| 1. |
- Alnegren, Patrik, 1988, et al.
(författare)
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Metallic Bipolar Plates for High Temperature Polymer Electrolyte Membrane Fuel Cells
- 2016
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 16:1, s. 39-45
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Tidskriftsartikel (refereegranskat)abstract
- High temperature polymer membrane fuel cells (HTPEMFCs) are promising devices for future mobile applications. To minimize phosphoric acid migration from the membranes and to reduce the total stack weight and size metallic bipolar plates are a promising alternative. So far only very few published results are available on the use of metallic bipolar plates in HTPEMFCs. During this work a single test cell was equipped with metallic endplates to investigate the possibility of using metallic bipolar plates in HTPEMFC stacks. Furthermore we tried to simulate the environments present in an HTPEMFC by furnace exposures in an attempt to develop a simplified test method for accelerated corrosion of bipolar plate materials. It was found that the performance of the HTPEM test cell decreased by about 15 mu V h(-1). More corrosion products were seen on the cathode side samples, whereas on the anode side sample the corrosion attack of the steel was more severe. These results were successfully replicated in simulated furnace experiments.
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| 2. |
- Amin, Muhammad, 1979, et al.
(författare)
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CMOS compatible on-chip decoupling capacitor based on vertically aligned carbon nanofibers
- 2015
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Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101. ; 107, s. 15-19
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Tidskriftsartikel (refereegranskat)abstract
- On-chip decoupling capacitor of specific capacitance 55 pF/mu m(2) (footprint area) which is 10 times higher than the commercially available discrete and on-chip (65 nm technology node) decoupling capacitors is presented. The electrodes of the capacitor are based on vertically aligned carbon nanofibers (CNFs) capable of being integrated directly on CMOS chips. The carbon nanofibers employed in this study were grown on CMOS chips using direct current plasma enhanced chemical vapor deposition (DC-PECVD) technique at CMOS compatible temperature. The carbon nanofibers were grown at temperature from 390 degrees C to 550 degrees C. The capacitance of the carbon nanofibers was measured by cyclic voltammetry and thus compared. Futhermore the capacitance of decoupling capacitor was measured using different voltage scan rate to show their high charge storage capability and finally the cyclic voltammetry is run for 1000 cycles to assess their suitability as electrode material for decoupling capacitor. Our results show the high specific capacitance and long-term reliability of performance of the on-chip decoupling capacitors. Moreover, the specific capacitance shown is larger for carbon nanofibers grown at higher temperature.
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| 3. |
- Amin, Muhammad, 1979, et al.
(författare)
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Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts
- 2015
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Ingår i: Science and Technology of Advanced Materials. - : Informa UK Limited. - 1468-6996 .- 1878-5514. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer-Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer-Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy) ethyl methacrylate)/Pd (LauMA(x)-b-AEMA(y)/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer-Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 degrees C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 degrees C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.
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| 4. |
- Göransson, Gert, 1967, et al.
(författare)
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Characterisation of pulse plated Ni and Ni-Zn alloys.
- 2014
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- Nickel, zinc and nickel-rich NiZn alloys were formed on platinum by galvanostatic pulse plating from aqueous sulfate baths. The alloys were formed in three steps, first in anomalous deposition by a current pulse, secondly by dissolution and oxidation during the open circuit potential in each cycle and finally by anodic stripping of the fully plated sample. The treatment leaves a stable phase with an alloy composition of Ni0.8Zn0.2. The potential-time curves during the plating procedure were used to qualitatively describe the nucleation and growth processes. For Zn a fully covered surface was obtained after one pulse while for Ni and NiZn three-dimensional clusters were obtained in the first pulse. Further growth of these layers involves nucleation on the substrate and deposited clusters. The films were characterized with optical microscopy, SEM/EDX, AFM, XPS, TEM and by electrochemical methods. XPS revealed that the surfaces become gently oxidized by the stripping in the plating solution. For Ni a bi-layer of NiO/Ni(OH)2 was found on the surface while for NiZn mainly the hydroxide was detected. The electrocatalytic properties of the layers toward oxygen reduction in alkaline solution were explored and the NiZn alloy was proven to be an excellent catalyst for hydrogen peroxide production.
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| 5. |
- Göransson, Gert, 1967
(författare)
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Electrocatalytic properties of Ni hydroxides with Zn or Co in the Ni matrix
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The majority of the work in this thesis has been made with the improvement of the systems for electrochemical co-generation of chemicals and electricity in mind. This is an appealing but challenging way of producing chemicals with energy as a bi-product, and is commonly referred to as “green chemistry”. In this study electrocatalytic reactions have been investigated on electrodes for which Ni is the main active species with minor addition of Zn and Co in the Ni matrix. Three important reactions have been investigated; the oxygen reduction reaction (ORR) and propenol oxidation in alkaline solution, and the proton reduction reaction (PRR) at pH 2.8. The main focus has been on the improvement of Ni based catalysts for O2 reduction to H2O2 in alkaline solution. Ni has the advantage to forms a very stable oxide/hydroxide under alkaline conditions and Zn and Co are under certain conditions known to promote a 2e- reduction of O2. A novel type of Ni-rich NiZn alloys were produced by pulse plating under anomalous deposition of Ni and Zn in a sulphate electrolyte at pH 2.8. The alloys were seen to grow in isolated 3D clusters with substantial height before the surface became completely covered. EDX measurements showed a Ni-rich alloy of NixZn1-x where x is between 0.14 and 0.21 depending on plating conditions. The long range order of these alloys was not possible to determine and the short range order was therefore investigated by XAFS. The result showed that the alloy was organised as a multiphase system consisting of hcp- and ccp-like structural moieties with non-homogeneous distribution of Zn, rather than the expected solid solution. The correlation of the catalytic activity between structure and proton reduction for the NiZn alloy was not unambiguous, but the reaction rate was however clearly enhanced compared to solid Ni. The catalytic activity towards oxygen reduction in alkaline environment was studied on pulse plated Ni and NiZn. Alloying Ni with Zn clearly favoured the reaction path towards H2O2 and also lowered the overpotential for the reaction, even though the limiting currents indicated recessed electrode behaviour. Direct electrochemical oxidation of propen and propenol on the pulse plated Ni and NiZn electrode was investigated in alkaline solution by CV and DEMS. The direct oxidation of propen has been reported in the literature but could not be repeated. The oxidation of propenol overlapped with oxidation of the substrate and oxygen evolution in a complex manner, with propenal as the main product. It was shown that water oxidation starts when half of the Ni(OH)2 sites were oxidised to NiOOH which indicates a bi-nuclear water oxidation mechanism. A Ni(OH)2/NiOOH mediated reaction mechanism was proposed in analogy with previous studies for other alcohols and amines. To investigate the importance of the underlying Ni metal NiO was synthesised and made to an electrode by mixing it with carbon paste (CP). Ni0.75Co0.25O and CoO were also synthesised for comparison with NiO in the reactivity towards the ORR. 67 wt% NiO in CP increased the rate constant by 25 times compared to pure CP and showed the highest overall efficiency for ORR, for which the reduction to H2O2 prevails.
