| 61. |
- Esseen, Per-Anders, et al.
(författare)
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Broad-scale distribution of epiphytic hair lichens correlates more with climate and nitrogen deposition than with forest structure
- 2016
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Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 46:11, s. 1348-1358
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Tidskriftsartikel (refereegranskat)abstract
- Hair lichens are strongly influenced by forest structure at local scales, but their broad-scale distributions are less understood. We compared the occurrence and length of Alectoria sarmentosa (Ach.) Ach., Bryoria spp., and Usnea spp. in the lower canopy of > 5000 Picea abies (L.) Karst. trees within the National Forest Inventory across all productive forest in Sweden. We used logistic regression to analyse how climate, nitrogen deposition, and forest variables influence lichen occurrence. Distributions overlapped, but the distribution of Bryoria was more northern and that of Usnea was more southern, with Alectoria's distribution being intermediate. Lichen length increased towards northern regions, indicating better conditions for biomass accumulation. Logistic regression models had the highest pseudo R2 value for Bryoria, followed by Alectoria. Temperature and nitrogen deposition had higher explanatory power than precipitation and forest variables. Multiple logistic regressions suggest that lichen genera respond differently to increases in several variables. Warmingdecreased the odds for Bryoria occurrence at all temperatures. Corresponding odds for Alectoria and Usnea decreased in warmer climates, but in colder climates, they increased. Nitrogen addition decreased the odds for Alectoria and Usnea occurrence under high deposition, but under low deposition, the odds increased. Our analyses suggest major shifts in the broad-scale distribution of hair lichens with changes in climate, nitrogen deposition, and forest management.
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| 62. |
- Esseen, Per-Anders, et al.
(författare)
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Multiple drivers of large-scale lichen decline in boreal forest canopies
- 2022
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Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:10, s. 3293-3309
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Tidskriftsartikel (refereegranskat)abstract
- Thin, hair-like lichens (Alectoria, Bryoria, Usnea) form conspicuous epiphyte communities across the boreal biome. These poikilohydric organisms provide important ecosystem functions and are useful indicators of global change. We analyse how environmental drivers influence changes in occurrence and length of these lichens on Norway spruce (Picea abies) over 10 years in managed forests in Sweden using data from >6000 trees. Alectoria and Usnea showed strong declines in southern-central regions, whereas Bryoria declined in northern regions. Overall, relative loss rates across the country ranged from 1.7% per year in Alectoria to 0.5% in Bryoria. These losses contrasted with increased length of Bryoria and Usnea in some regions. Occurrence trajectories (extinction, colonization, presence, absence) on remeasured trees correlated best with temperature, rain, nitrogen deposition, and stand age in multinomial logistic regression models. Our analysis strongly suggests that industrial forestry, in combination with nitrogen, is the main driver of lichen declines. Logging of forests with long continuity of tree cover, short rotation cycles, substrate limitation and low light in dense forests are harmful for lichens. Nitrogen deposition has decreased but is apparently still sufficiently high to prevent recovery. Warming correlated with occurrence trajectories of Alectoria and Bryoria, likely by altering hydration regimes and increasing respiration during autumn/winter. The large-scale lichen decline on an important host has cascading effects on biodiversity and function of boreal forest canopies. Forest management must apply a broad spectrum of methods, including uneven-aged continuous cover forestry and retention of large patches, to secure the ecosystem functions of these important canopy components under future climates. Our findings highlight interactions among drivers of lichen decline (forestry, nitrogen, climate), functional traits (dispersal, lichen colour, sensitivity to nitrogen, water storage), and population processes (extinction/colonization).
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| 63. |
- Fretz, Samuel Joseph, 1987, et al.
