| 1. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
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Enhanced thermoelectric properties of Mg2Si by addition of TiO2 nanoparticles
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:2
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Tidskriftsartikel (refereegranskat)abstract
- The effects on the thermoelectric properties of Mg2Si when adding TiO2 nanoparticles have been evaluated experimentally. A batch of Mg2Si was prepared through direct solid state reaction and divided into portions which were mechanically mixed with different amounts of TiO2 nanoparticles ranging from 0.5 to 3 vol% and subsequently sintered to disks. All materials showed n-type conduction and the absolute value of the Seebeck coefficient was reduced with increasing amount of TiO2 added, while the electrical resistivity was greatly reduced. The thermal conductivity was surprisingly little affected by the addition of the nanoparticles. An optimum value of the thermoelectric figure-of-merit ZT = TS2 sigma/k was found for the addition of 1 vol% TiO2, showing almost three times higher ZT value than that of the pure Mg2Si. Larger TiO2 additions resulted in lower ZT values and with 3 vol% added TiO2 the ZT was comparable to the pure Mg2Si. The sintering process resulted in reduction or chemical reaction of all TiO2 to TiSi2 and possibly elemental titanium as well as reduced TiOx. The increased electrical conductivity and the decreased Seebeck coefficient were found due to an increased charge carrier concentration, likely caused by the included compounds or titanium-doping of the Mg2Si matrix. The low observed effect on the thermal conductivity of the composites may be explained by the relatively higher thermal conductivity of the included compounds, counter-balancing the expected increased grain boundary scattering. Alternatively, the introduction of compounds does not significantly increase the concentration of scattering grain boundaries.
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| 2. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
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Thermoelectric properties of partly Sb- and Zn-substituted Ba8Ga16Ge30 clathrates
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:11, s. 113711-
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Tidskriftsartikel (refereegranskat)abstract
- The effects on the thermoelectric properties of n-Ba8Ga16Ge30 when substituting small amounts of the Ga or Ge with Sb or Zn have been investigated. A number of syntheses were prepared in quaternary systems of Ba8Ga16Ge30 substituted with either Sb or Zn but only three samples were found to yield single phase products with nominal compositions of Ba8Ga15Sb1Ge30, Ba8Ga15Zn1Ge30 and Ba8Ga16Ge28Zn2, respectively. When Ge was substituted for Zn the resulting sample remained n-type and an increase in thermopower and a decrease in thermal conductivity were achieved. These positive effects were accompanied with an increased electrical resistivity and thus the ZT was only somewhat improved up to about 400 °C. When substituting Ga with either Sb or Zn samples remained n-type but showed decreased thermopower and increased electrical resistivity and thermal conductivity. It is thus concluded that substitution of Ga with Zn or Sb is detrimental for the thermoelectric properties of Ba8Ga16Ge30, whereas substitution of Ge with Zn appears a potent method for improving its performance.
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| 3. |
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| 4. |
- DAWODY, JAZAER, 1959, et al.
(författare)
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E4-Mistra, a research program for the development of an energy efficient low emission exhaust aftertreatment system for heavy duty vehicles
- 2012
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Ingår i: World Renewable Energy Forum, WREF 2012, Including World Renewable Energy Congress XII and Colorado Renewable Energy Society (CRES) Annual Conference. - : American Solar Energy Society. - 9781622760923 ; , s. 4530-4536
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Konferensbidrag (refereegranskat)abstract
- This paper presents a unique system approach applied in a joint academic - industrial research program, E4 Mistra, to reach the goals of energy efficiency and low emissions exhaust aftertreatment system for heavy duty vehicles. The high energy efficiency is achieved by heat recuperation, on-board hydrogen production for use in both an auxiliary power unit and for NOx reduction and by finding new solutions for making the after-treatment system active at low exhaust temperatures. To reach low particulate emissions a mechanical filter using a sintered metal filter is developed. Low NOx emissions are achieved by an efficient NOx reduction catalyst. The system is based on four technological advances: Thermoelectric material s for heat recuperation, catalytic reduction of NOx over innovative catalyst substrates using hydrocarbons from the fuel and H2 from a high efficiency fuel reformer, and particulate filtration over a porous metal filter.
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| 5. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
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Optimization of fuel cell membrane electrode assemblies for transition metal ion-chelating ordered mesoporous carbon cathode catalysts
- 2014
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 2:12, s. Art. no. 121102-
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal ion-chelating ordered mesoporous carbon (TM-OMC) materials were recently shown to be efficient polymer electrolyte membrane fuel cell (PEMFC) catalysts. The structure and properties of these catalysts are largely different from conventional catalyst materials, thus rendering membrane electrode assembly (MEA) preparation parameters developed for conventional catalysts not useful for applications of TM-OMC catalysts. This necessitates development of a methodology to incorporate TM-OMC catalysts in the MEA. Here, an efficient method for MEA preparation using TM-OMC catalyst materials for PEMFC is developed including effects of catalyst/ionomer loading and catalyst/ionomer-mixing and application procedures. An optimized protocol for MEA preparation using TM-OMC catalysts is described.
