| 1. |
- Pourrahimi, Amir Masoud, 1985, et al.
(författare)
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Making an ultralow platinum content bimetallic catalyst on carbon fibres for electro-oxidation of ammonia in wastewater
- 2019
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Ingår i: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 3:8, s. 2111-2124
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Tidskriftsartikel (refereegranskat)abstract
- Electrocatalysis of wastewater containing ammonia is a promising alternative to chemical and biological water purification for several reasons, one being that energy-rich hydrogen gas is generated as a by-product while the reaction can be strictly controlled to meet demands. An objective has been to reduce the loading of expensive platinum (Pt) in the catalyst electrodes, and to reduce the poisoning of the metal surface during the electrolysis. Herein, the co-deposition of a copper-platinum (Cu-Pt) bimetallic alloy onto carbon filaments, stripped from their polymeric coating, is shown to give an electrocatalytic performance superior to that of pure Pt at a content of less than 3 wt% Pt. The key to the enhanced performance was to take advantage of micrometer-sized carbon filaments to distribute a very large bimetallic alloy surface uniformly over the filaments. The Cu-Pt-alloy-coated filaments also suffer less electrode poisoning than pure Pt, and are bonded more strongly to the carbon fibre due to better mechanical interlocking between the bimetallic alloy and the carbon filaments. High-resolution electron microscopy studies combined with a tuned electro-deposition process made it possible to tailor the catalyst micro/nano morphology to reach a uniform coverage, surrounding the entire carbon filaments. The results are promising steps towards large-scale wastewater treatment, combined with clean energy production from regenerated hydrogen.
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| 2. |
- Ahmed, Abdelsalam, et al.
(författare)
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Fire-retardant, self-extinguishing triboelectric nanogenerators
- 2019
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 59, s. 336-345
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Tidskriftsartikel (refereegranskat)abstract
- The development of highly sensitive sensors and power generators that could function efficiently in extreme temperatures and contact with fire can be lifesaving but challenging to accomplish. Herein, we report, for the first time, a fire-retardant and self-extinguishing triboelectric nanogenerator (FRTENG), which can be utilized as a motion sensor and/or power generator in occupations such as oil drilling, firefighting or working in extreme temperature environments with flammable and combustible materials. The device takes advantage of the excellent thermal properties of carbon derived from resorcinol-formaldehyde aerogel whose electrical, mechanical and triboelectric properties have been improved via the introduction of Polyacrylonitrile nanofibers and graphene oxide nanosheets. This FRTENG is not flammable even after 90 s of trying, whereas conventional triboelectric materials were entirely consumed by fire under the same conditions. The developed device shows exceptional charge transfer characteristics, leading to a potential difference up to 80 V and a current density up to 25 mu A/m(2). When integrated into firefighter's shoes, the FRTENG is able to discern the movements of a firefighter in hazardous situations, while providing the high thermal stability missing in conventional TENGs. The fire-retardant and self-extinguishing characteristics offered by the FRTENG makes it a path-breaking device for lifesaving wearable applications.
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| 3. |
- Becerra Garcia, Marley, 1979-, et al.
(författare)
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High field conduction in mineral oil based zno nanofluids prior to negative streamer inception
- 2021
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Ingår i: Journal of Physics Communications. - : IOP Publishing. - 2399-6528. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- The electric conduction under intense electric fields (up to ∼ 10 V/m) in nanofluids using surface-modified ZnO–C nanoparticles dispersed in mineral oil as host, is investigated with both experiments and numerical simulations. The measurements are used to estimate unknown parameters necessary to represent the generation and loss of electrons in an electrohydrodynamic model for mineral oil with and without ZnO–C nanoparticles in a needle-plane configuration. The model suggests that ZnO–C nanoparticles induce an enhanced field emission from negative needles, explaining the significantly larger conduction currents measured in the nanofluid compared with those in the host liquid. It is also found that the scavenging of electrons by ZnO–C nanoparticles is a process which is negligible compared with the loss of electrons due to attachment in mineral oil. It is shown that ZnO–C nanoparticles hinder the streamer initiation process by reducing the effective electric field at the tip of the needle. This electric field reduction is caused by the combined effect of enhanced electron injection through ZnO–C nanoparticles and strong electron attachment in mineral oil. Thus, the electric field on the needle tip reaches the same threshold value when the streamer is incepted in the nanofluid as in mineral oil, although at a larger voltage. Solid evidence indicating that the additional electron scavenging and the reduced electron mobility introduced by nanoparticles has no effect in the conduction currents and in the negative streamer inception in the tested ZnO–C nanofluids is shown.
