| 1. |
- Ekström, Henrik, et al.
(författare)
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Nanometer-thick films of titanium oxide acting as electrolyte in the polymer electrolyte fuel cell
- 2007
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 52:12, s. 4239-4245
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Tidskriftsartikel (refereegranskat)abstract
- 0–18 nm-thick titanium, zirconium and tantalum oxide films are thermally evaporated on Nafion 117 membranes, and used as thin spacer electrolyte layers between the Nafion and a 3 nm Pt catalyst film. Electrochemical characterisation of the films in terms of oxygen reduction activity, high frequency impedance and cyclic voltammetry in nitrogen is performed in a fuel cell at 80 ◦C and full humidification. Titanium oxide films with thicknesses up to 18 nm are shown to conduct protons, whereas zirconium oxide and tantalum oxide block proton transport already at a thickness of 1.5 nm. The performance for oxygen reduction is higher for a bi-layered film of 3 nm platinum on 1.5 or 18 nm titanium oxide, than for a pure 3 nm platinum film with no spacer layer. The improvement in oxygen reduction performance is ascribed to a higher active surface area of platinum, i.e. no beneficial effect of combining platinum with zirconium, tantalum or titanium oxides on the intrinsic oxygen reduction activityis seen. The results suggest that TiO2 may be used as electrolyte in fuel cell electrodes, and that low-temperature proton exchange fuel cells could be possible using TiO2 as electrolyte.
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| 2. |
- Eriksson, Björn, et al.
(författare)
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Quantifying water transport in anion exchange membrane fuel cells
- 2019
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Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 44:10, s. 4930-4939
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Tidskriftsartikel (refereegranskat)abstract
- Sufficient water transport through the membrane is necessary for a well-performing anion exchange membrane fuel cell (AEMFC). In this study, the water flux through a membrane electrode assembly (MEA), using a Tokuyama A201 membrane, is quantified using humidity sensors at the in- and outlet on both sides of the MEA. Experiments performed in humidified inert gas at both sides of the MEA or with liquid water at one side shows that the aggregation state of water has a large impact on the transport properties. The water fluxes are shown to be approximately three times larger for a membrane in contact with liquid water compared to vaporous. Further, the flux during fuel cell operation is investigated and shows that the transport rate of water in the membrane is affected by an applied current. The water vapor content increases on both the anode and cathode side of the AEMFC for all investigated current densities. Through modeling, an apparent water drag coefficient is determined to −0.64, indicating that the current-induced transport of water occurs in the opposite direction to the transport of hydroxide ions. These results implicate that flooding, on one or both electrodes, is a larger concern than dry-out in an AEMFC.
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| 3. |
- Gao, Weiming, et al.
(författare)
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Binuclear iron-sulfur complexes with bidentate phosphine ligands as active site models of Fe-hydrogenase and their catalytic proton reduction
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 46:6, s. 1981-1991
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Tidskriftsartikel (refereegranskat)abstract
- The displacement of CO in a few simple Fe(I)-Fe(I) hydrogenase model complexes by bisphosphine ligands Ph2P-(CH2)(n)-PPh2 [with n = 1 (dppm) or n = 2 (dppe)] is described. The reaction of [{mu-(SCH2)(2)CH2}Fe-2(CO)(6)] (1) and [{mu-(SCH2)(2)N(CH2CH2CH3)}Fe-2(CO)(6)] (2) with dppe gave double butterfly complexes [{mu-(SCH2)(2)CH2}Fe-2(CO)(5)(Ph2PCH2)](2) (3) and [{mu-(SCH2)(2)N(CH2CH2CH3)}Fe-2(CO)(5)(Ph2PCH2)](2) (4), where two Fe2S2 units are linked by the bisphosphine. In addition, an unexpected byproduct, [{mu-(SCH2)(2)N(CH2CH2CH3)}Fe-2(CO)(5){Ph2PCH2CH2(Ph2PS)}] (5), was isolated when 2 was used as a substrate, where only one phosphorus atom of dppe is coordinated, while the other has been converted to PS, presumably by nucleophilic attack on bridging sulfur. By contrast, the reaction of 1 and 2 with dppm under mild conditions gave only complexes [{mu-(SCH2)(2)CH2}Fe-2(CO)(5)(Ph2PCH2PPh2)] (6) and [{mu-(SCH2)(2)N(CH2CH2CH3)}Fe-2(CO)(5)(Ph2PCH2PPh2)] (8), where one ligand coordinated in a monodentate fashion to one Fe2S2 unit. Furthermore, under forcing conditions, the complexes [{mu-(SCH2)(2)CH2}Fe-2(CO)(4){mu-(Ph2P)(2)CH2}] (7) and [{mu-(SCH2)(2)N(CH2CH2CH3)}Fe-2(CO)(4){mu-(Ph2P)(2)CH2}] (9) were formed, where the phosphine acts as a bidentate ligand, binding to both the iron atoms in the same molecular unit. Electrochemical studies show that the complexes 3, 4, and 9 catalyze the reduction of protons to molecular hydrogen, with 4 electrolyzed already at -1.40 V versus Ag/AgNO3 (-1.0 V vs NHE).
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| 4. |
- Jenssen, Anders, et al.
(författare)
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Effect of bwr environment on the fracture toughness of alloy X-750
- 2013
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Ingår i: Environmental Degradation of materials in nuclear power systems. - Houston : NACE International.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fracture toughness testing is normally performed in air on specimens provided with a transgranular pre-crack generated in air by fatigue loading. However, stress corrosion cracks in nuclear power plants are usually intergranular and in contact with reactor coolant. Fracture toughness data used in e.g., flaw tolerance analyses are generated in air with transgranular pre-cracks. Since the effects of the fracture mode of the pre-crack and the reactor coolant on the fracture toughness are not known in detail, it is important to investigate if the data used today are sufficiently conservative. Compact tension (CT) specimens of Alloy X-750 with thickness (B) 9.3 mm and width (W) 18.6 mm were tested under various conditions with the objective to investigate the possible effects of an intergranular pre-crack as well as BWR coolant on the fracture toughness. Three specimens were tested under constant stress intensity (K) in simulated BWR normal water chemistry (NWC) in order to generate an intergranular pre-crack. One specimen was removed from the autoclave and then fracture toughness tested in air at 288 ºC. The other specimens remained in the autoclave in the presence of simulated BWR coolant during the fracture toughness test. For comparison, specimens with a transgranular pre-crack were tested in air at 288 ºC. Neither the fracture mode, nor the BWR coolant appeared to have any adverse effects on the fracture toughness in these tests.
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| 5. |
- Ryen, Øyvind, et al.
(författare)
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Strengthening mechanisms in solid solution aluminum alloys
- 2006
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 37A:6, s. 1999-2006
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Tidskriftsartikel (refereegranskat)abstract
- A number of commercial and high-purity non-heat-treatable aluminum alloys are investigated in this work. It is found that both magnesium and manganese in solid solution give a nearly linear concentration dependence of the strength at a given strain for commercial alloys. This deviates from high-purity AlMg binary alloys, where a parabolic concentration dependence is found. Mn in solid solution is found to give a considerably higher strengthening effect per atom than Mg, both in terms of yield stress and initial work hardening rate. This strengthening effect is stronger comparing commercial grades to high-purity alloys. This enhanced strengthening is believed to be a synergy or clustering effect caused by interaction between Mn atoms and trace elements, probably silicon, in solid solution.
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