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| 6. |
- Göransson, Gert, 1967, et al.
(författare)
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Local Structure of Pulse Plated Ni Rich Ni-Zn Alloys and Its Effect on the Electrocatalytic Activity in the Hydrogen Evolution Reaction
- 2012
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Ingår i: Journal of The Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 159:9
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Tidskriftsartikel (refereegranskat)abstract
- Ni rich NiZn alloys were prepared on Pt substrates by galvanostatic pulse plating from baths of variable Ni:Zn ratio. The pulse plated NiZn alloys are crystallographically amorphous and their overall chemical composition shows relatively weak dependence on the pulse plating conditions. The local structure of the NiZn alloys determined from EXAFS spectra conforms to a model assuming coexistence of cubic and hexagonal-like arrangements. In the case of alloys plated from baths of lowZn content the cubic environment is zinc free and in the case of alloys plated from bath of high Zn content the Zn enters both cubic and hexagonal arrangement. The fraction of each of the coexisting local structures reflects the pulse plating conditions. The Ni rich NiZn alloys are active in the hydrogen evolution reaction showing electrocatalytic activity superior to that of bulk nickel. The electrocatalytic activity of the alloy samples in hydrogen evolution increases with increasing fraction of hexagonal local structure. This behavior is attributed to the residual strain mainly in the hexagonal-like environment.
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| 7. |
- Göransson, Gert, 1967, et al.
(författare)
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Oxidation of propenol on nanostructured Ni and NiZn electrodes in alkaline solution.
- 2014
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 139, s. 345-355
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of propenol on nanostructured pulse plated Ni and NiZn alloys in alkaline solution gives the corresponding aldehyde, propenal, as the major product. The process is redox mediated by the NiOOH/Ni(OH)2 couple and starts as soon as NiOOH is formed on the surface. Depending on the applied potential, propenol oxidation takes place in parallel with water oxidation. The latter requires a higher surface concentration of NiOOH compared to propenol oxidation, indicating that a binuclear mechanism for oxygen evolution prevails at low overpotentials. The redox reaction of nickel oxide is markedly slower at the NiZn alloy than for solid Ni or pulse plated Ni, which also is reflected in the oxidation of water and propenol. Separation of all three oxidation currents (Ni(OH)2, water and propenol) shows that pulse plated Ni is more efficient as catalyst than NiZn per NiOOH site, for both water and propenol oxidation. The role of Zn ions in the mixed NiZn hydroxide is discussed and a mechanism for propenol oxidation is suggested
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| 8. |
- Göransson, Gert, 1967, et al.
(författare)
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Oxygen reduction in alkaline solution using mixed carbon paste/NixCo1-xO electrodes
- 2014
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 146, s. 638-645
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen peroxide is a valuable chemical used in various applications and there is a demand for small on-site production plants. An attractive way to produce hydrogen peroxide is by electrochemical reduction of oxygen, using electrocatalytic materials that favour formation of hydrogen peroxide instead of water. Oxygen reduction on carbon in alkaline solution is known to produce mainly hydrogen peroxide but the overpotential is large and electrocatalytic materials need to be used in combination with carbon. In the present study, the mechanism of oxygen reduction in alkaline solution was studied using NiO, Ni0.75Co0.25O and CoO powders in a matrix of carbon paste. The desired product is hydrogen peroxide and the rotating ring disc technique was used to measure the amount of hydrogen peroxide formed. Two separate processes are observed with a peak shaped wave at low overpotentials and a sigmoidal process at high overpotentials. The charge involved in the first process and the heterogeneous rate constant for the second process were determined and found to be higher in the presence of oxide compared to pure carbon paste. Maximum increase was found for the NiO containing electrode with five times higher charge in the low overpotential region and 25 times higher rate constant in the high overpotential region. The mechanism of oxygen reduction comprises redox mediated electron transfer reactions involving Ni(II)/Ni(III) states on the surface. In the low overpotential region, where oxygen reduction on carbon is mediated by native quinone groups, the increased activity is explained by an interplay between the quinone and Ni(OH)2/NiOOH redox couples.
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| 9. |
- Kuzmenko, Volodymyr, 1987, et al.
(författare)
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Capacitive effects of nitrogen doping on cellulose-derived carbon nanofibers
- 2015
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584. ; 160, s. 59-65
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Tidskriftsartikel (refereegranskat)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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| 10. |
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