| 1. |
- Ayedh, H. M., et al.
(författare)
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Controlling the carbon vacancy in 4H-SiC by thermal processing
- 2018
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Ingår i: ECS Transactions. - : Electrochemical Society Inc.. - 1938-6737 .- 1938-5862. ; , s. 91-97
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Konferensbidrag (refereegranskat)abstract
- The carbon vacancy (Vc) is perhaps the most prominent point defect in silicon carbide (SiC) and it is an efficient charge carrier lifetime killer in high-purity epitaxial layers of 4H-SÌC. The Vc concentration needs to be controlled and minimized for optimum materials and device performance, and an approach based on post-growth thermal processing under C-rich ambient conditions is presented. It utilizes thermodynamic equilibration and after heat treatment at 1500 °C for 1 h, the Vc concentration is shown to be reduced by a factor-25 relative to that in as-grown state-of-the-art epi-layers. Concurrently, a considerable enhancement of the carrier lifetime occurs throughout the whole of >40 urn thick epi-layers.
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| 2. |
- Abedin, Ahmad, et al.
(författare)
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Epitaxial growth of Ge strain relaxed buffer on Si with low threading dislocation density
- 2016
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Ingår i: ECS Transactions. - : Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; , s. 615-621
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Konferensbidrag (refereegranskat)abstract
- Epitaxial Ge with low dislocation density is grown on a low temperature grown Ge seed layer on Si substrate by reduced pressure chemical vapor deposition. The surface topography measured by AFM shows that the strain relaxation occurred through pit formation which resulted in freezing the defects at Ge/Si interface. Moreover a lower threading dislocation density compared to conventional strain relaxed Ge buffers on Si was observed. We show that by growing the first layer at temperatures below 300 °C a surface roughness below 1 nm can be achieved together with carrier mobility enhancement. The different defects densities revealed from SECCO and Iodine etching shows that the defects types have been changed and SECCO is not always trustable.
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| 3. |
- Beale, S. B., et al.
(författare)
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Combined two-phase co-flow and counter-flow in a gas channel/porous transport layer assembly
- 2020. - 9
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Ingår i: PRiME 2020 : Polymer Electrolyte Fuel Cells and Electrolyzers 20 (PEFC and E 20) - Polymer Electrolyte Fuel Cells and Electrolyzers 20 (PEFC and E 20). - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 98:9, s. 305-315
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Konferensbidrag (refereegranskat)abstract
- This paper considers a detailed numerical analysis of combined liquid-gas co-flow in a gas channel, with liquid-gas counter-flow in a porous transport layer, as is typically found on the cathode side of a polymer electrolyte fuel cell. The geometry is obtained by digital reconstruction of nano-computer tomography images. From this, the domain is tessellated with an unstructured castellated or octree mesh, upon which the equations of mass and momentum are solved by means of a volume of fluid method. Liquid water is produced from an electrode where gaseous oxygen is simultaneously consumed by electrochemical reduction; Liquid-gas counter flow in the porous transport layer results in liquid drops being entrained in co-flow in the gas channels and convected by the gas downstream.
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| 4. |
- Carlson, Annika, et al.
(författare)
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Kinetic parameters in anion-exchange membrane fuel cells
- 2019
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Ingår i: ECS Transactions. - : Electrochemical Society Inc.. - 1938-6737 .- 1938-5862. - 9781607685395 ; , s. 649-659
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Konferensbidrag (refereegranskat)abstract
- Understanding limitations in an operating AEMFC is essential to .enhance the technology. Here the electrode processes are studied experimentally as well as by two physics-based models taking the porosity of the electrodes into account. The aim is to use the models to determine kinetic parameters specific for in-situ operation. The models can also be used to explain the experimental .behavior. From the impedance model of a symmetric H2/H2 cell it is shown that the hydrogen oxidation reaction (HOR) proceeds through the Tafel-Volmer reaction pathway, with the hydrogen adsorption as the slower reaction step. Based on the HOR model a •steady-state model of an O2/H2 cell is used to evaluate data from 14 experimental I-V curves, obtained for different gas partial pressures and catalyst loadings, in order to study the effects of the oxygen reduction reaction and overall cell limitations. The results show that the oxygen reduction reaction kinetics limit the cell performance for low current densities. However, at higher currents the uneven current distribution and locally low hydrogen adsorption at the anode increasingly affect the overall performance. Uneven current distribution is also observed at the cathode and likely caused by insufficient effective ionomer conductivity.
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| 5. |
- Chen, J. T., et al.
(författare)
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Carbon-doped GaN on SiC materials for low-memory-effect devices
- 2016
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 75:12, s. 61-65, s. 61-65
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Konferensbidrag (refereegranskat)abstract
- AlGaN/GaN on SiC HEMT structures suitable for high power, high frequency applications are demonstrated. The material manifests record breaking thermal management and electron mobility. Moreover, thanks to the fact that the buffer layer is doped with carbon, the memory effect of processed devices is very low making system design and manufacturing significantly easier and less expensive.
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| 6. |
- Debela, A. M., et al.