(författare)
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Amine- and Amide-Functionalized Mesoporous Carbons: A Strategy for Improving Sulfur/Host Interactions in Li-S Batteries
- 2020
-
Ingår i: Batteries and Supercaps. - : Wiley. - 2566-6223. ; 3:8, s. 757-765
-
Tidskriftsartikel (refereegranskat)abstract
- Lithium-sulfur (Li-S) batteries are of great interest due to their potentially high energy density, but the low electronic conductivity of both the sulfur (S-8) cathode active material and the final discharge product lithium sulfide (Li2S) require the use of a conductive host. Usually made of relatively hydrophobic carbon, such hosts are typically ill-suited to retain polar discharge products such as the intermediate lithium polysulfides (LiPs) and the final Li2S. Herein, we propose a route to increase the sulfur utilization by functionalizing the surface of ordered mesoporous carbon CMK3 with polar groups. These derivatized CMK3 materials are made using a simple two-step procedure of bromomethylation and subsequent nucleophilic substitution with amine or amide nucleophiles. We demonstrate that, compared to the unfunctionalized control, these modified CMK3 surfaces have considerably larger binding energies with LiPs and Li2S, which are proposed to aid the electrochemical conversion between S-8 and Li2S by keeping the LiPs species in close proximity to the carbon surface during Li-S battery cycling. As a result, the functionalized cathodes exhibit significantly improved specific capacities relative to their unmodified precursor.
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| 64. |
- Fretz, Samuel Joseph, 1987, et al.
(författare)
-
Bromomethylation of high-surface area carbons as a versatile synthon: Adjusting the electrode-electrolyte interface in lithium-sulfur batteries
- 2019
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7:34, s. 20013-20025
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Tidskriftsartikel (refereegranskat)abstract
- A two-step procedure for the surface functionalization of carbon materials has been developed. In the first step, mesoporous carbon (CMK3), carbon black (XC-72R Vulcan), and activated carbon (AC) are bromomethylated efficiently under mild conditions using commercially available reagents, resulting in reproducible surface bromine loadings, the concentrations of which correlate to the carbon's surface area. The resulting bromomethylated materials display excellent stability over the course of months when stored under ambient conditions. In the second step, substitution reactions with a variety of nucleophiles proceed efficiently. Example nucleophiles include azide, amines, ammonia and iodide, and exhibit high conversion yields. To demonstrate the application of this two-step functionalization method, bromomethylated CMK3, Br-CMK3, was reacted with ethylenediamine (EN) to form EN-CMK3, which was used as the conductive host for the sulfur cathode in lithium-sulfur (Li-S) batteries. Impregnation of EN-CMK3 with a lithium polysulfide-containing electrolyte with either lithium nitrate (LiNO3) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the supporting electrolyte increases the battery performance relative to pristine CMK3. With LiNO3, the surface-bonded EN allows for increased sulfur use and results in higher capacities of ca. 300 mA h g-1; with LiTFSI, the EN groups attenuate the polysulfide shuttle (LiPS shuttle) and the initial charging efficiency (ICE) is increased substantially from 3% to 73%. These results provide a proof-of-principle of the versatility of bromomethylated carbons as a useful starting material for a variety of functional materials. © 2019 The Royal Society of Chemistry.
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| 65. |
- Fretz, Samuel Joseph, 1987, et al.
(författare)
-
Influence of Iron Salt Anions on Formation and Oxygen Reduction Activity of Fe/N-Doped Mesoporous Carbon Fuel Cell Catalysts
- 2019
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:18, s. 17662-17671
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Tidskriftsartikel (refereegranskat)abstract
- Doping carbon materials with transition metal ions can greatly expand their utility, given these metal ions' unique catalytic activity, for example, in oxygen reduction in proton exchange membrane fuel cells. Unlike main group dopants, a counter anion to the metal cation must be selected and this choice has hitherto received little attention for this synthesis method. Herein, we describe the profound effects that the anion has on the resultant iron/nitrogen-doped ordered mesoporous carbons (Fe-OMC). To increase the iron loading and the number of iron-centered catalytically active sites, we selected three iron salts Fe(OAc)2, Fe(OTf)2, and Fe(BF4)2·6H2O, which show greatly enhanced solubility in the liquid carbon precursor (furfurylamine) compared to FeCl3·6H2O. The increased solubility leads to a significantly higher iron loading in the Fe-OMC prepared with Fe(OTf)2, but the increase in performance as cathode catalysts in fuel cells is only marginal. The Fe-OMCs prepared with Fe(OAc)2 and Fe(BF4)2·6H2O exhibited similar or lower iron loadings compared to the Fe-OMC prepared with FeCl3·6H2O despite their much higher solubilities. Most importantly, the different iron salts affect not only the final iron loading, but also which type of iron species forms in the Fe-OMC with different types showing different catalytic activity.
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| 66. |
- Fretz, Samuel Joseph, 1987, et al.
