Graphene and its functionalized derivatives, such as nitrogen-doped graphene, have recently become a popular substrate material for the proton exchange membrane fuel cell (PEMFC) due to its enhanced electrical conductivity, electrochemical stability, and increased surface area when compared to the conventional, carbon black. In order to further develop the alternative fuel industry, the Pt catalyst within the PEMFC must also be considered. Single Pt atoms have a higher surface area to volume ratio when compared to nanoparticles, thus offering the potential to create a more affordable and efficient PEMFC. In this thesis, electrode materials comprising single Pt atoms and clusters, produced using atomic layer deposition (ALD) on various C derivatives, including graphene, N-doped graphene, carbon nanotubes (CNTs), and N-doped CNTs (NCNTs) are investigated through the utilization of aberration corrected transmission electron microscopy.
Structural and chemical analysis was performed on thermally exfoliated N-doped graphene and CVD-produced graphene that was exposed to N+ ion sources. It was determined that the thermally exfoliated N-doped graphene maintained the short-range order of the graphene lattice; however, local inhomogeneities existed for the total N concentration, and the specific N-dopants within and between graphene sheets. More importantly, Pt atoms and clusters were observed and determined to be primarily stabilized at the edge of the N-doped graphene sheets. The stabilization of the Pt atoms and clusters resulted in a significantly higher mass and specific activity for the hydrogen evolution reaction, when compared to the use of a graphene substrate and Pt nanoparticles on C black. The N+ ion implantation in the CVD graphene showed the incorporation of N-dopants; however, electron energy loss spectroscopy revealed structural damage to thin sheets.
NCNTs were also characterized in this thesis as possible gas containers, and as a substrate material to examine the effects of varying ALD conditions. It was determined that the NCNTs were an effective N2 gas conduit, wherein a decreasing pressure was observed with an increase to the inner diameter of the nanotubes. Using similar NCNTs, the effect of dosing time, temperature, and substrate on the Pt size were analyzed using ALD. While no singular condition resulted in the sole production of single Pt atoms, modifying both the substrate and dosing time were shown to provide the greatest potential for producing individual Pt atom catalysts. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22845 |
| Date | January 2018 |
| Creators | Stambula, Samantha |
| Contributors | Botton, Gianluigi A, Materials Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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