| 1. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
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Capacitive effects of nitrogen doping on cellulose-derived carbon nanofibers
- 2015
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In: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584. ; 160, s. 59-65
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Journal article (peer-reviewed)abstract
- Carbons with valuable electrochemical characteristics are among the most convenient electrode materials used for energy storage. At the moment, their production is mostly reliant on unsustainable fossil fuels. A preferential sustainable production of enhanced carbonaceous electrodes can be achieved with more extensive utilization of abundant renewable resources instead of fossils. In this study, nitrogen-doped carbon nanofibers (CNFs) were synthesized from cellulose, the most abundant renewable resource, via consecutive steps of cellulose acetate electrospinning, subsequent deacetylation to cellulose, impregnation with nitrogen-containing additive (ammonium chloride), and carbonization. Results of material characterization showed that the carbonization of functionalized cellulose samples led to formation of CNFs doped with 4–5.6 at.% of nitrogen. In comparison with pristine CNFs N-doped samples had a slightly lower specific surface area, but higher conductivity and hydrophilicity. Moreover, electrochemical measurements indicated that the enhanced N-doped materials had about 2.5 times higher specific capacitance which was increasing throughout 1000 charge–discharge cycles. These results suggest that nitrogen doping method used in this study has a positive pseudocapacitive effect on the electrochemical performance of carbonized cellulose materials.
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| 2. |
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| 3. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
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Carbon nanotubes/nanofibers composites from cellulose for supercapacitors
- 2014
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In: 16th European Conference on Composite Materials, ECCM 2014; Seville; Spain; 22 June 2014 through 26 June 2014.
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Conference paper (peer-reviewed)abstract
- Cellulose-based carbon nanofibers (CNFs) with high mechanical strength and electrochemical stability were nitrogen-doped and functionalized with carbon nanotubes (CNTs) via two different methods. The diameter of incorporated CNTs was in the range of 1-20 nm. The doping with nitrogen atoms and incorporation of CNTs into the CNFs improved conductivity, while CNTs also increased surface area of the produced material. As a result, the composite materials with capacitance values up to 241 F/g were obtained.
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| 4. |
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| 5. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
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Hierarchical cellulose-derived carbon nanocomposites for electrostatic energy storage
- 2015
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 660:1, s. Art. no. 012062-
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Conference paper (peer-reviewed)abstract
- The problem of energy storage and its continuous delivery on demand needs new effective solutions. Supercapacitors are viewed as essential devices for solving this problem since they can quickly provide high power basically countless number of times. The performance of supercapacitors is mostly dependent on the properties of electrode materials used for electrostatic charge accumulation, i.e. energy storage. This study presents new sustainable cellulose-derived materials that can be used as electrodes for supercapacitors. Nanofibrous carbon nanofiber (CNF) mats were covered with vapor-grown carbon nanotubes (CNTs) in order to get composite CNF/CNT electrode material. The resulting composite material had significantly higher surface area and was much more conductive than pure CNF material. The performance of the CNF/CNT electrodes was evaluated by various analysis methods such as cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy and cyclic stability. The results showed that the cellulose-derived composite electrodes have fairly high values of specific capacitance and power density and can retain excellent performance over at least 2 000 cycles. Therefore it can be stated that sustainable cellulose-derived CNF/CNT composites are prospective materials for supercapacitor electrodes.