(författare)
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Lithium Sulfonate Functionalization of Carbon Cathodes as a Substitute for Lithium Nitrate in the Electrolyte of Lithium–Sulfur Batteries
- 2020
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 30:35
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Tidskriftsartikel (refereegranskat)abstract
- A method for grafting lithium sulfonate (LiSO3) groups to carbon surfaces is developed and the resulting carbons are evaluated for their potential to reduce the lithium polysulfide (LiPS) shuttle in lithium–sulfur (Li–S) batteries, replacing the common electrolyte additive lithium nitrate (LiNO3). The LiSO3 groups are attached to the ordered mesoporous carbon (CMK3) surface via a three-step procedure to synthesize LiSO3-CMK3 by bromomethylation, sodium sulfite (Na2SO3) substitution, and cation exchange. As a comparison, ethylenediamine (EN)-substituted CMK3, EN-CMK3, is also synthesized and tested. When used as a cathode in Li–S batteries, the unfunctionalized CMK3 suffers from strong LiPS shuttling as evidenced by its low initial Coulombic efficiencies (ICEs, <10%) compared to its functionalized derivatives EN-CMK3 and LiSO3-CMK3 (ICEs >75%). Postcycling analysis reveals the benefits of cathode surface functionalization on the lithium anode via an attenuated LiPS shuttle. When monitored at open circuit, the functionalized cathodes maintain their cell voltages much better than the CMK3 control and concurrent electrochemical impedance spectroscopy reveals their higher total cell resistance, which provides evidence for a reduced LiPS shuttle in the vicinity of both electrodes. Overall, such surface groups show promise as cathode-immobilized “lithium nitrate mimics.”.
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| 67. |
- Heijl, Richard, 1984, et al.
(författare)
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Thermoelectric properties of Ba8Ga16Ge30 with TiO2 nanoinclusions
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:4
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Tidskriftsartikel (refereegranskat)abstract
- The effects on thermal and electrical properties of adding small amounts of TiO2 nanoinclusions to bulk Ba8Ga16Ge30 clathrate have been investigated. The thermal properties were analysed using the transient plane source technique and the analysis showed a significant decrease in thermal conductivity as the volume fraction of TiO2 increased from 0 vol. % to 1.2 vol. %. The introduction of TiO2 nanoparticles caused a shift in the peak value of the Seebeck coefficient towards lower temperatures. The maximum value of the Seebeck coefficient was, however, only little affected. The introduction of TiO2 nanoparticles into the bulk Ba8Ga16Ge30 resulted in an increased electrical resistivity of the sample, thus simultaneously reducing the charge carrier contribution to the thermal conductivity, partly explaining the decrease in total thermal conductivity. Due to the large increase in resistivity of the samples, ZT was only somewhat improved for the material with 0.4 vol. % TiO2 while the ZT values of the other materials were lower than for the reference Ba8Ga16Ge30 material without TiO2 nanoparticles. The combined results are consistent with a scenario where the nanoparticle introduction causes a light doping of the semiconductor matrix and an increased concentration of phonon scattering centres.
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| 68. |
- Holma, Thomas, 1974, et al.
(författare)
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Continuous lean NOx reduction with hydrocarbons over dual pore system catalysts
- 2004
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 48:2, s. 95-100
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Tidskriftsartikel (refereegranskat)abstract
- In order to reduce CO2 emissions there is a trend towards an increased use of more fuel-efficient lean burn combustion engines and thus an increased need for deNOx catalysts for such engines. In this study a mechanical mixture of CoFER and HZSM-5 zeolites was studied as a dual pore system catalyst for the continuous lean reduction of NOx with isobutane as reducing agent. The degree of NOx conversion was found to be strongly dependent on the oxygen concentration in the gas mixture, and the highest degree of reduction was achieved with 10% O2. This optimum is explained by the need for NO2 as an intermediate for the catalyst to work efficiently, and that above a certain oxygen concentration O2 oxidises the hydrocarbon resulting in a lower reduction potential for NOx. At an operating temperature of 350 °C the conversion of NOx to N2 was 52% under steady-state conditions, but the efficiency can be improved further by optimisation of the oxidising zeolite and of the mixing ratio of the two zeolites.
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| 69. |
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| 70. |
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