| 41. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
-
Thermal stability and thermoelectric properties of p-type Ba8Ga16Ge30 clathrates
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 106:7, s. 074509 (artno)-
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of p-type Ba(8)Ga(16)Ge(3)0 clathrates grown from gallium flux has been tested by heat treatment in low pressure Ar atmosphere at 400, 600, and 800 degrees C. Significant gallium loss was observed for all samples during heat treatment. The treatment at 400 degrees C does not significantly change the sample properties, and the samples remain p-type and comparable to the untreated, as-prepared, sample. At 600 degrees C the sample switches from extrinsic p-type to extrinsic n-type, presumably due to significant loss of Ga, and shows a high thermopower but a reduced electrical conductivity compared to as-made n-type samples. Surprisingly, after a thermal treatment at 800 degrees C, the crystal structure seemingly loses less Ga, only reducing the hole concentration to near intrinsic levels and thus has a negative impact on ZT. Regardless of the heat treatment temperature of the p-type samples the thermal conductivity remained exceptionally low, for some samples 0.9 W/m K. Heat treatment can thus greatly affect the thermoelectric properties of p-type Ba(8)Ga(16)Ge(3)0, but the crystal structure remains intact. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3236635]
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| 42. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
-
Thermoelectric properties of partly Sb- and Zn-substituted Ba8Ga16Ge30 clathrates
- 2010
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:11, s. 113711-
-
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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| 43. |
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| 44. |
- DAWODY, JAZAER, 1959, et al.
(författare)
-
An integrated system for energy-efficient exhaust aftertreatment for heavy-duty vehicles
- 2015
-
Ingår i: Renewable Energy in the Service of Mankind. - Cham : Springer International Publishing. - 9783319177779 - 9783319177762 ; 1, s. 133-143
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- © Springer International Publishing Switzerland 2015. This chapter presents a unique system approach applied in a joint academic- industrial research programme, E4 Mistra, to attain the goals of high energy efficiency and low emissions in an exhaust aftertreatment system for heavy-duty vehicles. The high energy efficiency is achieved by heat recuperation, onboard hydrogen production for NOx reduction, and by finding new solutions for making the aftertreatment system active at low exhaust temperatures. To reach low particulate emissions, a mechanical filter using a sintered metal powder is developed and coated with catalytic material to improve the soot oxidation efficiency. Low NOx emissions are achieved by an efficient NOx reduction catalyst. The integrated E4 Mistra system comprises four technological advances: thermoelectric (TE) materials for heat recuperation, catalytic reduction of NOx over innovative catalyst substrates using either the onboard diesel or biodiesel, H2 from a high-efficiency fuel reformer, and particulate filtration over a porous metal filter. The TE materials are used in a TE generator (TEG) which converts thermal energy into electricity. The TEG is used to recuperate heat from the exhaust-gas recirculation (EGR) circuit of heavy-duty trucks and is expected to generate ~1 kW electric power from 20 kW heat in the exhaust gas. The TEG is integrated in a plate heat exchanger (HEX) designed particularly for this application. Apart from the knowledge and experiences in TEG and heat exchange technologies, a thorough fluid dynamics and TE analysis are performed in this project to understand the governing processes and optimize the system accordingly. The components of the E4 Mistra system are explained in the chapter in addition to test results, which show the system's capacity for H2 production, NOx conversion, particulate matter filtration and soot oxidation, and finally electric power generation via heat recuperation from the exhaust gas using the developed TEG-HEX system.
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| 45. |
- DAWODY, JAZAER, 1959, et al.
(författare)
-
E4-Mistra, a research program for the development of an energy efficient low emission exhaust aftertreatment system for heavy duty vehicles
- 2012
-
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
-
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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| 46. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
-
One-pot synthesis of transition metal ion-chelating ordered mesoporous carbon/carbon nanotube composites for active and durable fuel cell catalysts
- 2017
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 357, s. 87-96
-
Tidskriftsartikel (refereegranskat)abstract
- Development of non-precious metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells with high activity and durability and with optimal water management properties is of outmost technological importance and highly challenging. Here we study the possibilities offered through judicious selection of small molecular precursors used for the formation of ordered mesoporous carbon-based non-precious metal ORR catalysts. By combining two complementary precursors, we present a one-pot synthesis that leads to a composite material consisting of transition metal ion-chelating ordered mesoporous carbon and multi-walled carbon nanotubes (TM-OMC/CNT). The resulting composite materials show high specific surface areas and a carbon structure that exhibits graphitic signatures. The synthesis procedure allows for tuning of the carbon structure, the surface area, the pore volume and the ratio of the two components of the composite. The TM-OMC/CNT composites were processed into membrane electrode assemblies and evaluated in single cell fuel cell measurements where they showed a combination of good ORR activity and very high durability.
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| 47. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
-
Optimization of fuel cell membrane electrode assemblies for transition metal ion-chelating ordered mesoporous carbon cathode catalysts
- 2014
-
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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| 48. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
-
Recent Progress in Synthesis, Characterization and Evaluation of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction
- 2016
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 16:1, s. 4-22
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Forskningsöversikt (refereegranskat)abstract
- The oxygen reduction reaction (ORR) is usually catalyzed by precious metals. As the kinetics of the reaction are sluggish comparatively large amounts of precious metal are needed to achieve satisfactory reaction rates. This results in high cost of technologies utilizing the ORR, like low temperature fuel cells. Recent years have seen tremendous research efforts in the development of non-precious metal catalysts (NPMCs) with a wide range of newly developed materials resulting in improved catalyst materials, an increased understanding of the ORR mechanism on NPMC materials and better knowledge of the active site structure. Here we summarize the developments from 2011 and onwards with a special focus on carbon-based NPMCs developed for use in acid environments. We include explicit comparisons of PEMFC measurement results in all referenced studies and detailed information on the physical characterization methods used in various publications.
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| 49. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
-
The Active Site Structure of Transition Metal Ion-Chelating Ordered Mesoporous Carbon Fuel Cell Catalysts
- 2016
-
Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 16:1, s. 23-31
-
Tidskriftsartikel (refereegranskat)abstract
- Transition metal ion-chelating ordered mesoporous carbons (TM-OMCs) were studied as polymer electrolyte membrane fuel cell cathode catalysts. The active site structure of the TM-OMCs was studied by X-ray absorption spectroscopy in combination with variations of a range of synthesis variables of the TM-OMCs. The variations were found to have significant influence on the catalyst structure both in the mesoscale and on the atomic local structure allowing for detailed conclusions on the nature of the active sites. The main active site was found to be FeNx chelates. An additional highly active site was found and proposed to be a FeNx-dioxygen site. It was further found that the catalytic activity could be increased threefold by acid washing and subsequent heat treatment of the as-synthesized TM-OMC materials.
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| 50. |
- Dombrovskis, Johanna, 1986, et al.
(författare)
-
Transition Metal Ion-Chelating Ordered Mesoporous Carbons as Noble Metal-Free Fuel Cell Catalysts
- 2013
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 25:6, s. 856-861
-
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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