Nanoparticle cerium oxide and mixed cerium oxides for improved fuel cell lifetime.

摘要

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 enrichment of cerium-praseodymium oxide nanoparticles and how both size and composition affected the catalytic properties. Finally, this project has given new direction for doped cerium oxide nanoparticles in hydrogen fuel cells. Both gadolinium and praseodymium doped cerium oxide nanoparticles have been shown to be poor choices for improving fuel cell lifetime, while zirconium doped cerium oxide nanoparticles show the greatest promise for improving fuel cell lifetime as the doped oxides give both better catalytic behavior than pure cerium, and unlike pure cerium oxide, does not ultimately dissolve to give a destructive nanoparticle.