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| 6. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
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Transition Metal Ion-Chelating Ordered Mesoporous Carbons as Noble Metal-Free Fuel Cell Catalysts
- 2013
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 25:6, s. 856-861
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Tidskriftsartikel (refereegranskat)abstract
- A new concept for noble metal-free polymer electrolyte membrane fuel cell catalysts has been developed. The catalysts consist of chelated transition metal ions incorporated in a nitrogen-functionalized ordered mesoporous carbon matrix, which is evidenced by a combination of X-ray absorption fine structure analysis and high-resolution transmission electron microscopy. The ordered mesoporous carbon matrix of the catalyst offers an exceptionally high specific surface area and allows conceptually for a high degree of tuning, enabling controlled variability of, e.g., pore size and curvature and thickness of the pore walls of the catalysts. Single cell fuel cell tests of membrane electrode assemblies prepared with a cathode made of iron- or cobalt-based versions of the catalyst show high power densities, reaching up to one-third of a commercial Pt/C catalyst at 0.6 V.
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| 7. |
- Erkfeldt, Sara U, 1974, et al.
(författare)
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Alumina-supported In2O3, Ga2O3 and B2O3 catalysts for lean NOx reduction with dimethyl ether
- 2012
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 117, s. 369-383
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Tidskriftsartikel (refereegranskat)abstract
- Alumina-supported In2O3, Ga2O3 and B2O3 were investigated as catalysts for lean NOx reduction with DME as reducing agent and compared to pure Al2O3 and In2O3. The In2O3-promoted alumina catalysts showed the highest NOx conversion at low temperatures, although with a narrow temperature window. Pure In2O3, on the other hand, was inactive for NOx reduction with DME. The Ga2O3- and B2O3-promoted alumina catalysts gave the highest NOx conversion at higher temperatures, showed a temperature window similar to pure alumina, but were less sensitive to H2O inhibition. Possible reasons for these observations are discussed.
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| 8. |
- Erkfeldt, Sara U, 1974, et al.
(författare)
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Influence of the reducing agent for lean NOx reduction over Cu-ZSM-5
- 2011
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 102:3-4, s. 547-554
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Tidskriftsartikel (refereegranskat)abstract
- A range of ethers, alcohols and alkanes were compared as reducing agents for NOx over a Cu-ZSM-5 lean NOx catalyst. The nature of the reducing agent was found to determine the degree of NOx reduction. Methanol and DME were virtually inactive as reductants over this catalyst, while higher ethers and alcohols showed high NOx conversion. A detailed study was performed to investigate the differences. Among the studied variables, the chemical structure of the reductant was found to be especially important. Despite having a lower reducing capacity than DME, ethylene glycol was active for NOx reduction. It is concluded that a C-C bond in the reducing agent is required for lean NOx reduction over Cu-ZSM-5. The absence of this bond in DME and methanol explains their low activity for NOx reduction over this catalyst.
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| 9. |
- Erkfeldt, Sara U, 1974, et al.
(författare)
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Lean NOx Reduction with Various Bio-Diesels as Reducing Agents
- 2011
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 54:16-18, s. 1219-1223
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Tidskriftsartikel (refereegranskat)abstract
- Commercial Cu-ZSM-5- and Ag/Al2O3-based lean NOx catalysts were evaluated in a synthetic exhaust gas bench with the fuels RME, B30, B15, Agrodiesel 15, GTL, NExBTL, and MK1 as reducing agents. The influence of reductant was larger for Ag/Al2O3, albeit moderate, whereas the Cu-zeolite showed the highest NOx conversion at lower temperature for all alternative fuels tested.
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| 10. |
- Erkfeldt, Sara U, 1974, et al.
(författare)
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Promoting Effect of Triglyme on Lean NOx Reduction Over Ag/Al2O3
- 2012
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 142:2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- The highly oxygenated hydrocarbon triethylene glycol dimethyl ether or triglyme (CH3O-(C2H4O-)(3)CH3) was found to efficiently reduce NOx under lean conditions over Ag/Al2O3, but gave a low NOx conversion over Cu-ZSM-5. Furthermore, triglyme showed an extraordinary promoting effect when added together with propene as reducing agent for NOx over Ag/Al2O3 at low temperature. This is most likely due to that triglyme promotes the activation of propene.
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