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| 4. |
- D'Auria, Silvia, et al.
(författare)
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Polyethylene Based Ionomers as High Voltage Insulation Materials
- 2023
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Ingår i: Advanced Functional Materials. - 1616-3028 .- 1616-301X. ; 33:36
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Tidskriftsartikel (refereegranskat)abstract
- Polyethylene based ionomers are demonstrated to feature a thermo-mechanical and dielectric property portfolio that is comparable to cross-linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct-current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high-pressure/high-temperature free radical copolymerization of ethylene in the presence of small amounts of ion-pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt-processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct-current (DC) electrical conductivity of 1 to 6·10−14 S m−1 at 70 °C and an electric field of 30 kV mm−1. Evidently, the investigated ionomers represent a promising alternative to XLPE-based high voltage insulation, which may permit to ease the production as well as end-of-use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts.
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| 5. |
- Gubanski, Stanislaw, 1950, et al.
(författare)
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Polymer composition and electrical devices
- 2021
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- The invention relates to a polymer composition comprising a polymer (a) and a nanoparticle filler (b), wherein the polymer composition comprises a volume percentage (vol. %) of the nanoparticle filler (b), which is Dvol vol. %, and has a center-to-center average distance, in nanometer (nm), in two dimensions (2D) and with a free radius, from one nanoparticle to its nearest nanoparticle neighbour, which is R1st nm, and wherein the polymer composition shows a dependency between said center-to-center average distance to nearest neighbour, R1st, and said volume percentage, Dvol vol. %, which is R1st=E/(Dvol+0.3)+F, wherein Dvol1≤Dvol≤Dvol2, E1≤E≤E2, F1≤F≤F2, and Dvol1 is 0.010 and Dvol2 is 4.4, E1 is 100 and E2 is 280, and F1 is 50 and F2 is 140; an electrical device, e.g. a power cable; and a process for producing an electrical device.
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| 6. |
- Hammarström, Thomas, 1974, et al.
(författare)
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DC Electrical Trees in Polymer Insulation Inflicted by Rapidly Decreasing Short Circuit Voltage Flanks
- 2022
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Ingår i: ICD 2022 - IEEE 2022 4th International Conference on Dielectrics, Proceedings. ; , s. 154-157
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Konferensbidrag (refereegranskat)abstract
- This work aims to study the appearance and changes in the partial discharge pattern due to electrical treeing degradation of XLPE, a copolymer blend, crosslinked through a byproduct-free curing reaction, and LDPE when exposed to a series of high voltage short circuits. A wire-plane type test object has been employed and the presence of electrical trees were detected visually and by measuring the partial discharge (PD) activity. It was observed that PD characteristics changed with increased number of short circuit events. In particular, both the summed amount of PD magnitudes as well as the number of PDs increased due to the growth of electrical trees. These results were in good agreement with the hypothesis of electromechanical stresses analogue to mechanical crack formation which increase the volume of the defects thus affecting the PD characteristics. Additionally, clear differences in the phase distribution of PDs were observed that allows to use them as indicators of material performance and as complement to DC conductivity measurements and frequency domain spectroscopy.
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| 7. |
- Hu, Wei, et al.
(författare)
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Axisymmetric and Asymmetric Naphthalene-Bisthienothiophene Based Nonfullerene Acceptors: On Constitutional Isomerization and Photovoltaic Performance
- 2020
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:6, s. 5734-5744
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Tidskriftsartikel (refereegranskat)abstract
- Two pairs of constitutional isomers of fused-octacyclic nonfullerene acceptors (NFAs) based on a naphthalene-bisthienothiophene core with or without fluorination at the ending groups have been developed. Compared with the axisymmetric NFAs N66-IC and N66-2FIC with two six-member-ring bridges, their asymmetric constitutional isomers N65-IC and N65-2FIC both with one six-member-ring bridge and one five-member-ring bridge exhibit remarkable red-shifted absorption, higher crystallinity, and slightly down-shifted LUMO energy levels. Organic solar cells based on PBDB-T-2F:N65-2FIC achieved a promising power conversion efficiency of 10.19%, which is three times higher than that of its counterpart PBDB-T-2F:N66-2FIC cell (3.46%). While being blended with PBDB-T as the donor material, the asymmetric acceptor analogue N65-IC based solar cell pronounces a PCE of 9.03%, being significantly improved from that of 5.45% for the PBDB-T:N66-IC based cell, which is in consistency with the results from those cells from their both fluorinated donor and acceptor counterparts. Design rules on either both fluorinated, both nonfluorinated, or cross-combined donor/acceptors for device fabrication has been explored. In addition, PBDB-T-2F:N65-2FIC possesses very promising device stability with 85% of its initial PCE after an exposure time of 1500 h under one sun illumination, which is meaningful for their future commercial devices.
