| 1. |
- Chamoun, Mylad, et al.
(författare)
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Electrochemical Performance and in Operando Charge Efficiency Measurements of Cu/Sn-Doped Nano Iron Electrodes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Fe-air or Ni-Fe cells can offer low-cost and large-scale sustainable energy storage. At present, they are limited by low coulombic efficiency, low active material use, and poor rate capability. To overcome these challenges, two types of nanostructured doped iron materials were investigated: (1) copper and tin doped iron (CuSn); and (2) tin doped iron (Sn). Single-wall carbon nanotube (SWCNT) was added to the electrode and LiOH to the electrolyte. In the 2 wt. % Cu + 2 wt. % Sn sample, the addition of SWCNT increased the discharge capacity from 430 to 475 mAh g−1, and charge efficiency increased from 83% to 93.5%. With the addition of both SWCNT and LiOH, the charge efficiency and discharge capacity improved to 91% and 603 mAh g−1, respectively. Meanwhile, the 4 wt. % Sn substituted sample performance is not on par with the 2 wt. % Cu + 2 wt. % Sn sample. The dopant elements (Cu and Sn) and additives (SWCNT and LiOH) have a major impact on the electrode performance. To understand the relation between hydrogen evolution and charge current density, we have used in operando charging measurements combined with mass spectrometry to quantify the evolved hydrogen. The electrodes that were subjected to prolonged overcharge upon hydrogen evolution failed rapidly. This insight could help in the development of better charging schemes for the iron electrodes.
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| 2. |
- Eldesouky, A., et al.
(författare)
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Effect of grain size reduction of AA2124 aluminum alloy powder compacted by spark plasma sintering
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 609, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline (Average grain size similar to 200 nm) bulk AA2124 alloy was produced through high energy ball milling of microcrystalline powder followed by spark plasma sintering (SPS) at 480 degrees C with a holding time of 10 min. The effect of initial particle and grain size on the microstructural evolution as well as on the relative density and mechanical properties of the specimens consolidated through SPS and hot pressing (HP) at the same temperature for 60 min was investigated for ball milled nano-powders (NP), as well as as-received micro-powders (MP). Results showed that the NP specimens consolidated with SPS had the highest microhardness values compared to the other specimens despite not achieving full densification. On the other hand, a general increase in density, hardness, and compressive strength was observed for all SPS consolidates compared to HP. The presence of aluminum oxide and its influence on the consolidation process as well as the resulting mechanical properties of the bulk specimens is also discussed. (C) 2014 The Authors. Published by Elsevier B.V.
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| 3. |
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| 4. |
- Paulraj, Alagar Raj, et al.
(författare)
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Electrochemical Performance and in Operando Charge Efficiency Measurements of Cu/Sn-Doped Nano Iron Electrodes
- 2019
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Ingår i: Batteries. - : MDPI. - 2313-0105. ; :1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Fe-air or Ni-Fe cells can offer low-cost and large-scale sustainable energy storage. At present, they are limited by low coulombic efficiency, low active material use, and poor rate capability. To overcome these challenges, two types of nanostructured doped iron materials were investigated: (1) copper and tin doped iron (CuSn); and (2) tin doped iron (Sn). Single-wall carbon nanotube (SWCNT) was added to the electrode and LiOH to the electrolyte. In the 2 wt. % Cu + 2 wt. % Sn sample, the addition of SWCNT increased the discharge capacity from 430 to 475 mAh g−1, and charge efficiency increased from 83% to 93.5%. With the addition of both SWCNT and LiOH, the charge efficiency and discharge capacity improved to 91% and 603 mAh g−1, respectively. Meanwhile, the 4 wt. % Sn substituted sample performance is not on par with the 2 wt. % Cu + 2 wt. % Sn sample. The dopant elements (Cu and Sn) and additives (SWCNT and LiOH) have a major impact on the electrode performance. To understand the relation between hydrogen evolution and charge current density, we have used in operando charging measurements combined with mass spectrometry to quantify the evolved hydrogen. The electrodes that were subjected to prolonged overcharge upon hydrogen evolution failed rapidly. This insight could help in the development of better charging schemes for the iron electrodes.
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| 5. |
- Rabbani, Faiz, et al.
(författare)
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Cobalt selenium oxohalides : catalysts for water oxidation
- 2014
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; 43:10, s. 3984-33989
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Tidskriftsartikel (refereegranskat)abstract
- Two new oxohalides Co4Se3O9Cl2 and Co3Se4O10Cl2 have been synthesized by solid state reactions. They crystallize in the orthorhombic space group Pnma and the monoclinic space group C2/m respectively. The crystal structure of the two compounds are made up of similar building blocks; Co4Se3O9Cl2 is made up of [CoO4Cl2], [CoO5Cl] and [SeO3] polyhedra and Co3Se4O10Cl2 is made up of [CoO4Cl2] and [SeO3] polyhedra. As several Co-containing compounds have proved to be good catalysts for water oxidation, the activities of the two new compounds were compared with the previously found oxohalide Co5Se4O12Cl2 in reference to CoO and CoCl2. The one electron oxidant Ru(bpy)33+ was used as oxidizing species in a phosphate buffer and it was found that the activities of the oxohalide species were in between CoO and CoCl2. The roles of Cl− and PO43− ions are discussed.
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| 6. |
- Svengren, Henrik, et al.
