevated temperatures. The stabilizer-based Method I NPs exhibited lower EOR activity, perhaps due to some residual capping ligand blocking the NP surfaces. The Method II NPs with thermally annealed Ru cores exhibited greater EOR activity than their non-annealed analogues. For both types of NPs, those with Pt shell coverages < 1 monolayer (ML) were quite promising for the EOR, ascribed to the bifunctional effect. This work also focused on examining thermally annealed Au and Pt thin films (3-4 nm each) sputter-deposited sequentially on chemically polished (CP) Ta. Interestingly, Au always migrated to the outer surface, with Pt beneath, suggesting that Pt@Au core@shell thin films were formed, independent of the Au and Pt sputtering sequence. Also, the underlying Pt thin film prevents thermal dewetting of the thin Au film, playing an important role in stabilizing Au electrochemistry after long thermal annealing times.