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| 8. |
- Kumara, Sarath, 1979, et al.
(författare)
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Comparison of Different Methods for Characterization of DC Conductivity of Insulating Polymers
- 2020
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Ingår i: Proceedings of the 2020 IEEE 3rd International Conference on Dielectrics, ICD 2020. ; , s. 435-438
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Konferensbidrag (refereegranskat)abstract
- Knowledge of the electrical conductivity of polymer insulation materials is important for designing cable components for high-voltage direct-current (HVDC) applications. The aim of this study is to compare three measuring techniques, namely, charging current, surface potential decay (SPD) and dielectric response measurements. The first method is time consuming because it requires that the bulk current through a material is recorded while a direct-current (DC) voltage is applied for a prolonged period of time. The DC conductivity is calculated from the steady state current, which is typically only approached after several hours to days. In SPD experiments, the decay of a surface potential, induced by corona charging, is monitored and utilized to estimate the field-dependent conductivity from one single measurement. Frequency domain dielectric spectroscopy (FDS) measurements allow to estimate the DC conductivity from the low frequency response. Two materials, low density polyethylene (LDPE) and cross-linked polyethylene (XLPE), were used. The SPD measurements overestimated the conductivities of both materials compared to those obtained by the charging current method for the entire studied range of temperature (30-70 ºC) and electric field (10–50 kV/mm). At the same, FDS measurements underestimated the temperature dependency of the conductivity for both LDPE and XLPE. It was noticed that the SPD technique demonstrated a very good repeatability and required significantly shorter measuring time compared to other methods.
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| 9. |
- Kumara, Sarath, 1979, et al.
(författare)
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DC Electrical Trees in XLPE Induced by Short Circuits
- 2021
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; 2021-December, s. 275-278
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Konferensbidrag (refereegranskat)abstract
- This study aims at understanding electrical treeing in XLPE due to DC short circuits. A wire-plane type test object has been excited by a series of short circuit events after applying DC voltages of different levels and duration. The development of thin filamentary trees and their morphology was correlated with the inception probability. It was observed that the latter as well as the length of the trees increased with the magnitude of the applied voltage and the number of short circuit events. These observations are in good agreement with the hypothesis that the release of stored energy during short circuit causes electromechanical stresses in the materials giving rise to treeing process analogous to mechanical crack formation. It is suggested that the application of an adequate number of short circuits at a suitable voltage level and a sufficient stress duration can be used as a DC treeing test procedure.
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| 10. |
- Kumara, Sarath, 1979, et al.
(författare)
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Electrical Characterization of a New Crosslinked Copolymer Blend for DC Cable Insulation
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- To design reliable high voltage cables, clean materials with superior insulating properties capable of operating at high electric field levels at elevated temperatures are required. This study aims at the electrical characterization of a byproduct-free crosslinked copolymer blend, which is seen as a promising alternative to conventional peroxide crosslinked polyethylene currently used for high voltage direct current cable insulation. The characterization entails direct current (DC) conductivity, dielectric response and surface potential decay measurements at different temperatures and electric field levels. In order to quantify the insulating performance of the new material, the electrical properties of the copolymer blend are compared with those of two reference materials; i.e., low-density polyethylene (LDPE) and peroxide crosslinked polyethylene (XLPE). It is found that, for electric fields of 10–50 kV/mm and temperatures varying from 30 °C to 70 °C, the DC conductivity of the copolymer blend is in the range of 10−17–10−13 S/m, which is close to the conductivity of crosslinked polyethylene. Furthermore, the loss tangent of the copolymer blend is about three to four times lower than that of crosslinked polyethylene and its magnitude is on the level of 0.01 at 50 °C and 0.12 at 70 °C (measured at 0.1 mHz and 6.66 kV/mm). The apparent conductivity and trap density distributions deduced from surface potential decay measurements also confirmed that the new material has electrical properties at least as good as currently used insulation materials based on XLPE (not byproduct-free). Thus, the proposed byproduct-free crosslinked copolymer blend has a high potential as a prospective insulation medium for extruded high voltage DC cables.
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