Activity enhancers, nanoparticles

Enhanced Catalytic Activity of Nanoparticles Supported on Mesoporous Materials... 

We demonstrated that a naturally derived polysaccharide, chitosan, is capable of forming composite nanoparticles with silica. For encapsulated particles, we used silicification and biosilicification to encapsulate curcumin and analyzed the physicochemical properties of curcumin nanoparticles. It proved that encapsulated curcumin nanoparticles enhanced stability toward ultraviolet (UV) irradiation, antioxidation and antitumor activity, enhanced/added function, solubility, bioactivities/ bioavailability, and control release and overcame the immunobarrier. We present an in vitro study that examined the cytotoxicity of amorphous and composite silica nanoparticles to different cell lines. These bioactives include curcumin mdAntrodia cinnamomea. It is hoped that by examining the response of multiple cell lines to silica nanoparticles more basic information regarding the cytotoxicity as well as potential functions of silica in future oncological applications could become available. 

So far, we have presented several types of dealloyed Pt binary and ternary nanoparticle catalysts, which showed substantially enhanced ORR activities compared with pure Pt. The activity enhancement originated from a lattice-strain-controUed mechanism. However, it is still unclear why different transition metals resulted in different activities and stabilities and how particle structural characteristics such as size, shape, and composition would come into play. To understand these issues, it is important to achieve an atomic-scale understanding of the core-shell fine structures... 

It was fotmd that subsurface vacancies (Pig. 20.5) induce relatively weaker binding energies of O and especially of OH, and reduced Pt-Pt surface distances, which can explain the experimentally observed activity enhancement. We remark that in addition to explaining the interesting ORR activity enhancement on these novel porous/hollow nanoparticles, further studies regarding their oxidation and their stability to potential cycling are still required. 

As to the mechanistic origin of the activity enhancement in dealloyed Pt-Cu catalyst, the authors believe geometric effects play a key role, because the low residual Cu near-surface concentrations make significant electronic interactions between Pt and Cu surface atoms unlikely. Therefore, they suspect that the dealloying creates favorable structural arrangements of Pt atoms at the particle surface, such as more active crystallographic facets or more favorable Pt-Pt interatomic distances for the electroreduction of oxygen, as predicted by DPT calculations [47]. A fourfold enhancement in Pt mass activity on monodispersed PtsCo nanoparticles with particle size of 4.5 nm was also reported recently [95]. 

Progress has already been made over the years in enhancing the activity of the Pt nanoparticles dispersed on carbon support catalysts by alloying Pt with base metals such as Co, Ni, Fe, Rh, Cu, and Ti. The activity enhancements are a factor of 2-4, although the performance decreases over time. The Pt-alloys/C also fortuitously... 

The mechanism of flie ORR activity enhancement induced by adding W2C to Pt is not yet clear. Experimental results show that most possibly this is due to the synergistic effect between tungsten carbide nanoparticles and Pt at the interface. 

The main structural components in modem PEFCs are the porous composite electrodes. The primary purpose of utilizing porous electrodes is to enhance the active surface area of the catalyst by several orders of magnitude in comparison to planar electrodes with the same in-plane geometrical area. In the CLs, the fluxes of reactant gases, protons, and electrons meet at the catalyst particle surface. Active catalyst nanoparticles are located at spots that are connected simultaneously to the percolating phases of proton, electron, and gas transport media. An important implication of the electrode s finite thickness is the necessity to provide transport of neutral molecules and protons through the depth of the porous electrode. Additional overhead is caused by the transport of neutral reactants through FF, GDL, and MPL. This leads to specific potential losses in the electrodes, which will be considered in detail in Chapter 4. ... 

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