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One of the biggest obstacles to commercializing polymer electrolyte membrane fuel cells is the use of platinum as a catalyst. One way to overcome this obstacle is to replace platinum with non-platinum group metal (non-PGM) catalysts, particularly for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The most realistic method of estimating the performance of non-PGM catalysts is testing within membrane electrode assemblies (MEAs). One key issue is that non-PGM catalysts are not as active as platinum. One way to increase their performance is to optimize the catalyst layer composition, specifically the components responsible for ionic and electronic conductivity. The first objective of this work was to determine the optimal ionomer-to-catalyst ratio and additional carbon content within the catalyst layer. Another problem that arises when replacing platinum with non-PGM catalysts is the catalyst layer thickness. Platinum catalyst layers are on the order of 10 μm whereas non-PGM catalyst layers are on the order of 60-120 μm. Although this increase in catalyst allows for more active sites it causes challenges in transport performance by elongating pore channels. From this the second objective of this work was to examine the chemistry and morphology of both the non-PGM catalysts and sprayed catalyst layers and their effects on MEA performance. Another polymer electrolyte membrane fuel cell and an alternative to PEMFCs are anion exchange membrane fuel cells (AEMFCs). Unlike the corrosive environment in PEMFCs, the alkaline environment of AEMFCs is much more conducive to non-PGM catalysts. The problem is that AEMFC technology is decades behind that of PEMFC, particularly the anion exchange membranes and their stability. Because of this there is very little data on alkaline MEA assembly and testing. The third objective of this work was to integrate new Ni-based hydrogen oxidation reaction (HOR) catalysts into alkaline MEAs. A large

While there is a rich body of literature concerning of properties of bulk cerium oxide and cerium cations in solution, the discussion has been inappropriately applied to nanoscale cerium oxide resulting in many unexpected or unexplained results. In particular, there is very limited understanding about the properties of cerium oxide and its potential use as a radical scavenger, and how the catalytic properties of cerium oxide change as the particle size approaches the nanoscale. For example, the involvement of Ce+4 and Ce+3 cations in reactions such as hydrogen peroxide decomposition have been investigated for both cerium cations and bulk cerium oxide. However, while both are assumed to decompose hydrogen peroxide through the same mechanism, whereby Ce+4 is involved in peroxide decomposition while Ce+3 is involved in radical scavenging, there has been very little done to address how the selectivity and activity of these reactions are affected by changing the majority cation population, as cerium cations in solution are predominantly in the +3 oxidation state while cerium cations are predominantly in the +4 oxidation state in cerium oxide. This matter is further complicated in cerium oxide nanoparticles where the surface concentration of Ce+3 cations is increased due to particle curvature effects. Due to the potential of controlling the surface cerium oxidation state using particle size and using this control to change the catalytic properties, this project investigated the effect of particle size and composition and the activity and selectivity of cerium oxide nanoparticles, and has served to expand the understanding of the properties of pure and mixed nanoparticle cerium oxide. This work explains the metric developed for measuring the catalytic properties of pure and mixed cerium oxide nanoparticles, which is also good at predicting the immediate and long-term behavior of nanoparticles in hydrogen fuel cells. This work also directly demonstrates praseodymium enrichm

Sintering of nanoparticles (NPs) of Ni supported on MgAl2O4 was monitored in situ using transmission electron microscopy (TEM) during exposure to an equimolar mixture of H2 and H2O at a pressure of 3.6 mbar at 750 °C, conditions relevant to methane steam reforming. The TEM images revealed an increase in the mean particle size due to disappearance of smaller, immobile NPs and the resultant growth of the larger NPs. A new approach for predicting the long-term sintering of NPs is presented wherein microscopic observations of the ripening of individual NPs (over a span of a few seconds) are used to extract energetic parameters that allow a description of the collective behavior of the entire population of NPs (over several tens of minutes).