(författare)
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Functionalized deoxynucleotides and DNA primers for electrochemical diagnostics of disease predispostions
- 2017
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Ingår i: ECS Transactions. - : Electrochemical Society Inc.. - 1938-6737 .- 1938-5862. - 9781607685395 ; , s. 1873-1883, s. 1873-1883
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Konferensbidrag (refereegranskat)abstract
- Redox labeled DNAs are of increasing interest for the fabrication of next generation molecular tools. In the present work we are investigating the use of various redox labeled dNTPs, ddNTPs and DNA primers for use in detection of diseases. We have reported the use of Polyoxometalate (POM) labeled DNA primers and dNTPs for use in PCR and subsequently used for direct electrochemical detection of PCR products. The use of POM labeled DNAs in PCR enabled us to check the compatibility with polymerases and PCR incorporability of the modified DNAs. Furthermore we have investigated the solid-phase array based primer extension (é-PEX) with redox labelled ddNTPs (ferrocene (Fc), anthraquinone (AQ) phenothiazine (PTZ) and methylene blue (MB)) to prove the strategy of detection of single nucleotide polymorphisms using the labeled ddNTPs. This strategy will allow the development of cost-effective, rapid and user-friendly platform for the screening of known and unknown genetic mutations.
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| 7. |
- Espinoza Andaluz, Mayken, et al.
(författare)
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A-Asterisk Algorithm as an Alternative to Evaluate the Geometric Tortuosity in Digitally Created SOFC Anodes
- 2021. - 1
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Ingår i: 17th International Symposium on Solid Oxide Fuel Cells, SOFC 2021. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 103:1, s. 1665-1671
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Konferensbidrag (refereegranskat)abstract
- A solid oxide fuel cell (SOFC) contains complex materials that facilitate the energy conversion process. The diffusion media play an important role in facilitating the reactant gases to reach the electrochemical active regions. Porosity and tortuosity are crucial parameters describing the diffusion to be analyzed in a SOFC anode. This paper aims to evaluate the feasibility of using the A-asterisk algorithm to compute the geometric tortuosity within SOFC anodes. A three-dimensional structure, which is digitally created, represents the SOFC anode, in which the possible paths that follow the fluid flow are analyzed. A-asterisk algorithm is used to generate possible paths, and therefore the geometric tortuosity can be computed considering an averaged distance. A tortuosity-porosity correlation is proposed, and the results are compared with previous studies. Results show that the A-asterisk algorithm is a capable algorithm to evaluate the geometric tortuosity values in SOFC anodes with different particle size distribution and porosities.
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| 8. |
- Espinoza-Andaluz, M., et al.
(författare)
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Pore-scale analysis of diffusion transport parameters in digitally reconstructed SOFC anodes with gradient porosity in the main flow direction
- 2017. - 1
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607685395 ; 78, s. 2785-2796
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Konferensbidrag (refereegranskat)abstract
- One of the promising devices to obtain electrical and thermal energy with considerable high efficiency is the solid oxide fuel cell (SOFC). The electrical energy is the result of the electrochemical reactions that occur inside the fuel cell (FC) when the reactant gases reach the so-called three-phase boundary (TPB). The nonhomogeneous and anisotropic characteristics of the layer between the gas channel and the TPB region require a pore-scale analysis to understand the effect of microstructural configurations. The purpose of this paper is to provide understanding of the behavior of the fluid flow through the digitally reconstructed SOFC anodes, with gradient porosity in the main flow direction, using the lattice Boltzmann method (LBM). The impact of the porosity distribution over the fluid behavior is determined for different digitally created SOFC anodes. The SOFC anodes are analyzed keeping the total porosity constant, but varying the local porosity in the flow direction. The impact of a gradient porosity over the gas-phase tortuosity and the normalized effective diffusion coefficient are presented.
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| 9. |
- Espinoza, R., et al.
(författare)
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Temperature-Dependent Study for Electrochemical Surface Area on a Catalyst Layer Used in a PEFC
- 2022
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Ingår i: Materials for Low Temperature Electrochemical Systems 8. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 108:7, s. 111-118
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Konferensbidrag (refereegranskat)abstract
- The total of catalytic particles is often unavailable to participate in the electrochemical reactions in a PEFC, which limits the PEFC performance. The electrochemical surface area (ECSA) becomes an important metric to diagnose the catalyst layer's performance and evaluate the development of new electrode materials to achieve better overall efficiency. This work intends to analyze the effects of a temperature sweep on the ECSA and determine the best model that fits the trend based on obtained results from in-situ cyclic voltammetry (CV) tests. The experiment was carried out using a single PEFC of 25 cm2 with a catalyst layer of 0.5mg Pt/cm2 and Nafion® 112 membrane, using hydrogen and nitrogen as reactant gases at 100% relative humidity (RH). The results show a loss of ECSA about 14% in the temperature range evaluated. Besides, it was found that a linear function is adequate to model the correlation based on the experimental data obtained.
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| 10. |
- Falk Windisch, Hannes, 1984, et al.
(författare)
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Metallic thin-film Co- and Ce/Co-coated steels as interconnect material in IT-SOFC
- 2017
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 78:1, s. 1607-1614
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Konferensbidrag (refereegranskat)abstract
- Cr vaporization, oxide scale growth, and the electrical scale resistance (ASR) were studied at 650°C on coated interconnects intended for IT-SOFC applications. The custom-made SOFC interconnect steel Sanergy HT was coated with thin-film Co- and Ce/Co-coatings and compared to the less expensive substrate steel AISI 441 which was coated with Ce/Co and a 15-20 μm thick commercial MCO-coating. All coated materials mitigated Cr vaporization, and due to the very thin chromia scales formed at the low exposure temperature, ASR values below 10 mΩcm 2 were measured for all materials after 500 h at 650°C. The results in this study show that thin-film metallic Co- and Ce/Co-coated steels show excellent properties as interconnect materials for IT-SOFCs. Thick MCO-coatings can also be used at low temperatures; however, the coating method might be a critical issue for lowtemperature applications.
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