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| 6. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
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Hierarchical cellulose- derived CNF/CNT composites for electrostatic energy storage
- 2016
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In: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 1361-6439 .- 0960-1317. ; 26:12, s. 124001-
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Journal article (peer-reviewed)abstract
- Today many applications require new effective approaches for energy delivery on demand. Supercapacitors are viewed as essential energy storage devices that can continuously provide quick energy. The performance of supercapacitors is mostly determined by electrode materials that can store energy via electrostatic charge accumulation. This study presents new sustainable cellulose-derived composite electrodes which consist of carbon nanofibrous (CNF) mats covered with vapor-grown carbon nanotubes (CNTs). The CNF/CNT electrodes have high electrical conductivity and surface area: the two most important features that are responsible for good electrochemical performance of supercapacitor electrodes. The results show that the composite electrodes have fairly high values of specific capacitance (101 F g(-1) at 5 mV s(-1)), energy and power density (10.28 W h kg(-1) and 1.99 kW kg(-1), respectively, at 1 A g(-1)) and can retain excellent performance over at least 2000 cycles (96.6% retention). These results indicate that sustainable cellulose-derived composites can be extensively used in the future as supercapacitor electrodes.
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| 7. |
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| 8. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
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Sustainable carbon nanofibers/nanotubes composites from cellulose as electrodes for supercapacitors
- 2015
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 90:2, s. 1490-1496
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Journal article (peer-reviewed)abstract
- Supercapacitors are efficient energy storage devices with long lifetime and safe service. Their effectiveness,to a big extent, is dependent on electrode materials used for accumulation of energy in form ofelectrostatic charges. Over the last decades, variety of carbonaceous electrode materials has been used insupercapacitors. Mostly the production of such electrodes is still oriented on unsustainable fossil fuels asprecursors instead of sustainable renewable resources. In this study, freestanding carbonaceous electrodematerials for supercapacitors were derived from cellulose, the most abundant renewable resource. Theywere synthesized via carbonization of fibrillar cellulose impregnated with CNTs (carbon nanotubes). Theensuing composite materials consisted of a CNF (carbon nanofiber) scaffold (fiber diameter in the rangeof 50-250 nm) covered with layers of CNTs (tube diameter in the range of 1-20 nm). Moreover, thesecomposites were tested as electrode materials for supercapacitors. Incorporation of the CNTs into theCNFs improved electrical conductivity and also increased the surface area of the produced compositematerials, which led to high specific capacitance values (up to 241 F/g), cyclic stability, and powerdensity of these materials in electrochemical measurements. These results suggest that cellulose-derivedoriginal CNF/CNT composites are sustainable and efficient carbonaceous electrodes for supercapacitors.
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| 9. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
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Sustainable supercapacitor components from cellulose
- 2015
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In: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. ; 2015-October, s. 456-458
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Conference paper (peer-reviewed)abstract
- Supercapacitors with superb electrochemical characteristics are very promising energy storage devices. At present, the production of various supercapacitor components is mostly dependent on unsustainable fossil resources. The preferential sustainable production of these components can be achieved with more extensive utilization of abundant renewable resources instead of fossils. In this study, cellulose-derived electrodes and separators were synthesized and electrochemically evaluated in a supercapacitor device. This device showed the following results: aerial capacitance of 64 μF cm-2, fast current-voltage response below 15s at current density of 2 A g-1 and capacitance retention of 97.9% after 2000 charge-discharge cycles.
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| 10. |
- Köhler, Elof, 1980, et al.
(author)
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Analytic modeling of a high temperature thermoelectric module for wireless sensors
- 2014
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 557:1
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Conference paper (peer-reviewed)abstract
- A novel high temperature thermoelectric module with thermoelectric materials never before combined in a module is currently researched. The module placement in the cooling channels of a jet engine where the cold side will be cooled by high flow cooling air (550 degrees C) and the hot side will be at the wall (800 degrees C). The aim of the project is to drastically reduce the length of the wires by replacing wired sensors with wireless sensors and power these (3-10mW) with thermoelectric harvesters. To optimize the design for the temperature range and the environment an analytic model was constructed. Using known models for this purpose was not possible for this project, as many of the models have too many assumptions, e.g. that the temperature gradient is relatively low, that thick electrodes with very low resistance can be used, that the heat transfer through the base plates are perfect or that the aim of the design is to maximize the efficiency. The analytical model in this paper is a combination of several known models with the aim to examine what materials to use in this specific environment to achieve the highest possible specific power (mW/g).
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