(författare)
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A transition metal oxofluoride offering advantages in electrocatalysis and potential use in applications
- 2016
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 188, s. 481-498
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Tidskriftsartikel (refereegranskat)abstract
- The recently described solid solution ( Co,Ni,Mn)(3)Sb4O6F6 has proved stable and efficient as a catalyst for electrocatalytic water oxidation. The end component Co3Sb4O6F6 was found to be most efficient, maintaining a current density of j = 10 mA cm(-2) at an overpotential of 443 mV with good capability. At this current density, O-2 and H-2 were produced in the ratio 1 : 2 without loss of faradaic current against a Pt-cathode. A morphological change in the crystallite surface was observed after 0.5 h, however, even after 64.5 h, the overall shape and size of the small crystallites were unaffected and the electrolyte contained only 0.02 at% Co. It was also possible to conclude from in situ EXAFS measurements that the coordination around Co did not change. The oxofluorides express both hydrophilic and hydrophobic surface sites, incorporate a flexible metalloid element and offer the possibility of a mechanism that differs from other inorganic catalytic pathways previously described.
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| 7. |
- Svengren, Henrik, et al.
(författare)
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An assessment of the density of a large carnivore using a non-invasive method adapted for pilot studies
- 2010
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Ingår i: South African Journal of Wildlife Research. - : Southern African Wildlife Management Association. - 0379-4369 .- 1996-8477. ; 40:2, s. 121-129
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Tidskriftsartikel (refereegranskat)abstract
- The recent increase in habitat fragmentation across our continents calls for concern with regard to the future survival of wildlife. In this respect corridors and stepping-stones are important. Targeting a wide-ranging top-trophic carnivore, the aim of this study was to estimate the density and abundance of leopards (Panthera pardus) in an area that might serve as a stepping-stone between other larger protected areas. We deliberately used a survey method designed to balance resource utilization and relevance of the results to fit the purpose of a pilot survey. The Sangare Ranch Conservancy is a newly established, privately owned park in Kenya. Using non-invasive techniques we identified 13 individual leopards composing of approximately 80% males. In addition, we found 28 leopard signs per 100 km walked, a predicted carrying capacity of around nine leopards/100 km(2) and a leopard predation pressure on neighboring goat stock of 5.6%. We suggest that the conservancy plays an important role for leopard ecology and comprises a geographical and ecological stepping-stone between other protected wild habitats in the region. The study also suggests more efficient methods for future non-invasive studies.
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| 8. |
- Svengren, Henrik, et al.
(författare)
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An Oxofluoride Catalyst Comprised of Transition Metals and a Metalloid for Application in Water Oxidation
- 2015
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 21:37, s. 12991-12995
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Tidskriftsartikel (refereegranskat)abstract
- The application of the recently discovered oxofluoride solid solution (CoxNi1-x)(3)Sb4O6F6 as a catalyst for water oxidation is demonstrated. The phase exhibits a cubic arrangement of the active metal that forms oxo bridges to the metalloid with possible catalytic participation. The Co3Sb4O6F6 compound proved to be capable of catalyzing 2H(2)OO(2)+4H(+)+4e(-) at 0.33V electrochemical and 0.39V chemical overpotential with a TOF of 4.410(-3), whereas Ni3Sb4O6F6 needs a higher overpotential. Relatively large crystal cubes (0.3-0.5mm) are easily synthesized and readily handled as they demonstrate both chemical resistance to wear after repeated insitu tests under experimental conditions, and have a mechanical hardness of 270V0.1 using Vickers indentation. The combined properties of this compound offer a potential technical advantage for incorporation to a catalytic interface in future sustainable fuel production.
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| 9. |
- Svengren, Henrik, et al.
(författare)
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Direct Synthesis of Two Inorganic Catalysts on Carbon Fibres for the Electrocatalytic Oxidation of Water
- 2017
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 23:3, s. 568-575
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Tidskriftsartikel (refereegranskat)abstract
- Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co3Sb4O6F6 and the new compound CoSbO4. The compounds express large differences in their morphology: CoSbO4 grows as thin needles whereas Co3Sb4O6F6 grows as larger facetted crystals. Despite the smaller surface area the latter compound shows a better catalytic performance. When the compound Co3Sb4O6F6 was used it gave a low increase of +0.028 mV h(-1) at an overpotential of eta = 472 mV after 10 h and a stability of +0.48 mV h(-1) at an overpotential of eta = 488 mV after 60 h. The leakages of Co and Sb were negligible and only <0.001 at% Co and approximately 0.02 at% Sb were detected in the electrolyte.
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| 10. |
- Svengren, Henrik, et al.
(författare)
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Radioisotope and metal content in a Lake Nakuru sediment core – accumulation rate and 3 inventories
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Nakuru environment is a hot spot both for human population and for biological conservation with a large number of species protected in the well visited Lake Nakuru National Park. Reoccurring mass die-off of the Lesser Flamingo in Lake Nakuru as well as cases of intoxication of humans within the water catchment area have gained attention and dedicated a significant amount of research over the recent decades. The toxicological histories of natural and anthropogenic activities are reflected by accumulated compounds in the water body sediments. In this study, a sediment core obtained from the central and deepest point of Lake Nakuru was sliced with 5 mm resolution and analyzed with the 210Pb dating method. The results show a linear accumulation rate of 1.3 mm y-1 and a mass accumulation rate of 0.027 g cm-2 y-1. Further analysis resulted in core profiles of organic material decay, phosphorus concentration gradient and total content of heavy metals in the lake water and in the sediment. In addition, analysis of 226Ra, 137Cs, 239+240Pu, 228Th/232Th was performed.
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